Impact of climate change on the groundwater run-off

Open Geosci. 2015; 7:1–14

Research Article

Open Access

Tomasz Olichwer* and Robert Tarka

Impact of climate change on the groundwater run-off in south-west Poland Abstract: The article discusses the variability of total runoff and groundwater run-off affected by global and local climate changes using the example of 17 selected river basins located in south-west Poland. Based on the data collected from 1966 to 2005, the average annual values of the total and groundwater run-off, as well as the seven-day annual minimum flows, were estimated, which provided useful information about droughts. The calculated parameters were compared with precipitation, air temperature, aridity index (the ratio of the precipitation and potential evapotranspiration), and the NAO (North Atlantic Oscillation) and AMO (Atlantic Multidecadal Oscillation) indices. There were no significant changes in the total run-off in the research area; however, there was a reduction in the groundwater run-off, which indicates change in groundwater recharge. The strongest relationship of total run-off, groundwater run-off and seven-day annual flow minimum was obtained from the NAO index, which confirms that the run-off from the study area is dependent on global factors. This is important for the estimation of changes in the runoff from the study area in response to the climate scenarios for the years 2011–2030, which indicate a fairly significant increase in air temperature and slight differences in precipitation. Based on extensive investigations, a reduction in the groundwater run-off in favour of increased surface run-off should be expected in the research area. Keywords: groundwater resources; climate change; longterm variability; south-west Poland DOI 10.1515/geo-2015-0001 Received April 8, 2014; accepted August 31, 2014

*Corresponding Author: Tomasz Olichwer: University of Wroclaw, Institute of Geological Sciences, pl. M. Borna 9, 50-204 Wroclaw, Poland, E-mail: [email protected]; Tel.: 0048713759217 Robert Tarka: University of Wroclaw, Institute of Geological Sciences, pl. M. Borna 9, 50-204 Wroclaw, Poland, E-mail: [email protected]; Tel.: 0048713759208

1 Introduction Climate change is a significant global problem which has been discussed for many years [5, 7, 15–19]. Recently (September 2013), a report published by UN experts [20] stated that humans are responsible for 95% of the greenhouse effect, which causes an increase in average air temperature, loss of snow and ice, and rising sea levels. CO2 leads to increases in run-off due to the effects of elevated CO2 concentrations on plant physiology [9]. The warming trend for the last 30-year period is roughly three times that for the past 100 years as a whole and it is expected that global temperatures will continue to rise by between 1.5 and 2.0 ∘ C by 2100 due to the emissions of greenhouse gases [20]. At the global scale, there is an evidence of change in annual run-off, with some regions experiencing an increase [36, 38] and others afflicted by a decrease, for example in West Africa and South America [26], respectively. Results of the UN report predict that the future climate in Europe will be warmer, the southern areas will get drier and the northern parts will become wetter. Climatic changes will determine river run-off patterns: namely, a decrease in annual river run-off in the south of Europe and an increase in the north. An indirect consequence of climate change is water resources modification [21, 27, 37]. Future climate change may have a significant impact on river flows and the likelihood and magnitude of extreme events, including droughts and flooding. This will directly affect groundwater resources, which are the main source of the world’s drinking water. Long-term analysis of groundwater run-off is necessary for the efficient management of water resources [13, 30]. Groundwater resources are much greater than surface water resources and are highly dependent on climatic conditions and human activities [1, 11, 12, 23]. Poland is one of the countries with the lowest amounts of renewable groundwater resources in Europe. The index of water availability in Poland equals 1,450 m3 /capita while in Europe it equals 4,500 m3 /capita on average. Although 3,000 km3 of static groundwater resources exist on Polish territory, only some 15.5 km3 /year can be effectively exploited due to poor

© 2015 T. Olichwer, R. Tarka, licensee De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License.

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2 | T. Olichwer, R. Tarka renewability of the resources [31]. For this reason, it is important to be able to estimate groundwater resources in the future, due to their great socio-economic importance. The river flows data are used for the assessment of groundwater resources represented by the groundwater run-off. The total run-off rate can be measured more accurately than other components of the water balance. Therefore, this type of data should be studied more precisely. This enables the groundwater run-off to be determined as a measure of groundwater resources. The main goal of this article is to examine fluctuations of total run-off and groundwater run-off due to changes in both global and local climate using the example of selected river basins in south-west Poland.

2 Case study

Figure 1: Map of the study area.

The study area is located in south-west Poland (Lower Silesia and Opole Silesia) and has a surface of 21,884.1 km2 (Figure 1). There are mountain ranges (Sudety Mountains) in the south, with Mt Śnieżka (the highest peak, 1603 m ASL) in the central part of this area, and plains (100–150 m ASL) in the north. The study area consists of 17 river catchments of different sizes and with different environmental characteristics (Table 1). The surface areas of the catchments range from 55.9 to 4,666.2 km2 . The research area is within the temperate climate zone with a predominance of oceanic influences, which results in significant annual variations in groundwater recharge. In the winter most of the precipitation is retained in the snow, while in summer the greater part of the water evaporates. The climate of the region is diverse. The northern, lowland part of the region is one of the warmest areas in Poland [2]. Summers are long and warm, while winters are short and mild [24]. Annual precipitation ranges from 500 to 1,100 mm (multi-annual period 1966–2005). The highest precipitation is recorded in the summer months [6] (Figure 2), and snow cover lasts for 50 days on average. In the southern, mountainous part, in the Sudety Mountains, the climate is much harsher. Here, the average annual precipitation ranges from 750 to 1,900 mm and the snow cover lasts from 60 to 150 days a year (longest in the Karkonosze Mountains and Śnieżnik Massif). The highest values of mean annual air temperature, as determined for the period 1966–2005, are recorded in lowland areas (8.9 ∘ C in Legnica, 8.8 ∘ C in Wrocław). With increasing altitude, the average annual temperature drops

