HR: 0800h
AN: C21B-0449    [Abstracts]
TI: Ecohydrological controls on snowmelt partitioning in a mixed-conifer sub-alpine forest, Valles Caldera, New Mexico
AU: * Molotch, N P
EM: molotch@seas.ucla.edu
AF: Department of Civil and Environmental Engineering, University of California, Los Angeles, 5732 Boelter Hall, Los Angeles, CA 90095, United States
AU: McConnell, J R
EM: joe.mcconnell@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, United States
AU: Litvak, M
EM: mlitvak@unm.edu
AF: Department of Biology, University of New Mexico, 167 Castetter Hall MSC03 2020, Albuquerque, NM 87131, United States
AU: Brooks, P D
EM: brooks@hwr.arizona.edu
AF: Department of Hydrology and Water Resources, University of Arizona, 1133 E James E. Rogers Way, Tucson, AZ 85721, United States
AB: The processes controlling the partitioning of snowmelt into the various hydrologic pathways are largely not understood. This knowledge gap and the complexity of interactions between the snowpack, vegetation, and the vadose zone water balance motivate comprehensive studies of the terrestrial water balance at hillslope to catchment scales. Instrument clusters, deployed along elevational transects in the Valles Caldera of New Mexico, are being used to study the distribution of rainfall, snowmelt, and soil moisture and associated influences on transpiration rates during the growing season. To fully understand the feedbacks between vegetation structure and water availability, a stratified sampling scheme is being used to evaluate micro-scale gradients in land-surface / atmosphere energy exchange and associated impacts on the distribution of snowmelt and soil moisture. Instrument clusters deployed at multiple elevations are being used to improve understanding of the sensitivity of these feedbacks to climate variability and associated changes in montane snow and vegetation distribution. Here, the potential for increased fire severity, decreased water availability, and changes to the terrestrial carbon budget drive the need to understand these feedbacks. Transects of co-located ultra-sonic snow depth sensors, water content reflectometers, soil thermistors, and sap flow sensors revealed that interception of snowfall by vegetation created substantial variability in snow depth; snow depth at under canopy sites was approximately 40% lower than open areas before snowmelt. Variability in melt fluxes at the sub-meter scale resulted in lower melt rates at under canopy sites as indicated by the persistence of snow at these locations despite the lower accumulation. Despite the lower snow accumulation in the sub-canopy environment, winter soil temperatures remained above freezing. The onset of snowmelt infiltration followed peak snow accumulation by 8 days while vegetation response to water availability in the sub-nivean soil was abrupt, with rapid increases in sap flow immediately following the onset of snowmelt infiltration. Co-located observations of CO₂ and H₂O vapor flux are also being used to explore the response of vegetation to water inputs and water related stress.
UR: http://www.sahra.arizona.edu/valles/
DE: 0794 Instruments and techniques
DE: 1218 Mass balance (0762, 1223, 1631, 1836, 1843, 3010, 3322, 4532)
DE: 1813 Eco-hydrology
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 1866 Soil moisture
SC: Cryosphere [C]
MN: 2007 Fall Meeting