Analyses of the relationship between drought occurrences and their causal factors in Tigray Region, Northern Ethiopia

Abstract

Drought is controlled and enhanced by changes in the local and global climate factors. The changes in the global factors mainly occur on the vast oceanic surfaces, while the changes in the local factors occur in the area of drought influence. In order to skilfully forecast and monitor drought occurrences, it is crucial that the specific causal factors be identified and their links studied. Based on this concept, this study tried to establish a relationship between the drought occurrences in Tigray region and the climate factors at the local and global scale. Monthly gridded Climatic Research Unit (CRU) Time-series (TS) data version 4.01 was used to calculate the Standardized Precipitation and Evapotranspiration Index (SPEI). As potential global causal factors, SOI (Southern Oscillation Index), Sea Surface Temperature Anomalies (SSTAs) of the tropical oceanic surfaces, the Red Sea and Nino 3.4 regions were obtained from various sources. Vegetation cover and albedo data were also considered as local drought causal factors. The analyses results show that the zero-time-lag SSTA in the tropical Indian Ocean was identified as statistically significant (p < 0.01) drought influencing factor accounting for 5.8% and 8% of the variations in SPEI, at 1-month and 6-month time scales respectively. At 12-month time scale, however, the SSTAs in the tropical Indian Ocean, tropical Atlantic Ocean, tropical Pacific Ocean, the Red Sea and Nino 3.4 regions were designated as drought influencing factors. Differently, at 24-month time scale, SOI was also identified as drought influencing factor in addition to the SSTAs in the tropical Indian Ocean, tropical Pacific Ocean and the Red Sea region. In general, the findings revealed the variability in the number and type of causal factors based on time scale and time-lag. Nevertheless, the ability of the identified factors to explain the variation in SPEI remained small at all timescales investigated. This, therefore, indicates the need for further investigation on other drought causal factors in the study area.

Droughts over Pakistan: possible cycles, precursors and associated mechanisms

“…SST is a key climate variable that defines the interaction among oceanic and atmospheric phenomena (Wmo, n.d;Bojinski et al 2014), and SST variations had triggered many drought events worldwide (Fan et al 2017;Tefera et al 2020). The OND SST anomalies (Figure 7) showed increasing trend and a warm pool in the Arabian Sea and Bay of Bengal which proposes development of convection in Arabian Sea that might be a reason of precipitation deficit which consequently cause severe droughts in the Indian subcontinent (Preethi et al 2017).…”

“…SST is one of the most important oceanic climate variables that can be employed to interpret the interaction among various oceanic and atmospheric phenomena (Wmo, n.d;Bojinski et al 2014;Reynolds et al 2007). Various studies have reported that variations in SST have triggered drought events in different parts of the World (Fan et al 2017;Rajagopalan et al 2000;Lu and Delworth 2005;Feng et al 2008;Annamalai et al 2013;Tefera et al 2020).…”

Precipitation Variability and its Teleconnection with the Global SST and ENSO Indices in the Food Insecure Rural Areas of Tigray

“…The global SST is among the key factor that plays a significant role in determining the variability of the monthly, annual and decadal precipitation patterns. Alhamshry Previous studies confirm that the spatial and temporal variability in the precipitation of Ethiopia is attributed to the variations in SSTs over the Atlantic, Indian, and Pacific Oceanic indices (Degefu et al, 2017;Zeleke et al, 2017;Dubache et al, 2019;Alhamshry et al, 2020;Molla, 2020;Tefera et al, 2020;& Bayable et al, 2021).…”

“…Besides, the drying trend in the southern and northern of Ethiopia is associated with Atlantic drought influencing factor in Ethiopia (Tefera et al, 2020).…”

“…The SST is among the major drivers of precipitation variability (Dittus et al, 2018), particularly for the Ethiopian precipitation (Alhamshry et al, 2020). Besides, the ENSO is the other most important determinant of precipitation variability, particularly in the precipitation pattern of Ethiopia (Kasie et al, 2019& Tefera et al, 2020. These two factors highly determine the intra-year and inter-year precipitation variability.…”