Evaluation of the Effects of Drought on Rangeland Dynamics in Ardabil Province Using SPI and NDVI Indices

Document Type : Research Paper

Authors

1 Professor, Department of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil, Iran.

2 PhD Graduate, Department of Physical Geography, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil, Iran.

3 Master’s Student, Department of Urban Planning, Faculty of Social Sciences, University of Mohaghegh Ardabili, Ardabil, Iran.

10.29252/aridbiom.2026.4246

Abstract

Drought, as a pervasive climatic hazard, exerts profound impacts on the sustainability and dynamics of rangeland ecosystems. The objective of this study is to monitor and analyze the effects of meteorological drought on the vegetation dynamics of rangelands in Ardabil Province during the growing season. To this end, the precipitation trends of selected meteorological stations were first evaluated using the Mann-Kendall test, and the Standardized Precipitation Index (SPI) was calculated at 1-, 3-, 6-, and 9-month timescales over a 24-year period (1996–2020). Subsequently, vegetation dynamics were extracted using Landsat imagery and the Normalized Difference Vegetation Index (NDVI). Finally, the relationships between drought indices and rangeland vegetation status were analyzed using the Pearson correlation test. The results indicated that the years 2013, 2006, 2017, and 2008 were the most frequent years of drought occurrence in the region. Spatially, the Meshgin-Shahr station experienced the highest frequency of drought, while the Pars-Abad station experienced the lowest. Furthermore, drought severity analysis revealed that the Khalkhal station faced severe to extreme droughts, whereas the Pars-Abad station primarily encountered mild droughts. The analysis of the NDVI index demonstrated that the growing season for the wintering (Gheshlagh) rangelands occurs from November to May, and for the summering (Yeylagh) rangelands, it spans from April to September; May and August exhibited the maximum and minimum NDVI peaks, respectively. Correlation analysis between drought indices and vegetation showed a significant positive correlation of 77% (p < 0.01) between precipitation and NDVI. In contrast, the 1-month SPI showed a moderate correlation of approximately 26% with NDVI, which was statistically insignificant. In general, vegetation changes in the rangelands of Ardabil Province are significantly influenced by precipitation patterns.

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Main Subjects

References

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Journal of Arid Biome
Volume 16, Issue 1
March 2026
Pages 37-55

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