Effects of vegetation dynamics on evapotranspiration and soil moisture in northwestern Mexico

摘要

Most land surface models use a fixed seasonal vegetationcycle and are unable to fully capture the spatiotemporalchanges in vegetation in northwestern Mexico, a regioncharacterized by an abrupt increase in rainfall and ecosystemgreen-up during the North American monsoon (NAM). In thisstudy, time-varying leaf area index (LAI) and a fixed seasonalLAI cycle, both inferred from the Moderate Resolution ImagingSpectroradiometer (MODIS), were compared as inputs to theVariable Infiltration Capacity (VIC) model over northwesternMexico during 2001-2008. Model results for the two sets ofsimulations were compared with latent heat fluxes observed bytwo eddy covariance tower sites for three summer periods. Theresults show that both vegetation greening onset anddormancy dates vary substantially from year to year with arange of more than half a month. Using the fixed season LAIcycle, the model tends to under- (over-) estimateevapotranspiration (ET)and over- (under-) soil moisture (SM)when vegetation greening occurs earlier (later) than the meangreening onset date. The discrepancies in ET were large,especially during a period of approximately two week at thebeginning of the monsoon. The effect of vegetation dynamicson ET estimates was about 10% in the Sierra MadreOccidental (SMO) and 30% in the continental interior east ofthe mountain range.