Climatic Controls on Snow-Vegetation Interactions Across an Elevational Gradient

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

In the higher elevations of the western U.S., seasonal snow accumulation provides the primary source of water input to the terrestrial ecosystem. Recent changes in climate and vegetation cover (e.g. fire suppression, beetle infestation, fire) have potentially large, yet unrealized implications for water availability and ecosystem health. Forest structure has profound effects on snow accumulation and snowmelt via interception, attenuation of solar radiation, and other processes. We currently lack the mechanistic understanding needed to address the impacts of annual, decadal and long-term forest dynamics on snowmelt dynamics and water resources. This project targets this knowledge gap via an integrated observing and modeling approach focused on rates of snow accumulation and snowmelt in open versus sub-canopy conditions across an elevational gradient. Distributed hydrologic instrument clusters spanning an elevational gradient in the Colorado Front Range will be used to explore interactions between snow and vegetation, and improve predictions of snow-vegetation interactions associated with climate and vegetation change. Detailed analyses of canopy radiative transfer using hemispherical photography will be used to explain observed differences in snowpack dynamics and to develop robust forcings for detailed snowmelt simulations. The distributed instrument clusters represent the first comprehensive network of co-located snow, soil, and vegetation water use measurements spanning a continental elevational gradient. The combination of the measurements with new modeling capabilities will enable new understanding of ecohydrological feedbacks and have the potential to fundamentally change our ability to predict ecosystem response to climate change. The mountain snowpack is the primary water source for 60 million people in the Western U.S. and one billion people globally. Recent changes in climate and vegetation cover (e.g. fire suppression, beetle infestation, fire) have potentially large, yet unrealized implications for snowmelt and water sustainability. Patterns of snow accumulation and snowmelt are highly variable in mountainous regions, varying with topography, climate, and vegetation. In mountain forests, the ecological impacts of potential changes in snowmelt and water availability are poorly known. The proposed research targets this knowledge gap using measurements of snow depth and other water-related variables in different types of mountain forests. The measurements will be used to improve models that estimate solar radiation and snowmelt, providing the tools needed to predict ecosystem response to changes in climate or land cover. In this regard, the project will improve understanding of the linkages between snowpack processes and land cover changes. The mountain snowpack is one of the most sensitive hydrologic states to changes in climate. Hence, the improved characterization of snowmelt will broadly address societal vulnerabilities to climate change. The new levels of understanding achieved in this research should have dramatic impacts on the research of others and the conceptual model by which snow covered forested systems are studied. For example, many biogeochemical and ecosystem models have parameterizations which represent the processes studied here. Hence the proposed work will broadly extend to collaborators working at the Niwot Ridge Long Term Ecological Research site and other highland systems. Further, the distribution of snowmelt in these systems dominates water inputs and therefore exerts a strong control on the rate of soil erosion and mineral weathering, affording collaborations with the earth surface and geomorphology communities via NSF?s Boulder Creek Critical Zone Observatory (CZO) network ? with implications for cross-CZO research. Data from this project will be made available to these communities through multiple portals providing a direct link to these other activities. Another important impact of the proposed research will be the educational opportunities.