Attributing intensification of precipitation extremes to human influence

This study attempts to quantify the human contribution to the observed intensification of precipitation extremes. We consider the annual maxima of daily (RX1day) and five-day consecutive (RX5day) precipitation amounts over the Northern Hemisphere land area for 1951-2005 and compare observed changes with expected responses to external forcings as simulated by multiple climate models participating in CMIP5. Model simulated responses to external forcings are consistent with the observations. The response to anthropogenic forcings can also be separately detected from that of natural forcing. We estimate that human influence has intensified annual maximum one-day precipitation in sampled Northern Hemisphere locations by 3.3% [1.1% to 5.8%, >90% confidence interval] on average. This corresponds to an average intensification in RX1day of 5.2% [1.3%, 9.3%] per degree increase in observed global mean surface temperature, consistent with the Clausius-Clapeyron relationship. As a consequence, an annual maximum 1-day precipitation event that was expected to recur once every 20 years on average in the early 1950s is estimated to have become a 15 year event in the early 2000s.