Development and testing of a dynamic CO2 input method in SWAT for simulating long-term climate change impacts across various climatic locations

Abstract

Water resources in semi-arid and arid regions are critical for sustainable agricultural development, and climate change imposes great challenges and brings about large uncertainties in water resource management and crop production. In this study, the effects of future climate change on hydrology and corn production in the U.S. High Plains region were assessed using a newly developed SWAT-CO2 model and GCMs under the RCP4.5 and 8.5 scenarios. Specifically, a new method to dynamically input annual CO2 concentration into SWAT was developed. This method, along with the SWAT default CO2 concentration (330 ppm), and a constant CO2 input option (one average CO2 concentration for a simulation period) were compared for simulating hydrology and corn yield in 21st century (2031–2100). Results showed the default CO2 concentration continuously simulated the highest crop evapotranspiration (ETc) and irrigation but the lowest water yield and corn yield among three methods, especially under the RCP8.5 scenario. However, the ETc and irrigation were higher for the dynamic input method before the mid-21st century and lower between mid- to late-21st century than for the constant input method. The contrast results were found for the corn yield simulations. Additionally, the improved SWAT-CO2 model was applied to predict the changes in hydrology and corn yields for three centuries (2031–2298) relative to the historical period (1970–1999). Results indicated that the overall trend of future irrigation, ETc, and corn yield could decrease significantly at the three sites compared to the historical period. The impacts of dramatically elevated CO2 and logarithmic increase in air temperatures were the key factors for the above changes. The study highlighted the necessity of considering the dynamic CO2 input for the SWAT applications in climate change studies. Long-term projected results of this study can inform local producers about the risks of future climate change in this water shortage environment.