Changes in average and extreme precipitation in two regional climate model experiments

Abstract

Two regional climate model experiments for northern and central Europe are studied focussing on greenhouse gas-induced changes in heavy precipitation. The average yearly maximum oneday precipitation P max shows a general increase in the whole model domain in both experiments, although the mean precipitation P mean decreases in the southern part of the area, especially in one of the experiments. The average yearly maximum six-hour precipitation increases even more than the one-day P max , suggesting a decrease in the timescale of heavy precipitation. The contrast between the P mean and P max changes in the southern part of the domain and the lack of such a contrast further north are affected by changes in wet-day frequency that stem, at least in part, from changes in atmospheric circulation. However, the yearly extremes of precipitation exhibit a larger percentage increase than the average wet-day precipitation. The signal-to-noise aspects of the model results are also studied in some detail. The 44 km grid-box-scale changes in P max are very heavily affected by inter-annual variability, with an estimated standard error of about 20% for the 10-year mean changes. However, the noise in P max decreases sharply toward larger horizontal scales, and large-area mean changes in P max can be estimated with similar accuracy to those in P mean . Although a horizontal averaging of model results smooths out the small-scale details in the true climate change signal as well, this disadvantage is, in the case of P max changes, much smaller than the advantage of reduced noise.generally point toward a continued upward trend

Uncertainty in the future change of extreme precipitation over the Rhine basin: the role of internal climate variability

“…The effect of spatial pooling also depends on geography and the season of interest. Our result is in accordance with Räisänen and Joelsson (2001) who observed that the internal climate variability of the 1-day annual maximum precipitation is reduced stronger at larger spatial scales than the internal climate variability of the annual mean precipitation, and with Hegerl et al (2004) who, noted that changes in moderately extreme precipitation should be better detectable than changes in the annual mean precipitation because of a greater consistency between the change patterns in these extremes in climate model simulations.…”

“…The uncertainty of the changes in extreme precipitation, has only been studied to a limited extent. Räisänen and Joelsson (2001) compared the changes in the annual mean and maximum precipitation in two 10-year control and 10-year future regional climate model simulations driven by different GCMs. They concluded that the differences between the changes in these two model experiments could be largely explained by internal climate variability as a result of the short lengths of the climate model simulations.…”

A new generation of climate-change experiments: events, not trends

“…2004). Studies generally predict increasing frequency of heavy rainfall for Central Europe (Christensen and Christensen 2003), the UK, and Bangladesh (Palmer and Raisanen 2002), as well as increasing intensity (Raisanen and Joelsson 2001). Enhanced summer droughts are expected for southern Europe and central North America (Seneviratne et al .…”

Projections of twenty-first century climate over Europe

“…These include Giorgi et al [31], Rotach et al [32], Jones et al [33], Deque et al [34], Machenauer et al [35], Raisanen et al [36], Raisanen and Joelsson [37], Rummukainen et al [38], Beniston et al [39], Christensen and Christensen [40,41], Kjellstrom [42], Semmler and Jacob [43], Sanchez et al [44], Pal et al [45], Schar et al [46]; Giorgi et al [47]; Raisanen et al [48]; Ekstrom et al [49], Deque et al [50], Gao et al [51], Diffenbaugh et al [52].…”