Evaluation and Enhancement of Community Land Model Hydrology Dennis P. Lettenmaier Kaiyuan Li University of Washington Gordon Bonan NCAR Eric F. Wood Princeton University Presentation to CCPP PI Meeting Cambridge, MA Apr 25, 2006

Objectives Use the Community Climate System Model (CCSM), in conjunction with a upgraded version of the Community Land Model (CLM) to evaluate the susceptibility of the U.S. to drought over the next century (e.g. Andreadis et al, 2005; Andreadis et al, 2006). Evaluate and enhance CLM hydrology to resolve deficiencies before it is coupled into CCSM to predict the future drought. Focus here is on the latter -- evaluating and upgrading CLM hydrology.

Evaluation Sites Three large river basins with contrasting hydroclimatic conditions Arkansas-Red Colorado USA Torne-Kalix (northern Scandinavia La Plata (South America) planned Column (tower flux) evaluations are for four sites Tropical forest site at Reserva Jaru (ABRACOS) in Brazil Prairie grassland (FIFE), Kansas Agricultural field at Caumont (HAPEX-Mobilhy) Europe Grassland at Valdai in central Russia.

Results – River basin analyses Arkansas-Red River VIC well reproduced observed runoff in terms of both magnitude and seasonality. CLM well captured the runoff seasonality, but in general overestimated runoff, especially in the west portion of the basin. Colorado River VIC well reproduced the observed streamflow both in terms of magnitude and seasonality. CLM largely overestimated runoff, and the snow-melting dominated runoff peak came one month earlier than observation. Torne-Kalix The VIC better captured the runoff magnitude and seasonality. CLM overestimated the runoff peak value for most subbasins The runoff peak of CLM, in general, came earlier than VIC and observations

Results – Tower flux evaluations FIFE CLM simulated net radiation, sensible and ground heat flux reasonably well but underestimated the latent heat due to overestimation of runoff. CLM largely undersimulated the soil moisture content in the subsurface layer due to larger runoff and hence less infiltration. ABRACOS CLM in general overestimated the sensible heat and underestimated latent heat. The poor performance of CLM are attributed to the larger estimation of runoff and poor simulation of soil moisture content. HAPEX-Mobilhy CLM underestimated latent heat and overestimated sensible heat for the growing season. In the non-growing season CLM markedly overestimated bare ground evaporation and hence underestimated soil moisture. This underestimation led to the underestimation of evapotranspiration for the growing season. Valdai CLM underestimated seasonal peak evapotranspiration. Soil moisture contents were poorly simulated by CLM with lower peak value than observations.

Enhancement of CLM soil hydrology Upgraded CLM by incorporating the 3-layer VIC surface runoff and baseflow schemes into the 10-layer CLM In the time order during a model time step: Surface runoff is calculated based on the 3-layer VIC scheme; Infiltration is based on 10-layers (CLM layer scheme) using information for VIC layers interpolated to specified CLM layers; Soil evaporation, root-water-uptake and water redistribution (upward and downward), soil thermal states and fluxes are based on 10 CLM methodology layers

Evaluation of upgraded CLM The Upgraded CLM, into which VIC runoff parameterization is incorporated, performs significantly better than original CLM based on river basin and tower site evaluations. The Upgraded CLM requires 5 VIC parameters, which are transferable to CLM without massive calibration although some systematic adjustment may be required for some basins. Enhancement of the CLM snow model remains to be done.