Figure 2: Monthly precipitation changes at the selected weather stations in the study area: 1966–2005.

in Lower Silesia by an average of 0.55 ∘ C per 100 m. On the top of Mt Śnieżka it is 0.7 ∘ C (Table 2). The southern part of the study area (mountains) has the highest precipitation, and this decreases towards the north (lowlands). The lowest average daily temperatures are recorded in the south, increasing towards the north. Observations in south-west Poland since 1966 show that there has been an increase in air temperature and a decrease in precipitation. Climate scenarios for the years 2011–2030 show a fairly significant increase in air temperature (+0.9 ∘ C for south-west Poland) and slight differences in precipitation. In terms of the occurrence and development of the groundwater resources, the research area can be divided into three regions following a NW–SE course: 1. Mountain region (Sudety Mountains): groundwater is recharged from fractured-porous, poorly isolated crystalline and porous fossil structures. The highest


Impact of climate change on the groundwater run-off in south-west Poland

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Table 1: River catchments of the study area.

River A B C D E F G H I J K L M N O P R

Gauging station Kłodzko Nysa Skorogoszcz Szalejów Dln. Lądek Zdrój Krasków Oława Białobrzezie Świerzawa Żagań Mirsk Staniszcze Wlk. Osetno Korzeńsko Dobra Cieszyn Chałupki

Nysa Kłodzka Bystrzyca Dusznicka Biała Lądecka Bystrzyca Oława Ślęza Kaczawa Bóbr Czarny Potok Mała Panew Barycz Orla Biała Olza Odra

Surface A [km2 ] 1084 3276.3 4514.5 174.8 164 683.4 957 180,9 133.7 4254.3 55.9 1107.4 4579.3 1127.2 353.4 454 4666.2

precipitation and groundwater run-off across the region ranges from 7 to 9 dm3 /s·km2 [3, 28]. 2. Foreland region (Sudetic Foreland): pore waters are in sand and gravel Quaternary and Tertiary deposits, and the base, in the fractured-porous poorly isolated crystalline formations, is a region of recharge and drainage. Groundwater run-off ranges from between 4 and 6 dm3 /s·km2 [3]. 3. Lowland region (Silesian Lowland): a groundwater feeding region in the porous Quaternary and Tertiary deposits with the Odra River as the main axis of drainage. The values of the groundwater run-off are in the range of 2 to 4 dm3 /s·km2 [3]. In the mountain catchments, dominated by forest cover (up to 77%), groundwater and total run-off are determined only by natural factors. In the foreland areas there is a stronger impact of anthropogenic factors: forests cover about 30% of the foreland area, while arable land covers up to 60% and urban areas up to 10% [8].

3 Data and methods The study of the water balance components is important in the assessment of future climate change, including the regional effects of global climate change. Long-term hydrological and meteorological observations provide a range

Type of river basin mountain, foothills mountain, foothills mountain, foothills, lowland mountain mountain mountain, foothills foothills, lowland foothills mountain, foothills mountain, foothills, lowland mountain lowland lowland, numerous ponds and swamps lowland foothills mountain, foothills mountain, foothills

of temperature, rainfall and river flow data. The river flow rate can be measured more accurately than other components of the water balance; therefore, this type of data should be studied more precisely. This information enables the groundwater run-off to be determined as a measure of groundwater resources. Data on river flow and meteorological characteristics are taken from the Institute of Meteorology and Water Management (IMWM). Data from the hydrological years 1966– 2005 includes daily river flow values from 17 gauging stations, mean daily temperatures from 11 weather stations and total monthly precipitation from 12 weather stations. The river flow is measured at the outlet of the investigated catchments. IMWM gauging stations closely studied river catchments. The water level is recorded and then the discharge is assessed through a rating curve. There is a permanent control of the stage–discharge relationship. IMWM has proprietary software to determine the curves in hydrometric profiles developed by the logarithmic method recommended by the International Organization for Standardization and the World Meteorological Organization guides. The method takes into account the shape of the stream channel and resistance to water movement, and its results are compared with the data obtained from the hydrodynamic model. When developing the components of the water balance it is important to check the homogeneity of the observation series of the balance sheet items. Such a study


4 | T. Olichwer, R. Tarka Table 2: Precipitation and temperature: 1966-2005

Weather station Bielsko Biała Jelenia Góra Kalisz Katowice Legnica Wrocław Śnieżka Kłodzko Opole Zielona Góra Ostrawa Racibórz Częstochowa Leszno

Precipitation [mm] avg. max. min. 985 1507 738 687 1004 462 509 721 318 728 1011 515 524 795 360 564 776 380 1181 1908 755 589 806 371 631 855 375 582 769 386 691 938 472 626 825 399 – – – – – –

Temperature [0 C] avg. – 7.4 – 8.2 8.9 8.7 0.7 7.5 8.8 8.6 8.5 – 8.0 8.5

– – – – Figure 3: Summation curve of Nysa Kłodzka River flow in Kłodzko.

