Improvement in runoff parameterization for global climate modelling

• Main Author: Liu, Jinliang
• Format: Thesis
• Language: English
• Published: 2001
• Subjects: Mackenzie River; Mackenzie river
• Online Access: http://hdl.handle.net/1807/15376; http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58635.pdf

grantor: University of Toronto Diagnosed runoff was estimated from NCEP/NCAR reanalysis data for an 8-year period from 1987 to 1994. Bonan's land surface model (LSM) was run for the same period coupled to NCAR's CCM3. Comparisons between the diagnosed and simulated runoff indicate that, the runoff parameterization in the original LSM cannot produce a reasonable diagnosed horizontal distribution of runoff, which is important to the model climate. One of the possible reasons is the exclusion of topographic effects in the original runoff parameterization. Therefore, based on previous research results on river re-distribution models, a modification on the original runoff parameterization was proposed and implemented in the original LSM. This modification has two aspects: firstly, the topographic slopes cause outflows from higher topography and inflows into the lower topography points; secondly, topographic slopes also cause decrease of infiltration at higher topography and increases of infiltration at lower topography. Then changes in infiltration result in changes in soil-moisture, surface fluxes and then in surface temperature. This mechanism is very clearly demonstrated in the point budgets analysis at the Andes Mountains vicinities. Analysis from a re gional scale perspective in the Canadian GEWEX basin, the Mackenzie River basin, shows that the modified runoff parameterization can generate an expected horizontal distribution of total runoff which is much closer to the horizontal distribution of the observed and diagnosed runoff, and which is much more consistent with topography and thus very easy to explain physically. This represents a significant improvement over the original LSM. More importantly, very detailed analysis from a global perspective shows many very encouraging improvements introduced by the modified model over the original model in simulating basic atmospheric climate properties such as thermodynamic features, precipitable water, net water exchange, and precipitation. The modified model somehow corrected some deficiencies evident in the AGCM. All of these improvements in the atmospheric climate simulation illustrate that the inclusion of topographic effects in the LSM can force the AGCM to produce a more realistic model climate. Analysis also shows that the modified model may improve the atmospheric 'CO '2 simulation which is very important to global environmental studies. Ph.D.