High-resolution characterization of a semiarid watershed: Implications on evapotranspiration estimates

Authors: TEMPLETON, RYAN - Arizona State University; VIVONI, ENRIQUE - Arizona State University; MENDEZ-BARROSO, LUIS - Arizona State University; PIERINI, NICOLE - Arizona State University; ANDERSON, CODY - Arizona State University; Rango, Albert; LALIBERTE, ANDREA - Consultant; Scott, Russell - Russ

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2013
Publication Date: 2/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58957
Citation: Templeton, R.D., Vivoni, E.R., Mendez-Barroso, L.A., Pierini, N.A., Anderson, C.A., Rango, A., Laliberte, A.S., Scott, R.L. 2014. High-resolution characterization of a semiarid watershed: Implications on evapotranspiration estimates. Journal of Hydrology. 509:306-319.

Interpretive Summary: In the Chihuahuan Desert, it is very difficult to characterize the temporal dynamics of water and energy fluxes at seasonal, monthly and storm event scales and provide insight into their spatial distributions and linkages. The problem is that high resolution hydrological measurements must be made under very difficult environmental conditions. We have combined ground-based and UAV measurements in a novel application of an environmental sensor network with hyperspatial imagery products to provide a first look at the importance of the spatial distribution of landscape conditions on the water and energy fluxes in a semiarid watershed. Overall, the combined use of an environmental sensor network and UAV-based imagery provide a new means for studying hydrologic processes in semiarid watersheds exhibiting a high degree of spatial heterogeneity and seasonal evolution in land surface characteristics. The approach developed here should be a great interest to scientists working in data-sparse semiarid regions for agencies like the NRCS and BLM.

Technical Abstract: The North American monsoon (NAM) contributes roughly half of the annual precipitation in the Chihuahuan Desert from July to September. Relatively frequent, intense storms increase soil moisture and lead to ephemeral runoff. Quantifying these processes, however, is difficult due to the sparse nature of existing observations. This study presents results from a dense network of rain gauges, soil probes, channel flumes, and an eddy covariance tower in a small watershed of the Jornada Experimental Range. Using this network, the temporal and spatial variability of soil conditions and channel runoff were assessed from June 2010 to September 2011. In addition, tower measurements were used to quantify the seasonal, monthly and event-scale changes in land-atmosphere states and fluxes. Results from this study indicate a strong seasonality in water and energy fluxes, with a reduction in the Bowen ratio (B) from winter (B=14) to summer (B=3.3). This reduction was tied to higher shallow soil moisture (q) availability during the summer (q=0.040 m3/m3) as compared to winter (q=0.004 m3/m359). Four consecutive rainfall-runoff events during the NAM were used to quantify the soil moisture and channel runoff responses and how water availability impacted land-atmosphere fluxes. The network also allowed comparisons of several approaches to estimate evapotranspiration (ET). Using a water balance residual approach, a more accurate ET estimate was obtained when distributed measurements were used, as opposed to single site measurements at the tower. In addition, the spatially-varied soil moisture data yielded a more reasonable daily relation between ET and q, an important parameterization in many hydrologic models. These analyses illustrate the value of high-resolution sampling in small watersheds to characterize hydrologic processes.