Climate scenarios for hydrological and environmental impact studies in Belgium

1. Climate scenarios for hydrological and environmental impact studies in Belgium Patrick Willems K.U.Leuven - Hydraulics Division

2. Recent and on-going climate change related research projects PhD researchers in italic Belgium: • Federal Science Policy: climate change impacts on hydrological extremes in Belgium (Victor Ntegeka) • Flemish Government of Belgium – WL: impacts on river high and low flows (Thomas Vansteenkiste) • Environment Agency (VMM): • Impacts on floods (EU Flood Directive implementation) • Update of urban drainage design guidelines • MIRA-S: review of climate change impacts on water management • INBO: climate scenarios for impact analysis on nature • Federal Science Policy: climate change impacts on river water quality (Liliana Pagliero) Nile Basin: impact on high and low flow extremes (Paul Ogiramoi Nyeko, Sara Girma Mille, Meron Teferi) Tarim basin China: impact on hydrology (Tie Liu) Paute basin Ecuador: impact on hydrology (Diego Mora)

3. Selected approach for hydrological impact analysis of climate change Hydrological / environmental impact model Historical today series Climate change Historical impact series climate change + perturbation scenario Hydrological system Climate system

4. Downscaling of climate model simulation results Large Scale General Circulation Models (GCMs) 150 – 300 km; seasonally – monthly Dynamical downscaling Regional Climate Models (RCMs) ± 50 km; weekly - daily ± 25 km; daily Statistical downscaling river subcatchment scale, point scale river catchment: hourly; urban drainage systems: 10 min Hydrological scale

5. Statistical downscaling GCMs 300 km RCMs 50 km RCMs 25 km • 3 types of methods considered and advanced: • Quantile-perturbation based methods (SD-A) • Weather typing based methods (SD-B) • Combined methods (SD-C) Large scale “predictants” Local scale “predictors” Rainfall-runoff model Hydrological system Climate system

6. GCM-RCM runs for Belgium simulations of IPCC greenhouse gas emission scenarios by 2100: European PRUDENCE project: 10 RCMs, 31 simulations (A2,B2) IPCC AR4: 21 GCMs, 27 simulations (A2, A1B, B1) DMI 25 km

7. Quantile perturbation factors RCM Probability distribution / IDF 30 years daily series today = control run (1961 – 1990) Comparison quantiles Probability distribution / IDF 30 years daily series scenario scenario = scenario run (2071 – 2100)

8. Rainfall IDF-relations 10 min Uccle series: Return period: 100 years 10 years 1 year 1 month

9. Change in IDF-relations Daily rainfall results, 17 ECHAM5 runs:

10. Change in IDF-relations SD-A-5, 17 ECHAM5 runs:

11. µ % change in rainfall, temperature and ETo by 2100 • Dependent on: • Time scale • (hour, day, week, month, season) • Return period / frequency • (incl. extreme rainfall) • Region • (15% higher at Belgian coast) • Accounting for uncertainties in climate model results and future greenhouse gas emissions (31 RCM runs A2/B2; 27 GCM runs A2/A1B/B1) : summarized in High, Mean and Low scenarios Rainfall extremes % rainfall change Return period Belgian coast

12. Climate change scenarios: perturbation factors on rainfall and ETo quantiles High scenario Mean scenario Low scenario Example: Perturbation factors for daily winter rainfall extremes:

13. CCI-HYDR high, mean and low climate change scenarios High / Wet IMPACT Floods Mean / Mild Low / Dry Low flows CCI-HYDR Perturbation Tool:

14. Selected approach for hydrological impact analysis of climate change Hydrological / environmental impact model Historical today series Climate change Historical impact series climate change + perturbation scenario Hydrological system Climate system

15. River high flow impact results Regional differences hourly runoff peaks: • Change in flood risks is highly uncertain • Runoff peaks due to rainfall/ETo change decrease in low scenario and increase in high scenario (up to 35%) • Major influence due to sea level rise (Scheldt tidal river)

16. River low flow impact results Regional differences low flow extremes: • Low flow risks increase significantly in all scenarios • May increase problems rel. water quality, navigation, drinking water production, ...

17. Spatial flood map impact results Flood mapping (before climate change): T = 100 year Current climate

18. Spatial flood map impact results Flood mapping (after climate change till 2100): T = 100 year High scenario

19. River water quality impact results Physico-chemical water quality processes considered:

20. Research challenges • High uncertainties in climate scenarios: • How to calculate? • How to communicate to end users? • How to incorporate in impact investigations? • How to limit number of required impact simulations (scenarios, physical consistency between rainfall, temperature, ETo, ...)? • Limited accuracy of RCM results for rainfall (extremes) • Direct use of rainfall RCM results versus weather typing based downscaling methods? • Statistical downscaling to 10min and point scales: • Several methods and assumptions: ensemble approach on different downscaling methods to be recommended?