Using Radar Information in Hydrological Modeling ...

Phys. Chem. Enrfh (B),

Pergamon

Vol. 25, No. 10-12, pp. 1305-1310,200O 0 2000 Elsevier Science Ltd 1464- 1909/00/$

All rights reserved - see front matter

PII: S1464-1909(00)00199-4

Using Radar Information

in Hydrological

Modeling:

COST 717 WG-1 Activities

M. Bruen Centre for Water Resources Received

16 June 2000;

Research,

accepted

Civil Engineering

Department,

Introduction

and

Dublin,

Ireland

current capabilities and of operational experiences and relies on a review of published literature. A number of sources have already been identified, e.g. - Previous COST actions, notably (i) COST 72 : capabilities and potential of radar for measuring preof weather cipitation, (ii) COST 73 : networking weather radar radars; (iii) COST 75 : Advanced systems; which studied (1) Conventional radar, (2) Doppler radar systems, (3) Polarisation diversity and (4) Conventional (Fast) Scanning and produced outline specifications for the Next-Generation European Weather Radar (“NEURAD”) (Collier ,200(1 1997). and (iv) COST 78 Development of Nowcasting techniques; which defined nowcasting as an observation-intensive approach to local, very short term weather forecasting. Typically this is up to 2 hours ahead, but COST 78 considered forecasting up to 12 hours ahead, (Conway et al., 1996; Conway & Labrousse , 1997). - WMO recently published a volume (Moore , 1998) describing the results of a Workshop on “Requirements and Applications of weather radar data in hydrology and water Resources”. It provides a start-ing point for many of the activities of WG-1. Some of the key issues identified by that workshop are (i) improved operational correction/adjustment methods are required, possibly based on vertical reflectivity profiles; (ii) Data resolutions better than 4bit formats are desirable, (iii) guidance is needed on optimal location and configuration of radars for hydrological purposes, (iv) there is an urgent need to maintain good archives of radar data for hydrological use, and (v) representative research basins should be established.

Background

The origin, objectives and structure of COST717 “Use of radar observations in hydrological and NWP models” have already been described by its chairman, Rossa (2000). The action is composed of three Working Groups (WGs). As chairman of Working Group 1 (WG-1) I describe in this paper its planned activities. WG-1 is investigating the use of radar information in hydrological modelling This task and the ideas reported here have emerged from the original Memorandum of Understanding and from the discussions of the working group members. The first task of WG-1 is to establish the current position in relation to the use of radar in hydrological models. This includes both an assessment of Correspondence

College

10 July 2000

Abstract. The COST 717 action is implemented by three working groups, each investigating different aspects of the use of radar observations in hydrological and NWP models. Working Group 1 (WG-I), the subject of this paper, looks at the use of radar observations in hydrological models. It has divided the work into 9 subject topics each being undertaken by teams of 2,3 or 4 members of the WG. Initially these focus on (i) identifying the current state of radar use in Europe and compiling a database of operational systems from which data may be obtained or research undertaken, and (ii) on identifying the sensitivity of hydrological model outputs to the type of high resolution, spatially distributed, precipitation inputs which can be provided by radar. This is the first step in identifying the need for and benefits from such inputs. Account will be taken of the differences between urban and rural catchment requirements. Once these have been done, WG-1 will investigate the use of combined radar/hydrological modelling systems and these together with NWP systems. 0 2000 Elsevier Science Ltd. All rights reserved.

1

University

- Other overviews to be used as a starting point for the literature review include that of Hall (1996)

to: M.Bruen 1305

M. Bruen: Using Radar Information

1306

and the “Advances in Radar proceedings (Almeida-Teixeira

2

hydrology” Workshop et al., 1994)

Tasks for Working Group 1: Using radar information in hydrological modelling

The scientific tasks for WG-1, specified randum Of Understanding (MOU) are: 1. Review models.

