2.1 Brief Model Description. GESIMA is a non-hydrostatic meteorological model that was validated for a wide range of phenomena (e.g., Claussen, 1988; ...
Meteorol. Atmos. Phys. 72, 47±68 (2000)
LIM ± Institut f ur Meteorologie, Universitat Leipzig, Stephanstraûe 3, 04103 Leipzig, Germany
Application of the Principle of Superposition to Detect Nonlinearity in the Short-Term Atmospheric Response to Concurrent Land-Use Changes Associated with Future Landscapes N. Molders With 16 Figures Received December 22, 1998 Revised September 1, 1999
Summary The changes in the atmospheric response (e.g., in the variables of state, the amount of cloud-and precipitating particles, the water- and energy ¯uxes) to concurrent landuse changes are exemplarly examined for various landscape scenarios since the cessation of open-pit mining. The principle of superposition is applied to detect areas where the atmospheric response is either enhanced or diminished according to concurrent land-use changes as compared to simple land-use changes. The results show that nonlinear behavior of a given quantity may occur in areas without signi®cant changes in this quantity and that a quantity may be signi®cantly changed without ®nding nonlinearity. Moreover, the concurrent land-use changes do not necessarily yield a stronger atmospheric response than simple landuse changes. In addition to the size of the patches, where land-use changes, the contrast in the hydrologic and thermal behavior of the changes is decisive in measuring the magnitude of the response. Enhancement and diminishment seem also to depend on the land-use adjacent to the altered land-use.
1. Introduction Land-use changes often proceed continuously with several types of changes occurring simultaneously. Therefore, some dif®culties exist to ®nd the effect of land-use changes by comparing observational data before and after the conver-
sion of land-use. Numerical modeling, however, provides a tool to overcome this problem. Here, the in¯uence of different land-use changes can be isolated by comparing results of simulations with simple land-use changes or various combinations of concurrent land-use changes to those without all or without some of the land-use changes. Herein, simple land-use changes are de®ned as the changes of various land-use types A, B, or C to only one land-use type D. Concurrent land-use changes are de®ned as the changes for which different land-use types A, B, C, etc. are simultaneously converted to various land-use types X, Y, Z etc. Recent numerical studies examined the impact of land-use changes on both the global and regional climate for large areas, where land-use type A was converted to B (e.g., Anthes, 1984; Zhang et al., 1996; Xue, 1996), or where the land-use changed on a continental scale (e.g., Copeland et al., 1996). Moreover, studies on climate-induced changes of biome and their in¯uence on the monsoon also exist for large scale areas (e.g., Claussen, 1997). The results of these studies indicate that coherent regions of substantial changes in screen height temperature, humidity, wind speed, and precipitation may be
48
N. M olders
Table 1. Acronyms of the Simulations. Urbanization Amounts to 21% of the Area of Already Existing Settlements REF MIN FLO URB MINURB FLOURB NU2050 2050
landscape before onset of open-pit mining landscape with open-pit mines landscape with totally ¯ooded open-pit mines landscape with urbanization landscape with open-pit mines and concurrent urbanization landscape with totally ¯ooded open-pit mines and concurrent urbanization recultivated open-pit mines as planned for 2050 and no concurrent urbanization recultivated open-pit mines as planned for 2050 and concurrent urbanization
Table 2. Extension and Assumed Re-Use of the Open-Pit Mines. Water Engineering is Realized as Water. Agriculturally-Used Land is Divided into Grassland and Agriculture, and Forestry is Divided into Deciduous, Mixed, and Coniferous Forest, Respectively. The Land-Use Type Denoted as ``other'' in the Planning Books is Set to Village. For Bitterfelder Revier, the Changes are Assumed to be Similar to those of Sudraum Leipzig. Data Given in Brackets Represents Coverage Before the Onset of Open-Pit Mining other (%)
reference
area (km2)
48.6 (13.2)
8.2 (1.0)
211
44.5 (88.7)
20.0 (6.0)
18.0 (0.7)
44.5 (87.3)
20.0 (12.7)
18.0 (0.0)
Biemelt (1997) Berkner (1995) assumed
water (%)
agriculturally used (%)
forestry (%)
Niederlausitz
26.5 (0.0)
16.7 (85.8)
S udraum Leipzig
17.5 (4.6)
Bitterfelder Revier 17.5 (0.0)
the outcome of a change in the use of land on the meso- -scale. The big changes of the aforementioned quantities were closely related to the changes of the vegetation parameters. In Europe, modern land-use changes (e.g., deforestation, afforestation, construction of water reservoirs, recultivation of open-pit mine sites, urbanization) often occur on the local scale. In East Germany, for instance, it is anticipated that open-pit mines will be recultivated and that urbanization will increase to about 21% over the already existing settlements until 2050. Here, the size of the patches that are subject to land-use changes is small as compared to what was assumed in the studies mentioned before. In a recent paper, Molders (1998) illustrated that local scale, simple land-use changes may have microphysical impacts on cloud- and precipitating particles. They may produce dynamic and kinetic perturbations on the conditions downwind of the changed land surface even in the short-term (up to 24 h). In light of the extreme nonlinearity of the alterations that are produced in the exchange processes by land-use changes, it is conceivable that cloud- and precipitation formation processes may be possibly diminished or enhanced by concurrent land-
55 151
use changes. Up to the present, in planning experts only considered simple land-use changes. Thus, the purpose of this case study is (1) to investigate whether concurrent land-use changes bring about enhancement or diminishment in the atmospheric response; (2) to show exemplarly under which conditions these changes occur in short-term; and (3) to check whether the locations of nonlinearity are identical to those of signi®cant changes in the atmospheric response. In this study, the atmospheric response to concurrent land-use changes is investigated in the short-term (up to 24 h) because synoptic situations with local recycling of previous precipitation can be found in comparable periods in mid-latitudes. Moreover, such a time scale is consistent with that relevant for micrometeorological processes (e.g., exchanges of energy and matter at the earth-atmosphere interface, which are strongly affected by changing the surface properties). Thus, a non-hydrostatic meteorological model of the meso- -scale is applied since it matches both the temporal and spatial scales relevant for the purposes of this study. In doing so, eight simulations were performed using GESIMA (GEesthacht's SImulation Model of the Atmosphere; Kapitza and Eppel, 1992; Eppel
Application of the Principle of Superposition
et al., 1995), for which landscapes with open-pit mines and with discontinued open-pit mines were assumed (Tables 1, 2). The principle of superposition is applied to detect areas of enhancement and diminishment in the processes involved. Hence, this study differs from the aforementioned studies in both the spatial and temporal scales, as well as in the possibility of detecting areas of nonlinear atmospheric response to concurrent land-use changes as compared to the sum of the responses to the simple land-use changes (principle of superposition). 2. Technical Information 2.1 Brief Model Description GESIMA is a non-hydrostatic meteorological model that was validated for a wide range of phenomena (e.g., Claussen, 1988; Kapitza and Eppel, 1992; Eppel et al., 1995; Devantier and Raabe, 1996; Hinneburg and Tetzlaff, 1996). M olders (1998) showed that GESIMA is also able to simulate the atmospheric response to surface characteristics usually observed. The dynamic part of GESIMA is based on (1) the equation of continuity used in the anelastic approximated form
