Assessment of the Spatiotemporal Dynamics of Agricultural Drought in the Tekeze Watershed, Northern Ethiopia

Abstract

Agricultural droughts often disrupt cropping patterns in the rain-scarce regions of Ethiopia. Understanding their temporal trends and geographical variations can greatly aid farmers in planning their farming activities. This paper examines the temporal trends, geographical extent, and severity of agricultural droughts in the Tekeze watershed, Ethiopia. Data were acquired from MODIS NDVI using the Earth Engine Data Catalogue and from the Central Statistics Agency (CSA) of Ethiopia. The normalised difference vegetation index (NDVI), enhanced vegetation index (EVI), vegetation condition index (VCI) and Random Forest Regression model were used for data analysis. Findings showed that August and September sustained the highest vegetation cover and health, whilst June and July had the lowest. Over the 24-year period analysed using the VCI, 14 years experienced drought conditions, with areal coverage percentages ranging from 52.45% in 2003 to 78.1% in 2015. The temporal EVI values show that all the years of the study period fall under mild drought conditions on average. Spatially, the EVI drought ranges from 66.1% in 2023 to 82.1% of the total area in 2014. The integrated drought class map created using weighted overlay analysis showed three drought categories (moderate, mild & no drought; consistently covering 0.38%, 63.9% and 35.9% of the area). Over 50% of the area was found affected by various drought levels for several years. The analysis of all indices indicates that the drought recurrence period is approximately 2 years, suggesting a deteriorating situation over time. The EVI analysis indicated that all the summer months during the study period were facing mild droughts, and none of the area was totally free from droughts. Furthermore, NDVI, EVI and VCI were moderately correlated with crop yields, explaining approximately 66%–73% of the variations observed in crop performance. These numerical results highlight the severity and distribution of drought conditions in the watershed. These results not only highlight the urgent need for effective drought management strategies but also stress the importance of continuous monitoring and adaptive planning for farmers in order to mitigate the adverse effects on crop yields.