The Strong Influence of Slope and Aspect on Mountainous Watersheds Hydro-biogeochemical Dynamics

Abstract:

As the water tower of earth, mountainous watersheds provide more than 60% of the world’s water resources and act as the genesis of biogeochemical cycling of nutrients and metals. Understanding hydrological and biogeochemical dynamics at mountainous watersheds is thus necessary for water and energy resources management with ongoing climate change. Although various approaches have been used for estimating energy and water balances, there’s still a significant challenge in mountainous watersheds due to complex terrains. The combination of slope, aspect and elevation promote significant variations in the water and energy balances, and thus result in distinctive differences in ecohydrological and biogeochemical responses. Quantifying the small-scale heterogeneity of energy and water dynamics at mountainous watersheds can provide pivotal information to improve our understanding of these dynamics. In this study, we integrated atmosphere-land interaction models, remote-sensing ECOSTRESS products and LANDSAT and LiDAR dataset at the East River Watershed in CO to distinguish the role of slope, aspect and elevation on the energy budget, land surface temperature, evapotranspiration and vegetation dynamics. Our analysis show that: 1) slope and aspect exert significant heterogeneity on incoming shortwave radiation; 2) mildly sloped south-facing hillslopes have significant earlier snowmelt and vegetation growth compared to other combinations of slopes and aspects; 3) slope exerts more control on energy budget and land surface temperature during growing season than aspect. Our results advance the understanding of the coupling among terrain, vegetation and hydrology and will enable improvements in predicting hydro-biogeochemical dynamics at mountainous watersheds.