Trend assessment of precipitation and drought index (SPI) using parametric and non-parametric trend analysis methods (case study: arid regions of southern Iran)

Abstract

In this study precipitation and standardised precipitation index (SPI) trends were analysed using linear regression, Mann-Kendall and Spearman's Rho tests at the 5% significance level. For this purpose, meteorological data from 20 synoptic stations in south of Iran over the period 1985-2013 were used. According to results two main drought periods were detected (1998-2003 and 2010-2012), while the extremely dry year was recorded in 2010 at all stations. Seasonal analysis of precipitation showed that trends in spring and winter precipitation series is decreasing. The decreasing precipitation trend was found in the summer and autumn series at 77.7% and 64% of the stations, respectively. Significantly trend was not found in the SPI-12 series at the 5% level. Results showed that base on Mann-Kendal method number of stations with decreasing trend in monthly and seasonal perception is more than Spearman's Rho tests and this method is more than percent linear regression.