- Director's Message
- Table of Contents
- Strategic Goals: Science, Facilities & Technology
- 1. Exploring atmospheric, Earth system, and solar processes, variability, and change
- 2. Investigating the interaction of the atmosphere, the broader Earth system, and human society
- 3. Improving prediction of weather, climate, and other atmospheric phenomena
- 4. Developing community models
- 5. Enabling innovative field experiments and measurement campaigns
- 6. Developing new instrumentation
- Research Catalog
Keith Oleson
General Information
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CGD - TIIMES
Project Scientist
Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: ML - 208
Telephone: 303-497-1332
Email: oleson@ucar.edu
Home Page - Vita
Research Focus FY08:
Soil Moisture Variability in the Community Land Model - Soil moisture anomalies in the top 2m of soil for CLM3.5 (top) and observations (bottom) for Illinois. High resolution figure
Simulating soil moisture variability in a land surface model
As reported in last fiscal year’s report, a multi-year project to improve the hydrology of the Community Land Model version 3 (CLM3), the land component of the Community Climate System Model (CCSM), was completed. Two manuscripts documenting the new version, submitted last fiscal year, were revised and published this fiscal year (see below). In recognition of the cooperative work in producing this improved version of the model, the CCSM Land Model Working Group was awarded the CCSM Distinguished Achievement Award at the 13th annual CCSM Workshop in June, 2008.
In Oleson et al. (2008), it was noted that despite the many hydrologic improvements exhibited by CLM3.5, the annual and interannual variability of soil moisture in the rooting zone appeared to be lower than observed. This translates into very little soil moisture stress simulated by the model which has important implications for simulating drought, dust, the carbon cycle, etc. An example of this for Illinois is shown in Slide 1 of the attached powerpoint presentation. It can also been seen from this figure that most of the soil moisture variability in CLM3.5 occurs deeper in the soil column, in contrast to observations.
Soil Moisture Variability in the Community Land Model - Soil moisture anomalies in the top 1m of soil for CLM3.5 (red), observations (squares), and alternative formulations for hydraulic conductivity and matric potential (Liu 2004) (blue) for the Bondville, Illinois flux tower site. High resolution figure
Soil Moisture Variability in the Community Land Model - Volumetric soil moisture anomalies by soil layer for CLM with site-specific changes by S. Swenson (top), and observations (bottom). Red is the shallowest layer while blue is the deepest. Figure courtesy S. Swenson. High resolution figure
Soil Soil Moisture Variability in the Community Land Model - Standard deviation of volumetric soil water with depth for CLM3.5 (red), the new model (blue), and observations (green) for Illinois. High resolution figure
Keith Oleson led a project to investigate causes and potential solutions to this problem. University collaborators included Robert Dickinson (Georgia Institute of Technology), Zong-Liang Yang and Guo-Yue Niu (University of Texas), and Xubin Zeng and Mark Decker (University of Arizona). NCAR collaborators included David Lawrence and Sean Swenson, an ASP post-doc with CGD. Early work showed that the presence of the shallow water table in the model produced strong upward fluxes of water to the rooting zone which essentially prevented the drying out of the rooting zone. It was theorized that the current hydraulic conductivity and soil matric potential formulations could be modified to slow down the upward flow of water. Alternative formulations were investigated; Slide 2 shows how one alternative formulation improved soil moisture variability. In particular, the drying events in 1983 and 1988 are better captured. However, there were issues of model stability and robustness.
Later work by Sean Swenson showed that the model was capable of reproducing quite well the Illinois soil moisture observations through a combination of reasonable site-specific changes to the model (deeper water table, decrease in hydraulic conductivity, corrected solar insolation, soil compaction, and increase in leaf area index). An example is shown in Slide 3 where the model shows similar soil moisture variability that is consistent with the observations in terms of amplitude, phase, and depth dependence. The main disadvantage of this approach is that it is difficult to apply globally.
At the June, 2008 CCSM workshop, project members met to decide on a final model configuration to improve soil moisture variability. The final configuration incorporates many of the ideas mentioned above and other ideas from university collaborators but is a compromise between matching limited observations of soil moisture variability and satisfying other global hydrologic constraints on the model as well as accounting for the influence of other concurrent model development (e.g., organic soil and litter). An example is shown in slide 4, where the unrealistic variability of soil moisture with depth in CLM3.5 is corrected in the modified model. These results will be submitted for publication once the performance of the new model (CLM4.0) has been demonstrated in coupled simulations.
Publications FY08 (abstracts):
Stockli, R., D. M. Lawrence, G.-Y. Niu, K. W. Oleson, P. Thornton, Z.-L. Yang, G. Bonan, A. Denning, S. Running, 2008: Use of FLUXNET in the community land model development. J. Geophys. Res., 113, G01025, doi: 10.1029/2007JG000562.
Oleson, K. W., G.-Y. Niu, Z.-L. Yang, D. M. Lawrence, P. Thornton, P. Lawrence, R. Stockli, R. Dickinson, G. Bonan, S. Levis, A. Dai, T. Qian, 2008: Improvements to the community land model and their impact on the hydrological cycle. J. Geophys. Res., 113, G01021, doi: 10.1029/2007JG000563.
Oleson, K. W., G. B. Bonan, J. Feddema, M. Vertenstein, C. S. B. Gimmond, 2008: An urban parameterization for a global climate model. Part I. Formulation and evaluation for two cities. J. Appl. Meteor. Climat., 47, 1038-1060, doi: 10.1175/2007JAMC1597.1.
Oleson, K. W., G. B. Bonan, J. Feddema, M. Vertenstein, 2008: An urban parameterization for a global climate model. Part II. Sensitivity to input parameters and the simulated urban heat island in offline simulations. J. Appl. Meteor. Climat., 47, 1061-1076, doi: 10.1175/2007JAMC1598.1.