Variations of land water storage over the last half century

Variations of land water storage over the last half century K. Laval, T. Ngo-duc, J. Polcher University PM Curie Paris/Lab Meteor Dyn /IPSL IUFRO_2005

Land Water Balance Variation of land water in Land Surface Models: -Precipitation (highly variable) -Melting of Snow and Ice -Evapotranspiration -Total Runoff Runoff yields river discharge Y to the surface water Network:integration over a basin IUFRO_2005

Outline • Construction of 53-year atmospheric data to force LSM Models • Results on river discharges (Mekong): Seasonal and interannual variations • Preliminary results on water storage (Grace Mission): Influence of inundated and irrigated areas IUFRO_2005

The ORCHIDEE land surface model of IPSLSECHIBA : surface energy and water balances (land and soil)STOMATE : surface biochemical processesLPJ :evolution of the vegetation and the carbon budget • Only Sechiba is used in the simulations. • Inclusion of a routing scheme, which routes water to oceans through a cascade of linear reservoirs. • Ducoudre,N, K. Laval and A. Perrier, 1993: a new set of hydrological exchanges at the land atmosphere interface. J. of Climate,6248-273. IUFRO_2005

Forced simulation over 53 years • Construction of 53-y forcing data and integrations of Land Surface Model • Validation of river discharges IUFRO_2005

Construction of NCC data NCEP/NCAR Reanalysis 6h; 1°.875; 1948-present Interpolation to the grid 1°×1°, differences in elevation between the grids were taken into account NCEP CRU (Climate Research Unit)precipitation 0.5°×0.5°, 1901-2000 NPRE CRU (Climate Research Unit) temperature 0.5°×0.5°, 1901-2000 NCRU Radiation: SRB (Surface Radiation Budget) NCC (NCEP/NCAR Corrected by CRU) 6-hourly, 1°x1°, 1948-2000 http://dods.lmd.jussieu.fr/cgi-bin/nph-dods/Dods/NCC/ (~40GB) Ngo-duc, T., J. Polcher and K. Laval (JGR, 2005)

Validation The river discharge of the world's 10 biggest rivers Station Obidos 55.51°W, 1.95°S • Observed discharge • GRDC (Global Runoff Data Center) • Data at UCAR (the University Corporation for Atmospheric Research)

OBS NCC • quality of the NCC forcing data is improved compared to NCEP/NCAR • high flow in simulated mean seasonal signal is too early NCEP/NCAR NCC OBS • the interannual signal is well described by the NCC experiment NCEP/NCAR Amazon River Discharge IUFRO_2005

Seasonal signal of Mekong discharge at Pakse IUFRO_2005

Annual Discharge simulated at Pakse IUFRO_2005

Taylor diagram: NCEP and NCC 1. Amazon 2. Congo 3. Orinoco 4. Changjiang 5. Brahmaputra 6. Mississippi 7. Yenisey 8. Parana 9. Lena 10. Mekong Precipitation: most important improvement Temperature: significant effect only at high latitudes Radiation: improves discharge amplitudes IUFRO_2005

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From Frappart et al submitted GJI. IUFRO_2005

Irrigated and Inundated areas IUFRO_2005

> 0.3 mm day-1 > 0.2 mm day-1 IUFRO_2005

Simulated Soil Moisture by Orchidee IUFRO_2005

Mekong discharge at the mouth of the river 18500 16600 IUFRO_2005

GRACE Mission (Gravity Recovery And Climate Experiment • GRACE, twin satellites launched in March 2002, measure the Earth's gravity field with unprecedented accuracy. This produces estimates of changes in water storage for given terrestrial regions. IUFRO_2005

Water storage variationas simulated by 2 versions of Orchidee (with and without routine scheme ) and evaluated by Grace Mission (o). The routine scheme improves the simulated water storage IUFRO_2005

Conclusions • Orchidee is able to reproduce seasonal and interannual changes of continental water reservoirs. • NCC data set was found reliable. • The influence of inundated and irrigated areas seems substantial for the water budget of Mekong basin. • Estimations from GRACE seem to confirm the role of ground water. IUFRO_2005

IUFRO_2005

GRACE ORCHIDEE with routing ORCHIDEE without routing Seasonal variations of continental water April/May – November 2002 The routing scheme improves the signals over tropical basins

Variations of land water storage over the last half century

Variations of land water storage over the last half century

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