High elevation semi-arid ecosystems are water limited environments where the timing and amount of water availability is a fundamental factor that controls processes such as weathering, organic matter decomposition, soil respiration, nutrient uptake, and biomass production among others. In turn, water fluxes at higher elevations are controlled by interactions between climate, vegetation and soils. Understanding of these interactions has been hindered by a lack of integrated measurements of governing fluxes and states. In the southwestern US, high elevation catchments are snowmelt dominated and recent research has shown a reduction in snowpack accumulation. The possible alterations in hydrologic pathways such as evaporation, runoff, infiltration, water residence time due to these reductions remain poorly understood. The main goal of this research is to improve our understanding of soil moisture dynamics and soil water fluxes at the pedon scale during extremely dry conditions in the southwestern United States.
There are high confidence predictions that snowpacks will continue to decline in northern New Mexico through the year 2100 and projections of snowpack accumulation for mid-century (2041-2070) show a marked reduction for snow water equivalent (SWE) of about 40%. During 2011, 2012 and 2013 total winter precipitation in the Jemez Mountains was reduced by 42%, 9% and 46%, respectively, compared to average conditions (353mm). Reductions of SWE during these years compared to average conditions (256mm) were 56%, 26% and 54%, respectively. The years 2011 and 2013 were the driest winters in terms of snow accumulation measured during the last 30 years on record. Similarly, the summer seasons 2011 and 2012 were dry and the total rainfall during the summer monsoons were 15% and 27% below average conditions (357mm). This study integrates co-located direct observations of snow depth, rainfall, radiation, air temperature, eddie covariance measurements, and soil moisture at four soil pits into a one dimensional pedon scale moisture dynamics and soil water balance model. Evaporation, throughfall, vegetation water use, water storage and infiltration are modeled at soil pits located under different tree canopy coverage and terrain aspect at a similar elevation of about 3000 meters on a landscape dominated by densely welded Bandelier Tuff (Tshrige Member) and associated rhyolite/rhyodacite rocks. Model results are validated by comparing soil moisture measurements and soil solution water stable isotopes at three different depths in each soil pit.
The study site and climatic conditions during the time period of analysis provide a unique setting and opportunity to study water partitioning, vegetation water use, deep infiltration and water residence time at the soil pedon scale under extremely dry conditions.
Zapata-Rios X., Troch P.A., McIntosh J. (2013): Pedon Scale Soil Moisture and Water Fluxes Dynamics During Extremely Dry Years in a High Elevation Snow Dominated Landscape. Abstract presented at AGU Chapman Conference on Soil-mediated Drivers of Coupled Biogeochemical and Hydrological Processes Across Scales, Biosphere 2, Tucson, Arizona, 21-24 October 2013 (Poster).