current

use of radar

data

in the Memo-

in hydrological

of different radar 2. Identify the error characteristics measurements at a range of scales (temporal and spatial) and examine how these impact on hydrological models. for radar data in 3. Provide a list of requirements different hydrological models for rural and urban catchments and for urban drainage models. tech4. Evaluate the use of radar data and calibration niques in hydrological models to provide quantitative precipitation forecast (QPF) information for hydrological models, over and above that provided by raingauge networks how radar measurements of precipita5. Investigate tion type can improve precipitation rate estimation for input to hydrological models. 6. Examine how radar observations ter means of coupling atmosphere els.

can provide a betand surface mod-

for radar developments needed 7. Establish a requirement for future distributed hydrological models and urban drainage models. The strategy adopted by the WG starts by initially treating the radar and hydrological modelling aspects separately and to put together, from existing sources and from new work by the WG members, a set of baseline information about (i) the ability of radar to estimate precipitation and (ii) the sensitivity of the outputs from hydrological or hydraulic models to spatial and temporal variations in precipitation estimates. There is a large body of existing work related to these topics already in the literature which WG-1 will use as a starting point. For instance, since distributed catchment models became widely available investigators have studied the sensitivity of flow predictions to spatial variability in many of their inputs and this included precipitation, e.g. Finnerty et al. (1997a); Ogden & Julien (1993, 1994). The latter concluded that the hydrological response was more sensitive at smaller space and time scales than at larger scales. Effects of spatial variability on hydrology have also been studied in large scale experiments,

e.g. Taylor et al. (1997). The range of uses for distributed hydrological modelling is continually expanding and spatially distributed precipitation information is even more important when the hydrologic models are used in environmental contexts, for instance to estimate the production of sediment or pollutants from the catchment, Chaubey & Blyth (1999). A recent quick review by the author revealed at least 15 models or modelling systems of this type; CREAMS, SWRRBWQ, SWAT, HSPF, BASINS, WATFLOOD, SWMM, TOPMODEL, OWLS, AGNPS, SHE, CLAWS, ANSWERS, TOPOG, CASC2D. Some of these are related or share components. When the individual studies are completed we intend to address the overall performance of the combination of radar and hydrological models.

3

Organisation

and Composition

of WG-1

The WGs activities will be of three types. The first, as described above, is to establish the current position relating to both the scientific state of the art and actual practice in relation to most of the tasks listed (tasks 1, 2, 3 & 4). This starts with a literature review, compilation of a database of published papers and reports and other contributed documents and a review of these. These activities have already started and most are due for completion in mid 2001. The second involves the contribution of the on-going work of the Working Group members, be it research or practical experience to addressing the issues raised (tasks 4, 5 & 6). An inventory of research or operational radar sites available to the working group members, or willing to contribute to the action, is being compiled. Much of the work envisaged is catchment based and involves measurement of precipitation and/or river flows and assessment of associated errors. The third is to evaluate the information acquired in the previous activities and propose potentially useful approaches to using radar information in hydrology (task 6) and establish their future data requirements (task 7). There is some overlap between the activities and liaison with the other two working groups in the Action will be required in some of the tasks, particularly in the links with NWP models (task 6). WG-1 currently consists of over 20 members from 12 different countries. We formed 8 sub-groups mainly consisting of 3 or 4 people to address the individual tasks described above. Two separate sub-groups have been set up for task 3, one to deal with urban and the other with rural catchments. Each member of WG-1 can join more than one sub-group depending on his interests and willingness to contribute. Each sub-group has a leader, responsible for the completion and reporting of its work. The Action began in 1999 and this short presentation reports on the current position of the above activities as of mid-2000. More detailed results will be presented at Conferences and Workshops during the course of the

1307

M. Bruen: Using Radar Information

Action.

4

(b) To review techniques for quantitative precipitation estimation and assess their error characteristics, the study will:

Description

of proposed study topics

The work was divided

topics mostly corresponding to the tasks outlined in the MOU. The initial topics are each addressed by a single sub-group, but some of the later topics will be addressed by all WG1 members together. The study topics are described briefly below. 4.1

into 9 study

WGl-1 : A review of the use of radar ical models.

in hydrolog-

This review will concentrate on (i) producing a database of world wide applications of radar in hydrology in terms of country, system used, resolution, applications and current research focus. A questionnaire may be used to reduce the possibility of missing unpublished applications; and (ii) identifying current operational users of radar data for hydrological applications and published literature or reports on their operational experience. As well as establishing the current state of the art in hydrological applications of weather radar, this study should identify sources of radar data and possible future experimental basins for further research. 4.2

