CLIMATE CHANGE EFFECTS ON THE WATER BALANCE IN THE FULDA CATCHMENT, GERMANY, DURING THE 21 ST CENTURY

Transcription

1 CLIMATE CHANGE EFFECTS ON THE WATER BALANCE IN THE FULDA CATCHMENT, GERMANY, DURING THE 21 ST CENTURY Manfred Koch and Gabriel Fink Department of Geohydraulics and Engineering Hydrology, University of Kassel, Germany Keywords: Climate change, dynamical downscaling, REMO, SWAT, water balance, Fulda catchment

2 Abstract Although a lot of progress towards the understanding of the impact of 21 st century possible climate change on the global water cycle has been made in recent years, the picture of the corresponding hydrological behavior on the regional and local scale is still blurred. Thus, even adjacent catchments in a relatively small country as Germany can react differently to changing climate conditions. The present study tries to improve the understanding the effects of predicted 21 st century climate changes on the regional water cycle in the 6930 km² Fulda catchment in central Germany. Furthermore, the intention is to provide administrative bodies with new guidelines and tools to be better prepared for the expected future effects on the water resources. Using the IPCC-Scenarios A1B, A2, and B1 for the 21 st century in the ECHAM5 AOCGM and its dynamically downscaled regional model REMO, high resolution climate data for the Fulda catchment were generated. These are then used as input in the distributed hydrological model SWAT (Soil and Water Assessment Tool) to simulate the future surface water budget in the basin. SWAT is calibrated and validated in the period with measurements from around 80 rain gauges, 23 climate gauges, and several runoff gauging stations. A good agreement between calculated and measured daily, monthly and yearly amount of runoff in the sub-basins is obtained, as indicated by high RN² of 0.89,0.94 and 0.97, respectively. The 21 st century runoff calculations and the analyses of the water balance result in statements, firstly, with regard to precipitation: In the period there are sequent years with significant higher yearly precipitation than in the reference period Although there is no trend in yearly precipitation, a redistribution to more precipitation in the winter and less in the summer is observed. Secondly, despite no precipitation change there is a significant decrease in the yearly runoff amount, especially for scenario B1. Within one year, the runoff will increase in winter, but will stay more or less constant in summer. The distribution of the yearly runoff is not stationary over the total 21 st century period. Thus multi-annual oscillations complicate trend detection. Due to a warmer climate, under the assumption that land use will not change in the future, evapotranspiration will decrease slightly because of less soil water content, resulting in more water stress.

3 Overview 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions 1.2 Climate change: Hydrological impacts: /Global/regional 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.1 Basics of water budget analysis and implications on sustainable water management 2.2 Scales and variability of climate and hydrological systems 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related to hydro-climate modeling 3.2 From global to local scale: downscaling from the climate to the hydrological model. 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin. 4.2 REMO SWAT water balance predictions for the 21 st century 5. CONCLUSIONS

4 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions

5 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions

6 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions

7 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions

8 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions

9 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts / general aspects Climate change impacts / general The hydrological cycle Climate change impacts/ water resources

10 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts/global

11 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts /global

12 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts/europe * Most General Circulation Models (GCMs) predict strong change in rainfall over the the Northern hemisphere with wetter winters and drier summers in Northern Europe GCM results indicate increases in both the frequency and intensity of heavy rainfall events under enhanced greenhouse conditions In Northern Europe 10 to 30 percent increase in the magnitude of rainfall events up to a 50 year return period by the end of the century is expected One of the most significant impacts of such changes may be on hydrological processes and, particularly, river flow Changes in seasonality and an increase in low and high rainfall extremes, such as the droughts of the 1990s and floods of 2000/01 affect the water balance of river basins. * This will influence rate of available water resources, as well as the frequency of flooding and damaging low-flows. Summer precipitation change in % for relative to

13 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts / Germany Changes in annual mean temperature, smoothed with a 11- year window Changes in annual precipitation, (Baur curves) smoothed with a 11- year window.

14 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.2 Climate change: Hydrological impacts/germany 21st century prediction from the Regional Climate Model (REMO) (MPI Hamburg, Germany) annual average temperature winter precipitation summer precipitation REMO predictions of temperature and precipitation changes for relative to

15 Overview 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions 1.2 Climate change: Hydrological impacts 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.1 Basics of water budget analysis and implications on sustainable water management 2.2 Scales and variability of climate and hydrological systems 3. MODELING THE IMPACT OF CLIMATE CHANGE IN THE FULDA CATCHMENT 3.1 General issues related to hydro-climate modeling 3.2 From global to local scale: downscaling from the climate to the hydrological model 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin. 4.2 REMO SWAT water balance predictions for the 21 st century 5. CONCLUSIONS

16 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.1 Basics of water budget analysis and implications on sustainable water management ds / dt = Qin - Qout Total water balance : ds T / dt = P + Qswi ET Qswi /Integrated model Surface water balance: ds S / dt = P ET O I /Surface water model Vadose zone balance: ds V / dt = I R /Vadose zone model Groundwater balance: ds G / dt = R + Gin Gout - Qp /Groundwater model

17 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.2 Scales and variability of climate and hydrological systems /atmosphere and ocean El Nino SST

