Monitoring droughts in Eastern Sub Saharan Africa using satellite remote sensing data

Abstract

Droughts pose significant challenges to Eastern Sub-Saharan Africa (including Kenya, Tanzania, and Uganda), affecting agriculture, water resources, and socio-economic development. A recent study by the United Nations Office for the Coordination of Humanitarian Affairs found that from July to September 2022, about 3.5 million people in Kenya alone are facing high levels of acute food insecurity, a 10% increase from the same period in 2021. Monitoring and early warning of droughts is crucial to implementing effective mitigation and adaptation strategies that are currently severely lacking in Eastern Sub Saharan Africa. This study aims to utilize satellite remote sensing data to analyze drought events in Kenya. The key datasets used in this study are the Normalized Difference Vegetation Index (NDVI) data product from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) measurements, as well as the Vegetation Health Index (VHI), and Vegetation Condition Index (VCI) derived from NDVI. Together with rainfall data from the final run estimates of the Integrated Multi-satellite Retrievals for GPM (IMERG) (developed by fusing together the precipitation estimates collected in 2000-2014 during the operation of the Tropical Rainfall Measuring Mission (TRMM) satellite with more recent precipitation estimates collected during operation of the GPM satellite), analysis of the temporal trend of vegetation health and precipitation was established in order to investigate the impacts of droughts. The results illustrated a significant decreasing trend in precipitation and vegetation across Kenya in the past decades. Monthly precipitation anomalies over both the dry season and wet season have evident troughs and peaks indicating drought events with lack of rainfall. Analyzing the dry season alone in the period from 2016 to 2018, the NDVI anomaly showed a consistent decreasing trend indicating a severe decline in vegetation health and in turn crop production. This decreasing trend of both precipitation and NDVI is strongly correlated with extreme drought events consistently hitting Kenya and other parts of East Africa.