i:e:, @ =@t 0 to suppress sound waves (e.g., Pielke, 1984); (2) the conservation equations for momentum, energy and various atmospheric components such as dry air, water vapor, liquid water, and ice; and (3) the equation of state (Kapitza and Eppel, 1992; Eppel et al., 1995). In recognition of the turbulent state in the troposphere, all equations have been averaged according to Reynolds and have been, in a further step, Boussinesq-approximated (see also Kapitza and Eppel, 1992). Soil-wetness is determined by a force-restoremethod (Deardorff, 1978). At the surface, a bulkparameterization is applied to calculate the ¯uxes of sensible and latent heat. To calculate the transpiration by plants, a Jarvis-type approach is considered for the bulk-stomatal conduction (Jarvis, 1976; Eppel et al., 1995; Molders, 1998). The soil heat-¯uxes and soil-temperatures are calculated by a one-dimensional heat-diffusion equation (cf. Eppel et al., 1995). The surface stress and near-surface ¯uxes of heat and water vapor are expressed in terms of dimensionless
49
drag coef®cients and transfer coef®cients of heat and moisture using the parametric model of Kramm et al. (1995). This parametric model is based on Monin-Obukhov similarity theory. The turbulent ¯ux of momentum for the region above the surface layer is calculated by a one-and-ahalf-order closure scheme. Here, the elements of the eddy-diffusivity tensor are expressed by the vertical eddy diffusivity KM,V , and the horizontal diffusivity, KM,H, where the latter is also related to KM,V by the simple linear relationship KM,H 2.3 KM,V. Furthermore, KM,V is expressed by the turbulent kinetic energy (TKE) and the mixing length, `, using the Kolmogorov-Prandtl relationship where the mixing length is parameterized by Blackadar's (1962) approach, slightly modi®ed by Mellor and Yamada (1974). The turbulent ¯uxes of sensible heat and water vapor for that region are expressed as functions of KM,V and the turbulent Prandtl number, Prt KM,V /KH,V , and the turbulent Schmidt number, Sct KM,V /KE,V , respectively. These characteristic numbers are considered to be functions of the thermal strati®cation. They are derived from the local stability functions, M and H, of Businger et al. (1971) by Prt (uz/ M) / (uz/ H) H / M, and the assumption that Sct Prt. Here, u, z and are the friction velocity, the height, and the von KaÂrmaÂn-constant, respectively. To determine the TKE, an additional budget equation for that quantity is solved where the energy production, due to horizontal shear, is neglected (for more detail, see Kapitza and Eppel, 1992). The heterogeneity of precipitation and landuse is considered by an explicit subgrid scheme (Seth et al., 1994; Molders et al., 1996). Its mathematical formulation is given in Molders et al. (1996). A fundamental assumption of this scheme is that the subgrid-scale near-surface meteorological forcing, which is experienced by the surface, is important in determining the net exchange of heat, moisture, and momentum at the earth-atmosphere interface, i.e., the horizontal ¯uxes between the different subgrid cells within a grid cell are small in comparison to the corresponding vertical transfer processes. Within the framework of the explicit subgrid scheme, each atmospheric grid cell (5 5 km2) is divided into 25 subgrid cells (1 1 km2) at the earthatmosphere interface and within the soil. The
50
N. M olders
Table 3. Parameters (from Eppel et al., 1995 and Literature Cited Therein) as Used for the Different Land-Use Types in the SoilVegetation Model. The Letters ks, ci, ", , zo, wk, c, and g1 are the Thermal Diffusivity of the Soil, Heat Capacity, Emissivity, Albedo, Roughness-Length, Field Capacity Weighted by the Uppermost Diurnally Active Soil Layer, the Capillary, and the Maximal Evaporative Conductivity, Respectively. Note that Open-Pit Mines Consist Mainly of Tertiary and Quaternary Sands. Only a Small Stripe of Coal of About 100 m Width is in Direct Contact with the Overlying Atmosphere. Therefore, the Soil Characteristics of Sand are Used in Assessing Open-Pit Mines
Water Open-pit mines Grassland Agriculture Deciduous forest Mixed forest Coniferous forest Suburb/village City
ks 10ÿ6 m2 /s
ci 106 J/(m3K)
"
0.15 0.84 0.56 0.74 0.70 0.70 0.70 1.0 1.0
4.2 2.1 2.1 2.9 2.5 2.5 2.5 2.0 2.0
0.94 0.90 0.95 0.95 0.97 0.975 0.98 0.90 0.95
calculated 0.3 0.0004 0.25 0.02 0.18 0.04 0.20 0.8 0.175 0.9 0.15 1.0 0.20 0.8 0.15 1.0
subgrid cells are considered to be homogeneously covered by their individual vegetation over horizontally homogeneous soil types (Table 3). The energy and water ¯uxes are solved for each of these subgrid cells with their own soil and near-surface meteorological forcing. The coupling of the subgrid cells to the atmospheric grid cell is realized by arithmetically averaging the subgrid ¯uxes. A great advantage of the subgrid-scheme is that the anthropogenic landuse changes can easily be considered in a realistic meso- -scale size. A bulk-parameterization scheme of cloud microphysics is used to describe cloud- and precipitation formation (Molders et al., 1997). This scheme considers the condensation and deposition of water vapor; the rainwater formation by autoconversion, coalescence as well as melting of ice and graupel; the riming of ice and graupel by cloud water; the homogeneous freezing of cloud water and rainwater; the evaporation of cloud water and rainwater; the sublimation of ice and graupel; and the sedimentation of rainwater, ice, and graupel. A simpli®ed two-stream method is used to calculate the radiative transfer (Eppel et al., 1995). The prognostic equations are solved with a predictor/corrector scheme. The advection of momentum and sensible heat is treated with a modi®ed MacCormack scheme as cited by Anderson et al. (1984), whereas the advection of the aforementioned trace constituents is dealt with by the Smolarkiewicz scheme (Smolarkie-
zo m
wk m
c 10ÿ3 kg/(m3s)
g1 m/s
1.0 0.002 0.010 0.003 0.010 0.010 0.010 0.003 0.002
1000 0.9 8.0 3.0 8.0 8.0 8.0 1.0 0.9
± ± 0.04 0.04 0.023 0.023 0.023 ± ±
wicz, 1984). The horizontal diffusion is computed using an explicit scheme, whereas any vertical diffusion is calculated implicitly. At the top of the model, a rigid lid, together with a sponge layer to absorb vertically propagating gravity waves, is applied. At the lateral boundaries, the Orlanski (1976) radiation-boundary condition is used for the normal component of momentum, and a zero-gradient method is applied for all other variables. 2.2 Initialization and Grid-Spacing of the Model In nature, land-use changes would possibly affect the pro®les in the atmospheric boundary layer (ABL). For comparability and to avoid additional degrees of freedom, all simulations started with the same vertical pro®les of wind, humidity, air and soil temperature (Fig. 1). The meteorological condition was orientated towards typical cases in spring, for which the local recycling of previous precipitation occurs in the area of interest. Such situations are, for instance, those of moderate easterly winds. Simulations start at 00 LT (local time) with a geostrophic wind of 7.5 m/s from 100 . Radiation is assumed for 122nd Julian day. The surface pressure is 1003 hPa. Soil-wetness factor, soil temperature in 1 m depth, and water surface temperature are set equal to 0.9, 285.0 K, and 282.6 K, respectively. The vertical resolution of the model varies from 20 m near the ground to 1 km at a height of
Application of the Principle of Superposition
51
