Abstract
Awash River basin (ARB) as a system is in a state of continuous change that requires successive studies to discern the changes or trends of climatic elements through time due to climate change/variability, and other socio-economical developmental activities in the basin. The livelihood of communities in the ARB is primarily based on rainfall-dependent agriculture. Effects of rainfall anomalies such as reduction of agricultural productivity, water scarcity, and food insecurity are becoming more prevalent in this area. In recent years, ARB experienced more frequent and intense spatio-temporal rainfall anomalies, which make the shift and trend analyses of rainfall associated with sea surface temperature crucial in providing guidance to improve agricultural productivity. Change-point detection tests (Pettit’s, the von Neumann ratio (VNR), Buishand’s range (BR) and standard normal homogeneity (SNH)) and Mann-Kendall (MK) trend analysis of rainfall and temperature data from 29 meteorological stations in the ARB were carried out from 1986 to 2016. A significant increasing trend of annual and seasonal temperature was found. The temperature change-points for the annual and major rainy season (MRS) were detected in 2001, while for the minor rainy season (mRS) in 1997. A significant decreasing trend, shift, and high variability of rainfall were detected in the downstream part of the ARB. The BR and SNH results showed that the mRS rainfall change-point was in 1998, with a subsequent mean annual decrease of 52.5 mm. The increase (decrease) of rainfall in the annual and MRS was attributable to La Nina (El Nino) events. The significant decreasing trend and change-point of rainfall in the mRS was attributable to the steady warming of the Indian and Atlantic Oceans, local warming, and La Nina events. With this knowledge of the current trends and change-point for rainfall and temperature in the ARB, it is therefore essential that appropriate integrated water management and water-harvesting technologies are established, especially in the downstream areas. Moreover, early detection of El Nino episodes would provide invaluable warning of impending rainfall anomalies in the ARB and would enable better preparations to mitigate its negative effects.
Highlights
In recent decades, several studies have reported the effects of climate change/variability as manifested by the increasing rainfall anomalies and temperature (Ramli et al, 2019; Asfaw et al, 2018; Alemayehu and Bewket, 2017)
The economy of Awash River Basin (ARB) in Ethiopia is highly reliant on rain-fed agriculture that is vastly sensitive to changes and variability of climate (Borgomeo et al, 2018)
The MK test indicated a significant increasing trend in temperature on annual, seasonal and monthly basis, except for December, which is the coldest month in Ethiopia (Table 1)
Summary
Several studies have reported the effects of climate change/variability as manifested by the increasing rainfall anomalies and temperature (Ramli et al, 2019; Asfaw et al, 2018; Alemayehu and Bewket, 2017). Rainfall amount is expected to decrease while its anomaly is likely to increase in the Sub-Saharan Africa (IPCC, 2014). Climate variability is likely to worsen the water scarcity in the Sub-Saharan Africa (IPCC, 2014). The effects of climate variability in the ARB is likely to be widespread due to ARB's high population, and is the most utilized river basin in Ethiopia that contributes greatly to the development of the national economy (Hailu et al, 2017; Bekele et al, 2017). Investigation of long-term trends and variation of rainfall and temperature in the ARB is of vital importance for managing of water resources and predicting weather-related disasters
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