Snow persistence (SP) (defined as the proportion of time a surface remains covered by snow) plays a critical role in Iran's hydrological and climatic systems, particularly in regulating water supply for arid and semi-arid regions. This study provides a comprehensive assessment of SP variability across Iran from 2002 to 2024 using the MODIS MOD09A1 8-day surface reflectance product (500 m). Snow-covered pixels were identified using the Normalized Difference Snow Index (NDSI >= 0.4), and SP was calculated as the proportion of snow-covered days for each hydrological year. The analysis was limited to regions with mean annual SP > 2 % to exclude areas with negligible snow occurrence. Long-term trends were quantified using the non-parametric Mann-Kendall test and Theil-Sen slope estimator. Results indicate a significant nationwide decline in SP, averaging -6.2 %, equivalent to an average reduction of approximate to 23 snow-covered days over 22 years. The most pronounced decreases occurred in the Zagros and Alborz Mountains, key snow accumulation zones for Iran's major river basins. Along the elevation gradient, SP exhibited a U-shaped pattern, with the strongest losses (approximate to-7 %) between 1900 and 2600 m a.s.l., while high elevations (>2600 m) showed relatively stable SP. A significant upward shift in the mean elevation of snow-covered areas was observed (29 m yr(-1); cumulative +638 m), reflecting elevation-dependent warming (0.07-0.09 degrees C yr(-1)). Using a Random Forest model (R-2 = 0.98, RMSE = 0.27), temperature was found to account for 58 % of the total influence on SP decline compared to 42 % for precipitation, confirming that warming trends are the dominant climatic driver of long-term snow reduction across Iran. Phenological analysis revealed that while the first snowy day (FSD) changed minimally, the last snowy day (LSD) advanced by approximately 23 days, shortening the snow season duration. MODIS-derived SP results were cross-evaluated with high-resolution composites from Landsat-8/9 and Sentinel-2 imagery, showing strong agreement (R-2 = 0.88). Additional validation using ERA5 and FLDAS reanalysis datasets confirmed consistent spatial patterns and magnitudes of SP decline in Iran. These integrated results highlight an accelerating reduction in Iran's snow persistence, emphasizing the urgent need for adaptive water-resource management and climate-resilience strategies in snow-dependent regions.