10 km. Above and below a height of 2 km there are 8 levels. The horizontal grid-spacing is 5 5 km2 for the grid cells and 1 1 km2 for the subgrid cells. 2.3 The Land-Use Data Sets
Fig. 1. Initial conditions for the 3D-simulations as obtained from 1D-simulation (after MoÈlders (1998))
All assumed land-use changes are of meso- scale size. Table 1 lists the different landscape scenarios. MIN represents the landscape (of 1986) with open-pit mine. The land-use data set assuming ¯ooded open-pit mine is called FLO. The reference landscape, REF, corresponds to that of 1986, but in the open-pit mines, the landuse before the onset of mining is assumed. The data set, URB, is based on REF, but an expected increase of 21% in the already existing settlements is assumed at the expense of grassland and agriculture. Further data sets assume urbanization in MIN and FLO, and are referred to as MINURB, and FLOURB, respectively. The land-use data set of the recultivation scenario, called 2050, is based on the planned fraction of the different land-use types (Table 2) that are randomly distributed over the former open-pit mines (Fig. 2). Moreover, in the former non-
Fig. 2. Distribution of land-use characteristics as assumed for 2050. The mining districts in the south of Leipzig, around Bitterfeld, and in Niederlausitz are denoted as S udraum Leipzig, Bitterfelder Revier, and Lausitz(er Revier), respectively
52
N. M olders
Fig. 3. Comparison of the fractional coverage of land-use for the landscapes assumed in this study
mining areas, the urban land increases by 21% over its former coverage. NU2050 assumes the same recultivation as in 2050, but without urbanization. Although such a landscape is not very realistic, it serves to evaluate the individual contributions of recultivation and urbanization. Figure 3 illustrates the percentages of land-use in the various landscapes. In the model, the various land-use types are characterized by varying plant physiology and physical parameters (Table 3). In the sense of the de®nition given in the introduction, the land-use changes from MINURB and NU2050 to 2050 are concurrent land-use changes. In this study, however, recultivation is treated as a ``simple land-use change''. The new terrain elevation of the former openpit mines is assumed to be the average terrain height of the neighboring 1 1 km2 areas that were not affected by mining or that are already ®lled according to this procedure. This procedure runs from the north to the south, and from west to
east. Note that the obtained domain-averaged height (h 112.69 m) differs marginally form other starting points and directions in this procedure (S to N, E to W h 112.72 m, N to S, E to W h 112.70 m, S to N, W to E h 112.72 m). 3. Design of the Investigation The results of simulations with concurrent landuse changes are evaluated with respect to the changes in the atmospheric response. It is examined whether the changes are signi®cant and whether nonlinearity occurs at all as compared with the sums of the responses to the respective simple land-use changes. 3.1 Signi®cance Tests To test the signi®cance of the changed atmospheric response, student-t-tests are applied. The null-hypothesis is that land-use changes provide
Application of the Principle of Superposition
53
Table 4. Percentage of Area (%) for Which the Land-Use Changes Cause Signi®cant Differences (90% Con®dence and Higher) in Predicted Precipitation, P, Ice, qi, Rainwater, qr , Cloud Water, qc, Solid and liquid water, qt, Soil-Wetness Factor, f, Vertical Component of the Wind Vector, w, Evapotranspiration, E, Surface Temperature, TG, Sensible Heat-Flux, H, and the Temperature at Reference Height, Tr . The Letters C and S Indicate Simple and Concurrent Land-Use Changes, Respectively
MIN : FLO MIN : FLOURB REF : FLOURB REF : FLO REF : MINURB REF : MIN URB : MINURB MIN : 2050 URB : FLOURB URB : 2050 REF : 2050 REF : URB FLO : FLOURB MIN : MINURB
change P
qi
qr
qc
qt
f
w
E
TG
H
Tr
S C C S C S S C S S C S S S
17.8 21.4 21.8 14.8 23.1 19.4 16.3 10.8 17.5 12.3 14.4 15.0 17.8 23.3
20.0 20.8 16.7 14.1 15.8 12.3 1.0 14.3 16.4 21.3 15.1 10.8 14.8 16.8
10.3 16.7 8.4 6.2 6.7 10.3 4.7 8.1 6.9 4.0 4.2 5.5 8.8 13.5
12.1 16.6 9.7 7.8 7.1 9.0 4.6 7.4 8.8 4.6 3.6 5.3 7.9 12.8
10.0 10.8 11.2 9.6 4.4 1.9 1.4 6.3 9.3 4.8 7.0 2.4 1.0 1.6
5.2 8.3 1.9 1.3 5.8 5.5 5.2 5.8 1.3 0.3 0.3 0.1 0.6 0.7
1.0 0.9 0.3 0.3 1.0 0.9 0.9 1.8 0 0.2 0.2 0 0 0
0.6 0.5 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0 0 0 0 0
0.5 0.6 0.1 0.3 0 0 0 0 0.3 0 0 0 0 0
0.1 0.1 0 0 0.3 0.3 0.2 0.2 0 0 0 0 0 0
26.4 23.9 20.3 21.9 18.2 12.2 9.8 24.3 18.5 23.8 18.5 16.8 12.1 15.1
no differences in the atmospheric response, while the alternative hypothesis is that they do. For each grid-point the individual sampling distributions used are the hourly values of wind, temperature, and humidity (all taken at reference height), soil-wetness, surface temperature, the energy- and water ¯uxes. For each grid-column the individual sampling distributions used are the hourly column-integrated values of the cloudand precipitation particles. At a grid-point/ column, a change in the abovementioned quantities will be regarded as statistically signi®cant if the data give evidence against the null-hypothesis so convincingly that an error probability of less than 0.1 exists. Table 4 gives the percentage of the domain that received signi®cant changes at a 90% level or higher for various combinations of concurrent land-use changes. Figures 4 to 7 illustrate the frequency and location of signi®cant changes. 3.2 The Method of Detecting Areas of Enhancement and Diminution It has to be assumed that the atmospheric response to concurrent land-use changes may be enhanced or diminished as compared to the atmospheric response resulting from simple landuse changes. In a linear response, the sum of the differentials in the ®eld quantities, water and
energy ¯uxes, cloud and precipitation particles caused by the simple land-use changes, would equal the differentials in the atmospheric response due to the concurrent land-use changes (principle of superposition). After some algebra, one arrives at the general formula 8 < > 0 enhancement n X p k i
nÿ1 j ÿ j j 0 superposition : i1 < 0 diminution:
1 Here, j denotes the quantity of interest at grid cell j (e.g., the daily or hourly ®eld quantities, water and energy ¯uxes, cloud- and precipitation particles). The index k represents the simulation with the landscape from which the changes start (e.g., REF); i 1, . . . , n stands for the simulations with the landscapes wherein only one landuse type was altered as compared to the origin landscape (e.g., MIN and URB, n 2); and p represents the simulation with the concurrent land-use changes (e.g., MINURB). Enhancement or diminution means a deviation from the principle of superposition. Enhancement is characterized by a positive difference () and diminution by a negative one (ÿ). Only those deviations from superposition will be discussed as relevant which, absolutely regarded, amount to more than the margin for error that typically
54
N. M olders
Fig. 4. Amount of quantities (soil-wetness, near-surface wcomponent of wind-vector, evapotranspiration, sensible heat¯uxes, near-surface humidity, near-surface air or surface temperature, column-integrated values of cloud water, rainwater, and ice) with changes at the 90%- or better statistical-signi®cance level, showing that the differences result from the concurrent land-use changes from REF to MINURB. Thick contour lines indicate areas of open-pit mining
Fig. 5. Like Fig. 4, but for the concurrent land-use changes from MIN to FLOURB
Application of the Principle of Superposition
55
Fig. 6. Like Fig. 4, but for the concurrent land-use changes from REF to FLOURB
Fig. 7. Like Fig. 4, but for the concurrent land-use changes from MIN to 2050
56
N. M olders
