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The Land Model Working Group met on Wednesday June 26. The format consisted of several 10-minute talks that provided updates to projects identified as priorities during the March working group meeting, followed by several 10-minute talks about new research directions.
Xubin Zeng (U. Arizona) discussed the readiness of the Dickinson et al. 2-m temperature diagnostic. This was identified as ready for implementation in CLM2 as a 24-hour average for a grassland tile. One problem that remains is how to specify LAI. It was thought that prescribed zonal average monthly LAI would suffice.
Guo-Yue Niu (U. Texas) reported on hydrology model development at the University of Texas under the direction of Zong-Liang Yang. This includes experiments in which the saturated hydraulic conductivity decay factor varies with topography (rather than being constant) and work with the old NCAR LSM snow cover fraction. These results are promising for a single watershed, but need to be extended to global simulations before they can be considered from implementation in CLM2.
Guiling Wang (GSFC) talked about new energy and water balance equations
for CLM2. Her new scheme results in faster solution convergence compared to
the existing scheme.
It is numerically more efficient and does not adversely affect model results.
Guiling Wang (GSFC) also talked about work with canopy interception that recognizes the sub-grid scale distribution of precipitation. The proposed parameterization reduces interception and therefore increases the amount of water reaching the ground. However, runoff also increased and for the model to have wetter soils (and higher transpiration) the sub-surface runoff parameterization had to be altered to reduce runoff.
Forrest Hoffman (ORNL) led a discussion about the requirements document for CLM. This document was accepted without dissent.
Gordon Bonan (NCAR) described standard model configurations to test new parameterizations. The stand-alone (single executable) CAM/CLM configuration was endorsed as the most computationally efficient way to test new CLM parameterizations. Standard simulations use prescribed monthly SST and sea ice for 1979-2000 with spun-up atmosphere and land initial conditions.
Keith Oleson (NCAR) introduced a diagnostics package that allows for thorough evaluation of CLM in the CCSM and CAM/CLM configurations (http://www.cgd.ucar.edu/tss/clm/diagnostics/index.html).
Peter Thornton (NCAR) gave a status report on proposed changes to model data structures. This new model (CLM2.1) gives the same answers as CLM2. The code review group formed at the March working group meeting has reviewed the code and given their unanimous endorsement of this as the basis for future model development.
Gordon Bonan (NCAR) described an urban land cover parameterization for CLM2 based on the concept of an urban canyon.
Johan Feddema (U. Kansas) described work being conducted jointly with the Climate Change and Assessment working group to address past and future land cover change.
Keith Oleson (NCAR) described work to study historical land cover change in the U.S.
Menglin Jin (U. Maryland) talked about using satellite-derived skin temperature to evaluate CLM.
Samuel Levis (NCAR) gave an update on work with dynamic vegetation. A canopy integration scheme similar to that proposed by Guiling Wang reduced interception and resulted in somewhat wetter soils and higher transpiration. This improved the simulation of vegetation somewhat. However, as found by Guiling Wang, much of the increased water reaching the ground runs off rather than sustaining higher evapotranspiration.
Xubin Zeng (U. Arizona) discussed developments in fractional vegetation cover based on satellite measurements.
Guo-Yue Niu (U. Texas) reported on snow model development at the University of Texas under the direction of Zong-Liang Yang. Simulations suggest that some Northern Hemisphere winter warm temperature bias can be eliminated by increasing the fraction of the ground covered by snow.
Tim Shippert (Battelle/PNNL) reported on work that Steve Ghan has being
doing to include subgrid orography in CCSM.
CSL proposal - This was submitted by Bonan. No members of the working group proposed specific simulations or requested computer time.
CLM requirements document - This was accepted.
CLM2.1 (Thornton data structures) - This was accepted as the basis for future model development.
Proposed new (answer changing) parameterizations for CLM - Dickinson et al.'s
2-m temperature diagnostic and Wang's efficient leaf temperature algorithm were
endorsed as is. Changes to fractional snow cover seem to be a promising way
to reduce warm winter temperatures in the Northern Hemisphere. Simulations will
be performed with CAM/CLM to further explore this. Guiling Wang and Xubin Zeng
both raised the issue of excessively high daytime ground temperatures and linked
this to the low within-canopy aerodynamic conductance. They have proposed changes
that will be evaluated with CAM/CLM. No changes to interception were as yet
endorsed because of the need to also alter runoff.
Leah May Ver