Water Security, Global Change and Land-Atmosphere Feedbacks

Simon Dadson1, Mike Acreman2, Richard Harding2 1University of Oxford (simon.dadson@ouce.ox.ac.uk) 2Centre for Ecology and Hydrology, Wallingford, UK

Photos: M. Acreman

Water use and ecosystem services

IRRIGATION AGRICULTURE

USANGU WETLANDS

RUAHA NATIONAL PARK HYDROPOWER FISHING

• Water use in the Rafiji Basin, Tanzania.

• Upstream irrigation has dried wetlands, affected wildlife and reduced

hydropower.

• Need to understand links between climate change, land use and water

management

• Feedbacks strongest in transition zones between wet and dry climates.

• Need to know state of soil moisture in order to provide accurate forecasts.

• Changes to water management can affect regional climate.

Hydrological feedbacks in the Earth system

Koster et al., 2004. Science 305:1138-1140

HYDROLOGY & WATER RESOURCES

BIODIVERSITY & ECOSYSTEM SERVICES

FOOD PRODUCTION & SECURITY

Key challenges

•  How can we understand the effects of water management decisions in context of global change?

•  We need models that can represent

hydrological processes, water management and climate feedbacks.

Flow routing and inundation in JULES Joint UK-Land Environment Simulator (JULES) takes temperature, wind speed, humidity, LW & SW radiation and precipitation from RCM;

Rainfall Snow Radiation Evaporation

Flux of soil moisture and heat

Diagnose state of soil moisture by using a Pareto distribution of soil moisture stores;

Convert to surface and subsurface flow.

Inundated wetland area calculated using sub-grid elevation data

wetland inundation

Dadson et al., 2010, J. Geophys. Res., 115: D23114

FOOD PRODUCTION & SECURITY

Irrigation alters South Asian monsoon

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•  Indus-Ganges largest continuous area of irrigation in the world •  Irrigation -> evaporation -> cooler land-surface •  Better representation of monsoon depressions with irrigation in

the model

Without irrigation With irrigation

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Land-atmosphere feedbacks in W. Africa

Dadson et al., 2010, J. Geophys. Res., 115: D23114

• Niger Inland Delta, Mali;

• Inundation drives water vapour flux and temperature anomaly;

• Seasonal flooding provides up to 50% of water vapour to atmosphere.

•  Development of a “wetland breeze”; •  50% more daytime storms during floods •  Better land-surface modelling will improve weather forecasts in

West Africa.

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Time of day

After flooding Before flooding

+50%

cooler warmer warmer

Meteosat 1982-2005: Chris Taylor, CEH

Observed land-atmosphere feedback

Dadson et al., 2010, J. Geophys. Res., 115: D23114 Taylor, (2010), Geophys. Res. Lett., 37, L041652

•  Proposed new 90 MW dam at Fomi will: –  reduce fish populations by up to 36% –  disrupt complex relation between flooding and ecology (3-4 million staging waterbirds) –  but increase rice production in newly-irrigated areas by 320,000 t (to meet 90% of

domestic demand) •  How can policymakers balance need for mitigation of & adaptation to climate

change with food security, wetland biodiversity, and other ecosystem services?

Water Resources and Ecosystem Services

Zwarts et al., 2005

Q & A