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  • Wang, J.F., and X.B. Zhang, 2006: Downscaling and projection of winter extreme daily precipitation over North America. J.Climate. In press.

Large scale atmospheric variables have been statistically downscaled to derive winter (December-March) maximum daily precipitation at stations over North America using the generalized extreme value distribution (GEV). Here, the leading principal components of the sea level pressure field and local specific humidity are co-variates of the distribution parameters. The GEV parameters are estimated using data from 1949-1999 and the r-largest method. This statistical downscaling procedure is found to yield skill over the southern and northern West Coast, central USA and areas of western and eastern Canada when tested with independent data.
The projected changes in co-variates or predictors are obtained from transient climate change simulations conducted with the CGCM3.1 model of the Canadian Centre for Climate Modelling and Analysis, forced by the IPCC A2 forcing scenario. They are then used to derive the GEV distribution parameters for the period 2050-2099. The projected frequency of the current 20-year return maximum daily precipitation for that period suggests that extreme precipitation risk will increase heavily over the south and central US but decrease over the Canadian Prairies. The difference between the statistical downscaling results and those estimated using GCM simulation is also discussed.

Last Updated: 2007-12-13

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