— March 26, 2021
Join us on March 26th at 3:30 pm to hear Stephanie Roussel from the New Mexico Tech present:
“Sines from ET: Breaking Down the Signals of Evapotranspiration after the Tiffany Fire”
Abstract: Seasonal riparian evapotranspiration (ET), dominated by vegetation, controls the magnitude and direction of flow from the aquifer to the atmosphere at a losing reach along the Middle Rio Grande. When the Tiffany fire burned 9200 acres of riparian forest in 2017, subsequent aquifer recharge suggested that the loss of vegetation was a source of water salvage. Classic ecological theory predicts that if water is limiting to growth, new plants will compete for the vacated resource. The fire presents an opportunity to track the rates and limits of vegetation recovery to prepare water managers for future regimes of fire, deforestation and defoliation by Tamarisk Beetle. Three years after the fire, do ET rates point to water-savings or to a rapid revegetation of prime riparian habitat? We compared the time-series of ET from remote-sensing and of ET from groundwater models between 2017 and 2021 to map the ET recovery rates over the Tiffany Fire burn scar. Remotely-sensed riparian ET (ETRS) was derived from the Sentinel-2 Normalized Difference Vegetation Index and the Blaney-Criddle reference ET using an empirical coefficient for southwestern riparian ecosystems. Groundwater ET (ETG) was calculated from the daily water table fluctuations measured in nine shallow wells located in the Tiffany basin. The hydrologic and spectral ET timeseries both showed that ET from riparian vegetation rebounded rapidly; however, recovery was affected by seasonal water availability and Tamarisk beetle activity. The models differed with seasonal changes in the aquifer properties and water partitioning between the saturated and unsaturated zones. The models agreed during early spring when the water table was high, but ET estimates diverged in the monsoon season from July-October. Two explanations amplify the differences: 1) ETG missed the larger fraction of vadose zone water transpired in the monsoon, and 2) ETRS captured growth from shallow rooting annuals that are not connected to the water table. The results are unsurprising because the ETRS assumes a ready supply of groundwater. However, the differences between the two methods suggest that incorporating depth to the water table may improve the models’ explanatory power and our understanding of ET recovery rates in response to a variable water supply.
Speaker Biography: Stephanie Roussel is a Hydrology M.S. student with a professional background in surface-water data collection and field ecology of the southwest. Her research interests include remote-sensing, modeling, watershed management, and how these fields contribute to understanding trends in water-availability, water-quality and climate. She enjoys free data exploration using tools in R language and Google Earth Engine, but she is equally adept at collecting data from the field using drones, boats and four-wheel drive. Her research at Tech marries her strengths in biology and hydrology through the study of evapotranspiration.
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https://zoom.us/j/98660993666
This is the third presentation for the Aquifer Mapping Program 2021 Seminar Series: