Rainfall trends analysis of Iran in the last half of the twentieth century

Abstract

The present study performs the spatial and temporal trend analysis of the annual and 24-hr maximum rainfall of a set of 145 precipitation gauging stations of Iran. The study shows that the annual rainfall is decreasing at 67% of the stations while the 24-hr maximum rainfall is increasing at 50% of the stations. The negative trends of annual rainfall are mostly observed in northern and northwestern regions, whereas positive trends of 24-hr maximum rainfall are mostly located in arid and semiarid regions of Iran. However, the Kolmogorov-Smirnov test for Mann-Kendall (MK) statistics show that the regional trend of annual rainfall is significant, but it is not significant for 24-hr maximum rainfall. On the other hand, the sequential MK test reveals that the trends of annual rainfall and 24-hr maximum rainfall began since 1970s for most of the stations. The negative trend of the rainfall for most of the country may show the initial stages of climate change in Iran, but further information and analysis is required for future studies. Copyright 2009 by the American Geophysical Union.