Simulation of crop yield using the global hydrological model H08 (crp.v1)

Abstract

Abstract. A better understanding of the food–water nexus requires the development of an integrated model that can simultaneously simulate food production and the requirements and availability of water resources. H08 is a global hydrological model that considers human water use and management (e.g., reservoir operation and crop irrigation). Although a crop growth sub-model has been included in H08 to estimate the global crop-specific calendar, its performance as a yield simulator is poor, mainly because a globally uniform parameter set was used for each crop type. In addition, the effects of CO2 fertilization and vapor pressure deficit on crop yield were not considered. Here, through country-wise parameter calibration and algorithm improvement, we enhanced H08 to simulate the yields of four major staple crops: maize, wheat, rice, and soybean. The simulated crop yield was compared with the Food and Agriculture Organization (FAO) national yield statistics and the global dataset of historical yield for major crops (GDHY) gridded yield estimates with respect to mean bias (across nations) and time series correlation (for individual nations). Our results showed that the effects of CO2 fertilization and vapor pressure deficit had opposite impacts on crop yield. The simulated yield showed good consistency with FAO national yield. The mean biases of the major producer countries were considerably reduced to 2 %, 2 %, −2 %, and −1 % for maize, wheat, rice, and soybean, respectively. The capacity of our model to capture the interannual yield variability observed in FAO yield was limited, although the performance of our model was comparable to that of other mainstream global crop models. The grid-level analysis showed that our model showed a similar spatial pattern to that of the GDHY yield in terms of reproducing the temporal variation over a wide area, although substantial differences were observed in other places. Using the enhanced model, we quantified the contributions of irrigation to global food production and compared our results to an earlier study. Overall, our improvements enabled H08 to estimate crop production and hydrology in a single framework, which will be beneficial for global food–water nexus studies in relation to climate change.