Analysis of long-term rainfall trend, variability, and drought in the Awash River Basin, Ethiopia

Abstract

Changes in rainfall and drought significantly impact agriculture and water management, making it vital for effective planning and management. This study aimed to analyze rainfall trends and drought conditions in the Awash River Basin, Ethiopia. Twenty meteorological (1985–2021) and nine streamflow (1985–2014) station data were used to analyze rainfall trends, variability, and drought conditions based on the Mann–Kendall test, innovative trend analysis, standardized precipitation index, agricultural standardized precipitation index, reconnaissance drought index, effective reconnaissance drought index, and streamflow drought index. Based on Mann–Kendall’s test results rainfall during the Bega season showed a decreasing trend at all stations while Tsedey and Kiremt seasons showed an increasing trend at the majority of the stations. However, the Belg season and annual rainfall showed no clear trend at the majority of the stations. A significant (p < 0.05) increase at Debre Berhan and a decrease at Awash7kilo and Ginchi were observed in annual rainfall by 44.1, 102.4, and 116.4 mm per decade, respectively. The innovative trend analysis revealed the Tsedey and Bega seasons showed increasing and decreasing trends in the majority of the stations for all rainfall categories, respectively. However, the annual, Belg, and Kiremt rainfall showed no clear trend in the majority of the stations for different rainfall categories. Annual rainfall showed increasing (Debre Berhan, Mojo, and Sheno) and decreasing (Awash7kilo, Dire Dawa, and Ginchi) trends for all rainfall categories. Generally, there is high variability in rainfall during Tsedey, Bega, and Belg, moderate and low variability during Kiremt, and annual with moderate and irregular rainfall distribution for the majority of the stations. The drought analysis revealed that 15.7, 17.3, 30.7, and 16.3% of drought periods were detected with annual standardized precipitation, agricultural standardized precipitation, reconnaissance drought, and effective reconnaissance drought indices, respectively. Hydrological drought conditions also showed a high probability of occurrence amounting to 47.6 and 48.2% for annual and three-month with severe indices of about -2.58 and -4.26 found at Awash Melka Sedi and Metehara gauge stations, respectively. Moderate to extreme hydrometeorological droughts have occurred approximately every six to eight years, with significant drought events recorded in 1987/88, 1991/92, 1996/97, 2001/02, 2003/04, 2014/15, and 2016/17. The results could have paramount importance for water resource policies and planning for rainfall variability and drought management and adaptation strategies in the Awash River basin.