Assessing crop growth model accuracy under droughts and heatwaves

Recent droughts and heatwaves have shown major impacts on the agricultural sector by inhibiting crop growth resulting in reduced crop yield. With an expected increase in the frequency and severity of droughts and heat waves due to climate change, accurate projections of crop yields under these hydroclimatic extremes are required. However, there is only limited knowledge on the accuracy of crop growth models under extreme events such as droughts and heatwaves. Understanding the accuracy of crop models under hydroclimatic extremes is a necessary first step to evaluate the significance of projections of crop yields under climate change.

To this end, our study addresses this gap by quantitatively evaluating three crop growth models— WOFOST, PCRGLOBWB2-WOFOST, and AquaCrop— in terms of their ability to simulate crop yield and hydrological fluxes under drought and heatwave conditions. The evaluation focuses on conditions of hydrological stress induced by droughts and heatwaves in the contiguous United States (CONUS) during the period 1981 to 2019. Our methodological framework utilises harmonised input data in terms of consistent climate forcing, cropping calendars and crop areas, to ensure a standardised comparison. Both rainfed and irrigated crops of three crop growth models are compared for the most abundant crop types (i.e. maize, wheat and soybean). 

The multiple output variables of these models are compared with reported data and satellite observations, most notably crop yield (reported on a county basis), irrigation water withdrawal (reported for a number of states) and leaf area index and evapotranspiration (from satellite observations). Additionally, we compare crop water requirements between the models. These methodological steps aim to discern structural differences among the models and identify key factors influencing performance variations, ensuring a thorough and rigorous evaluation. The findings and insights from this evaluation will advance our understanding of the intricate relationship between hydrological stress, crop growth, and sustainable agricultural practices under droughts and heatwaves.