Soil moisture and precipitation: The SM2RAIN algorithm for rainfall retrieval from satellite soil moisture

The standard approach for measuring instantaneous rainfall rates from space is based on the inversion of the atmospheric signals reflected or radiated by atmospheric hydrometeors, i.e., a "top-down" approach. Recently, a new "bottomup" approach has been proposed that exploits satellite soil moisture observations for obtaining accumulated rainfall estimates. The approach, referred to as SM2RAIN, is based on the inversion of the hydrological water balance. In this chapter, after a short description of the SM2RAIN algorithm and its application to satellite soil moisture data, the two most recent satellite rainfall products obtained by the application of SM2RAIN to ESA-CCI (European Space Agency - Climate Change Initiative) and ASCAT (Advanced SCATterometer) soil moisture products are illustrated. Then, we have investigated the use of SM2RAIN-derived rainfall products, in comparison with "top-down" precipitation products, for improving flood forecasting over 600 basins in Europe. Finally, the limitations of the SM2RAIN algorithm and the future research and technological developments to address such limitations are provided.