A note on the temporal and spatial variability of rainfall in the drought-prone Amhara region of Ethiopia

The aim of this study is to characterise rainfall variability and trend in the drought-prone Amhara Regional State of Ethiopia using standard rainfall statistical descriptors. A review of previous studies of Ethiopian rainfall shows different conclusions between studies about the existence of trends primarily due to their use of different periods of analysis. Various rainfall indicator series are presented and analysed for trend on annual, seasonal and daily time steps (including wet-day amounts and probabilities, percentiles and dry spell lengths). Two periods are used for analysis: 1975-2003 (12 stations) to optimise station density and 1961-2003 (five stations) to optimise record length in this relatively poorly monitored region. A complex picture of rainfall variability emerges from the analysis, both in terms of spatial variability and temporal variability, from decadal to daily timescales. The results generally support those of the previous studies in Ethiopia with the additional findings that: (1) High levels of spatial variability exist at subregional scales in Ethiopia that are unlikely to be fully explained by large-scale climate influences; (2) Choice of study period strongly influences the results of trend analysis in this region due to the effects of decadal variability (particularly because the 1980s was the driest decade and the 1990s the wettest decade on record); (3) Annual rainfall in the region recovered during the 1990s, although 2001-2003 were average or slightly lower; and (4) There are no consistent emergent patterns or trends in daily rainfall characteristics in this part of Ethiopia. Copyright (C) 2007 Royal Meteorological Society.