Observed heavy precipitation increase confirms theory and early models

The approach to illustrate observed changes in heavy precipitation has been repeated for gridded daily precipitation data for the US. Fig.S1a shows the same result as Fig.2b but for the contiguous US east of 100°W, specifically the region between 65° and 100°W and 25° and 49°N with data coverage (see domain in Fig.S5). Note that the period differs somewhat from Fig.2b since only data up to 2006 was available for the analysis. The changes are smaller than across Europe but consistent with the ClausiusClapeyron scaling reflecting the weaker warming consistent with “warming hole” in the eastern US1-3. For the Clausius-Clapeyron scaling the observed daily precipitation data in the period 1951-1980 was scaled by 3.2% according to the observed temperature change signal between the two periods derived from ERA interim reanalysis. Fig.S1b shows the same analysis as Fig.2c but for the CMIP5 models over the same area as above. Again, the simulated changes are less pronounced than over Europe. Note however that no GCM shows a consistent decrease across all heavy rainfall bins but all GCMs show positive changes in one or the other heavy rainfall bin. The analysis was also performed over the whole of the contiguous US (not shown). The results are consistent in sign but comparison is complicated since over many gridpoints in the western half of the US more than 90% of the days are dry days and thereby the percentiles analyzed here equal zero. SUPPLEMENTARY INFORMATION DOI: 10.1038/NCLIMATE3110