Soil moisture, as an important hydrological component, plays a crucial role in land–atmosphere interactions. Understanding variations in soil moisture content is highly valuable for effective water resource management, agricultural activities, and climate adaptation. The objective of this study is to analyze the spatiotemporal variations of surface soil moisture (0–7 cm) across Iran during the period 1979–2024. To achieve this, daily gridded data with a spatial resolution of 0.1° from the ERA5-Land dataset provided by ECMWF were used. The results showed that the spatial distribution pattern of soil moisture content follows the spatial patterns of precipitation, rainy days, and temperature across Iran. The modified Mann–Kendall test and Sen's slope estimator were applied to detect trends and their magnitudes at a 95 % confidence level. The findings indicated that soil moisture content across Iran has shown a decreasing trend, with an average reduction of 0.0032 m3 m−3 per decade. Temporally, the greatest reduction in soil moisture occurred during the cold and rainy seasons. Spatially, the decrease in soil moisture volume during winter was significantly higher in the northeastern part of the country compared to other regions. In some areas of the Alborz and Zagros highlands, however, soil moisture content exhibited an increasing trend. The findings of this study suggest that changes in soil moisture can be a potential predictor of climate change and can be applied to the fields of water resource management, agriculture, flood management, and hydrology.
