Spatiotemporal Rainfall Variability in the Borena Zone, Southern Ethiopia, and Its Linkage to Large-Scale Climate Oscillations: Implications for Food Security Among Pastoral Households

Abstract

This study focuses on daily extreme climate indices and their underlying causes, rather than traditional average climate investigations. The primary aim is to effectively strategize adaptation measures for climate extremes and ensure food security. The research was conducted in the Borena Zone, an area that has experienced recurrent extreme weather events, particularly droughts, over the past few decades. Utilizing daily rainfall and temperature data sourced from the National Meteorological Agency (NMA) spanning from 1981 to 2020, the study examines the variability of climate extreme indices within the Borena Zone. In addition to mean maximum and mean minimum temperatures, six extreme temperature indices and five extreme rainfall indices were employed for a comprehensive analysis. The results from temporal analysis indicate that maximum daily maximum temperature (TXx), maximum daily minimum temperature (TNx), minimum daily maximum temperature (TXn), and maximum daily minimum temperature (TNn) exhibit significantly increasing trends ranging from 0.016 to 0.053°C/year. Conversely, the extreme temperature indices for cool days (TX10) and cool nights (TN10p) show decreasing trends ranging from 0.058 to 0.406%/year. The spatial analysis of extreme indices also reveals an overall increase in temperature across the zone, confirming a higher warming trend in the area. Among the extreme rainfall indices, the total precipitation (PRCPTOT) shows a very significant increasing trend (p = 0.006) of 3.65 mm/year. The number of very heavy rainfall days (R20mm) and the number of very wet days (R95p) also exhibit significant increasing trends, ranging from 0.05 to 2.044 mm/year. Conversely, continuous wetdays (CWD) show a decreasing trend, while continuous dry days (CDD) demonstrate an increasing trend. The spatial analysis of rainfall indices corroborates the findings from the temporal analysis. Correlation analysis of daily rainfall with global indices such as Sea Surface Temperature (SST) and Sea Level Pressure (SLP) reveals a significant positive correlation with consecutive dry days (CDD) and a negative correlation with consecutive wet days (CWD). The results of this study indicate warming trends in the area, accompanied by erratic rainfall patterns that significantly affect evaporation rates and various key sectors, notably rainfed agriculture, leading to increased drought conditions.