arises in routinely measuring the respective quantity, j. Equation (1) allows analysis of certain areas where concurrent land-use changes cause such a nonlinear behavior. 4. Discussion In all the simulations, the concurrent land-use changes do not affect the predicted quantities of state, nor the wind above the ABL, except in areas of deep convection. The daily domainaverages of the predicted air temperatures, wind, net-radiation, and humidity hardly differ among simulations, while those of cloudiness and precipitation differ signi®cantly. For the various landscapes, the predicted ¯uxes vary more strongly during the day, when the energetic input is high, than at night. The distributions of evapotranspiration match those of the prevailing land-use. Thus more water is supplied to the atmosphere over the forest-dominated northeast than over the agriculturally-dominated southwest of the domain. Signi®cant changes occur in cloud- and precipitating particles, precipitation, soil-wetness, vertical velocity, evapotranspiration, nearsurface air and surface temperature (e.g., Table 4; Figs. 4±16). As in simple land-use changes (cf. M olders, 1998), the greatest differences in ®eld quantities, water- and energy ¯uxes occur at most extreme over and in the lee-side regions of the land-use changes. The changes in predicted cloud- and precipitation particles and rainfall are not restricted to the location of the land-use conversion. Out of all investigated quantities, the cloud- and precipitation particles react the most
sensitively to the land-use changes, followed by precipitation, and soil moisture (Table 4). Generally, soil-wetness factors increase signi®cantly where precipitation is more plentiful in one of the compared simulations or where it only occurs in one of the simulations. All simulation results show no relevant nonlinearity according to Eq. (1) for the daily averages of cloud water and ice, but for the hourly values. The daily averages of the u- and vcomponent of the wind vector, the near-surface air temperature, humidity, and rainwater also deviate only slightly from the principle of superposition (Table 5). However, relevant positive or negative differences, , occur for surface temperatures (e.g., Figs. 8±10), soil-wetness factors, and for all components of the energy balance (Table 5). The absolute differences, jj of the daily values, are lower for the sensible heat-¯uxes than for net-radiation or soil heat¯uxes, because the latter are also strongly affected by differences in cloudiness. While the principle of superposition is nearly ful®lled for the daily averages of the near-surface air temperatures (Table 5), it is not for the hourly values. In contrast to the daily averages, there exist deviations from the principle of superposition for the hourly latent heat-¯uxes in Niederlausitz which are here expressed in terms of evapotranspiration (Figs. 11, 14, 15). Although Sudraum Leipzig ( southern outskirts of Leipzig), and Bitterfelder Revier ( open-pit-mining district of Bitterfeld) were also subject to concurrent land-use changes, here no nonlinearity can be detected for evapotranspiration (Figs. 11, 14, 15). Contrastingly, the hourly values of
Table 5. Maximum Diminution and Enhancement, According to Eq. (1) for Daily Averages. For Location (see Discussion in the Text) Air temperature u-component v-component Water vapor Rainwater Net radiation Soil heat-¯ux Sensible heat-¯ux Latent heat-¯ux Wetness factor Surface temperature
Unit
REF to MINURB
MIN to FLOURB
REF to FLOURB
MIN to 2050
K m/s m/s g/kg g/kg Wmÿ2 Wmÿ2 Wmÿ2 Wmÿ2 ± K
ÿ0.1 ÿ0.1 ÿ0.1 ÿ0.02 ÿ0.01 ÿ35 ÿ23 ÿ19 ÿ10 ÿ0.04 ÿ0.6
ÿ0.2 ÿ0.1 ÿ0.1 ÿ0.01 ÿ0.01 ÿ37 ÿ25 ÿ20 ÿ13 ÿ0.02 ÿ0.6
ÿ0.1 ÿ0.1 ÿ0.1 ÿ0.01 ÿ0.01 ÿ33 ÿ18 ÿ10 ÿ10 ÿ0.04 ÿ0.7
ÿ0.2 ÿ0.2 ÿ0.1 ÿ0.02 ÿ0.01 ÿ69 ÿ41 ÿ22 ÿ13 ÿ0.03 ÿ0.6
0.1 0.1 0.1 0.01 0.01 42 25 12 12 0.03 0.6
0.1 0.1 0.1 0.01 0.01 37 24 13 12 0.03 0.6
0.1 0.1 0.0 0.01 0.01 22 15 12 14 0.03 0.5
0.1 0.1 0.1 0.01 0.01 67 40 21 11 0.03 0.7
Application of the Principle of Superposition
57
Fig. 8. Differences, (in K) for the daily averages of the surface temperatures according to Eq. (1) for the concurrent land-use changes from REF to MINURB. The grey and white patches represent positive and negative values, respectively. The contour lines within these patches indicate areas with an appreciable enhancement or diminution of the atmospheric response to the concurrent land-use changes. Dark-grey boxes indicate grid cells with changes at the 90%- or better statistical-signi®cance level, showing that the differences in surface temperature result from the concurrent land-use changes
Fig. 9. Like Fig. 8, but for the concurrent land-use changes from MIN to FLOURB
net radiation and soil heat-¯uxes differ also in other areas (e.g., Flaming, the surroundings of Lindenberg) due to different cloudiness in the diurnal course, while the sensible heat-¯uxes
show no deviation from superposition for hourly values at noon, for instance. The areas of signi®cant change in one or more of the quantities and sizes of these areas differ
58
N. M olders
Fig. 10. Like Fig. 8, but for the concurrent land-use changes from MIN to 2050
with the kind of concurrent land-use changes (Table 4; e.g., Figs. 4±7). As will be discussed later on, the comparison of these areas with those for which nonlinearity was detected shows (1) that signi®cant changes may be linear, and (2) that a quantity may achieve a nonlinear reaction to concurrent land-use changes, although it does not achieve a signi®cant change in this quantity in that area (e.g., Figs. 4±16). 4.1 Urbanization and Open-Pit Mines (REF to MINURB) Suburbs, cities and open-pit mines have in common both similar thermal characteristics (thermal diffusivity of the soil, heat capacity; Table 3) and hydrologic characteristics (®eld capacity, capillarity; Table 3). The albedo and roughness length of open-pit mines and suburbs, however, differ appreciably (Table 3) so that these land-use types in¯uence dynamics and radiation differently. Earlier studies suggest that urban areas increase convection (e.g., Landsberg, 1970) and lead to enhanced precipitation in and downwind of a city (e.g., Changnon and Huff, 1986; M olders, 1998). Moreover, urbanization (URB) leads to enhanced surface temperatures and lessens evapotranspiration as compared to vege-
tation (REF; cf. Molders, 1998). Hereafter, these effects will be denoted as urban effect. An openpit mine (MIN) signi®cantly reduces evapotranspiration. Both these simple land-use changes provide a slightly drier and warmer ABL, as well as a lower domain-averaged 24 h-accumulated precipitation than REF (cf. Molders, 1998). 4.1.1 Signi®cance As in MIN and URB the lower ABL of MINURB is slightly warmer than in REF nearly everywhere, especially over open-pit mines and conurbation. However, even here the maximum differences are lower than for open-pit mines alone. In Niederlausitz, surface temperatures (Fig. 8) and near-surface air temperatures increase signi®cantly (e.g., about 5.4 K and 0.7 K at noon) for the change from REF to MINURB. On the average, the tendency to a slightly drier near-surface speci®c humidity, and lower cloudiness but with an enhanced convection in the lee of large cities also exists for MINURB. The nearsurface speci®c humidity decreases the most in the areas of concurrent changes to suburbs and open-pit mines (e.g., south of Leipzig, Niederlausitz, especially around Cottbus, and in Bitterfelder Revier). The decrease (e.g., more than
Application of the Principle of Superposition
59
Fig. 11. Like Fig. 8, but for the difference ( in mm/h) in evapotranspiration at 12 LT for the concurrent land-use changes from REF to MINURB. Darkgrey boxes indicate grid cells with changes at the 90%- or better statistical-signi®cance level, showing that the differences in evapotranspiration result from the concurrent land-use changes
