Dynamics of Carbon and Water Fluxes in the Southern United States in Responses to Changes in Climate and Atmospheric Composition during 1900-2099

Abstract

The southern United States (SUS) has experienced dramatic changes in climate, atmospheric composition, and land cover type over the past century. These changes are expected to be continuous in this century, which may substantially alter the structure and function of terrestrial ecosystems and then affect the regional carbon and water fluxes in the SUS. Thus, understanding the dynamics of carbon and water in the terrestrial ecosystems across the SUS in response to historical and projected changes in climate and atmospheric composition is essential for wisely dealing with future climate change and maintaining the sustainability of human society. Based on our previous study which investigated the changes in carbon and water fluxes in the SUS over the 20th century in the context of multifactor global change, this research further investigated the potential changes in carbon and water fluxes under the projected changes in climate and atmospheric composition during 2010-2099, by using a process-based ecosystem model-Dynamic Land Ecosystem Model (DLEM). The simulation results indicate that net primary productivity (NPP) over the SUS increased from 1900 to 2099, while net ecosystem productivity (NEP) increased from 1900 to 2080s and then decreases; ET increased before the 1970s, and then decreased to the 2020s, and increases to the 2080s before a decline. There are inter-annual variations of simulated NPP, NEP, and ET over the study period. The NPP-based WUE kept relatively stable before the 1950s and then increases by the end of the 21st century; and the NEP-based WUE increased from the 1900s to the 2080s with large inter-annual variations, and then decline after the 2080s. Under the projected climate change, the NPP decreases under A2 scenario, keeps relatively stable under B1 scenario, while increases under A1B scenario over the time period of 2010-2099; the NEP decreases under all three scenarios, with the highest decrease under A2 scenario, and the lowest decrease under B1 scenario; the ET increases under all three scenarios, with the highest increase under A1B scenario, and lowest increase under B1 scenario. This study is among the first attempts to examine the spatiotemporal variations of carbon and water fluxes over the SUS in the context of multiple factor global change in the 21st century. The results obtained in this study might improve the understanding of both the public and scientific community on the effects of future global change. The factorial attribution of the variations of carbon and water fluxes over the SUS would provide insights for policy makers who aim to mitigate and adapts to global change. Since the changes in climate and atmospheric composition are inevitable in the near future, it is critical to assess and explore the management strategies to ensure the adaptation of terrestrial ecosystems in the SUS to these changes.