A comprehensive understanding of the role vegetation plays in partitioning rainfall to evapotranspiration, recharge, and streamflow is central to the sustainable management of both natural and built environments. Considerable progress has been made incorporating advances in plant physiological ecology in to ecohydrological models and spatial patterns in vegetation long have been used to scale both landsurface-atmosphere exchanges of water. However, a critical challenge remains in distributing plant-scale, short-duration processes to predict the effects of land cover change on regional hydrology. To address this challenge we employ a range of complementary data sources and analyses including high resolution LiDAR, GPR, isotopes, water, soil, and foliar chemistry, and both low-dimensional and process modeling to identify feedbacks between biotic and abiotic processes at and near the land surface.
These analyses highlight the diverse ways in which vegetation interacts both with climate and abiotic aspects of landscape structure to control how land cover change influences hydrologic partitioning. Interactions between topography and vegetation structure alter both local energy availability and near surface turbulence by factors of 3 or more relative to a flat, open surface. These interactions suggest a “sweet spot” for canopy cover that represents a tradeoff between increasing transpiration and decreasing evaporation. At management scales these tradeoffs help explain why large-scale forest disturbance may either increase, decrease, or have no effect on streamflow. Moving below the land surface, isotopes and chemistry both highlight the importance of topographically-driven subsurface drainage in determining plant available water by creating areas that experience either much lower or much greater water availability than supplied by local precipitation. These longer term feedbacks between the surface energy balance and subsurface hydrology control spatial patterns in above ground biomass accumulation over century times scales while creating a mosaic of resistance and resilience to disturbance over years to decades. As the pace of climate and land use changes increases, incorporating these biotic-abiotic interactions in to predictive models becomes a pressing applied science question.
Brooks, P.D., Barnard, H.R., Biederman, J.A., Harpold, A., Singha, K., Swetnam, T.L., Tai, X. (2018): Multi-disciplinary Insights in to the Effects of Vegetation Change on Hydrologic Partitioning (Invited). Abstract H21A-06 presented at 2018 AGU Fall Meeting, Washington, D.C., 10-14 Dec.