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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
Page 1
Projected changes in global water stress
Mediterranean already experiencing
water stress. Projections indicate this
region will experience some of the
largest increases in water stress in the
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
University of Southampton
Page 2
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.
Page 3
Part 2. Understanding large-scale feedbacks between atmospheric and landsurface 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.
Page 4
Additional drivers of climate change: biophysical effects of
land cover change using GCM
Ramankutty and Foley (1999)
Effect of
historical land
cover change on
temperature (K)
Page 5
Feedbacks of irrigation on temperature using GCM
Water vapour flux from
irrigation (kg m-2 year-1)
Small +ve radiative forcing
due to increased water vapour,
but overall cooling at surface
Difference in surface
temperature (K):
irrigated – non-irrigated
Boucher et al (2004)
Page 6
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
• Climate change leads to
changes in means and
seasonality of flows
Pete Falloon (HC)
Page 7