Spatio‐temporal variations of wet and dry spells in Iran and their association with large‐scale climatic indices

Abstract

AbstractThe spatial and temporal variations of wet and dry spells may be related to large‐scale climatic indices. To date, no comprehensive study has been conducted on Iran's spatial and temporal variations of wet and dry spells. To fill this gap, 14 wet/dry spell indices were calculated for 512 rain gauges across Iran from 1985 to 2016. The modified non‐parametric Mann–Kendall test was then used to examine the temporal variations of wet and dry spell indices. Whether any relationships between spell indices and 13 large‐scale climatic indicators existed was determined. The maps showing the degree of correlation between wet/dry spell indices and two climatic indicators that reflect short‐ and long‐term El Niño oscillation were presented. The results demonstrated that precipitation typically occurs in bursts of 1 or 2 days in length, with most of the annual precipitation coming from a few exceptionally heavy or extreme events. Most dry spells in Iran occur from 6 to 27 days or longer. The length, frequency, and intensity of wet spells declined in southern Iran while expanding in northern Iran. However, extreme wet spells have intensified significantly across the country. When El Niño occurs, Iran experiences wetter weather. However, long‐term oscillations in sea‐surface temperatures in the Pacific Ocean are found to be significantly correlated with wet/dry spells, outperforming those obtained for shorter periods. A smaller portion of the country showed a significant correlation in extreme spell indices, though.