18 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.2 Scales and variability of climate and hydrological systems /precipitation and streamflow Monthly precipitation and wavelet spectrum in Hamburg Monthly discharge and wavelet spectrum of Elbe river close to Hamburg

19 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.2 Scales and variability of climate and hydrological systems/ groundwater aquifer Effects of drought on groundwater levels and associated subsidence in California. Regional groundwater flow system with at different scales Water elevations in wells in a surficial aquifer in Florida

20 Overview 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions 1.2 Climate change: Hydrological impacts 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.1 Basics of water budget analysis and implications on sustainable water management 2.2 Scales and variability of climate and hydrological systems 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related to hydro-climate modeling 3.2 From global to local scale: downscaling from the climate to the hydrological model. 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin. 4.2 REMO SWAT water balance predictions for the 21 st century 5. CONCLUSIONS

21 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related of hydro-climate modeling /climate and hydrological models Types of climate models Atmosphere general circulation models (AGCMs) Ocean general circulation models (OGCMs) Coupled atmosphere-ocean general circulation models (AOGCMs) Fundamental equations Numerical discretization in AOGCMs

22 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related of hydro-climate modeling /climate models Historical development of climate models Synopsis of GCMs (starting point for all impacts studies, due to anthropogenic forcing): Advantages: information physically consistent, long simulations + different SRES scenarios, many variables, data readily available; Disadvantages: coarse-scale information where regional or local-scale climate information is essential, daily characteristics may be unrealistic except for very large regions, computationally expensive

23 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related of hydro-climate modeling / hydrological models

24 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.2 From global to local scale: downscaling from the climate to the hydrological model Why downscaling? Because there is a mismatch of scales between what global climate models can supply and what hydrological impact models require.

25 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.2 From global to local scale: downscaling from climate to the hydrological model # 8 7 # 6 # # 1 # # 4 Rayong Province 3 # 12 # ; 11 # # 5 #

26 Overview 1. WATER RESOURCES IN THE FACE OF CLIMATE CHANGE 1.1 Climate change: Observations and predictions 1.2 Climate change: Hydrological impacts 2. SYSTEM ANALYSIS OF SURFACE - AND GROUNDWATER RESERVOIRS 2.1 Basics of water budget analysis and implications on sustainable water management 2.2 Scales and variability of climate and hydrological systems 3. MODELING THE IMPACT OF CLIMATE CHANGE ON SURFACE- AND GROUNDWATER 3.1 General issues related to hydro-climate modeling 3.2 From global to local scale: downscaling from the climate to the hydrological model. 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin. 4.2 REMO SWAT water balance predictions for the 21st century 5. CONCLUSIONS

27 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin / Fulda catchment Weser Objectives of the study: 1. Evaluation of the effects of climate change on water cycle in central Europe Pegel Bonaforth AE = 6930 km² Kassel Eder reservoir W er ra Eder a ld Fu 2. Better understanding of water resources change on the regional scale in a global context Germany erg elsb Vog Fulda N 15km The Fulda catchment with the Eder reservoir and gauge station Bonaforth

28 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin/ Method

29 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 SWAT- hydrological modeling of the Fulda basin

30 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century /C-20 period precipitation

31 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century /REMO-predictions/ Temperature Future temperatures Increase between 2 and 4 degrees, depending on SRES Least increase for the optimistic B1 scenario Delay effect for the A1B scenario at the end of the 21 st century

32 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century /REMO-predictions/ Precipitation Future Precipitation Periods of significantly higher yearly precipitation No long-term trend in yearly precipitation More precipitation in winter /less in summer

33 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century /REMO-predictions / Runoff Future Runoff Increase of yearly flow rate in all scenarios Most runoff increase is detected in the optimistic B1 scenario Significant increase of winter runoff in all scenarios Oscillation of the mean yearly runoff amount

34 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for 21 st century /REMO-predictions/Evapotranspiration Future Evapotranspiration Small decline of evapotranspiration in all scenarios due to less soil moisture and subsequent decreasing water stress of the plant cover

35 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century /SWAT- streamflow predictions Moving average of the calculated yearly runoff amount (mean of 23 years)

36 4. IMPACT OF CLIMATE CHANGE ON THE WATER BALANCE IN THE FULDA CATCHMENT 4.1 REMO --> SWAT- water balance predictions for the 21 st century / SWAT- streamflow predictions Change of monthly runoff amount for A1B scenario Change of monthly runoff amount for A2 scenario Change of monthly runoff amount for B1 scenario

37 5. CONCLUSIONS REMO-predicted climate changes across Germany affect basins inhomogeneously on the regionale scale, because results for adjacent catchment basins differ from those here. In the Fulda catchment area precipitation, runoff, and evapotranspiration will generally change to less water in summer and more water in winter. This study additionally shows the difficulty to quantify future hydrological changes. Chain of errors begins with the evaluation of emission scenarios and ends with SWAT s systematic errors. Only results that are statistically significant are enumerated and used in related studies to evaluate the future hydrology in the basin, such as the occurrence of extreme events. At this stage no reason for concern with respect to major detrimental climate impacts on the water resources in the Fulda basin.