Contributions of climate change and human activities to changes in the virtual water content of major crops: An assessment for the Shijiazhuang Plain, northern China

Abstract

The virtual water content (VWC), which quantified the water consumption per unit of a food product, serves as a critical variable to the virtual water study. Because of the climate-dependent nature of VWC and its vulnerability to human influence, we still have little knowledge to interpret VWC variation regarding the contribution of climate change and human activities. This study aims to address this gap by proposing a VWC contribution analysis framework. In this framework, we applied the hydrological sensitivity method to a newly developed crop VWC calculation formula. We firstly separated the study period into baseline and change periods to calculate the change of VWC over time (ΔVWC). Based on the VWC calculation formula, the partial derivatives of VWC to precipitation (P) and potential evapotranspiration (PET) are mathematically derived. These partial derivatives were served as the sensitivity coefficients in the hydrological sensitivity method. We used them to differentiate and quantify the impact of climate change and human activities on ΔVWC and finally calculate its corresponding relative contribution. We demonstrate this framework in Shijiazhuang Plain, an agricultural district in northern China where the VWC of major crops has decreased in recent decades. We found that the relative contribution of human activities to the changes of VWC was greater than 97%, versus less than 3% for climate change. This finding suggests that human activities play a dominant and essential role in shaping the evolution of VWC as the region's water scarcity increases.