Fig. 12. Comparison of 24-h concurrent precipitation as predicted by REF (grey-shaded) and MINURB (dotted). Maximum values are 1.3 and 1.4 mm/d for REF and MINURB, respectively
0.32 g/kg at noon) is slightly greater here than for simple land-use changes (e.g., 0.12 and 0.27 g/kg for URB and MIN, respectively). Around Dresden, urbanization alone reduces the near-surface speci®c humidity nearly as much as the common effect of urbanization and open-pit mining in the Leipzig area. This is due to the fact that in Dresden, urbanization takes place at the expense of grassland, while in Leipzig, the
changes are mainly from agriculture to suburbs or open-pit mines. Agriculture, on average, evapotranspires less than grassland. Hence, in the conurbation of Dresden, the surface characteristics are more strongly altered than in the surroundings of Leipzig. In the conurbation of Leipzig and in Niederlausitz, signi®cantly less water is evapotranspired (e.g., up to 0.1 mm/h at noon) in MINURB than in REF (Fig. 11).
60
N. M olders
Fig. 13. Like Fig. 12, but for MIN (grey-shaded) and FLOURB (dotted). Maximum values are in both cases 1.4 mm/d
Fig. 14. Like Fig. 11, but for the concurrent land-use changes from MIN to FLOURB
Due to the greater heating generated by openpit mines and suburbs as compared to the previous vegetation, the vertical component of the wind vector changes signi®cantly in the ABL over Niederlausitz, Bitterfelder Revier, and S udraum Leipzig. In addition, differences in cloudiness signi®cantly alter the vertical motions in Flaming for a change from REF to MINURB. The amount of cloud water changes signi®cantly only over Flaming, while ice also changes
signi®cantly in the lee-side region of Leipzig. Convection is enhanced by the concurrent landuse changes. Cloud tops reach higher into the mid-troposphere in the lee-side region of Leipzig, for instance. In higher tropospheric layers, air is cooler and more ice nucleii become activated. Thus, more rainwater is built via the cold path of precipitation formation, i.e., water vapor deposition onto ice nucleii and ice particles, growth during sedimentation by riming
Application of the Principle of Superposition
61
Fig. 15. Like Fig. 11, but for the concurrent land-use changes from MIN to 2050
Fig. 16. Like Fig. 12, but for MIN (grey-shaded) and 2050 (dotted). Maximum values are 1.4 and 1.9 mm/d for MIN and 2050, respectively
processes, and later melting of ice particles at temperatures above the freezing point. Since the saturation pressure of ice is lower than that of water the shift towards a higher preference of the ice processes which is caused by the altered use of land also contributes to more ef®cient use of water vapor for cloud- and precipitation formation processes and, hence, signi®cant changes of cloud water and ice.
Although rainwater is built from cloud water (by autoconversion and coalescence) or ice (by melting), rainwater forces additional signi®cant changes in Sudraum Leipzig, Bitterfelder Revier, the lee-side of Niederlausitz, and the water meadows between Torgau and Riesa. In the area between Torgau and Riesa, rainwater is formed by autoconversion and coalescence only. The differing distributions and intensities of precipi-
62
N. M olders
tation (Fig. 12) yield signi®cant differences in soil-wetness factors (e.g., 0.19) that again modify evapotranspiration even far away from land-use changes. 4.1.2 Nonlinearity To investigate whether there exists nonlinear response to the concurrent land-use changes from vegetation to open-pit mines and suburbs, the results of the simulations REF, URB, MIN, and MINURB have to be used in Eq. (1). A nonlinear response of the daily averages of surface temperatures (Fig. 8), net radiation, and soil heat-¯ux also occurs at considerable distance from the concurrent land-use changes (e.g., in Flaming, near Meiûen). This nonlinearity results from the different temporal development of cloudiness due to variations in the advection of heat and moisture. Looking at the hourly values of the nearsurface air temperatures shows that in Niederlausitz, these values are lower in the immediate vicinity of the concurrent land-use changes in areas dominated by forest (e.g., at noon about 0.4 K) and higher in areas dominated by grassland (e.g., at noon about 0.2 K south of Cottbus) than expected from the principle of superposition. In the southern Bitterfelder Revier and in S udraum Leipzig where agriculture dominates (Fig. 2), the concurrent land-use changes hardly in¯uence each other in their effect on the near-surface air temperatures (e.g., at noon jj < 0.1 K). According to Eq. (1), over Niederlausitz, enhancement as well as diminution of evapotranspiration (e.g., up to more than 0.1 mm/h at noon, Fig. 11) can be found in the same areas as for the near-surface air temperatures. Additionally, diminution occurs east of Dresden (Fig. 11) that can be explained by the interaction between evapotranspiration, temperature, and cloudiness. The nonlinear dependence of saturation on temperature, among others, contributes to the deviation from superposition by large changes in evapotranspiration, condensation, and deposition even for moderate temperature changes. East of Dresden, for instance, the cloud cover provided by URB is signi®cantly greater than that supplied by REF or MINURB. In URB, less water enters into the atmosphere at the urban sites than at the
rural ones. In the latter, however, the slightly warmer, on average, ABL of URB favors evapotranspiration as compared to REF, for which cloudiness increases (positive feedback). This increased cloudiness, however, reduces insolation and lessens evapotranspiration later (negative feedback). An important difference between the results of MIN and MINURB is that reducing the urban effect by open-pit mines (cf. Molders, 1998) is over-compensated for by the increase of the urban effect due to urbanization. While at midnight the clouds have already diluted in the lee-side region of Leipzig in MIN (Molders, 1998), here cloud- and precipitating particles still exist in MINURB. The presence of open-pit mining reduces the urban effect (and the urbanization effect) that would usually have contributed to enhanced cloud- and precipitation formation over and in the lee-side region of Leipzig. Therefore, in MINURB, the clouds expand less than in REF. The 24 h-accumulated precipitation of MINURB, however, exceeds that of REF (Fig. 12) because convection is enhanced. Thus more air is lifted upwards and is replaced by humid air from the upwind surroundings. In MINURB, the domain-averaged 24 h-accumulated precipitation is less and the precipitation ®elds are less extended than in REF (Fig. 12). Seemingly, the simultaneous conversion to landuse types that have similar hydrologic and thermal surface characteristics may affect precipitation in both positive or negative directions. The areas of high-amount quantities that bring about signi®cant changes due to the concurrent land-use changes (Fig. 4) are not the same as those areas for which nonlinearity occur (e.g., Figs. 8, 11). This means that nonlinear behavior of a quantity, for instance, the hourly evapotranspiration (e.g., Fig. 11), may occur in an area for which this quantity did not result in signi®cant changes. 4.2 Urbanization and Water Some recent studies investigated the in¯uences of urban, rural, and lacustrine effects on clouds and precipitation on the local scale via observational or satellite data (e.g., Changnon, 1980; Rabin et al., 1990; O'Neal, 1996). Large water surfaces usually tend to stabilize warmer season
Application of the Principle of Superposition
63
Urbanization and ¯ooding of open-pit mines replace dry and warm patches of different sizes by wet and cool patches and vice versa.
