Rangelands Food Security Monitoring: Synthetic Aperture Radar (SAR) Applications for Famine Early Warning Systems

Traditional waterpoints are essential to pastoral communities in arid and semiarid regions of the world, whose livelihoods depend on grazing livestock in rangelands. These small surface waterbodies provide water for livestock in areas characterized by limited rainfall and desiccating weather conditions. However, monitoring the status of this critical resource is limited by sparse in-situ hydrologic observations in these regions. Satellite remote sensing methods have been shown to be a viable approach to monitoring surface water change in data-poor regions. For example, since 2013, the U.S. Geological Society waterpoint monitor (https://earlywarning.usgs.gov/fews/waterpoint/index.php) has assessed the status of waterholes in pastoral areas of Africa using a water balance model driven by satellite-based precipitation. This study uses synthetic aperture radar (SAR) observations from the European Space Agency’s Sentinel 1 satellites to estimate the seasonal presence and areal extent of waterpoints in pastoral areas of East Africa for the period of record for that Sentinel 1 SAR data is available (2014-present). While this record covers both drought and flood periods in East Africa, it is too short to derive descriptive statistics. To overcome this limitation, outputs from the Famine Early Warning Systems Network Land Data Assimilation System (FLDAS) are related to SAR-based surface water area and used to estimate a long-term surface water area dataset. Standardized indices and anomalies derived from this record may be used as an indicator of the status of the pastoral waterpoints. It is hoped that the fusion of SAR observations and modeled systems will improve our ability to monitor this critical resource.