PS 41-131 - Increasing Tree Cover Leads to Decreasing Water Yield Under Climate Change in the Southern Great Plains

Abstract: The southern Great Plains (SGP) has experienced a rapid increase in woody plant encroachment, which can increase ecosystem carbon sequestration and change the capacity of ecosystems to provide water. A better understanding of the impact of increased woody coverage on carbon storage and water yield and their potential tradeoffs is critical for managing the resilience of the SGP ecosystems under the current climate and as the climate changes into the future. In this study, we used the Soil and Water Assessment Tool (SWAT) to simulate changes in runoff and net primary productivity (NPP) by converting all grassland for grazing to forest under different climate change scenarios (CCSM RCP 4.5 and RCP 8.5). Our results showed that the runoff would reduce the most in the semiarid watershed (up to 50%) and the least in the humid forest watershed (about 10%) under current climate conditions. However, under climate change scenarios, the impact of vegetation conversion on runoff will decrease in the semiarid and subhumid watersheds but increase in the humid forest watershed. Increased woody plant coverage resulted in higher NPP in all three watersheds under both current climate conditions and the climate change scenarios, although the increase was smaller under the climate change scenarios. Our study highlights the importance of considering regional differences in hydrological response when making decisions about land management practices, particularly in the face of climate change. While increasing woody cover can store more atmospheric carbon, it can also impact water yield, especially in water-limited regions. Furthermore, the combined effects of increased woody cover and climate change were not additive. Overall, this research provides valuable insights into the complex relationships between vegetation cover, water yield, and climate change in the Great Plains region. Therefore, it is crucial to consider the impacts of forest cover change on regional water yield when designing management strategies to control woody plant encroachment and making reforestation plans in the SGP.