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

Abstract

The 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 shortand 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.

Analysis of the trend of dry spells and how ocean factors affect its patterns during the summer monsoon in Bangladesh using the Mann-Kendall and Frontier Atmospheric General Circulation Model

“…Dry spells are crucial for controlling the dynamics of soil moisture, terrestrial energy exchange, and vegetation development (Agbazo et al 2021;Sanchi et al 2021). Additionally, dry spells have an impact on the drainage basin's water quality, which could have an impact on society's health and hinder the production of energy in hydroelectric power plants (Whitworth et al 2012; Mahbod et al 2023). The greatest threat to food security in this region is the occurrence of dry spells and changing rainfall frequency and timing during the growing season which results in a lack of soil moisture, also re risks (Zhang et al, 2018;Burton et al, 2021).…”