Evapotranspiration in a subarctic agroecosystem: field measurements, modeling and sustainability perspectives

Abstract

Northern latitudes are known to be the most vulnerable regions already witnessing the impacts of climate change. These impacts have not only affected a broad spectrum of ecological conditions but also physical and socio-economic functions and activities across the region. Uncertainties in climate change and its progression exposes agroecosystem development and sustainability to a great risk. Yet, not fully understood, climate feedbacks and influencing factors such as human population growth and consumption imposes economical and financial stress in the sustainability of agroecosystem activities. On the opposite direction, trends in this activity can drive regional modifications to climate to an extent that is still unknown and not yet forecasted. Over time, as the acreages of agricultural lands increase from conversion of natural lands such as boreal forests, unexpected changes in surface energetics and particularly overturning of evapotranspiration rates and changes in soil moisture regime may potentially accentuate regional climate change. These changes therefore are expected to introduce new challenges for Alaskan agriculturists because of increasing vulnerabilities and affecting conditions that shape resilience of agricultural systems and production. This research focused on improving understanding of surface energetics in an agroecosystem of Interior Alaska. A synthesis study was conducted combining the analysis of intensive field experiments including direct measurements of micrometeorological, hydrological, meteorological variables and computational modelling during the summer growing season. The evaluation of evapotranspiration (ET) dynamical regime and surface energy processes showed that ET represented a large portion of surface energy balance with similar aspects to surface fluxing levels in Arctic tundra, and in contrast, with more abundant flux levels than in subarctic boreal forest. Surface heterogeneities due to soil moisture and temperature regime drive differences in energy balance closure as a function of spatial scales despite the mostly flat surfaces and stationary atmospheric surface layer flows in the experimental area. A fully coupled numerical simulation was performed to model fluxes at the land-atmosphere interface and compared to independent observations of surface energy. A final assessment of experimental methodologies and numerical modeling is presented in preparation for integrative data fusion analysis and studies involving new satellite remote sensing capabilities, physical modeling and network field observations.