The southern United States (SUS) has experienced significant changes in climate, atmospheric composition, and land-use and land-cover types since the late 20th century. Much concern has been raised about the impacts of climate and other environmental factors on ecosystem productivity and water resources through the climate-water-food nexus. Understanding the responses of ecosystem productivity and water use efficiency to environmental changes in SUS ecosystem is particularly important because the SUS is a traditionally ‘water-rich’ region and the ‘timber basket’ of the country. By using the Dynamic Land Ecosystem Model (DLEM) driven by spatially-explicit information on land use, climate and other environmental changes, we have assessed the spatial and temporal patterns of net primary productivity (NPP), evapotranspiration (ET) and water use efficiency (WUE) across the SUS in the past four decades (1980-2018). Specifically, we have examined the following two questions: 1) How have SUS NPP and ET been affected by climate variability and land use change during the study period and 2) What are the relative roles of climate change and land use change in altering ecosystem water use efficiency?
Results/Conclusions:
Our preliminary results indicate that NPP, ET and WUE showed substantial inter-annual and spatial variability, which was induced by the non-uniform distribution patterns and change rates of environmental factors across the SUS. Annual ET increased and decreased slightly during the first and second half of the study period and NPP increased consistently from 1980 to 2018. As a result, the average WUE of SUS significantly increased during the whole period. Our study further suggests that accurate projection of the regional impact of climate change on carbon and water resources must consider the effects of land-use and land cover change and climate change.