Dry spell trend analysis of Isfahan Province, Iran

In the present study the spatiotemporal trend analysis of the annual maximum dry spell length (AMDSL) and the annual number of dry spell periods (ANDSPs) of Isfahan Province in the center of Iran has been conducted based on daily rainfall records taken from 17 rain gauge stations. The autocorrelation functions (ACFs) of dry spell time series showed the randomness of dry spells. The use of Mann-Kendall test for trend revealed two stations with significant negative trend of the AMDSL located in east and west of the province. The trend analysis of the ANDSP showed three stations with significant upward trend in east and one station with significant negative trend in the west of the province. The sequential Mann-Kendall test showed an evidence of an individual abrupt change in the magnitudes of dry spells from 1980s, especially in eastern arid and semi-arid regions of the province. However, the binomial and uniform distribution of Mann-Kendall statistics reveals that individual trend in a region is not strong enough to conclude the large-scale regional climatic effects on dry spell characteristics in the entire Isfahan Province. Copyright (C) 2008 Royal Meteorological Society