– is carried out using an analysis of the summation curves of, for example, the river outflow. If the observation series are considered as homogeneous, then summation curves can be compensated for by straight lines. If the summation curve has to be compensated for by two or more straight lines this indicates a lack of uniformity, and in this case the balance should be defined separately for each segment. Summation curves for the river outflow values of all the rivers were made for this study and the results confirmed the homogeneity of the data used for characteristics of runoff (see the example in Figure 3). Hydrological and meteorological data were subjected to mathematical and statistical transformation in order to obtain the following data set: – Total annual precipitation and mean monthly precipitation for the multi-annual periods of 1966–1975, 1976–1985, 1986–1995, 1996–2005 and 1966–2005,

Altitude [m ASL] 325 342 140 284 122 120 1603 356 176 192 275 205 293 91

and the maximum and minimum monthly precipitation totals in the multi-annual period 1966–2005. Mean annual and monthly air temperatures for each year in the multi-annual period 1966–2005. Mean annual and monthly total run-off for each year in the period 1966–2005. Mean total run-off for the multi-annual periods of 1966–1975, 1976–1985, 1986–1995 and 1996–2005. Mean total run-off for the multi-annual period 1966– 2005. Mean total run-off in summer and winter seasons by decade: 1966–1975, 1976–1985, 1986–1995 and 1996– 2005.

Data were processed using Excel, Grapher and Statistica softwares. Due to the complex nature of water-bearing structures and their varying and poorly identified inflow parameters, the most suitable hydrological methods in this study area are those based on the measurement of water flow in the rivers, which are the drainage base for the surrounding rock formations. The most common method for calculation of the regional dynamic resources is to assess the groundwater run-off, which recharges underground rivers [10]. According to the definition given in [4], the groundwater run-off is a part of the run-off which has passed into the ground, becomes groundwater, and is discharged into a stream channel as spring or percolation water. Groundwater run-off comes from the drained aquifers in the river basin.



To determine the total run-off and groundwater runoff, the generic hydrograph separation method was applied. According to this method an analysis of the course of the falling curve is made, which illustrates the recession of the flood wave. Groundwater run-off was calculated using Method 1 (fixed-interval method) of the hydrograph separation and analysis HYSEP program [32]. According to this method, in order to determine the groundwater runoff, the lowest value of the flow on the hydrograph is estimated for a fixed time period (usually a few days) for all days, starting with the first day of the period of record. On the basis of groundwater run-off calculations the following time series were obtained: – Mean annual and monthly groundwater run-off for each year in the period 1966–2005. – Mean groundwater run-off for the multi-annual periods of 1966–1975, 1976–1985, 1986–1995 and 1996– 2005. – Mean groundwater run-off for the multi-annual period 1966–2005. – Mean groundwater run-off in summer and winter seasons by decade: 1966–1975, 1976–1985, 1986–1995 and 1996–2005. The total run-off and groundwater run-off is also characterised by the division of seasons into summer (May– October) and winter (November–April). Trend analysis was applied to the annual value of the total run-off and groundwater run-off (for the hydrological year) as well as for the summer and winter periods. Moreover, an analysis of the incidence of days in the hydrological year with discharge below the 10th percentile was performed. For the calculation of periodic changes of groundwater, total run-off and precipitation, data from the decades 1966–1975, 1976– 1985, 1986–1995 and 1996–2005 were used. The results of the run-off in annual mode, over decades and during the entire measurement period for all 17 catchments, are presented in the Tables 3, 4, 5. On the basis of total and groundwater run-off and meteorological data, the following different analyses and evaluations were made: – Estimation of groundwater recharge coefficient (α = Qg Q ). – Estimation of groundwater run-off module (Mg). – Estimation of run-off coefficient (comparing the total run-off to the precipitation). – Comparison of groundwater run-off in winter and summer seasons. – Variation of groundwater run-off in decades.