over the former open-pit mines when they become water (Fig. 9). Over and upwind of the ¯ooded open-pit mines, the lower ABL of FLOURB is signi®cantly cooler (e.g., up to 1 K at noon) than in MIN. During the night, when the land cools, the differences in surface temperatures decrease and the lakes and their surroundings become warmer than the respective areas in MIN, except for Sudraum Leipzig. Here, the larger cloudiness of FLOURB reduces the longwave irradiation as compared to MIN. Due to the differences in stability and heating caused by the concurrent land-use changes, the vertical components of the wind vector decrease signi®cantly over some of the ¯ooded open-pit mines during the day, while signi®cant changes in both directions occur at night. The urban effect, which is further increased by urbanization, as well as the ®rst reduced and later on enhanced cloud- and precipitation formation that occurs over ¯ooded open-pit mines, can also be found if urbanization and ¯ooding of open-pit mines take place concurrently. On average, in FLOURB, the lower ABL is slightly more humid than in MIN, especially over and in the surroundings of the ¯ooded open-pit mines (e.g., 0.2 g / kg). Compared to MIN, cloudiness, during the night, increases signi®cantly in FLOURB in the lee of Leipzig. Here, and south of Flaming, the concurrent land-use changes alter cloudiness and precipitation signi®cantly (Fig. 13). Again, the altered moisture convergence and paths of cloud- and precipitation microphysical processes that result from the concurrent land-use changes, lead to the signi®cant modi®cation of precipitation.
4.2.1.1 Signi®cance. The altered surface characteristics (Table 3) modify the turbulent ¯uxes of sensible and latent heat that again change the humidity and temperature of the lower ABL. The partitioning of the energy changes signi®cantly (e.g., about 115 Wmÿ2 for the sensible and 50 Wmÿ2 for the latent heat ¯ux at noon) over ¯ooded open-pit mines as compared to openpit mines, especially in Niederlausitz. In the urban areas, surface temperatures increase in FLOURB (e.g., up to 12.9 K at noon). The surface temperatures decrease signi®cantly
4.2.1.2 Nonlinearity. Since the comparison of URB to FLOURB would include the open-pit mines as a former land-use, the results of MIN, FLO, FLOURB, and MINURB have to be used in Eq. (1). In Niederlausitz, the daily averages of surface temperatures are higher than expected for linear behavior ( up to 0.6 K; Fig. 9; Table 5), while in Flaming, they are lower than expected ( ÿ 0.6 K; Table 5). The latter deviation is again caused by the different temporal and spatial developments of cloudiness that result from the land-use changes.
convection because the water temperatures are generally cooler than the air (e.g., Changnon, 1980). For instance, evidence was found that Lake Michigan may inhibit the in¯uence of Chicago on the enhancement of cloudiness and rainfall (Changnon, 1980). In the present study, however, both the water surfaces and urban areas are smaller than either Chicago or Lake Michigan, and are also similar to each other in size. Therefore, a possible diminishing must be expected to be weaker. In the simulations assuming ¯ooded open-pit mines or other arti®cial bodies of water as simple land-use changes, the water surfaces were found to stabilize the lower ABL. Over the water, cloud- and precipitation formation was retarded (about 2 h) as long as the water surfaces were cooler than the overlying air. When they became warmer than the overlying air, they led to a destabilization of the lower ABL and enhanced the cloud- and precipitation formation (cf. M olders, 1998). During the daytime the lower ABL was heated less over the water, while over the (expanding) cities, it was heated more than before the landuse changes. Thus, the temperature gradient grows in the areas for which urbanization and a change in favor of water occur concurrently within a short distance (e.g., Leipzig to Sudraum Leipzig). 4.2.1 Urbanization and Flooded Open-Pit Mines (MIN to FLOURB)
64
N. M olders
Looking at the hourly near-surface air temperatures, the concurrent land-use changes south of Cottbus lead to values (about ÿ0.2 K at noon) lower than expected for a linear response. On the contrary, north of Senftenberg, an enhancement can be found (e.g., 0.4 K at noon). Here, the location of enhancement and diminution are the reverse of the case for the changes from REF to MINURB. This means that besides the land-use type dominating in the surroundings of the concurrent land-use changes, the kind of change of the land-use type determines the direction of the deviation from superposition. In FLOURB, as compared to FLO, the urbanization leads to a modi®ed partitioning of the energy into the ¯uxes of sensible and latent heat over the ¯ooded open-pit mines (e.g., Fig. 14). North of Senftenberg, for instance, the concurrent land-use changes provide higher evapotranspiration (e.g., up to 0.14 mm/h at noon) than would be expected from the principle of superposition (Fig. 14). South of Cottbus, however, in an area dominated by grassland, the atmospheric response to the concurrent land-use changes diminishes with respect to evapotranspiration, leading at noon, for instance, to up to 0.14 mm/h lower values than expected for an additive behavior (Fig. 14). Slight deviations from a linear behavior also occur east of Dresden. Here, the reasons are the signi®cant differences in the cloudiness of MIN and FLOURB and their impact upon evapotranspiration, sensible and soil heat-¯uxes. In contrast to MIN, for which over and in the lee-side region of Leipzig no precipitation reaches the ground at night, in FLOURB, precipitation still occurs. The maximum accumulated precipitation of FLOURB exceeds that of MIN by about 0.5 mm/d (Fig. 13). Both positive and negative deviations from superposition for precipitation occur. Again, the areas of nonlinearity in the response to concurrent land-use changes are not the same as the areas that bring forth signi®cant changes in the considered quantity (e.g., Figs. 5, 9, 14). Comparison of the differences between MIN±FLO and MIN±FLOURB shows that urbanization seems to be of less importance in the districts near ¯ooded open-pit mines than in an environment of grassland (e.g., Dresden).
