In Situ and Earth Observation-Based Monitoring of Water Availability in Rangeland Areas of the Sahel and East Africa

Abstract

Rangeland water is critical to food security early warning systems in Africa.  Rangelands feed more than half of Africa’s livestock, providing a source of income to 268 million pastoralists and agropastoralists. Rangeland ponds are a vital source of water for pastoral livestock, directly contributing to household food security and health.  However, rangeland areas of the Sahel and East Africa are water-limited, drought prone, and very food insecure.  In December 2022, the United States Agency for International Development’s (USAID) Famine Early Warning Systems Network (FEWS NET) identified >35 million extremely food insecure people in the countries located in the Sahel and East Africa.  The NASA-funded “Earth Observation-Based Monitoring and Forecasting of Rangeland Water Resources” (Rangelands Monitoring and Forecasting System) project partners with FEWS NET to develop new capabilities for monitoring and forecasting water availability in African rangeland ponds.  FEWS NET partner, the U.S. Geological Survey, maintains the Water Point Viewer (https://earlywarning.usgs.gov/fews/software-tools/25), an interactive map that monitors the relative depth and area of 338 water points across arid and semi-arid regions of the Sahel and East Africa, from Senegal to Somalia.  The Rangelands Monitoring and Forecasting System project aims to significantly expand and improve the existing FEWS NET Water Point Viewer by increasing the locations monitored, developing new time series of water point surface area using high-resolution satellite data, improving overall model physics, and developing new forecasting capabilities.  These advanced data streams aim to improve pastoral resilience to climate shocks by increasing the capacity of stakeholders to plan for and respond to drought emergencies. In this presentation, we introduce the Rangelands Monitoring and Forecasting System project and present first results from the 2022 field season.  During the 2022 West African rainy season, Action Contre la Faim collected water level observations from staff gauges installed in twelve ephemeral ponds located along transhumance corridors in Senegal.  Over the same period, the surface water extent of each pond was estimated using Sentinel 1 synthetic aperture radar, Sentinel 2 multispectral data, and Landsat multispectral data.  Additionally, the FEWS NET Water Point Viewer simulated water levels in nearby ponds.  The observed water levels were compared to the modeled surface water levels and the satellite data-based surface water extents to understand how well the FEWS NET Water Point Viewer and remotely sensed data streams capture the seasonal variation of water availability in the ponds. This presentation: 1) presents the comparison results and discusses the accuracy of the model- and satellite-based estimates of water availability; 2) discusses the limitations of using remotely sensed estimates of water availability in the West Africa Sahelian region; and 3) presents lessons learned from conducting a field campaign in rural areas of West Africa.  The results from the first year of the project will inform the development of the next generation of the FEWS NET Water Point Viewer and new satellite-based remote sensing data streams for monitoring water availability in pastoral regions.