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– Variation of total run-off and groundwater run-off in the multi-annual period 1966–2005 for each river basin. – Variation of total run-off and groundwater run-off in winter and summer seasons (the multi-annual period 1966–2005) for each river basin. – Long-term precipitation changes at the weather stations. – Long-term mean temperature changes at the weather stations. – Relation between mean annual precipitation and mean module of the groundwater run-off. – Relation between mean annual temperature and mean module of the groundwater run-off. – Correlations between annual run-off and climate characteristics. – The number of days with flows below the 10th percentile. European climate, and thus also Polish climate, is significantly affected by changes in atmospheric circulation over the North Atlantic [40]. The nature of the variability of the atmospheric circulation over the North Atlantic is easily described by two particular indicators: the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO). In this article we use the NAO index from Hurrell [14], which describes the pressure difference between Lisbon and Stykkisholmur/Reykjavík averaged for the December–March period. The indicator values were obtained from the UCAR website (). The AMO index shows the variability of the intensity of the thermohaline circulation over the Atlantic. Some researchers consider the AMO as one of the main long-term regulators of climate change on a global scale, not only in the tropical Atlantic and Atlantic–European circulation sector. AMO variability is determined by the AMO index, which does not have a standardised, universally accepted form. Generally, the AMO index is an appropriately modified value of the average annual sea surface temperature anomaly in the North Atlantic. In Poland, the negative phase of the NAO in the winter is associated with harsh winters and hot and stormy summers with increased precipitation and late-spring floods. The positive phase of the NAO results in warmer winters, an increase in the number of rainy days and reduction in the river flow ranges [25, 41]. To provide forecasts of groundwater resources, the authors used information included in the climate change scenarios for Poland from the IMWM for the years 2011–2030. Using statistical-empirical models (statistical downscaling), the relationship between the large-scale force field (regional atmospheric pressure field over Europe and the


6 | T. Olichwer, R. Tarka Table 3: Mean total and groundwater run-off: 1966-2005

Q [m3 /s] Qg [m3 /s] 1 2 3 1 2 3 A 13.4 14.4 12.4 7,94 8.59 7.29 B 30.0 27.9 32.0 16.6 16.7 16.6 Nysa Kłodzka C 36.6 34.8 38.4 21.7 22.3 21.1 D Bystrzyca Dusznicka 2.25 2.64 1.86 1.4 1.59 1.22 E Biała Lądecka 3.56 3.18 3.94 2.91 2.73 3.10 F Bystrzyca 4.49 4.86 4.1 2.12 2.58 1.66 G Oława 3.84 4.22 3.4 2.56 2.86 2.26 H Ślęza 0.53 0.56 0.5 0.3 0.34 0.26 I Kaczawa 1.18 1.34 1.02 0.65 0.77 0.54 J Bóbr 38.5 43.9 33.0 26.5 30.5 22.5 K Czarny Potok 0.9 1.01 0.79 0.42 0.51 0.34 L Mała Panew 7.44 8.69 6.19 4.72 5.5 3.94 M Barycz 15.6 20.7 10.6 9.54 12.6 6.44 N Orla 4.48 6.65 2.32 2.29 3.46 1.11 O Biała 1.15 1.23 1.07 0.75 0.84 0.65 P Olza 8.48 9.2 7.77 3.32 4 2.63 R Odra 43.7 46.9 40.6 22.4 26.2 18.7 Q – total run-off; Qg – groundwater run-off; 1 – 1966–2005; 2 – winter; 3 – summer. River

Table 4: Mean total and groundwater run-off by decades

Q [m3 /s] Qg [m3 /s] 1 2 3 4 1 2 3 14.87 12.69 12.26 13.85 8.95 7.25 7.45 36.48 30.02 23.88 29.62 20.61 14.73 14.79 Nysa Kłodzka 44.85 38.05 26.16 37.46 27.49 21.10 16.62 Bystrzyca Dusznicka 2.23 2.13 2.29 2.36 1.38 1.31 1.51 Biała Lądecka 4.14 3.18 3.26 3.65 3.33 2.63 2.85 Bystrzyca 4.98 4.88 2.86 5.23 2.56 2.27 1.48 Oława 3.71 4.5 3.94 3.2 2.25 2.86 3.11 Ślęza 0.66 0.69 0.27 0.49 0.41 0.38 0.14 Kaczawa 1.16 1.32 1.01 1.22 0.65 0.73 0.59 Bóbr 40.23 42.12 33.83 37.85 28.76 28.24 24.59 Czarny Potok 0.9 1.05 0.88 0.77 0.49 0.47 0.42 Mała Panew 9.07 8.64 4.85 7.2 5.63 5.53 3.35 Barycz 17.03 17.37 13.14 15.17 10.76 10.31 8.17 Orla 4.68 4.9 3.88 4.47 2.35 2.4 2.13 Biała 1.21 1.55 0.86 0.98 0.75 0.92 0.65 Olza 8.16 8.53 7.83 9.41 3.28 3.26 3.2 Odra 50 45.99 34.71 44.38 24.12 23.39 19.4 1 – 1966–1975; 2 – 1976–1985; 3 – 1986–1995; 4 – 1996–2005. River

A B C D E F G H I J K L M N O P R

North Atlantic Ocean) and the elements of the climate of Poland were determined. The construction of the models

4 8.12 16.60 21.83 1.42 2.84 2.19 2.03 0.27 0.66 24.69 0.32 4.37 8.93 2.27 0.66 3.53 23.06

was based on the data from the period 1971–1990, using two methods of statistical downscaling: canonical corre-



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Table 5: Groundwater run-off in summer and winter seasons

River


Nysa Kłodzka Bystrzyca Dusznicka Biała Lądecka Bystrzyca Oława Ślęza Kaczawa Bóbr Czarny Potok Mała Panew Barycz Orla Biała Olza Odra

1966-1975 winter summer 9.19 8.71 20.8 20.3 28.1 26.8 1.54 1.22 2.88 3.79 3.07 2.04 2.65 1.85 0.44 0.38 0.77 0.52 32.5 24.9 0.57 0.4 6.58 4.47 14.5 6.98 3.71 1 1.2 0.73 3.75 2.81 27.8 20.4

