Unidirectional trends in daily rainfall extremes of Iraq

Abstract

The unidirectional trends in rainfall and rainfall-related extremes in Iraq have been assessed using long-term daily rainfall data (1965–2015). The modified version of Man-Kendall (m-MK) test which can discriminate the multi-scale variability from unidirectional trend was used along with Mann-Kendall (MK) test to confirm the trends in the presence of long-term persistence (LTP). The MK test revealed decrease in annual number of rainy days, heavy rainfall days, and consecutive wet days at 60, 53, and 47% stations, respectively, and the same indices during winter at 47, 47, and 33% stations, respectively. Significant decrease in annual and winter total rainfall was also found at a few stations. An increasing tendency in dry spell was observed due to the decrease in total rainfall and the number of rainy days; however, it was still not significant in most of the stations. The Student’s t test and F test revealed significant changes in daily rainfall mean and variability between two 30-year periods, 1965–1994 and 1986–2015. The m-MK test confirmed the results obtained using the MK test in most of the stations. However, the number of stations with significant change was found to decrease when the m-MK test was used. This indicates that some of the significant changes estimated by MK test were due to the presence of LTP. The obtained results confirmed the increase in dry spells and droughts in the region.