Spatiotemporal changes in air temperature and precipitation extremes over Iran

In this study, a comprehensive trend analysis was employed to study the spatiotemporal changes in precipitation characteristics with air temperature increasing over time. The nonparametric Mann–Kendall test and the quantile regression methods were applied to detect the plausible temporal trends in 11 extreme rainfall indices and three air temperature indices employed in this study. The results showed there was little evidence to suggest that increases in the maximum of 3-h and 24-h precipitation at higher temperatures resulted in similar increases in the annual precipitation, with most stations throughout Iran showing drying features with higher temperatures. Generally, most regions over Iran scaled negatively, implying a reduction in the annual precipitation ranging from −2.64 to −0.44 mm/°C at higher temperatures. The linear tendencies of the maximum 24-h precipitation ranged from −0.4 to 0.23 mm/°C. The annual precipitation of the stations located at Urmia Lake, Caspian Sea, and the Eastern Border Basins showed a decreasing trend (−3.70 to 1.11 mm/year), while the number of rainy days increased (−2.78 to 4.72), which showed the occurrence of lighter rainfall in these regions. The increasing trend in the maximum 24-h precipitation over Western and Central Iran implied a higher probability of extreme precipitation with a higher intensity. This study revealed that the shift in precipitation extremes shifted from fall to winter by increasing the elevation, but these effects have no statistical significance in Iran.