Multi-Source Earth Observation Data for Drought Monitoring in the Borena Region in Southern Ethiopia

Abstract

Drought is a recurring phenomenon in the Borena region of Southern Ethiopia. The imbalance between potential evaporation and precipitation during the growing season often results in drought conditions, posing significant threats to the biodiversity, agriculture and human activities. The zone has endured severe drought risk due to consecutive years of no rainfall, significantly impacting ecosystem services, livestock and agro-pastoralist communities. To mitigate the effects of droughts and to provide quick decision-making with timely information for an effective response, it is crucial to regularly analyze the information about its severity and its extent in terms of spatial and temporal pattern. This study analyzes the spatial and temporal pattern of drought in the Borena region, using integrated indices such the Composite Drought Index (CDI) from 2000 to 2022. The CDI, which incorporates the Precipitation Drought Index (PDI), the Temperature Drought Index (TDI), and the Vegetation Drought Index (VDI), are used as input to examine spatial and temporal drought patterns, providing a comprehensive view of drought conditions over the given area. Additionally, the Mann–Kendall trend test and Sen’s slope were employed to understand the trends of these indices and determine their magnitude of change.The study identified the occurrence of extreme drought events in recent years during 2007, 2011, 2014, 2016, 2017, and 2021 in Borena Zone. The findings also showed a decreasing trend in rainfall, an increase in temperature, and a diminishing trend in vegetation condition during the study period. Specifically, the computed mean growing season of the Normalized Difference Vegetation Index (NDVI) values ranged between -0.02352 to 0.0312, with 57.67% of the Borena region showing a decreasing trend. Future work will incorporate actual evapotranspiration (ET) estimates based on thermal infrared (TIR) imagery within the CDI, as this has the potential to more rapidly detect water stress in vegetation compared to spectral indices such as NDVI. These findings can guide the development of climate policies, disaster risk reduction and strategies in Ethiopia, contributing to the mitigation of future drought impacts and the promotion of sustainable dryland natural resources practices, including supporting early drought warning detection systems for agro-pastoralist communities.