Qg [m3 /s] 1976-1985 1986-1995 winter summer winter summer 7.73 6.77 8.19 6.71 15.2 14.2 14.3 15.2 21.7 20.5 16.9 16.2 1.42 1.2 1.75 1.26 2.41 2.86 2.9 2.8 2.78 1.76 1.84 1.11 3.11 2.6 3.36 2.85 0.41 0.34 0.19 0.1 0.85 0.61 0.73 0.44 30.8 25.6 29.1 20.1 0.56 0.39 0.54 0.3 6.31 4.75 4.06 2.64 13.3 7.24 11.8 4.51 3.36 1.44 3.48 0.78 1.68 0.79 1.03 0.51 3.83 2.7 4.11 2.29 26.8 19.9 23.9 14.9

lation and redundancy analysis. Information about future changes in atmospheric circulation was obtained from two global simulations: ECHAM-5 and HadCM3 [39].

4 Results and discussion 4.1 Characteristics of Total and Groundwater Run-off in South-West Poland The groundwater run-off, part of the total run-off, comes from the draining of aquifers located within the catchment area, and is highly dependent on the spatial distribution of the elements of climate, especially precipitation [22, 29]. Recognition of the size and dynamics of the run-off plays an important role in understanding the water balance and allows better use of groundwater. The definition of groundwater run-off coincides with the notion of dynamic groundwater resources; thus, these two terms will be used interchangeably. The values for the groundwater run-off modules, in the study area, are much higher in the mountain catchments than in the lowland ones [3, 28]. Higher values for the total run-off and groundwater run-off are observed in the winter season (Ta-

1995-2005 winter summer 9.26 6.98 16.3 16.8 22.7 20.9 1.63 1.21 2.71 2.97 2.65 1.73 2.3 1.75 0.34 0.21 0.73 0.58 29.8 19.5 0.38 0.25 5.4 3.7 10.8 7.01 3.29 1.24 1.01 0.56 4.33 2.72 26.3 19.7

bles 3, 5), while precipitation reaches its highest values in the summer season. There is a high correlation (0.7–0.8) between the total annual precipitation and mean annual groundwater run-off. Under natural conditions, groundwater recharge occurs due to the infiltration of rainwater and melting snow cover. The intensity of these factors and their seasonal variability determine the amount of groundwater recharge. Groundwater recharge in the study area occurs primarily in the late winter and early spring seasons, when large amounts of water are released by snow melting, which is accompanied by high rainfall. This period plays a decisive role in shaping the water regime of the research area [33, 35]. Of the annual water balance, the summer water supply makes a lower contribution to the groundwater recharge, although this increases with altitude. However, in the lower parts of the study area (lowland) the summer– autumn supply can be quite irrelevant [35]. The analysed river catchments show medium total run-off from 0.53 (Ślęża River) to 43.7 m3 /s (Odra River, Chałupki) (Table 3). Total run-off during winter is from 11% to 49% higher than in summer, with the exception of the catchments of the rivers Biała Lądecka and Nysa Kłodzka (gauging stations in Nysa and Skorogoszcz), where it is 10% to 20% lower. Comparing the run-off size to the precipitation at the nearest weather station, the run-off coef-


8 | T. Olichwer, R. Tarka Table 6: Mean total and groundwater run-off: 1966-2005

α [%} Mg dm3 /s·km2 ] 1 2 3 1 2 3 59.2 59.5 58.8 7.33 7.93 6.73 55.6 59.7 52 5.09 5.1 5.09 Nysa Kłodzka 59.4 64.3 55 4.82 4.96 4.68 Bystrzyca Dusznicka 62.3 60 65.6 8.03 9.07 6.99 Biała Lądecka 81.8 85.8 78.7 17.77 16.62 18.91 Bystrzyca 47.3 53.2 40.3 3.1 3.78 2.43 Oława 66.7 67.7 65.6 2.68 2.98 2.36 Ślęza 57.1 61.8 51.8 1.66 1.9 1.43 Kaczawa 55.6 57.6 52.9 4.9 5.77 4.03 Bóbr 69 69.6 68.2 6.25 7.19 5.3 Czarny Potok 47.1 50.7 42.6 7.6 9.16 6.03 Mała Panew 63.4 63.2 63.7 4.26 4.96 3.56 Barycz 60.9 61 60.6 2.08 2.76 1.41 Orla 51 52.1 48.1 2.03 3.07 0.99 Biała 65 68.7 60.8 2.11 2.38 1.84 Olza 39.1 43.5 33.8 7.31 8.82 5.79 Odra 51.4 55.9 46.2 4.82 5.61 4.02 α− groundwater recharge coeflcient; Mg – groundwater run-off module; 1 – 1966–2005; 2 – winter; 3 – summer. River


