Spatiotemporal Assessment of Agricultural Drought Using a Cell-Based Daily Soil Water Analysis Model

Abstract

This study developed a cell-based daily soil water analysis model (CellSW) for evaluating agricultural drought and calculated an agricultural drought index called the "Rainfall Effectiveness Index for Crop" (REIC). The model analyzed a daily soil water balance based on crop types, growth stages, soils, and climate. It adopted the rasterized daily rainfall, daily evapotranspiration, crop coefficient (by crop growth stage), and root depth as input parameters; it also consecutively generated the daily surface layers of the water balance items in each cell, such as the consumptive use, effective rainfall, available soil water, and irrigation requirements. The model was applied in a test area in Illinois and Iowa, targeting corn and soybeans; the soil water balance was analyzed during the growing period from 2000 to 2018. The model calculated the seasonal REIC, defined as the ratio of supply quantity (effective rainfall) to demand quantity (crop evapotranspiration). In addition, the accumulated REIC values were estimated. The REIC was confirmed to accurately reflect drought situations in the relevant areas, based on comparisons with drought records. The cell-based model can be applied to different types of cultivated crops, growth stages, and soil conditions without spatial and temporal limitations, even in mixed farming.