4.2.2 Urbanization and Arti®cial Lakes (REF to FLOURB) The comparison of REF to FLOURB represents concurrent urbanization and the construction of arti®cial lakes. In contrast to the changes from MIN to FLOURB, here mainly vegetation is converted to either suburbs or water. 4.2.2.1 Signi®cance. Urbanization in the landscapes of REF or FLO means that grassland and agriculture are converted to suburbs, i.e., change from a wetter to a drier surface. Contrastingly, during the day, ¯ooding open-pit mine converts warm and dry surfaces to cool and wet ones, while the construction of arti®cial lakes changes wet and cool surfaces to even wetter and cooler surfaces, with an especially different heat capacity and lower aerodynamic roughness (Table 3). At noon, for instance, near-surface air and surface temperatures increase 0.8 K and 9.3 K for Leipzig, while they decrease about 0.3 and 2.8 K in the areas of the arti®cial lakes. As compared to the concurrent land-use changes discussed in Sect. 4.1, the extensions of the areas which are altered signi®cantly by concurrent land-use changes are smaller except for soil-wetness (Table 4). Moreover, signi®cant changes occur less frequently than for the landuse conversion from MIN to FLOURB (Figs. 5, 6). For the land-use conversion from REF to FLOURB the cloud- and precipitation particles, precipitation, evapotranspiration, and vertical component of the wind vector are altered signi®cantly at nearly the same places than in the case of regarding the land-use changes from MIN to FLOURB. 4.2.2.2 Nonlinearity. For the concurrent land-use changes assumed here, deviations from the principle of superposition occur in nearly the same areas as for ¯ooded open-pit mine and urbanization. The affected areas, however, are smaller in the case of urbanization plus arti®cial lakes than in the former case. The signs of the deviations from the principle of superposition are the same as in the case discussed in the previous section (e.g., for the hourly distributions of near-surface air temperature ÿ0.3 K south of Cottbus, 0.3 K north of Senftenberg, and evapotran-
Application of the Principle of Superposition
65
The change from MIN to 2050 represents the changes from the landscape of 1986 to that assumed for the year 2050 (Figs. 2, 3). By urbanization and recultivation at different places, cool/wet, and warm/dry surfaces convert to warm/dry and cool/wet surfaces, respectively.
Fig. 15). Note that in 2050, evapotranspiration even increases slightly in the recultivated areas when compared to REF because of the preference for forest and water in the recultivation. Despite the urbanization in Sudraum Leipzig, here, the urbanization reduces less the evapotranspiration than the recultivation leads to an increased evapotranspiration. The soil-wetness factors signi®cantly increase (e.g., 0.16) in the recultivated areas because the ®eld capacity and the capillarity of the tertian and quaternary sands are appreciably lower than those of the recultivated soils (Table 3). Due to the enhanced moisture supply the amount of graupel grows signi®cantly in Sudraum Leipzig when recultivating the openpit mines. With the exception of graupel, the cloud- and precipitating particles change signi®cantly over FlaÈming. Over FlaÈming, the atmospheric humidity increases due to the enhanced water supply from the recultivated areas of Niederlausitz. Due to this additional humidity, there is enough water vapor to ensure that precipitation reaches the ground in 2050 (Fig. 16).
4.3.1 Signi®cance
4.3.2 Nonlinearity
In 2050, the near-surface air and surface temperatures slightly increase due to urbanization (e.g., up to 0.1 K and 4 K at noon). In the recultivated areas and their surroundings, however, they decrease (e.g., at noon up to 0.3 K and 2.8 K, respectively). The vertical velocities decrease signi®cantly over the recultivated areas because of the great differences in the thermal behavior of open-pit mine and the soils of the recultivated areas (Table 3). Over Leipzig and Dresden, the vertical velocities increase signi®cantly due to the higher heating of the surfaces (see also Fig. 10), and the upward motions reach higher layers in 2050 than in MIN. During the daytime, the lower ABL of 2050 is more humid (e.g., up to 0.1 g/kg at noon) than in MIN over and downwind of the recultivated areas, while it is drier over the urban areas (e.g., up to 0.2 g/kg at noon). The recultivated areas provide signi®cantly more water (e.g., about 0.1 mm/h at noon) to the atmosphere than the former open-pit mines (e.g.,
To detect nonlinearity, the results of MIN, NU2050, MINURB, and 2050 are used in Eq. (1). Again the daily averages of surface temperatures deviate from superposition ( 0.4 K) in Niederlausitz (Fig. 10). North of Dresden, one can detect a diminution of the in¯uences of the concurrent land-use changes on the daily averages of the surface temperatures ( ÿ0.6 K; Fig. 10). Investigation of the hourly values of nearsurface air temperatures shows an enhancement north of Senftenberg and northwest of Bautzen (e.g., > 0.4 K at noon). Around noon, the concurrent land-use changes lead to a stronger hourly evapotranspiration (up to 0.14 mm/h at noon; Fig. 15) in the northwestern part of Niederlausitz than would have been expected by the superposition principle. In the northeastern and southern part of Niederlausitz, diminution for evapotranspiration can be detected at the same time (up to ÿ0.14 mm/h; Fig. 15). In southern Niederlausitz, the aforementioned deviation again results from the
spiration ÿ0.09 mm/h south of Cottbus, 0.17 mm/h north of Senftenberg at noon, and for the daily averages of the surface temperatures > 0.5 K in Niederlausitz, < ÿ 0.7 K in Flaming; see also Table 5). On the domain average, the 24 h-accumulated precipitation of FLOURB exceeds that of REF (Figs. 12, 13). In FLOURB, the precipitation ®elds are less extended than in FLO, but exceed those of URB. Moreover, the intensity of precipitation increases in FLOURB as compared to REF. This increase is nonlinear at most places. The maximum values are 1.9, 1.4, 1.8, and 1.3 mm/d in FLOURB, URB, FLO, and REF, respectively. 4.3 Urbanization and Recultivation of Open-Pit Mines (MIN to 2050)
66
N. M olders
altered cloudiness that is caused by differences in advection of heat and moisture. Downwind of Leipzig, urbanization enhances convection resulting in an increase of precipitation as compared to MIN (Fig. 16). The domainaveraged 24 h-accumulated precipitation of 2050 exceeds that of MIN (and URB; see also Molders, 1998). However, the maximum 24 haccumulated rainfall of 2050 hardly differs from that of MIN (Fig. 16). Looking at hourly values both diminution and enhancement for precipitation can be detected. In a region dominated by relatively wet surfaces (forests, grassland), concurrent urbanization and recultivation will diminish evapotranspiration (e.g., Fig. 15) and air temperatures if the areas adjacent to the concurrent land-use changes are dominated by agriculture in a wider environment of dominance by forest and grassland (see Fig. 2). However, evapotranspiration and air temperatures can be enhanced if forests or grassland prevail in the areas adjacent to the concurrent land-use changes (compare, e.g., Figs. 2, 15). In SuÈdraum Leipzig and Bitterfelder Revier, no deviation from the principle of superposition was detected. Here, the prevailing surfaces are relatively dry and warm (agriculture; see Fig. 2). As for the concurrent land-use changes discussed before, the areas where response to concurrent land-use changes was nonlinear, are not the same as those areas where the regarded quantity undergoes signi®cant changes or where many of the regarded quantities (e.g., air temperature, air humidity, and wind all taken at reference height, surface temperature, soil moisture, column-integrated cloud- and precipitation particles, turbulent ¯uxes of sensible and latent heat, etc.) achieved signi®cant changes (e.g., Figs. 7, 10, 15). 5. Conclusions This case study was motivated by the ongoing concurrent land-use changes in East Germany. The main intents were to analyze the short-term impact of variously hypothetical landscapes since the discontinuation of open-pit mining on the atmospheric response and to examine whether areas with nonlinear response exist, i.e., whether planning experts may apply the
