A comparison of extreme European daily precipitation simulated by a globaland a regional climate model for present and future climates

The intensity and distribution of daily precipitation is predicted to chang e under scenarios of increased greenhouse gases (GHGs). In this paper, we a nalyse the ability of HadCM2, a general circulation model (GCM), and a high -resolution regional climate model (RCM), both developed at the Met Office' s Hadley Centre, to simulate extreme daily precipitation by reference to ob servations. A detailed analysis of daily precipitation is made at two UK gr id boxes, where probabilities of reaching daily thresholds in the GCM and R CM are compared with observations. We find that the RCM I generally overpre dicts probabilities of extreme daily precipitation but that, when the GCM a nd RCM simulated values are scared to have the same mean as the observation s, the RCM captures the upper-tail distribution more realistically To compa re regional changes in daily precipitation in the GHG-forced period 2080-21 00 in the GCM and the RCM, we develop two methods. The first considers the fractional changes in probability of local daily precipitation leaching or exceeding a fixed 15 mm threshold in the anomaly climate compared with the control. The second method uses the upper one-percentile of the control at each point as the threshold. Agreement between the models is better in both seasons with the latter method, which we suggest may be more useful when c onsidering larger scale spatial changes. On average, the probability of pre cipitation exceeding the 1% threshold increases by a factor of 2.5 (GCM and RCM) in winter and by 1.7 (GCM) or 1.3 (RCM) in summer.