Spatio-temporal drought monitoring in the Megech-Dirma watershed, Ethiopia, using Google Earth engine

Drought is a recurrent hazard with significant ecological and socioeconomic impacts, requiring continuous monitoring and assessment. This study evaluates the occurrence and spatial-temporal distribution of drought in the Megech-Dirma Watershed, Ethiopia, over the period 2001-2022. Agricultural drought indices Vegetation Condition Index (VCI), Temperature Condition Index (TCI), Vegetation Health Index (VHI) and the meteorological Standardized Precipitation Index (SPI) at 3-month temporal scales were analyzed using the Google Earth Engine platform. The time-series analysis revealed minimum VCI values, indicating severe drought, in 2009 and 2010, while moderate to no drought conditions dominated during 2001 to 2009 and 2010 to 2021. Moderate droughts also showed a declining trend in 2009 and 2010. The TCI series identified frequent extreme drought events in 2002, 2003, 2004, 2009, 2013, 2016, and 2019, with severe drought recorded in 2006, 2007, 2010, 2014, 2015, 2017, 2021, and 2022. Mild to moderate droughts occurred in 2001, 2002, 2008, 2018, 2020, and 2022. Minimum VHI values, also indicating severe drought, were observed in 2002, 2003, 2004, 2009, 2012, 2013, and 2016, while 2001, 2006, 2007, 2010, 2014, 2015, and 2017 to 2022 were dominated by mild to moderate drought conditions. SPI revealed moderate drought conditions, showing weak correlations with the vegetation-based indices (correlation coefficients: -0.08 with TCI, -0.04 with VCI, and - 0.06 with VHI). Drought severity increased spatially in the watershed's northern regions. Of the total area, 9.63% experienced extreme drought, 20.95% severe drought, 29.12% moderate drought, 26.94% mild drought, and 13.36% no drought. Drought hazard maps revealed extreme and severe drought concentrated in the northern and southern parts, whereas moderate, mild, and no drought conditions were distributed across the southwest, east, and central regions. These findings highlight the spatial-temporal complexity of drought in the watershed and provide a robust basis for drought monitoring, water resource management, and ecological protection. The results emphasize the importance of continuous observation, proactive measures, and adaptive strategies to mitigate the impacts of drought.