Climate Change and Climate Disaster

Spatiotemporal Variability of Dry Day Occurrence in Iran

Document Type : Original Article

Authors

Ali Reza Karbalaee Doree 1
saeideh ashrafi 2

1 Department of Climatology Faculty of Geographical Sciences, Kharazmi University, Tehran, Iran.

2 Department of Geography, Tabriz University, Tabriz, Iran

10.30740/cccd.2026.2080909.1094
Abstract
This study investigates the spatio-temporal variations in the frequency of dry days (precipitation < 1 mm) and their longest consecutive spells across Iran during the period 1970–2021, using daily data from 411 synoptic stations. Kriging interpolation was applied for spatial analysis, the Mann–Kendall test for trend detection, and the Alexandersson test (SNHT) for identifying significant breakpoints. Results indicate that the national annual mean frequency of dry days is 328 days, with a minimum of 247 days in the southwestern Caspian region and a maximum of 355 days in western Sistan and Baluchestan. Approximately 62.6% of the country's area experienced frequencies above the spatial mean. A significant increasing trend was observed over 89.12% of the territory, whereas only 10.64% showed a decreasing trend. The longest recorded consecutive dry spell (>600 days) occurred in western Sistan and Baluchestan in December 2016. The Alexandersson test identified 1998 as a significant shift point; thereafter, the mean frequency of dry days increased by approximately 8 days, and the maximum dry spell duration nearly doubled. Anomaly analysis of frequency and duration reveals that these changes predominantly occurred in central, southern, and eastern regions. This pattern aligns with alterations in the general atmospheric circulation over Southwest Asia. The findings warn that Iran is transitioning from seasonal dryness toward more extreme and persistent aridity conditions.

Keywords

Dry day
Dry spell duration
Mann-Kendall test
Alexandersson test
Climate shift
Subjects

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