WGl-2 : A review of different types of radar techniques for (a) identifying precipitation type and (b) estimating quantity of precipitation

This activity includes understanding the error characteristics of the estimators, cf Moore (1998); Barbosa (1994); Dalezios (1988); Dalezios et al. (1984). There may be some overlap with tasks in WG-2. (a) The hydrological response to precipitation depends critically on the type of precipitation. A classical example is the difference between snow which may accumulate in the catchment and not run off for months and rain which may run off very quickly. Also, for instance, precipitation amounts may be overestimated when there is wet hail. To review the available techniques used to identify precipitation types, this study will consider the following factors: 1. Data

pattern ground

sources: Polarization DLR, Satellite, models, recognition, vertical profiles, radiosondes, truth.

might be identified by in2. Convective stratification vestigating temporal and spatial variability of the reflectivity, detection of wind shear and by setting intensity level thresholds. 3. Sources

of error.

4. Scope for automating

these techniques.

between 1. Distinguish of radar data.

quantitative

and qualitative

use

of precip2. Identify error sources in radar estimation itation and investigate their relationship with temporal and spatial scales, range and other factors. 3. Investigate data.

advances

in methods

for processing

radar

methods for improving radar data with 4. Investigate additional information from ground truth, satellite, models, sondes. 4.3

WGl-3 : A review of hydrological forecasting in rural catchments.

models

for flow

There is a considerable amount of information available on general hydrological models for flood forecasting, e.g. Singh (1995), or through the WMO-HOMS (www.wmo.ch) information sharing programme, and on model performance, e.g. WMO (1992) which compared operational models on catchments ranging in size from below 10 km2 to over 2000 km2. There is less comparative information on the type of distributed catchment models which are likely to make best use of the spatial nature of radar estimates of precipitation. Using these and other sources, the study will (a) Establish the requirements for radar data in hydrological models used in Europe and (b) Establish a short-list of models used both in research and operational forecasting for more detailed analysis by other sub-task groups of WG-1. To do this the study will : 1. Identify criteria and a classification scheme for the selection of model-types to be considered in the review. 2. Identify types of catchmentfclimate models have been implement,ed 3. Identify

previous

review

works

4. Establish an internal format (iteratively with next step) 5. Collect steps

model

6. Extend

to recently

7. Suggest

specific

descriptions

developed

models

8. Identify requirements listed models

regimes in which

for model

according

description

to previous

models

for use in Task No.5 for ra,dar data

in the short-

M. Bruen: Using Radar Information

1308

4.4

WGl-4 : A review of hydrological/hydraulic els for flow forecasting in urban catchments

mod-

The differences between models used for flow forecasting for rural and urban catchments justify a separate study for each. The former tend to be hydrological (mainly empirical or conceptual) while the latter tend to have a larger physically-based hydraulic component. Much work has already been done to assess the use of radar for flow forecasting in an urban context. For instance Cluckie et al. (1994) have assessed the influence of ihe temporal and spatial resolution of radar rainfall information on the resulting flood forecast from a urban storm sewer model. This study will (i) review the current use (operational and research) of hydrological and hydrodynamic models with a focus on urban runoff processes and (ii) will provide a list of projects already using or planning to use radar data in an urban context. As well as providing a state of the art review, the goal is to identify commonalities in existing operational approaches and to explain differences in results. To do this, the study will : about 1. Compile a list of models with information countries/locations where they are used.

the

performance criteria to be in4. Establish important vestigated in sensitivity analyses of the hydrological model outputs to the types of errors and uncertainties in radar estimates of precipitation. 5. Do a sensitivity such errors.

and descriptions

3. Analyse the type of equipment, plications involved. 4. Categorise the applications of radar data used 5. Obtain information and assessments. 6. Identify possible investigations 7. Obtain able 4.5

comparison

about

projects

about

algorithms

4.6

with reference

operational

for further

or evaluation

where avail-

models to spa-

To describe the sensitivity of hydrological models to spatial variability in their input data and to use this information to infer sensitivities to the types of error in radar estimates of precipitation. This study will: 1. Classify

