Satellite WRSI-Based Drought Vulnerability Functions and Agricultural Drought Risks Using Paired CHIRPS and Reference ET GRIDS in Senegal

FEWS NET has started a multi-year research project conducting probabilistic risk analysis of agricultural droughts in drought- and famine-prone countries using satellite-estimated rainfall in Africa. This project aims to quantify rain-fed crop productivity losses by developing drought vulnerability functions using satellite derived Water Requirement Satisfaction Index (WRSI) as the hazard index. This spatialized WRSI was generated by running the GeoWRSI software (developed by the Climate Hazards Group at the University of California Santa Barbara), which is one of the multiple indices operationally used to monitor drought-related food insecurity in Africa. The exposure component in this agricultural drought-risk study is represented by the crop yield losses due to deficit soil moisture conditions during historical (1981-2015) drought-affected seasons in Senegal.

In the first phase of this study, constant reference ET was used to force GeoWRSI, due to non-availability of long-term records of reference ET data. However, with the availability of year-specific reference ET grids (1981 onwards) based on the NASA MERRA2 reanalysis, a new time series of WRSI (1981-2015) using paired sets of CHIRPS and reference ET was generated using GeoWRSI. This presentation highlights the improvement in identifying historical agricultural droughts using year-specific reference ET (1981-2015). The results also highlight the comparative influences on the nature of crop-drought vulnerability functions in Senegal. It is observed that new reference ET data set has a significant influence in estimating agricultural drought risks in Senegal.