Description

Precipitation is the first input in water balance studies and water management, however the spatial resolution of the observation is often not adequate for practical purposes. There are many satellite based observation but various uncertainties exist and their spatial resolution are very coarse. Numerous evaluations of available satellite precipitation products have been conducted (Maggioni et al., 2016, J. Hydromet.) for different climates and CMORPH, CHIRPS, and TRMM (and by extension GPM, Gebregiorgis et al., 2018, JGR-Atmos.) showed consistently high performance (Kimani et al. 2017, RS). Nevertheless there remains the necessity for downscaling global products to local estimates to account for the spatiotemporal characteristics of error as well as its relation to rain rate (e.g. AghaKouchak et al., 2012, GRL; Sun et al., 2018, Rev. Geophys.).
In the past years, several satellite evapotranspiration products have been generated, among which, the MOD-16 ET (Mu et al., 2007, RSE) at 1km and daily interval, PM-ET (Zhang et al., 2010, WRR) at 8km and monthly interval, GLEAM (Mirallies et al., 2011, HESS) at 0.25 degree and daily interval, ALEXI-ET (e.g. Anderson et al., 2010, HESS) at various spatial and temporal scales, and SEBS-ET (Su, 2002; Chen et al., 2014) at 5km monthly and 1km daily scale. Evaluations of these and other global evapotranspiration products (e.g. Mueller et al., 2011, GRL; Vinukollu et al., 2011, HP; Wang and Dickinson, 2012, Rev. Geophys.) concluded that all have different uncertainties for local scale studies (e.g. Bhattarai et al., 2018, HESS).

Objectives and Methodology

ITC has established several regional in-situ soil moisture and soil temperature observation networks in the Twente area in the Netherlands, in the Tibetan plateau in China and in Kenya. The soil moisture probes are usually installed at depths of 5, 10, 20, 40 and 80cm below the surface. When one takes into account of the soil properties, the registered soil moisture content should correspond to the forcings due to precipitation and evapotranspiration and as such it can be inferred that by inversing the soil moisture measurements, one can determine the forcings and when taking into different mechanisms (e.g. immediately after a precipitation event or in a period without precipitation), one may estimate such forcings as precipitation and evapotranspiration separately.

Further reading