Verification of GCM-generated regional seasonal precipitation for current climate and of statistical downscaling estimates under changing climate conditions

Empirical downscaling procedures relate large-scale atmospheric features wi th local features such as station rainfall in order to facilitate local sce narios of climate change. The purpose of the present paper is twofold: firs t, a downscaling technique is used as a diagnostic tool to verify the perfo rmance of climate models on the regional scale; second, a technique is prop osed for verifying the validity of empirical downscaling procedures in clim ate change applications. The case considered is regional seasonal precipitation in Romania. The down scaling model is a regression based on canonical correlation analysis betwe en observed station precipitation and European-scale sea level pressure (SL P). The climate models considered here are the T21 and T42 versions of the Hamburg ECHAM3 atmospheric GCM run in "time-slice" mode. The climate change scenario refers to the expected time of doubled carbon dioxide concentrati ons around the year 2050. The downscaling model is skillful for all seasons except spring. The genera l features of the large-scale SLP variability are reproduced fairly well by both GCMs in all seasons. The climate models reproduce the empirically det ermined precipitation-SLP link in winter, whereas the observed link is only partially captured for the other seasons. Thus, these models may be consid ered skillful with respect to regional precipitation during winter, and par tially during the other seasons. Generally, applications of statistical dow nscaling to climate change scenarios have been based on the assumption that the empirical link between the large-scale and regional parameters remains valid under a changed climate. In this study, a rationale is proposed for this assumption by showing the consistency of the 2 x CO2 GCM scenarios in winter, derived directly from the gridpoint data, with the regional scenari os obtained through empirical downscaling. Since the skill of the GCMs in r egional terms is already established, it is concluded that the downscaling technique is adequate for describing climatically changing regional and loc al conditions, at least for precipitation in Romania during winter.