Soil water balance is an essential element to consider for management of agricultural land use as well as in the study of agricultural droughts. Consequently, it is important to evaluate the water consumption of a crop in each of its phenological phases and the status of water reserves during critical hydrologic periods. The aim of this study was to develop an agricultural drought index conceptualiced with a water balance model considering the vegetation stress caused by soil moisture deficit. This proposed index was call: Standardized Soil Moisture Deficit Index (SMODI), which uses meteorological information, soil moisture from SMOS satellite, hydrophysical properties of the soil and crop evapotranspiration. Information from 61 weather stations located in the dry zone of Tolima was used for estimating the water balance. SMODI was compared with the most common drought indexes: Standardized Precipitation - Evapotranspiration Index (SPEI), the Palmer Self-Calibrated Drought Index (scPDSI), and other eleven macroclimatic indices. Pearson´s (r) and Spearman´s (r s) correlation coefficients, Tukey's test, and analysis of variance were appied to analyze the degree of association between SMODI and the contrasting indexeses on a quarterly basis. The proposed approach considers fundamental factors influencing soil moisture distribution and retention but also considers the water stress thresholds that plants have evolved to withstand during drought periods. When these thresholds are surpassed, they represent a water risk for plant health. Consequently, this integrated approach enhances the assessment of agricultural drought by relying on pertinent physical processes. This approach has empowered SMODI to identify extremely dry, severe, and moderate drought conditions in areas characterized by Entisols, Inceptisols, and Andisols, where rice and fruit crops and pasturelands are cultivated. It is concluded that SMODI has a high correlation with the macroclimatic indexes and is able to express the effect of climate variability on vegetation water stress.