Heavy precipitation in a changing climate: Does short‐term summer precipitation increase faster?

Abstract

Climate models project that heavy precipitation events intensify with climate change. It is generally accepted that extreme day-long events will increase at a rate of about 6-7% per degree warming, consistent with the Clausius-Clapeyron relation. However, recent studies suggest that subdaily (e.g., hourly) precipitation extremes may increase at about twice this rate. Conventional climate models are not suited to assess such events, due to the limited spatial resolution and the need to parametrize convective precipitation (i.e., thunderstorms and rain showers). Here we employ a convection-resolving model using a horizontal grid spacing of 2.2 km across an extended region covering the Alps and its larger-scale surrounding from northern Italy to northern Germany. Consistent with previous results, projections using a Representative Concentration Pathways version 8.5 greenhouse gas scenario reveal a significant decrease of mean summer precipitation. However, unlike previous studies, we find that both extreme day-long and hour-long precipitation events asymptotically intensify with the Clausius-Clapeyron relation. Differences to previous studies might be due to the model or region considered, but we also show that it is inconsistent to extrapolate from present-day precipitation scaling into the future.

Climate change in the next 30 years: What can a convection-permitting model tell us that we did not already know?

“…Analysis performed for the Wagner et al (2012) paper (personal communication) shows similar decreases in mean precipitation KO = 0.5(θ 700 + θ 500 − θ 1000 − θ 850 ) in JJA for all three realizations of ECHAM5 downscaled by CLM7, and cases of increases in precipitation seems to be more related to natural variability than a result of climate change. Notice that those differences in the precipitation pattern related to the complex orography are not seen in Ban et al (2015), who with a similar model showed consistently decreasing intensities for the current domain.…”

“…Trenberth et al 2003), or rather a super-CCrate (Lenderink and van Meijgaard 2008;Berg et al 2013;Westra et al 2014). When comparing historical to end of century projections in the RCP8.5 scenario, Ban et al (2015) found an intensification of the extremes according to the standard CC-rate over the Alps and surrounding regions, while for the southern UK, Kendon et al (2014) found that the increase in convective precipitation was consistent with a super-CC-rate. The scaling between precipitation intensity and temperature is strongly affected by the inclusion or not of dry days in the calculation of the extreme percentiles (Ban et al 2015).…”

“…When comparing historical to end of century projections in the RCP8.5 scenario, Ban et al (2015) found an intensification of the extremes according to the standard CC-rate over the Alps and surrounding regions, while for the southern UK, Kendon et al (2014) found that the increase in convective precipitation was consistent with a super-CC-rate. The scaling between precipitation intensity and temperature is strongly affected by the inclusion or not of dry days in the calculation of the extreme percentiles (Ban et al 2015). According to Chan et al (2015), future CC-scaling rate might be different compared to present observed scaling for southern UK when the changes in the large-scale weather pattern modify moisture availability.…”

“…Kendon et al 2014;Ban et al 2015) investigated the climate change signal of precipitation statistics at daily and sub-daily time scale using long simulations at convection-permitting resolution, and they compared these projections with those from standard parameterised RCMs. However, the two papers disagree on the final conclusions.…”

“…The effects of this underestimation on the society could be enormous if, as Kendon et al (2014) mention, the summer extreme events intensify above expectations from the Clausius-Clapeyron relation (Lenderink and van Meijgaard 2008;Berg et al 2013). Ban et al (2015) investigated climate change signals for the Alps region, and found that both daily and hourly precipitation extremes intensify according to the ClausiusClapeyron relation when considering all days, and that in general convection-permitting and coarser resolution agree on the magnitude of the changes. The disagreements indicate either a regionally dependent pattern of changes, or a model dependency of the results.…”