Spatial and temporal variation in evapotranspiration and the surface energy balance in a sub-Arctic mixed boreal and tundra ecosystem

Tall shrubs and trees are expanding into tundra ecosystems previously dominated by short graminoid and shrub species. Vegetation changes can alter ecosystem energy balance and evapotranspiration through changes in leaf area and canopy shading. We assess temporal variability in evapotranspiration and radiative fluxes using observations from the National Ecological Observatory Network in a mixed boreal and tundra ecosystem at Healy, Alaska. We demonstrate the utility of pairing remote sensing from small Uncrewed Aerial Systems (sUAS) and satellite imagery with flux data to facilitate a better understanding of spatial and temporal heterogeneity. We find spatial variation in surface temperature is linked to vegetative cover. In the summer, net radiative fluxes are positive. Surface temperatures tend to be warmer than the air during the day. Temporal variation in evapotranspiration is largely driven by micrometeorological conditions rather than vegetative landcover. We demonstrate that remote sensing approaches paired with continuous temporal data can help elucidate the influences of vegetation on energy and water cycling. The impacts of vegetation change on water and energy cycling should consider heterogeneous microclimate conditions associated with vegetative landcover.