Forecast of soil moisture change

Soil moisture

Evaporation, inflitration and recharge of the groundwater usually occur through the unsatured vadose zone which is the hydrological connection between the surface water and the groundwater. The root zone of the vegetation, the zone where vegetation takes-up water, is within the vadose zone and is therefore the interface between the vegetation and the hydrological system. The amount of water available in the vegetation controls plant transpiration and photosynthesis and as such CO₂ sequestration. It is also directly linked to the ability of the soil to produce drainage after rainfall. The soil-vegetation-atmosphere transfer (SVAT) schemes used in meteorology and hydrology are designed to describe the basic evaporation processes at the surface, together with the water partitioning between vegetation transpiration, drainage, surface runoff and soil moisture variations.

In operational simulations a realistic initial value of the amount of water in the vadose zone must be provided to SVAT models. Time series of surface soil moisture allow to determine by means of assimilation the amount of water available in the vadose zone and that of the surface fluxes (evapotranspiration). When dealing with bare soil or sparsely covered vegetation, evaporation rate and runoff can be calculated from surface soil moisture time series. When dealing with vegetation covered surfaces, the amount of water in the vegetation (vegetation optical depth) has to be accounted for. The vegetation optical depth itself may be a very useful product to monitor the vegetation dynamics.

Ocean salinity

Knowledge of the distribution of salt in the global ocean and its annual and inter-annual variability are crucial in understanding the role of the ocean in the climate system. Ocean circulation is mainly driven by the water and heat flux through the atmosphere-ocean interface, but salinity is also fundamental in determining ocean density and hence thermohaline circulation. Ocean salinity is also linked to the oceanic carbon cycle, as it plays a part in establishing the chemical equilibrium, which in turn regulates the CO₂ uptake and release. Therefore the assimilation of sea surface salinity measurements into global ocean bio-geo-chemical models could improve estimates of the absorption of CO₂ by the oceans.