Introduction: The cultivation of saffron is highly important due to the distinctive characteristics of this valuable crop. Since Iran is the main global production center of saffron and a large proportion of farmers’ livelihoods, especially in northeastern Iran, depend on this plant, evaluating its various climatic conditions is essential. Given the economic importance of this crop, special attention must be paid to its growth conditions during the critical season, particularly autumn. Among the most important meteorological variables affecting saffron growth are precipitation and temperature; a decrease in precipitation and an increase in temperature can lead to drought and, consequently, serious damage to saffron plants.

Materials and Methods: In this study, monthly temperature and precipitation data for eight synoptic meteorological stations over a 20-year period (2004–2023) were used, and the data were obtained from the Meteorological Organization of Iran. The study area was Razavi Khorasan Province, located in northeastern Iran, within the geographical coordinates of 33.5° to 37.5° N latitude and 56° to 61.5° E longitude. To analyze the effect of drought on saffron, a 3-month period was calculated for both drought indices because this period precisely overlaps with autumn, the active growth period of saffron. The index calculations were performed using R software. In this study, autumn was considered as the three months of September, October, and November, according to the World Meteorological Organization recommendations. Trend graphs were plotted for each station and each index over the two decades, and the trends and their significance were evaluated using the Mann–Kendall slope. Drought with an intensity lower than −1.5 in the SPI/SPEI indices leads to reduced bud formation, decreased flowering, and reduced corm growth. Therefore, all values lower than −1.5 were extracted for the autumn season and presented using a heatmap. Based on the number of extreme events at each station, the study area was classified into three categories—low-risk, moderate-risk, and high-risk—in terms of autumn drought risk for saffron. Finally, to determine the spatial pattern of autumn drought in Razavi Khorasan Province, the 20-year average of the two indices was calculated for each station.

Results and Discussion: Drought conditions at the eight synoptic stations were evaluated over the 20-year period based on the Mann–Kendall slope and significance levels. A negative slope indicated a downward trend (intensifying drought), while a positive slope indicated an upward trend (weakening drought). Drought risk classification based on the number of events (0–1: low-risk, 2–4: moderate-risk, 5 or more: high-risk) revealed that Mashhad and Neyshabur were high-risk stations with 7 and 5 events, respectively. In contrast, Kashmar and Torbat Jam were classified as low-risk stations with only one event each. Zoning maps of both indices showed that eastern parts of Razavi Khorasan Province experienced more severe drought conditions compared to the western parts. In other words, autumn moisture stress was lower in the western region, making it more suitable for saffron cultivation. Trend analysis indicated that the SPI index did not exhibit any statistically significant trends at any station, whereas the SPEI index showed significant trends at six stations: three stations at the 99.9% significance level and three at the 99% significance level. This highlights the critical role of temperature and evapotranspiration in intensifying drought across the region. The highest number of extreme drought events occurred at the Mashhad station (7), while the lowest occurred at Kashmar and Torbat Jam stations (1 each).

Conclusion: The findings of this study indicate that the eastern parts of the study area are more sensitive and susceptible to drought, while the western parts, owing to lower drought risk, provide more favorable conditions for saffron cultivation. The results further suggest that precipitation-deficit droughts were more destructive in terms of intensity than thermal–evaporative droughts.