ficient in winter is on average two and a half fold greater than in summer. The least amount of difference is recorded for the Biała Lądecka River (1.91), and the most for the Bystrzyca Dusznicka River (3.37). Mean values of the total run-off in individual years vary from two and a half times (Biała Lądecka River) to more than 17 times (Ślęża River). The smallest variation of the mean annual total run-off occurs in the mountainous catchments, but as the average height of the catchment decreases the difference between the highest and lowest annual total run-off increases in the considered period. Since the 1990s, the number of days with low flows has increased. This trend is illustrated in Figure 4, which for the selected rivers shows the number of days with flows below the 10th percentile. There have been 42 such days a year on average for each of the rivers since the end of the 1980s, while in the years 1990–2005 there were over 56 such days. The analysed catchments have an average groundwater run-off from 0.3 m3 /s (Ślęża River) to 26.5 m3 /s (Bóbr River) (Table 3). The module of dynamic groundwater resources in the study area for the years 1966–2005 ranged from 1.66 dm3 /s·km2 (Ślęża River) to 17.71 dm3 /s·km2 (Biała Lądecka River). The highest values were observed in small catchments in mountain areas (southern part of the research area). The lowest val-

Figure 4: Number of days with river flows below the 10th percentile in selected catchments of the study area.

ues of modules were recorded for the lowland catchments (Table 6). Throughout the entire area the underground drainage in winter was from 1% (Nysa Kłodzka-Nysa River) to 68% (Orla River) higher than in the summer, which confirms the primacy of the winter–spring groundwater recharge (Table 3, 5). The exception is the catchment of the Biała Lądecka River where the groundwater run-off in summer is 12% higher than in the winter season. This exception is the result of very high rainfall recorded in summer (Mt Śnieżnik weather station, 1425 m). In most cases the coefficient of the groundwater recharge (Qg/Q) in the



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Figure 5: Trends of change of total and groundwater run-off in selected catchments of the study area: 1966–2005. Figure 6: Trends in total and groundwater run-off in summer and winter seasons in the Bóbr River catchment (in Żagań): 1966–2005.

described area is in the range of 50% to 60%: the lowest values are recorded in the catchment of the Olza River (39%), while the highest are in the catchment of the Biała Lądecka River (81%). The highest mean values of dynamic resources throughout the area were recorded for the period of 1966–1975, while the lowest were in the years 1986–1995 (Table 5). The groundwater run-off regime in the area has changed over the decades, predominantly due to climate change. The vast majority of the catchments in the research area, regardless of their location and nature, show a trend towards reduced total run-off and groundwater runoff in the multi-annual period 1966–2005 (see examples shown in Figure 5). The exception to this rule is the run-off regime in two mountainous catchments of the rivers Olza and Bystrzyca Dusznicka, where no change in the total run-off and groundwater run-off in the multi-annual period 1966–2005 was recorded. Such run-off in both catchments was affected by the trend towards an increase in the winter season and a decrease in the summer season. In most of the discussed catchments, both in summer and winter, there are downward trends in total runoff and groundwater run-off, as shown in the example of the catchment of the Bóbr River (gauging station in Żagań) (Figure 6). The downward trends in the total run-off in relation to the groundwater run-off are clearly shown, especially in the summer season.

Figure 7: Bar graph of the long-term precipitation changes at the selected weather stations.

4.2 Influence of Climate Change on Groundwater Resources Precipitation and air temperature are very important elements of climate that directly or indirectly affect the size of groundwater resources. The data from the multi-annual period 1966–2005 indicate a tendency toward decreased precipitation at most of the weather stations taken into account. Figure 7 shows the mean annual precipitation values at the weather stations representing mountain areas (Mt Śnieżka), the forelands (Kłodzko) and lowlands (Wrocław). In the case of air temperatures, the overall upward trend of mean annual values is observed at all 11 weather stations. Data for some stations representative of the general trends are shown in Figure 8. In the study area


10 | T. Olichwer, R. Tarka

Figure 8: Long-term mean temperature changes at the selected weather stations.

there is a very close link between the groundwater run-off and precipitation, as evidenced by the high value of the Pearson correlation coefficient (0.83). What is also apparent is the relationship between the groundwater run-off and the temperature: the Pearson correlation coefficient is −0.55. In order to assess the impact of climate change on total run-off and groundwater run-off, correlation coefficients, reflecting the evolution of the drainage over time, were calculated (Table 7). For the requirements of the following interpretation, the level of significance α = 0.1 was adopted. For the level 0.1, the statistical significance of the correlation coefficient (r) has a value above 0.28 and below −0.28. The calculations indicate that there is no relation between the changes of total run-off and groundwater run-off over time in the 10 studied catchments at the assumed significance level of 0.1. In the remaining seven catchments there is a relation between decreasing run-off, with the correlation coefficients ranging from r = −0.28 (Oława River) to r = −0.48 (Mała Panew River). A similar situation is seen in the changes over time for the seven-day annual minimum flow. In the 11 studied catchments there is no dependence, while in the remaining six the correlation coefficient ranges from r = −0.28 (Biała River) to r = −0.59 (Bóbr River). However, in the case of the groundwater runoff the situation is different since, statistically, only in six catchments was there no decrease in the groundwater runoff over time. For the remaining 11 catchments the calculations showed a decrease in the groundwater run-off during the period 1966–2005, with the correlation coefficients ranging from r = −0.29 (Biała Lądecka River) to r = −0.51 (Mała Panew River). In the second phase of the study, the authors compared the change in the total and groundwater run-off and the seven-day annual minimum flow with the meteorological characteristics and indicators of the characteristics of climate change (Table 7). The total run-off shows the most

