Assessing Phenological Controls on Carbon and Water Fluxes Using a Process-based Ecohydrological Model Incorporating Field Observations and Remote Sensing Data

Phenology is the first and distinctive feature indicating vegetation response to climate forcing, and a major determinant of the timing and amount of the biogeochemical fluxes of carbon, water and nutrients. There are a growing number of researches investigating the primary factors controlling the timing, predicting the phenological changes under climate changes, and estimating their impacts on the carbon and water fluxes using eddy-flux data, remote sensing analyses and ecosystem models, yet our understanding is still limited. Here we (1) present optimization and validation of the process-based ecohydrological model, Regional Hydro-Ecologic Simulation System (RHESSys), using remote-sensing data and flux tower observations from the Harvard Forest, a Long-Term Ecological Research site in the northeastern United States. In the study site, growing season length has been observed to be gradually increasing over the last two decades along with short-term fluctuations. We then (2) disassemble the net effects of climate change and phenological change by regulating phenological timings so that we finally (3) assess the impact of lengthening of the growing season on carbon and water cycles through the use of simulated growth primary productivity, evapotranspiration, and streamflow results at the plot scale as well as at the watershed scales.