Variability and trend analysis of temperatures, rainfall, and characteristics of crop-growing season in the eastern zone of Tigray region, northern Ethiopia

In this study, auto-correlated Mann-Kendall (MK) and Sen's slope estimator tests were utilized to determine trends of rainfall, temperatures, and characteristics of crop-growing season during 1980-2009. Moreover, the Van Belle and Hughes' for homogeneity of general trend and Pettitt's test for the occurrence of abrupt changes were applied. On monthly, Kiremt (June-September) and annual time scale, the MK-trend test for rainfall exhibited non-significant increasing trend, while in Belg (February-May) rainfall season exhibited non-significant decreasing trend at the most of the stations. On the contrary, temperatures showed significant increasing trends in annual and Belg at the 5% significant level. In Kiremt season, however, the maximum temperature showed non-significant increasing, while the minimum temperature showed non-significant decreasing trend. Results of homogeneity for general trend obtained by the Van Belle and Hughes' test seem fairly consistent with those of the MK-trend test. Moreover, results of Pettitt's test indicated a homogeneous trend in monthly, annual, and seasonal rainfall series and no break point was distinguished, except few stations. On the contrary, the abrupt changes were found to be quite variable in temperatures. The study also found that trends of growing season characteristics (June-September) have not changed significantly at the 5% significant level. Nevertheless, the high coefficient of variation in Kiremt rainfall (21-31%) as well as dry spell length (25-43%) in conjunction with the short nature of the length of growing period (68-90 days) had negative implications to crop production in the eastern zone of Tigray region.