statistically significant correlation with the tested characteristics. This relationship is significant in the case of temperature for 16 out of the 17 catchments, in the case of precipitation for 12 catchments, and in the case of the NAO and the AI for 14 catchments. In the case of the groundwater run-off, there is a significant relationship with temperature in 13 catchments, with the precipitation and the AI in 11 catchments, with the NAO in 10 catchments, and with the AMO in one catchment. Relatively, the lowest number of significant correlations was obtained for the sevenday annual minimum flow. However, the value of this flow shows dependence in the case of AI for 10 catchments, of precipitation for nine catchments, and of the NAO index for eight catchments. Only in three catchments (the rivers Oława, Czarny Potok, Mała Panew) were statistically significant correlations of the flow characteristics with the value characterising the AMO demonstrated (Table 7). The obtained statistically significant negative correlations of the examined flow characteristics with the NAO suggest that at the negative NAO phases the corresponding run-off characteristics increase. Higher negative correlations are visible in the case of the total run-off (Table 7). On the basis of the study, no relationship was observed between the changes in the total run-off and groundwater run-off and the seven-day annual minimum flow with the size or location of the catchment.

4.3 Hydrological Droughts Hydrological drought is manifested by decreased water flow in watercourses and a lowered water level in natural and artificial water bodies. A lowered level of shallow groundwater in contact with surface waters is also related to hydrological drought [34]. The occurrence of extreme conditions that produce hydrological droughts is important for the formation of dynamic groundwater resources. The inter-annual precipitation variability for the multi-annual period 1966–2005 in the described area is approximately 50%; persistent droughts are not uncommon. The largest precipitation deficits occurred in the years 1982–1984, 1988–1992, 1999–2000 and 2003–2004 (Figure 9), resulting in the occurrence of low values of groundwater run-off and the formation of hydrological droughts. Periods of low water levels are broken by periods of increased groundwater run-off during increased water recharge (winter–spring). Droughts in the early 1990s and early 21st century are the result of low precipitation during those periods. In the late 1980s and early 1990s precipitation remained below average for four years. In 1992



Table 7: Correlations between annual run-off and climate characteristics (1966-2005). River

Characteristic Years Temperature Precipitation AI NAO Q 0.05 −0.28 0.38 0.41 −0.21 Qg 0 −0.21 0.38 0.40 −0.13 Bystrzyca Dusznicka 7 days 0.06 −0.03 0.11 0.12 0.08 Q −0.25 −0.28 0.28 0.32 −0.24 Qg −0.29 −0.16 0.23 0.25 −0.11 Biała Lądecka 7 days 0.17 −0.04 −0.18 −0.18 0.21 Q −0.28 −0.44 0.26 0.30 −0.31 Qg −0.2 −0.36 0.19 0.22 −0.11 Oława 7 days −0.10 −0.11 −0.05 −0.03 0.21 Q −0.42 −0.43 0.40 0.44 −0.59 Qg −0.47 −0.42 0.42 0.45 −0.59 Ślęza 7 days −0.56 −0.45 0.30 0.34 −0.49 Q −0.17 −0.35 0.39 0.42 −0.48 Qg −0.34 −0.39 0.51 0.54 −0.49 Bystrzyca 7 days −0.25 −0.30 0.41 0.43 −0.33 Q −0.12 −0.38 0.21 0.30 −0.38 −0.38 0.26 0.34 −0.30 Qg −0.19 Kaczawa 7 days 0.14 −0.16 0.35 0.37 −0.28 −0.34 0.13 0.23 −0.27 Q −0.26 Qg −0.50 −0.50 0.14 0.25 −0.21 Czarny Potok 7 days −0.20 −0.29 0.15 0.16 −0.30 −0.35 −0.41 0.09 0.19 −0.48 Q Qg −0.35 −0.39 0.22 0.3 −0.40 Odra 7 days −0.02 −0.19 0.27 0.33 −0.23 Q 0.12 −0.17 −0.22 −0.18 −0.26 Qg 0.09 −0.13 −0.19 −0.16 −0.19 Olza 7 days 0.11 −0.04 −0.04 −0.01 −0.15 −0.43 −0.51 0.39 0.48 −0.38 Q Qg −0.37 −0.39 0.48 0.53 −0.24 Biała 7 days −0.28 −0.11 0.41 0.42 −0.04 Q −0.48 −0.48 0.52 0.60 −0.43 Qg −0.51 −0.46 0.56 0.64 −0.39 Mała Panew 7 days −0.56 −0.30 0.42 0.49 −0.35 Q −0.21 −0.30 0.42 0.47 −0.34 Qg −0.23 −0.13 0.50 0.51 −0.28 Nysa Kłodzka - Kłodzko 7 days −0.36 0 0.50 0.51 −0.31 Q −0.40 −0.42 0.49 0.58 −0.40 Qg −0.38 −0.31 0.47 0.53 −0.33 Nysa Kłodzka - Nysa 7 days −0.09 0.01 0.24 0.29 −0.07 Q −0.38 −0.49 0.35 0.40 −0.48 Qg −0.40 −0.47 0.36 0.40 −0.47 Nysa Kłodzka - Skorogoszcz 7 days −0.31 −0.11 0.37 0.4 −0.52 Q −0.24 −0.38 0.65 0.70 −0.35 Qg −0.30 −0.35 0.71 0.75 −0.25 Bóbr 7 days −0.59 −0.32 0.47 0.53 −0.11 Q −0.16 −0.38 0.40 0.42 −0.31 Qg −0.14 −0.37 0.40 0.42 −0.29 Orla 7 days −0.24 −0.36 0.24 0.26 −0.64 Q −0.26 −0.48 0.52 0.55 −0.31 Qg −0.27 −0.46 0.53 0.55 −0.36 Barycz 7 days 0.05 −0.05 0.19 0.17 −0.22 Q – total run-off; Qg – groundwater run-off; 7-day – seven-day annual minimum flow; AI – aridity index; grey patch – at the significance level of 0.1.


