Soil moisture is considered a key index of agricultural drought monitoring systems due to its importancefor plant growth and biological interactions. In this research, a Soil Wetness Deficit Index (SWDI) wasdeveloped based on a Soil Wetness Index to evaluate soil moisture deviation as an indicator of agriculturaldrought. The Soil Wetness Index is derived using a triangle space concept between the land surfacetemperature (LST) and vegetation index (NDVI). To acquire the triangle space concept, 8-day-productsof land surface reflectance and LST derived from MODIS satellite data over Isfahan were used. The datawas collected in the period of 2000–01 (dry year) and 2004–05 (wet year) on an 8-day time step. Theresults indicated that the SWDI index has the capability of mapping the spatial distribution of areasaffected by drought, as well as the drought intensity. The estimated cumulative number of dry days (with−4 < SWDI < 0) in the period of 2000–01 was 184 days. The results also confirmed the existence of wetdays in the period 2004–05. Moreover, shifts in drought condition at the end of the wet and dry periodswere detected in the area. Results also showed that the presence of vegetation plays an important rolein balancing soil moisture variation.

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