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Clim Dyn (2009) 32:649662
DOI 10.1007/s00382-008-0435-1
Impact of sub-grid variability of precipitation and canopy water storage on hydrological processes in a coupled landatmosphere model
Dagang Wang Guiling Wang
Emmanouil N. Anagnostou
Received: 21 October 2007 / Accepted: 10 June 2008 / Published online: 28 June 2008 Springer-Verlag 2008
Abstract The impact of sub-grid variability of precipitation and canopy water storage is investigated by applying a new canopy interception scheme into the Community Atmosphere Model version 3 (CAM3) coupled with the Community Land Model version 3 (CLM3). Including such sub-grid variability alters the partitioning of net radiation between sensible heat ux and latent heat ux on land surface, which leads to changes in precipitation through various pathways/mechanisms. The areas with most substantial changes are Amazonia and Central Africa where convective rain is dominant and vegetation is very dense. In these areas, precipitation during DecemberJanuary February is increased by up to 2 mm/day. This increase is due to the enhanced large-scale circulation and atmospheric instability caused by including the sub-grid variability. Cloud feedback plays an important role in modifying the large-scale circulation and atmospheric instability. Turning off cloud feedback mitigates the changes in surface convergence and boundary layer height caused by inclusion of sub-grid variability of precipitation and water storage canopy, which moderate the effect on precipitation.
1 Introduction
Realistic representation of land-atmosphere exchanges is important in simulating or predicting land surface hydro-logical and climate state. Due to the limitations in
computational resources, the spatial resolution of current global climate models is often as coarse as a few degrees. On the other hand, land surface characteristics and hydrologic processes exhibit variability at a wide range of spatial scales, which leads to signicant spatial variability in exchanges between land and atmosphere. Mengelkamp et al. (2006) conducted simulations using regional climate models with different spatial resolutions in EVA-GRIPS project, and concluded that the simulated latent heat ux at coarse resolution is signicantly different from that with sub-grid variability of surface characteristics included. Decharme and Douville (2006) used a land surface model for a series of ofine simulations with a variety of parameterization related to sub-grid variability of precipitation and surface characteristics, and found that including the representation of sub-grid variability exert a substantial impact on the water budget...