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

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

3. 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

4. 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.

5. 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

6. 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 ...)

7. 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

8. 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.

9. 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.

11. 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 ??

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