Searching for Added Value in Simulating Climate Extremes with a High-Resolution Regional Climate Model over Western Canada. II: Basin-Scale Results

摘要

We evaluate the capacity of a regional climate model to simulate the statistics of extreme events, and also examine the effect of differing horizontal resolution, at the scale of individual hydrological basins in the topographically complex province of British Columbia, Canada. Two climate simulations of western Canada (WCan) were conducted with the Canadian Regional Climate Model (version 4) at 15 (CRCM15) and 45km (CRCM45) horizontal resolution driven at the lateral boundaries by global reanalysis over the period 1973-1995. The simulations were evaluated with ANUSPLIN, a daily observational gridded surface temperature and precipitation product and with meteorological data recorded at 28 stations within the upper Peace, Nechako, and upper Columbia River basins. In this work, we focus largely on a comparison of the skill of each model configuration in simulating the 90th percentile of daily precipitation (PR90). The companion paper describes the results for a wider range of temperature and precipitation extremes over the entire WCan domain.Over all three watersheds, both simulations exhibit cold biases compared with observations, with the bias exacerbated at higher resolution. Although both simulations generally display wet biases in median precipitation, CRCM15 features a reduced bias in PR90 in all three basins in summer and throughout the year in the upper Columbia River basin. However, the higher resolution model is inferior to CRCM45 with respect to rarer heavy precipitation events and also displays high spatial variability and lower spatial correlations with ANUSPLIN compared with the coarser resolution model. A reduction in the range of PR90 biases over the upper Columbia basin is noted when the 15km results are averaged to the 45km grid. This improvement is partly attributable to the averaging of errors between different elevation data used in the gridded observations and CRCM, but the sensitivity of CRCM15 to resolved topography is also clear from spatial maps of seasonal extremes. At the station scale, modest but systematic reductions in the bias of PR90 relative to ANUSPLIN are again found when the CRCM15 results are averaged to the 45km grid. Furthermore, the annual cycle of inter-station spatial variance in the upper Columbia River basin is well reproduced by CRCM15 but not by ANUSPLIN or CRCM45. The former result highlights the beneficial effect of spatial averaging of small-scale climate variability, whereas the latter is evidently a demonstration of the added value at high resolution vis-a-vis the improved simulation of precipitation at the resolution limit of the model. RESUME[Traduit par la redaction] Nous evaluons la capacite d'un modele regional de climat a simuler les statistiques d'evenements extremes. Nous examinons aussi l'effet de diverses resolutions horizontales, a l'echelle de basins hydrologiques individuels, en Colombie-Britannique, une province du Canada a la topographie complexe. Deux simulations du climat pour l'ouest du Canada ont ete menees avec le Modele regional canadien du climat (version 4), a une resolution horizontale de 15km (MRCC15) et de 45km (MRCC45). Les conditions limites provenaient de reanalyses mondiales s'etendant de 1973 a 1995. Les simulations ont ete evaluees a l'aide d'ANUSPLIN, un produit representant sur une grille les observations quotidiennes de temperature en surface et de precipitations, et avec des donnees meteorologiques mesurees a 28 stations situees dans les bassins versants de la partie superieure de la riviere de la Paix, de la Nechako et du haut Columbia.