The Importance of Spatial Variability in Estimating Evapotranspiration From a Subalpine Wetland

ABSTRACT The Canadian Rocky Mountains are a critical component to the hydrology, feeding water to many rivers. However, little is still known about the magnitude of hydrological processes (i.e., evapotranspiration (ET), discharge etc.) that comprise the alpine and subalpine hydrologic cycle. Sub‐alpine wetlands have received recent attention for their potential role as water retainers and sources for downstream systems. This purpose of this study was to quantify the ecohydrological controls on ET in a sub‐alpine wetland, using closed chamber measurements. Spatial patterns in evapotranspiration were modelled using the METRIC approach with data collected via a remote aerial vehicle (RAV). Closed chamber measurements for ET were taken in August, 2021, and the results indicated that vapour pressure deficit and net radiation were the significant controls on ET, while no significant influence was seen in vegetation type. The influence of the headwall was also clear as there were significant differences in ET between sunny (avg rate 0.14 ± 0.1 mm/h) and shady (avg rate 0.06 ± 0.4 mm/h) conditions. METRIC ET demonstrated considerable spatial variability, with higher rates located in the western portion of the field site, highlighting the complexity of quantifying ET in subalpine wetlands. When validated against the closed chamber data, METRIC ET captured the general range of ET measurements reasonably well, and had a modelled root mean square error (RMSE) of 0.07 mm/h. However, we recommend that future research test METRIC performance under different seasonal conditions to better quantify the model's capabilities.