Regional Scale Spatiotemporal Variations of Rainfall Over Agroclimatic Zones of Wollo Highlands, Northeastern Ethiopia

Abstract

Rainfall is one of the key climatic variables that affect spatiotemporal patterns of water availability and analyzing its trends and variability  is important from both the scientific as well as socio-economic point of view. In this study, longterm rainfall trends were investigated in  annual, seasonal and monthly scales based on 16 climate-stations in the Agroclimatic zones of Wollo highlands, Northeastern Ethiopia  over the past 60 years. After testing homogeneity, Mann-Kendall and Sen’s slope estimator tests were applied to detect trends of rainfall  data and magnitude of changes over a time period. In order to detect the most probable change year, the Petit test was applied. Results  of the study showed an increase in annual rainfall trend in northwest and northeast whereas decreasing trend detected in the northern,  western and southeastern parts of Wollo highlands. The magnitude of significant increasing trends of annual rainfall vary up to 1.99 mm/ year. Three seasons: Kiremt, Belg and Bega were used to compare seasonal variations. Kiremt rainfall variations were higher compared  with those other two seasonal series with values varying from 2.14-3.98 mm/season. A noticeable decrease in Belg season was observed  in all the regions except western parts of Wollo, besides no significant trends were detected in Belg and Bega rainfall series. This study’s  results also show an increasing trend from June to August, little or no trend from November to January and decreasing trends in the  remaining months. The findings of this study could support the researchers to realize monthly, seasonal and annual variability of rainfall  over agroclimatic zones of Wollo highlands and a groundwork for further studies.