Abstract
Here we present an analysis of drought occurrence and variability in Ethiopia, based on the monthly precipitation data from the Climate Research Unit (CRU-v3.22) over the period from 1960 to 2013. The drought events were characterized by means of the Standardized Precipitation Index (SPI) applied to precipitation data at a temporal scale of 12 months. At the national scale, the results reveal a statistically significant decrease in the severity of droughts over the 54-year period, a pattern that is mostly attributed to a statistically significant decrease in the frequency of high intensity drought episodes (i.e., extreme and very extreme droughts), compared to moderate droughts. To assess the general patterns of drought evolution, a principal component analysis (PCA) was applied to the SPI series. PCA results indicate a high spatial heterogeneity in the SPI variations over the investigated period, with ten different spatially well-defined regions identified. These PCA components accounted for 72.9% of the total variance of drought in the region. These regions also showed considerable differences in the temporal variability of drought, as most of the regions exhibited an increase in wetness conditions in recent decades. In contrast, the regions that receive less than 400 mm of annual precipitation showed a declining trend, with the largest changes occurring over Afar region. Generally, the highly elevated regions over the central Ethiopian Highlands showed the weakest changes, compared to the lowlands. This study confirms the local character of drought evolution over Ethiopia, providing evidence for policy makers to adopt appropriate local policies to cope with the risks of drought. Over Ethiopia, the detailed spatial assessment of drought evolution is required for a better understanding of the possible impacts of recurrent drought on agriculture, food production, soil degradation, human settlements and migrations, as well as energy production and water resources management across Ethiopia.
Highlights
Drought is a climate phenomenon of importance across a range of disciplines, with implications and impacts in hydrological, agricultural and environmental applications (Brando et al, 2014; Hunt et al, 2014)
A linear trend analysis applied to a 60-month moving average of the Standardized Precipitation Index (SPI) regional series suggests a significant decline in the frequency of drought over the study period (-0.16 Z-unit per decade, p
Based on the Climate Research Unit (CRU) 3.22 monthly gridded precipitation data set for 405 grid points across the country, the Standardized Precipitation Index (SPI) was computed on a 12-months timescale for each grid point
Summary
Drought is a climate phenomenon of importance across a range of disciplines, with implications and impacts in hydrological, agricultural and environmental applications (Brando et al, 2014; Hunt et al, 2014). Hydrological droughts over Ethiopia (e.g., Sheffield et al, 2012; Dai, 2013; Hunt et al, 2014; Vicente-Serrano et al, 2015a). Sheffield et al (2012) have suggested little change in the global drought over the past 60 years, other research has highlighted the potential implications of future climate changes on drought frequency and severity (Sheffield and Wood, 2008; Dai, 2011), with changes likely to enhance land degradation, in arid and semi-arid regions (Vicente-Serrano et al, 2015b). Over Africa, numerous studies have reported a significant decrease in rainfall amounts across vast parts of the continent (e.g., Meinke et al, 2005; Hoerling et al, 2006; Ngongondo et al, 2011; Williams et al, 2012)
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