3. Determine such data.

usual

data required. types

of variability

and errors

: Evaluation

of flow forecasting

systems

WGl-7 : Future ment models

requirements

for distributed

catch-

WGl-8 : Methods Forecasting (QPF)

for Quantitative

Precipitation

will

1. Review current use of QPF in hydrological models. First distinguish between qualitative and quantitative use of radar data. We have to focus on the quantitative use. 2. Compare different QPF methodologies and trends. Then identify the error sources of radar and assign it to temporal and spatial scales. 3. Establish

performance

4. Assess methods ria.

criteria.

with respect

to performance

crite-

5. To investigate further possibilities for operational QPF. Discuss the methods for advanced radar data processing as well as investigate improvements, possible by the use of additional information from ground: satellite, models, radiosondes etc.

types of model to be investigated.

2. List types of input

WGl-6

This sub-task

experimental

to

This activity will start once the others have made sufficient progress and will use the knowledge and experience built up within the COST 717 team to project forward and predict future requirements. All members of WG-1 will contribute to this activity, which will start with a “brain-storming” session. 4.8

experiences

reports

WGl-5 : Sensitivity of hydrological tial variability and radar errors

to type

of models

This study will evaluate the performance of hydrological forecasting systems which include radar estimation of precipitation. It will start by developing appropriate performance criteria and then proceed to assess the accuracy and reliability of forecasts using these criteria. It will build on and synthesise the information from already published studies, but will attempt to focus on existing operational experience. In particular, scalerelated influences will be examined, e.g. Koren et al. (1999) and the effects of heterogeneity, e.g. Roux et al. (1995).

the

and ap-

of a sub-set

analysis of the same subset of mod6. Do a sensitivity els to the types of error usually associated with radar data.

4.7 2. Obtain documentation projects.

analysis

in 6. Undertake

own research

on QPF.

M. Bruen:

4.9

WGl-9 : Coupling of radar hydrological models.

with atmosphere

Using Radar Information and

This study will depend on the results of previous activities and also of Working Groups 2 and 3. Its components cannot be defined at this stage and is included here to emphasise the intended linkage between the Working Groups.

5

Links

with

work

on other

continents

Some US agencies have already built up considerable experience with using raingauge information together with doppler radar (WSR-88D) products (e.g. one hour precipitation and total storm precipitation products) for precipitation estimation (Seo , 1998; Finnerty et al. , 199713; Smith et al., 1996) in connection with the NEXRAD project, (Klazura & Imy , 1993; Fan et al. , 1996). This is important given the weaknesses identified in precipitation inputs in earlier flood warning systems e.g. for the 1993 Mississippi flood, NOAA (1994 ). That work can be compared with the European experience, e.g. Uijlenhoet et al. (1994), Da Silva et al. (1994). However, one difference is that much European work is concentrated on using weather radar in mountainous regions, e.g. Andrieu et al. (1996); Andrieu et al. (1997), Creutin et al. (1997)) Delrieu et al. (1999).

6

Other hydrological ered here.

uses

of radar

not

consid-

Some related hydrological uses of radar which will not be directly considered by WG-1, but which might be sources of useful information, techniques or ideas are - Use of radar

on satellites,

e.g. Biggin

- Radar sensing of soil moisture, e.g. Wooding (1996); Kane et al. (1993). - Radar sensing (1998).

of snowpack,

e.g.

(1996). Griffiths

Fassnacht

&

et al.

- Radar used in checking precipitation models, e.g. Lee & Georgakakos (1996); Cluckie & Wild (1999). Acknowledgements. The author is happy to acknowledge the contribution of WG-1 members to preparing the workprogramme described here. The COST action is funded by the European Community.

