1. Page 1 Met Office contribution to RL5 Task 5.1.2. ‘Large-scale interactions between atmospheric moisture and water availability - coupling of atmospheric and hydrological RCMs’ Debbie Hemming and Richard Betts Hadley Centre, UK Met Office, Exeter UK

2. Page 2 Mediterranean already experiencing water stress. Projections indicate this region will experience some of the largest increases in water stress in the future. Change in water stress, due to climate change, in countries using more than 20% of their potential water resources. Water availability will be the major issue in the coming century. Pressure on water supplies comes not only from climate change but also population growth and increased consumption. Projected changes in global water stress University of Southampton

3. Page 3 Part 1. Water availability projections Quantify current and future projections of water availability utilising data (precipitation, evapotranspiration, runoff, soil moisture) from RCM runs forced by future socio-economic scenarios (from RLs 1 and 2). Assess changes in water availability spatially, using GIS mapping techniques (ArcGIS 9.2), and temporally, on monthly and inter-annual time scales for two time horizons; 2020-40’s and 2080s-2100. Examine the causes of water availability changes by quantifying changes in its components, i.e. precipitation and evaporation. Assess uncertainties in current and future water availability projections using ensembles of RCM runs (from RLs 1 and 2). Provide suitable datasets of water availability and its components, under current and future projected climates, for regional impacts assessments and case studies (links with RL11). Report water availability projections to stakeholders interested in water stress adaptation and mitigation policies.

4. Page 4 Part 2. Understanding large-scale feedbacks between atmospheric and land- surface components of the water cycle Run coupled RCM over Mediterranean with the latest land-surface (MOSES II land surface model) and hydrological (river routing scheme) specifications. Quantify major feedbacks of atmospheric and land-surface changes on water cycle, i.e. runoff, river flow, soil moisture, precipitation, and compare these for current and future climate scenarios. Examine sensitivity of feedbacks by forcing the RCM with changes in land-surface characteristics, including vegetation and urban cover. Report these sensitivities to stakeholders interested in water stress adaptation and mitigation policies.

5. Page 5 Additional drivers of climate change: biophysical effects of land cover change using GCM Ramankutty and Foley (1999) Present-day cropland coverage Effect of historical land cover change on temperature (K)

6. Page 6 Feedbacks of irrigation on temperature using GCM Boucher et al (2004) Water vapour flux from irrigation (kg m -2 year -1 ) Difference in surface temperature (K): irrigated – non-irrigated Small +ve radiative forcing due to increased water vapour, but overall cooling at surface

7. Page 7 Hydrological impacts in Hadley GCM - river routing model fully incorporated % Change in river flow from 1961-1990 average 2071-2100 SRES A1B River model is an integral component of the climate model Climate change leads to changes in means and seasonality of flows Pete Falloon (HC)