Thursday, 16 May 2002: 3:10 PM
Land-surface parameterizations in northern regions: Results from PILPS Phase 2(e)
The potential sensitivity of land-atmosphere interactions to climate warming at high latitudes has motivated improvements to parameterizations of cold region processes in the land surface schemes used in numerical weather prediction and climate models. PILPS (Project for Intercomparison of Land surface Parameterization Schemes) Experiment 2(e) was designed to evaluate the performance of uncoupled land surface schemes for a high latitude watershed, the Torne/Kalix River system in northern Scandinavia. The Torne and Kalix Rivers drain 58,000 km2 along the border between Sweden and Finland, a domain that was represented by 218 grid boxes at 1/4 degree spatial resolution for the ten-year period 1989-1998. Participants were asked to estimate parameters of their models using streamflow observations for two small sub-catchments within the Torne/Kalix basin, prior to running models over the entire domain. Streamflow at the basin mouth(s) was not provided to the participants, although observations were available for subsequent model evaluation. All twenty-one models participating in PILPS-2(e) were able to capture the broad dynamics of snowmelt and runoff, but large differences in snow accumulation, turbulent heat fluxes and streamflow were apparent. The results showed that limited net radiation in this high latitude environment (varying between 15 and 28 W/m2 on annual average) provides a lower bound on runoff generation. Net radiation during the snow accumulation season is primarily controlled by surface temperature, which in turn influences turbulent fluxes. Those models with the largest negative near surface temperature gradients tended to suppress turbulent fluxes through stability corrections. Although the timing of runoff was dominated primarily by snowmelt, annual runoff volume was controlled in large part by sublimation. Estimates of effective aerodynamic resistances for 13 of the models showed a clear trend toward reduced sublimation and increasing snow accumulation with increasing resistance.
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