Investigating the Relationship between Meteorological and Agricultural Droughts in Northwest Iran

Aims: This study aims to assess the variations in the trend of drought using indices in Northwest Iran as vegetative cover plays a vital role in environmental stability. Materials & methods: To achieve this goal, the study includes three stages: determining the Standardized Precipitation Evapotranspiration Index (SPEI) using monthly temperature and precipitation data from meteorological stations, calculating the Vegetation Health Index (VHI) based on derived datasets from MODIS satellite images for the period ۲۰۰۱-۲۰۲۱, and examining the correlation between indices to determine the duration of vegetation cover response to water scarcity and identify trends at ۳, ۶, ۹, and ۱۲-month time scales. Findings: Based on the results of the Mann-Kendall test, the stable (۴۸.۵۶%) and increasing (۵۰.۴۳%) trends cover most of the studied areas and a smaller area had a decreasing trend (۱.۰۱%) trend. Additionally, positive correlations between VHI and SPEI were observed across all time scales. The SPEI-۳ months showed the highest Pearson correlation (R۲= ۰.۸۳) with VHI values for the growing season, indicating that water accumulation in the past ۳ months had the greatest impact on vegetation cover. Conclusion: This study, while emphasizing the necessity of monitoring and managing drought, with a focus on vegetation cover status in Northwest Iran, especially in East Azerbaijan province, introduces drought indices as a crucial component of the drought monitoring system.

کلیدواژه ها:

Trend Analysis ، Drought Index ، Time Scale ، Northwest of Iran