Analysis of trends in temperature data in arid and semi-arid regions of Iran

Trend analysis of climatic variables has received a great deal of attention from researchers recently. The main aim of this study was to investigate trends in maximum (Tmax) and minimum (Tmin) air temperatures in the annual, seasonal and monthly time-scales for 19 synoptic stations in the arid and semi-arid regions of Iran during 1966–2005. From the results it is clear that the majority of the trends in the annual, seasonal and monthly Tmax and Tmin time series showed increasing tendency during the last decades, while the increasing trends in the Tmin series were stronger than those in the Tmax series. The trend in annual Tmax and Tmin averaged over all 19 stations was 0.090 and 0.444 °C per decade, respectively. The Tmax and Tmin warming trends were more obvious in summer and winter than in autumn and spring. On the monthly basis, the highest Tmax and Tmin increases of 0.827 and 1.585 °C per decade were found at the stations located in the northeastern corner of the region in January and September, respectively.