Testing for long-term trends in climatic variables in Iran

Analysis of long-term climatic datasets is currently of unprecedented interest to the scientific community. In this study, the trends of the annual maximum (Tmax), minimum (Tmin) and mean (Tmean) air temperatures and precipitation (P) time series were examined in the west, south and southwest of Iran for the period 1966–2005. The magnitude of the climatic trends was derived from the slopes of the regression lines, and the statistical significance was determined by means of the Mann–Kendall, Mann–Whitney and Mann–Kendall rank statistic tests. Pre-whitening was used to eliminate the influence of serial correlation on the Mann–Kendall test. The results showed a warming trend in annual Tmean, Tmax and Tmin at the majority of the stations which mostly began in the 1970s. On average, the magnitudes of the significant positive trends in annual Tmean, Tmax and Tmin were (+)0.412, (+)0.452 and (+)0.493 °C per decade, respectively. However, the variations of the P series were not uniform over the region and there were various patterns (increasing and decreasing trends).