Impact of climate change on water cycle: trends and challenges Dr Richard Harding Centre for Ecology & Hydrology Wallingford UK rjh@ceh.ac.uk Coordinator of the FP 6 WATCH Integrated Project – Water and Global Change

Global Drivers of Change: interactions Climate rainfall Land cover GHGs Water Resources food fuel GHGs Population, Increasing consumption

But: there is considerable uncertainty … We know there will be changes in rainfall regimes (it is arguable there already have) but the detail is unclear There is good agreement that: Globally rainfall will increase Nearly everywhere temperatures will increase Extremes will increase Generally dry areas get drier and wet wetter Sea level will rise There is not good agreement: Rainfall trends in many regions of the world The magnitude of the changes are uncertain Different hydrological models give different responses to rainfall drivers

Regional Rainfall Changes White areas are where less than 66% of the models agree in the sign of the change and stippled areas are where more than 90% of the models agree in the sign of the change.

The WATCH Integrated Project analyse and describe the current global water cycle evaluate how the global water cycle and its extremes respond to future drivers of global change evaluate feedbacks in the coupled system as they affect the global water cycle evaluate the uncertainties in the predictions develop a modelling and data framework to assess the future vulnerability of water as a resource

Coupling Climate and Hydrological models WATCH products: Global hydrological products (50km) Regional products (12km) Modelling and Downscaling tools Scale Model biases Missing processes (biology, human intervention ...)

Downscaling – linking global models to catchments Upper Guadiana Basin GCM’s Cell Size: 50*50 km2 RCM’s 10*10 km2 Hydrogeo. Model 2.5*2.5 km2 dynamic statistical Global Test basins Regions: Europe, India, W Africa

Estimating Floods in 21st century River S max Subsurface flow - routing Surface flow Drainage, D = K d 3 Topographic gradient, g Precipitation, P Evaporation, E Return fl ow Saturation excess s urface runoff Grid to Grid Percentage change in the magnitude of the 20-year return period flow across the UK using the CEH G2G 1 km model driven with data from the UK Met Office Hadley Centre Regional Climate Model.

Sources of Uncertainty in Flood prediction for 21st Century The variation in the impact of climate change on flood frequency, from various sources (‘ic’ is ‘initial condition’), for five return periods (2, 5, 10, 20 and 50 years). The impact is shown as the percentage change in flood frequency from the current period to the 2080s. The potential range of current natural variability is also shown for comparison.

Linking to Hydrology to Hydro-ecology models Integrated models for climate change impact analysis Mean flow Extreme events (flood and droughts) Stream temperature Pollution Interventions (dams, extractions, power stations etc) Erosion and sediments River morphology Ecological function (plant and animal) NOW MONTHS 1-2 YEARS 3-5 YEARS ??

How can WATCH team help you? Workshops? Briefing/ guidance notes? Sectorial analyses Modelling tools? WEB site? ….