Journal of Arid Environments Journal of Arid Environments 70 (2007) 344–355 Rainfall trends in arid and semi-arid regions of Iran Reza Modarres a,Ã , Vicente de Paulo Rodrigues da Silva b a Faculty of Natural Resources, Isfahan University of Technology, Iran b Department of Atmospheric Sciences, Federal University of Campina Grande, Av. Aprı´gio Veloso, 882, Bodocongo ´, 58109-970 Campina Grande, Brazil Received 6 October 2005; received in revised form 21 December 2006; accepted 23 December 2006 Available online 16 February 2007 Abstract Time-series of annual rainfall, number of rainy-days per year and monthly rainfall of 20 stations were analyzed to assess climate variability in arid and semi-arid regions of Iran. The results showed mixed trends of increasing and decreasing rainfall, which were statistically significant (po0.05 and po0.01) only for Sabzevar and Zahedan stations by the Mann–Kendall test. Also, with the exception of Kashan and Torbat stations there was no statistically significant trend in the mean number of rainy-days per year. Increasing and decreasing monthly rainfall trends were found over large continuous areas in the study region. These trends were statistically significant mostly during the winter and spring seasons, suggesting a seasonal movement of rainfall concentration. Results also showed that there is no significant climate variability in the arid and semi-arid environments of Iran. r 2007 Elsevier Ltd. All rights reserved. Keywords: Climate variability; Nonparametric methods; Mann–Kendall test; Rainy-days 1. Introduction Iran is located in the mid-latitude belt of arid and semi-arid regions of the Earth. The arid and semi-arid regions cover more than 60% of the country. In this agro-pastoral transition region, the rains are highly variable in time, space, amount and duration, and water is the most important limiting factor for biological and agricultural activities. Seasonal changes in rainfall pattern may alter the hydrological cycle and environmental ARTICLE IN PRESS www.elsevier.com/locate/jaridenv 0140-1963/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jaridenv.2006.12.024 Ã Corresponding author. Tel.: +98 311 3913556. E-mail addresses: r_m5005@yahoo.com (R. Modarres), vicente@dca.ufcg.edu.br (V. de Paulo Rodrigues da Silva).