Sensitivity of a general circulation model to global changes in leaf area index

Abstract

Methods have recently become available for estimating the amount of leaf area at the surface of the Earth using satellite data. Also available are modeled estimates of what global leaf area patterns would look like should the vegetation be in equilibrium with current local climatic and soil conditions. The differences between the actual vegetation distribution and the potential vegetation distribution may reflect the impact of human activity on the Earth's surface. To examine model sensitivity to changes in leaf area index (LAI), global distributions of maximum LAI were used as surface boundary conditions in the National Center for Atmospheric Research community climate model (NCAR CCM2) coupled with the biosphere atmosphere transfer scheme (BATS). Results from 10‐year ensemble averages for the months of January and July indicate that the largest effects of the decreased LAI in the actual LAI simulation occur in the northern hemisphere winter at high latitudes despite the fact that direct LAI forcing is negligible in these regions at this time of year. This is possibly a result of LAI forcing in the tropics which has long‐ranging effects in the winter of both hemispheres. An assessment of the Asian monsoon region for the month of July shows decreased latent heat flux from the surface, increased surface temperature, and decreased precipitation with the actual LAI distribution. While the statistical significance of the results has not been unambiguously established in these simulations, we suspect that an effect on modeled general circulation dynamics has occurred due to changes of maximum LAI suggesting that further attention needs to be paid to the accurate designation of vegetation parameters. The incorporation of concomitant changes in albedo, vegetation fractional coverage, and roughness length is suggested for further research.

Impacts of weather conditions modified by urban expansion on surface ozone: Comparison between the Pearl River Delta and Yangtze River Delta regions

“…Changes in land use and land cover (LULC) alter the exchange of energy, momentum, moisture, and other trace gases within the vegetation-soilatmosphere continuum, subsequently affecting the global and regional climate (Charney et al, 1977;Chase et al, 1996;Foley et al, 2005), and hence impacting the dispersion of pollutants and air quality. The Pearl River Delta (PRD) and the Yangtze River Delta (YRD) regions are the most two advanced economic districts in China, which have experienced remarkable economic development and urbanization in the past two decades.…”

Influence of Leaf Area Index Prescriptions on Simulations of Heat, Moisture, and Carbon Fluxes

“…While LAI affects the interactions between the atmosphere at a point or grid scale (Bonan et al 1993), this scales up to continental scales (Pitman et al 1999) in uncoupled simulations. There is additional evidence that LAI affects the atmosphere at larger scales (Chase et al 1996). Most recently, van den Hurk et al (2003) demonstrated that using remotely sensed LAI in a weather forecasting system affected the surface evaporation when evaporation formed a large term in the surface energy balance.…”

Impact of canopy representations on regional modeling of evapotranspiration using the WRF-ACASA coupled model

“…Specifically, the LAI strongly influences the amount of absorbed solar radiation and its partitioning into sensible and latent energy fluxes. Studies using General Circulation Models (GCMs) have demonstrated the importance and influence of LAI on the short-and long-term evolution of surface hydrology, including snowpack evolution, soil wetness, and evapotranspiration (ET) (Chase et al, 1996;Pitman et al, 1999;Bounoua et al, 2000;Hales et al, 2004). Gao et al (2008) further examined the sensitivities of land surface climate to the changes in spatial distribution of LAI from different treatments of surface properties: natural inter-annually varying vegetation versus a 10-year climatological annual cycle.…”