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Crop and Location Specific Agricultural Drought Quantification: Part I. Method Development

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 60(3): 721-728. (doi: 10.13031/trans.11649) @2017
Authors:   Rachel L. McDaniel, Clyde Munster, J. Tom Cothren
Keywords:   Crop modeling, Drought, Drought index, Hydrologic modeling, SWAT, Water conservation, Water management, Water stress.

Abstract. The prevailing definition of drought is low moisture conditions over a period of time; however, no single definition exists for drought. The numerous drought definitions and classifications have led to many indices that attempt to quantify drought. Most of these indices rely on a single variable, such as precipitation or soil moisture, and do not consider crop-specific information such as threshold values, which cause crop stress when exceeded. An example of a crop threshold is the soil moisture value below which the crop experiences stress. The goal of this study was to provide a new methodology to quantify drought for a specific crop at a specific location, allowing water management decisions on a crop-specific basis. This was achieved by scaling and combining five factors: precipitation, temperature, biomass production, soil moisture, and transpiration. The scaled temperature and soil moisture are calculated using crop-specific stress thresholds, whereas the scaled precipitation is calculated by using location-specific normal values. Transpiration stress is a crop and location specific value that is calculated by comparing the actual transpiration to the daily maximum transpiration. The biomass production is also a crop and location specific value that uses the normal values for linear scaling. The variables are combined with multiple linear regression models that estimate crop yields. A single model is created for each week of the growing season using the variable or variables that are significant for that week. The predicted yield deciles indicate the yield trend based on crop water stress and are therefore used as the crop-specific drought index.

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