Super-Clausius–Clapeyron Scaling of Extreme Hourly Convective Precipitation and Its Relation to Large-Scale Atmospheric Conditions

Abstract

Present-day precipitation–temperature scaling relations indicate that hourly precipitation extremes may have a response to warming exceeding the Clausius–Clapeyron (CC) relation; for the Netherlands the dependency on surface dewpoint temperature follows 2 times the CC relation (2CC). The authors’ hypothesis—as supported by a simple physical argument presented here—is that this 2CC behavior arises from the physics of convective clouds. To further investigate this, the large-scale atmospheric conditions accompanying summertime afternoon precipitation events are analyzed using surface observations combined with a regional reanalysis. Events are precipitation measurements clustered in time and space. The hourly peak intensities of these events again reveal a 2CC scaling with the surface dewpoint temperature. The temperature excess of moist updrafts initialized at the surface and the maximum cloud depth are clear functions of surface dewpoint, confirming the key role of surface humidity on convective activity. Almost no differences in relative humidity and the dry temperature lapse rate were found across the dewpoint temperature range, supporting the theory that 2CC scaling is mainly due to the response of convection to increases in near-surface humidity, while other atmospheric conditions remain similar. Additionally, hourly precipitation extremes are on average accompanied by substantial large-scale upward motions and therefore large-scale moisture convergence, which appears to accelerate with surface dewpoint. Consequently, most hourly extremes occur in precipitation events with considerable spatial extent. Importantly, this event size appears to increase rapidly at the highest dewpoint temperature range, suggesting potentially strong impacts of climatic warming.

Response of Extreme Precipitating Cell Structures to Atmospheric Warming

“…The experimental setup follows the approach developed in Loriaux et al (), specifically designed to produce a simple but yet realistic forcing for convective situations. Based on a catalog of rainfall events in the Netherlands from the past 20 years (Lenderink et al, ), we create a composite of approximately 300 days with heavy hourly precipitation in the summer season (April to September) in the afternoon hours (1200 to 2000 CET). Our selection is further constrained to the top 20% most intense events at dew point temperatures above 14 °C.…”

Prognostic Power of Extreme Rainfall Scaling Formulas Across Space and Time Scales

“…It is important to note that this minimum threshold does not necessarily apply to other studies and should be derived in each case because the type of events counted as extreme depends on the definition chosen. This is true in particular if the definition of extremes excludes dry days or if the physical domain is subject to substantial synoptic forcing, such as for Lenderink et al () and Panthou et al (). Even though no statement can a priori be made about the accuracy of scaling approximations in previous work, one should be careful when interpreting results focusing on low‐percentile ranks.…”

Evaluation and projected changes of precipitation statistics in convection-permitting WRF climate simulations over Central Europe

“…Observation based studies suggest that the increase of hourly precipitation extremes with temperature can exceed C-C scaling rates for daily mean temperatures above 12 °C. This exceedance is most probably related to the release of latent heat in convective precipitation and in updrafts and the accompanied enhanced moisture convergence (Lenderink and van Meijgaard 2008;Berg et al 2013;Lenderink et al 2017). Globally, extreme precipitation scaling rates with temperature differ between regions (Utsumi et al 2011;Wang et al 2017).…”