DOWNSCALING THE HYDROLOGICAL CYCLE IN THE MACKENZIE BASIN WITH THE CANADIAN REGIONAL CLIMATE MODEL

The Canadian Regional Climate Model (CRCM) has been nested within the Canadian Centre for Climate Modelling and Analysis' second generation General Circulation Model (GCM), for a single month simulation over th e Mackenzie River Basin and environs. The purpose of the study is to a ssess the ability of the higher resolution CRCM to downscale the hydro logical cycle of the nesting GCM. A second 1-month experiment, in whic h the CRCM was nested within analyzed fields of a global data assimila tion system, was also performed to examine the sensitivity of the basi n moisture budget to atmospheric lateral boundary forcing. We have fou nd that the CRCM can produce realistic lee cyclogenesis, preferentiall y in the Liard sub-basin, along with associated circulation and precip itation patterns, as well as an improved rainshadow in the lee of the Rocky Mountains compared to the GCM. While these features do quantitat ively affect the monthly average climate statistics, the basin scale m oisture budgets of the models were remarkably similar though some of t his agreement is due to compensating errors in the GCM. Both models pr oduced excessive precipitation compared to a recent climatology for th e region, the cause of which is traced to lateral boundary forcing. A second experiment, identical to the first except that the CRCM was for ced with analyzed fields at the lateral boundaries, produced a qualita tively different basin moisture budget, including a much more realisti c precipitation field Errors in the moisture budget of the first exper iment appear to be associated with the poor representation of the Aleu tian Low in the GCM, and do not appear to be strongly connected to (lo cal) surface processes within the models. This suggests that art effec tive strategy for modelling the hydrological cycle of the the Mackenzi e Basin on the fast climate timescale - a major requirement of the Mac kenzie GEWEX Study - will involve nesting the CRCM within analyzed (or re-analyzed) atmospheric fields.