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Andrieu, H., French, M.N., Thauvin, V. & Krajewski, W.F. (1996) Adaptation and application of a quantitative rainfall forecasting model in a mountainous region. J.Hydrol. 184(3-4), pp.243259 Barbosa,-S.(1994) Brief review of radar-raingauge adjustment techniques. in Almeida-Teixeira,M.E., Fantechi,R., Moore,R. & Silva,V.M. Advances in radar hydrology, Proc. Intern. Workshop Lisbon, 1991, European Commission, Brussels, EUR 14334 Biggin,-D.S.; Blyth,-K. (1996) A comparison of ERS-1 satellite radar and aerial photography for river flood mapping. J. Inst. Water Environ. Manage. 10:(l) PP. 59-64 Chaubey, I., Haan, C.T., Grunwald,S. & Salisbury,J.M. (1999) Uncertainty in the model parameters due to spatial variability of rainfall. J. Hydrol. 220:48-61 Cluckie, I.D. & Wild, A.D. (1999) Multi-sensor data and coupled hydrological meteorological modelling in real-time forecasting. In Casale, R., Borga, M., Baltas, E. & Samuels (eds.) River basin modelling, management and flood mitigation. European Commission, Brussels. Cluckie, I.D., Yuan, .I & Shepherd, G.W. (1994) “Radar rainfall data for design, rehabilitation and active control or urban drainage systems” in Almeida-Teixeira,M.E., Fantechi,R., Moore,R. & Silva,V.M. Advances in radar hydrology, Proc. Intern. Workshop Lisbon, 1991, European Commission, Brussels, EUR 14334 Collier, C.G. (ed) (1997) Summary of workshop discussions, COST 75 Workshop on Doppler weather radar, Cervignano de1 Friuli, October 1996. European Commission Collier, C.G. (ed) (2000) Advanced Weather Radar Systems. Final Report of the management committee of COST 75 (1993-1997) Conway, B.J., Gerard, L., Labrousse, J., Liljas, E., Senesi,S., Sunde,J. & Zwatz-Meise, V. 1996, Meteorology-Nowcasting, a survey of current knowledge, techniques and practice. Phase 1 report, European Commission EUR 1.6861 Conway, B. & Labrousse, J. 1997 : Improvement in Nowcasting techniques, International Workshop, Bologna March 1996. European Commission EUR 16996 Creutin, J.D., Andrieu, H. & Faure, D. (1997) Use of a weather radar for the hydrology of a mountainous area. Part II: Radar measurement validation. J. Hydrol. 193( l-4)) pp.26-44 Dalezios, N.R., 1988: Objective’Rainfall Evaluation in Radar Hydrology. J. of Water Resow. Plan. nnd Management, ASCE, 114(5), Sep., 531-546. Dalezios, N.R., 1984: On the Accuracy of Rainfall Measurements by Weather Radar. Proc. 9th Canadian Symposium on Remote Sensing St.John’s, Newfoundld., 13-17 Aug., CRSS, 309-315. Dalezios, N.R., C. Domenikiotis, A. Lo&as, & C. Stoforiadis, 2000. “Discriminating Hailstorms and Rainstorms by Using METEOSAT (Ir) and Weather Radar Data”, XXV General Assembly of the European Geophysical Society, April 2000, Nice, France. Delrieu, G., Serrar, S., Guardo, E. & Creutin, J.D (1999) Rain measurement in hilly terrain with X-band weather radar systems: Accuracy of path-integrated attenuation estimates derived from mountain returns. J. Atmos. Ocean. Technol. 16:(6) pp.405-416 Fan, Y., Wood,E., Baeck, M.& Smith,J.A. (1996) Fractional coverage of rainfall over a grid: Analyses of NEXRAD data over the southern Plains. Wat. Resour. Res. :32:9 pp.2787-2802. Fassnacht, S.R., Soulis, E.D. & Kouwen,N. (1998). Distributed snowpack simulation using weather radar with hydrologic and land surface models. In Hardy, J., Albert, M. & Marsh, P. (eds.) Int. Conf. Snow Hydrology, Brownsville, Ott 1998. Fattorelli, S., Scaletta, M., Borga, M. (1994) Real-time flood forecasting models intercomparison. in Almeida-Teixeira,M.E., Fantechi,R., Moore,R. & Silva,V.M. Advances in radar hydrology, Proc. Intern. Workshop Lisbon, 1991, European Commis-

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