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28 October 2007
STATEMENT FOR HYDROLOGY (as seen from the French side….)
I.
Global water cycle : general
The global water cycle describes the exchange of water between the various components of the climate system, in response to climate variability/change and anthropogenic forcing. On land, water is stored as surface water, and ground water, ice and snow (not discussed here). Surface water includes rivers, lakes, artificial reservoirs, the surface expression of swamps, and ephemerally inundated areas. Due to climate variability, climate change and direct anthropogenic forcing, land water storage fluctuates both in time and space. However due limited and heterogeneous in situ networks, the spatio-temporal distribution of surface waters remains poorly known. At the river basin scale, the water budget is described by the water balance equation which relates water storage to precipitation, evapotranspiration and runoff. Each component plays a major role in the water cycle : Precipitation : major forcing term Evaporation/ canopy transpiration : regulates mass and energy exchange with lower atmosphere (depends on many parameters, amongst these is soil moisture) - Runoff : directly linked to the water balance - Water storage : includes several components o Soil moisture : regulates evapotranspiration; links to the carbon cycle o Snow pack : influence albedo, hence the radiative budget o Ground waters : important for water resources, in particular in semi arid regions o Surface waters: directly linked to precipitation; linked to water resources, carbon cycle, etc. The WATER-HM mission will provide global, high-precision, high-resolution monitoring of the water storage surface component. II. Other complementary satellite missions for studying the global water cycle (recent and future missions) Precipitation : GPM; Megha-Tropiques Soil moisture (SMOS; SMAP) Total water storage : GRACE-1 and Follow-on (?) -
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Develop III. Parameters measured by WATER-HM Lakes and reservoirs : water level, area; volume Rivers : water level, slope, width; discharge Floodplains and wetlands: water level, area, slope;
water volume
2 By-products : land topography, ….
Develop IV: Applications IV.1 : Climate science Contribution to the water balance at river basin scale and links with climate variability and anthropogenic forcing Improvement of global land surface models (better description of floodplains, wetlands, etc.) contribution to improved climate prediction with global coupled models.
IV.2 Regional hydrology : Separation of climate change/variability and anthropogenic forcing (irrigation, dam building, deforestation, etc.) impact on the water balance impact on river discharge, lake levels, floodplains, wetlands, etc impact on water resources predictions and management
IV.3 Hydrological modelling improvement of global/regional water balance modelling for climate science (seasonal to interannual) (see IV.1) hydrological modelling at river basin-scale (> 100x100 km) (time scale : days to weeks) data assimilation Improvement of flood prediction models ( time scale : hours to days ; spatial scale : 10 kmx10 km) data assimilation
IV.4. Oceanography Fresh water input from rivers : impact on small-scale ocean circulation and on large-scale thermohaline circulation Improvement of Ocean Global Circulation Models –OGCMs- (most OGCMs currently use climatological runoff) Sea level : role of terrestrial waters –anthropogenic component- on sea level change Coastal erosion : role of coastal currents, storm surges, sea level rise, etc.
IV.5 Other applications V. Human health (e.g., link between malaria and wetlands extent ) Carbon cycle : exchange of CO2 between wetlands/floodplains and lower atmosphere Sediment transport in hydrographic basins Ecosystems dynamics Navigation ….. Science requirements (in terms of vertical and horizontal resolution, time resolution, data acquisition delay)
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Lakes, FP, rivers Level
Horz. res. 100m
Vert. res. <5 cm
Time res. - low latitude weekly - arctic basins 2-3 days - flooding daily
delay - offline - offline - NRT -offline
GCOS ECV X
Lakes, FP, Rivers slopes Lakes, FP extent
1 cm/km
100m
- low latitude weekly - arctic basins 2-3 days - flooding daily
- offline - offline - NRT Both NRT And offline
X
River width
< 100 m
Table 1 : requirements for primary parameters (ECV: Essential Climate Variable as defined by GCOS –Global Climate Observing System-)
Discharge Surf. Water volume
Precision Horz. Res.