principle of superposition when estimating the impact of concurrent land-use changes. The simulation results support a 90% (and better) con®dence that land-use changes lead to statistically signi®cant changes in cloud- and precipitating particles, soil-wetness factors, and the w-components of the wind vector (Table 4) within the lee-side regions of their occurrence (e.g., Figs. 4±7). Concurrent land-use changes do not necessarily provide greater changes in the atmospheric response to the underlying surface than simple land-use changes. Thus, the most signi®cant response of the atmosphere for all investigated quantities occurs for a change from open-pit mine to ¯ooded open-pit mine (cf. Table 4). Urbanization, which seems to have the less signi®cant impact on the local weather of all the assumed land-use changes, affects the atmosphere differently for different landscapes (cf. Table 4). In a landscape with greatly expanded water surfaces, urbanization has a more signi®cant in¯uence on cloud- and precipitationformation than does open-pit mines at the other extreme. For the synoptic situation of this case study, the domain-averaged 24 h-accumulated precipitation increases with the increasing fractional coverage of wet surfaces. Note that no such dependence can be detected for cloudiness. The magnitude of the atmospheric response to concurrent land-use changes seems not necessarily to depend on the fraction of the domain that experienced these land-use changes. In addition to the size of the patches where the individual changes take place, the contrast in the hydrologic and thermal behavior of the changes is decisive for the magnitude of the response. The principle of superposition was applied to detect such areas of diminution and enhancement in the atmospheric response to concurrent landuse changes. It was found that diminution and enhancement also occur in areas without a signi®cant change in the respective quantity. Whether the atmospheric response for evapotranspiration or near-surface air temperature is enhanced or diminished by concurrent land-use changes (as compared to the superposition of the response to the simple land-use changes), depends on both the thermal and hydrologic characteristics active during concurrent land-use changes as well as on unchanged land-use
Application of the Principle of Superposition
adjacent to the land undergoing conversion (compare, e.g., Sudraum Leipzig with Niederlausitz in Figs. 11, 15). The deviations from superposition determined using the daily values of surface temperature, sensible heat-¯ux, soil heat ¯ux, and net radiation occur in areas where large (and sometimes signi®cant) differences occur in cloudiness. This behavior means that the temporal course of the energy- and water cycle may be nonlinearly in¯uenced by concurrent landuse changes also by secondary effects. According to these ®ndings, one must consider the prevailing land-use adjacent to the converted areas because the same concurrent land-use changes may provide another atmospheric response in different surroundings. One must conclude that meso- -scale meteorological models have to be applied by planning experts in the case that the impacts of local scale concurrent land-use changes on the local weather conditions are to be estimated. To improve an understanding of the impact of concurrent land-use changes on local weather, future studies should examine whether concurrent land-use changes provide a different response to the atmosphere under different synoptic conditions. Moreover, one should investigate whether the nonlinearity and signi®cance of the impact also exist in the long-term (e.g., vegetation period, hydrological year, climate). If such clues are found, regional climate simulations will urgently require sophisticated biome models to correctly evaluate climate impact on water resources, for example. Moreover, uncertainty analysis on the impact of anthropogenic land-use changes are an urgent need. Acknowledgements I would like to express my thanks to the Deutsche Forschungsgemeinschaft (DFG) for the support of this study under contracts Mo770/1-1 and Mo770/l-2. Thanks also to K. Friedrich who provided the land-use and topography data. I also wish to thank G. Kramm, K. E. Erdmann, G. Tetzlaff, and the anonymous reviewers for fruitful discussions and helpful comments. I also thank N. R ohrs for help with the language. References Anderson, D. A., Tannehill, R. H., Fletcher, A., 1984: Computational Fluid Dynamics and Heat Transfer. New York: Hemispheric Publishing Corporation.
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Anthes, R. A., 1984: Enhancement of convective precipitation by mesoscale variations in vegetative covering in semiarid regions. J. Climate Appl. Meteor., 23, 541±554. Berkner, A., 1995: Die beeintrachtigten Ober¯achengewasser des S udraumes Leipzig mit besonderer Ber ucksichtigung der Pleiûe. In: Zukunft S udraum Leipzig. Beitr age zu Lehre und Forschung der HTWK, 10±20. Biemelt, 1997: Private communication. Blackadar, A. K., 1962: The vertical distribution of wind and turbulent exchange in a neutral atmosphere. J. Geophys. Res., 67, 3095±3103. Businger, J. A., Wyngaard, J. C., Izumi, Y., Bradley, E. F., 1971: Flux pro®le relationship in the atmospheric surface layer. J. Atmos. Sci., 28, 181±189. Changnon, S. A., 1980: Evidence of urban and lake in¯uences on precipitation in the Chicago area. J. Appl. Meteor., 10, 1137±1159. Changnon, S. A., Huff, F. A., 1986: The urban-related nocturnal rainfall anomaly at St. Louis. J. Climate Appl. Meteor., 25, 1985±1995. Claussen, M., 1988: On the surface energy budget of coastal zones with tidal ¯ats. Contrib. Phys. Atmos., 61, 39±49. Claussen, M., 1997: Modeling bio-geophysical feedback in the African and Indian monsoon region. Climate Dynamics, 13, 247±257. Copeland, J. H., Pielke, R. A., Kittel, T. G. F., 1996: Potential climatic impacts of vegetation change: A regional modeling study. J. Geophys. Res., 101D, 7409±7418. Deardorff, J. W., 1978: Ef®cient prediction of ground surface temperature and moisture with inclusion of a layer of vegetation. J. Geophys. Res., 84C, 1889±1903. Devantier, R., Raabe, A., 1996: Application of a quasispectral cloud parameterization scheme to a mesoscale snowfall event over the Baltic Sea. Contrib. Atmos. Phys., 69, 375±384. Eppel, D. P., Kapitza, H., Claussen, M., Jacob, D., Koch, W., Levkov, L., Mengelkamp, H.-T., Werrmann, N., 1995: The non-hydrostatic mesoscale model GESIMA. Part II: Parameterizations and applications. Contrib. Atmos. Phys., 68, 15±41. Hinneburg, D., Tetzlaff, G., 1996: Calculated wind climatology of the South-Saxonian/North-Czech mountain topography including an improved resolution of mountains. Ann. Geophysicae, 14, 767±772. Jarvis, P. G., 1976: The interpretation of the variations in leaf water potential and stomatal conductance found in canopies in the ®eld. Phil. Trans. R. Soc. Lond., B 273, 593±610. Kapitza, H., Eppel, D. P., 1992: The non-hydrostatic mesoscale model GESIMA. Part I: Dynamical equations and tests. Contrib. Phys. Atmos., 65, 129±146. Kramm, G., Dlugi, R., Dollard, G. J., Foken, T., M olders, N., M uller, H., Seiler, W., Sievering, H., 1995: On the dry deposition of ozone and reactive nitrogen compounds. Atmos. Environ., 29, 3209±3231. Landsberg, H. E., 1970: Man-made climatic changes. Science, 170, 1265±1274. Mellor, G. L., Yamanda, T., 1974: A hierarchy of turbulence closure models for planetary boundary layers. J. Atmos. Sci., 31, 1791±1806.
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N. Molders: Application of the Principle of Superposition
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