Trends in climate extremes at local farming calendar timescale: evidence from Merti District, Ethiopia

Abstract

This study analysed trends in extreme rainfall and temperature indices at three local farming calendar time (LFCT) periods, namely land preparation period (LPP), sowing and maintenance period (SaMP) and harvesting and threshing period (HaTP). The study was carried out over three agro-climatic zones (ACZs) (Kolla, Woina-Dega and Dega) of Merti district, Ethiopia. The three LFCT periods for the main Meher season in each ACZ were defined through focus group discussions (FGDs). Eight and five indices were defined from daily rainfall and temperature data series, respectively, for three stations for the period 1985–2014. INSTAT+ software and Microsoft Office EXCEL were employed to compute the indices. Mann Kendall’s and Sen’s methods were used to determine statistical significance and magnitude of the changes in the indices, respectively. Unlike Dega ACZ, most extreme rainfall indices in Kolla and Woina-Dega have shown decreasing tendency during LPP, while increasing tendency during HaTP. More complex trend results in extreme rainfall indices have been observed during SaMP than during LPP and HaTP. However, the trend tests revealed upward trends for most of the extreme temperature indices. Although the observed trends were not statistically significant for most of the extreme rainfall indices, the upward and downward signals could have negative implications for Meher crop production in Merti district. Because rainfall extreme indices in different ACZs tend to reflect LFCT-specific trends, adaptation interventions in Meher crop production in the study area tend to be based on LFCT- and ACZ-specific climate evidence.