Rainfall and temperature variability and trend in the Horro Guduru Wallaga Zone, Northwestern Ethiopia

Climate change significantly impacts countries that rely on rainfed agriculture. This study examined the patterns and trends of temperature and precipitation, rainfall onset, rainy season dry spells, rainfall cessation, and length of the growing season in Horro Guduru Wallaga Zone. Gridded daily rainfall, minimum temperature and maximum temperature data (1981-2020) were collected from seven stations operated by the Ethiopian Meteorological Institute (EMI). Climate variability was assessed using the coefficient of variation, precipitation concentration index, and standardized rainfall anomaly. The trend and their magnitude were determined using the Mann‒Kendall test and Sen's slope estimator, respectively. Results show that the spring and winter seasons exhibited high variability while autumn displayed moderate variability. There is an overall increase in annual rainfall with statistically significant trends at three out of seven stations. Autumn, summer, and spring seasons showed increasing trends whereas winter exhibited a downward trend. Moreover, 71% and 86% of the stations experienced a significant upward trend in mean annual minimum and maximum temperatures, respectively. Overall, both minimum and maximum temperatures are experiencing upward trends, with significant variations in rainfall patterns across different seasons. The distribution of rainfall was predominantly irregular with extreme and severe droughts occurring in 1984, 1986, and 2015. Earlier onset dates and later cessation dates were also detected in this study. These irregularities can lead to land degradation, which results to yield loss appropriate climate change adaptation measures.