Research Programs

CLM Hydrology & Land Cover and Land Use Change
FY2006 activities

TIIMES Theme:
WCAS

Compiled by Gordon Bonan - CGD - TIIMES

Reserach Team: Gordon Bonan-CGD& TIIMES, David Lawrence-CGD, Sam Levis-CGD& TIIMES, Keith Oleson-CGD& TIIMES

Collaborators: Robert Dickinson (Georgia Institute of Technology), Johan Feddema (University of Kansas), Sue Grimmond (King’s College London), Peter Lawrence (University of Colorado), Guo-Yue Niu (University of Texas), Reto Stockli (Colorado State University), Zong-Liang Yang (University of Texas), Johan Feddema (University of Kansas), Gordon Bonan, and Keith Oleson

CLM Hydrology

Comparison for 12 river basins of two estimates of change in water storage derived from the GRACE satellite mission with that simulated by CLM3 and CLM3 with hydrologic modifications.

Keith Oleson, David Lawrence, Gordon Bonan, and Sam Levis (Climate and Global Dynamics Division) led a project within the CCSM land model working group to improve the surface hydrology of CLM. Numerous university colleagues contributed to this project including, but not limited to, Robert Dickinson (Georgia Institute of Technology), Zong-Liang Yang and Guo-Yue Niu (University of Texas), Reto Stockli (Colorado State University), and Peter Lawrence (University of Colorado). A basic deficiency in version 3 of CLM is the partitioning of latent heat flux into evaporation of water intercepted by plant canopies, transpiration, and soil evaporation. The model has too much interception and soil evaporation and too little transpiration, in part due to dry soils. New parameterizations of hydrologic processes in CLM greatly improve the simulated hydrologic cycle. This improvement is seen in comparisons for several river basins of simulated soil water storage to that derived from the GRACE satellite.

Land cover and land use change

June-July-August temperature differences in 2050 and 2100 due to land-cover change in the B1 and A2 scenarios. Values were calculated by subtracting the greenhouse gas–only forcing scenarios from a simulation including land-cover and greenhouse gas forcings.

Johan Feddema (University of Kansas), Gordon Bonan, and Keith Oleson studied the effects of historical and future land cover change on global climate. Adding the effects of changes in land cover to the A2 and B1 transient climate simulations described in the Special Report on Emissions Scenarios (SRES) by the Intergovernmental Panel on Climate Change leads to significantly different regional climates in 2100 as compared with climates resulting from atmospheric SRES forcings alone. Agricultural expansion in the A2 scenario results in significant additional warming over the Amazon. Agricultural expansion in the mid-latitudes produces cooling and decreases in the mean daily temperature range over many areas.

Average diurnal cycle of simulated and observed heat fluxes for the Mexico City site (Me93) for days 336-341 (Dec 2-7, 1993).

Oleson, Bonan, and Feddema developed and tested an urban land cover parameterization for CLM.  The parameterization uses concepts from urban canyon models to simulate the radiative balance of a city, turbulent energy fluxes, and the hydrologic cycle. The model is designed to be compatible with structural and computational constraints of CLM for coupling to a global climate model, yet complex enough to explore physically-based processes known to be important in determining urban climatology.  The city representation is based upon the urban canyon concept which consists of roofs, sunlit and shaded walls, and canyon floor.  The canyon floor is divided into pervious (e.g., residential lawns, parks) and impervious (e.g., roads, parking lots, sidewalks) fractions.  Trapping of longwave radiation by canyon surfaces and solar radiation absorption and reflection is determined by accounting for multiple reflections.  Separate energy balances and surface temperatures are determined for each canyon surface.  A one-dimensional heat conduction equation is solved numerically for a ten-layer column to determine conduction fluxes into and out of canyon surfaces.  The urban model was compared to observed fluxes and temperatures for Mexico City and Vancouver in collaboration with Sue Grimmond (King’s College London). The model captures the behavior of urban land cover compared with rural land cover and gives insights to the urban heat island.