AMO 0.25 0.19 −0.01 −0.07 −0.16 −0.04 −0.16 −0.20 0.27 −0.02 −0.02 −0.07 −0.01 −0.11 0.09 −0.11 −0.19 0.17 −0.24 −0.37 0.14 −0.16 −0.09 −0.05 0.05 0.04 0.04 −0.21 −0.15 −0.21 −0.23 −0.25 −0.38 0.05 0.05 −0.12 −0.10 −0.08 −0.03 −0.05 −0.02 −0.08 0.01 −0.03 −0.34 0.07 0.06 0.05 −0.08 −0.09 0.03

| 11

12 | T. Olichwer, R. Tarka precipitation was slightly higher than the average, which improved the water balance in the river basins of the study area. The drought of 2003–2005 was the result of a very low precipitation level in 2003–2004, ending after high precipitation in 2005 [34]. The drought in the years 1999–2000 was a relatively minor one, which occurred at a time when precipitation was at a medium level (in the year 1999), or even a bit higher (2000). It was the consequence of a shortage of precipitation in the summer and very high air temperatures – the year 2000 was the warmest in the multiannual period 1966–2005, and the mean annual air temperature was 1.5 ∘ C above its mean value at that time.

Figure 9: Diagrams of the number of days with the river flow below the 10th percentile in chosen river basin of research area.

The frequency of drought is illustrated by the diagrams showing the number of days with the water flow below the 10th percentile (Figure 9). The figure presents the typical situation observed at all the studied river catchments in the research area. In the multi-annual period 1966–2005 there are four periods with a significant number of days with low river flows, which coincide with the largest precipitation deficits. In particular, a significant increase in days with low flows, and hence low groundwater run-off, can be seen in the 25 years between 1980 and 2004.

5 Conclusions There is a clear link between climate and hydrology. The general circulation of the atmosphere is connected to the total and groundwater run-off regime. For all selected emissions scenarios for the period 2011–2030, the mean annual air temperature will increase by about 0.9∘ C in south-west Poland [39]. The climate reports show that in the 21st century in the described area the climate will be getting warmer twice as fast as it did in the 20th century. In terms of precipitation, the climate scenarios for the research area for the period 2011–2030 indicate a very small

increase in total annual precipitation (up to 5%) or the lack of such changes. However, seasonal changes will be observed. On the one hand, in the winter and spring seasons the precipitation will increase by up to 10%; on the other hand, during the summer and autumn seasons, there is expected to be a decline in precipitation, sharpest in the autumn [39]. Precipitation will be a little less frequent, but may be more intense, which may result in more frequent droughts and floods. These climate scenarios for the years 2011–2030 forecast small changes in precipitation and significant changes in air temperatures, with increasing surface evaporation, which currently accounts for about 50% of water losses in the overall water balance in the area under study. Increased evaporation will reduce the groundwater run-off, especially in the summer and autumn seasons, during which significant deficits in groundwater resources may appear. Warmer winters and springs, and thus earlier snow melting, will increase total run-off and, to a lesser extent, groundwater run-off during the late winter and early spring. These scenarios also indicate a change in the precipitation pattern due to its increased intensity. Based on extensive investigations, a reduction in the groundwater run-off in favour of increased surface run-off should be expected in the Sudety Mountains and in their foreland. Thus, the slight variations expected in surface water resources will be accompanied by a reduction in groundwater resources. The overall conclusion of this study is that for the years 1966–2005 there were no significant changes in total run-off in the Sudety Mountains and in their foreland. However, in most catchments in the research area there was a reduction of the groundwater run-off during this time. Decreased groundwater run-off with no major changes in the total run-off indicates a change in the pattern of groundwater recharge, which could be a result of the change in the precipitation pattern in the form of a reduction in the number of precipitation events in favour of fewer events with increased intensity. The strongest association between changes in the total and groundwater run-off and seven-day annual flow minimum was obtained for the NAO. This confirms that there is a partial influence of global factors on the run-off from the Sudety Mountains and their foreland. This is significant for the assessment of expected changes in the run-off from the Sudety Mountains in accordance with the climate scenarios for the years 2011–2030, which indicate a fairly significant increase in air temperature and slight differences in precipitation.



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