Improving the seasonal-deciduous spring phenology submodel in the Community Land Model 4.5: Impacts on carbon and water cycling under future climate scenarios

Abstract:

A seasonal-deciduous phenology model that combines photoperiod with accumulated heating and chilling to predict spring leaf out dates is optimized using PhenoCam observations and coupled into the Community Land Model 4.5. In head-to-head comparison (using start of spring dates derived from MODIS remote sensing for validation) across Northern Hemisphere boreal and temperate deciduous forests (5.5 million km²), the revised model substantially out-performed the standard model. Forward model runs suggested a stronger advancement (up to 7 days) of spring leaf out by the end of the 21^st century for the revised model. The earlier spring leaf out predicted by the revised model increased both gross primary production (up to 0.5 Pg C yr^-1) and evapotranspiration (up to 25 mm yr^-1) when results were integrated across the study region. To reduce errors in model predictions of key land-atmosphere interactions and feedbacks, the standard seasonal-deciduous phenology submodel in CLM should be reconsidered.