Storm type effects on super Clausius–Clapeyron scaling of intense rainstorm properties with air temperature

Abstract

Abstract. Extreme precipitation is thought to increase with warming at rates similar to or greater than the water vapour holding capacity of the air at ~ 7% °C−1, the so-called Clausius–Clapeyron (CC) rate. We present an empirical study of the variability in the rates of increase in precipitation intensity with air temperature using 30 years of 10 min and 1 h data from 59 stations in Switzerland. The analysis is conducted on storm events rather than fixed interval data, and divided into storm type subsets based on the presence of lightning which is expected to indicate convection. The average rates of increase in extremes (95th percentile) of mean event intensity computed from 10 min data are 6.5% °C−1 (no-lightning events), 8.9% °C−1 (lightning events) and 10.7% °C−1 (all events combined). For peak 10 min intensities during an event the rates are 6.9% °C−1 (no-lightning events), 9.3% °C−1 (lightning events) and 13.0% °C−1 (all events combined). Mixing of the two storm types exaggerates the relations to air temperature. Doubled CC rates reported by other studies are an exception in our data set, even in convective rain. The large spatial variability in scaling rates across Switzerland suggests that both local (orographic) and regional effects limit moisture supply and availability in Alpine environments, especially in mountain valleys. The estimated number of convective events has increased across Switzerland in the last 30 years, with 30% of the stations showing statistically significant changes. The changes in intense convective storms with higher temperatures may be relevant for hydrological risk connected with those events in the future.

Describing the interannual variability of precipitation with the derived distribution approach: effects of record length and resolution

“…These are all 10 min precipitation depths, with 0.1 mm resolution, measured over the exact same period with the same Lambrecht tippingbucket instruments, with standardized calibration and maintenance. These rainfall data are of very good quality and have recently been used in other studies of storm properties in Switzerland (e.g., Gaál et al, 2014;Molnar et al, 2015).…”

Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling

“…The intensity of sub-daily precipitation extremes is more sensitive to temperature changes compared to the intensity of daily extremes (Westra et al 2014). CC scaling can be also affected by local and regional factors that can limit moisture availability, especially in mountain valleys (Molnar et al 2015).…”

“…There is observational evidence that extreme precipitation intensity has increased in many places (Trenberth et al 2003, Lende rink et al 2011, Benestad 2013, O'Gorman 2015, Molnar et al 2015 and climate simulations have revealed that this characteristic will be maintained and even intensified under future global warming (Pall et al 2007, Allan & Soden 2008, Scoccimarro et al 2013, Ban et al 2015. This behaviour is supported from a theoretical point of view by the so-called Clausius-Clapeyron relation (hereafter referred to as 'CC scaling'), which states that atmospheric humidity will increase at a rate that follows the saturation vapor pressure dependency on temperature (a rate of ~6−7% °C −1 ), under conditions of constant relative humidity (Trenberth et al 2003, Pall et al 2007, Westra et al 2014, Molnar et al 2015. A recent review on this topic is presented by O'Gorman (2015).…”

“…However, recent studies have revealed that the relationship between precipitation extremes and temperature is very complex and depends on many factors, such as storm duration (Hardwick-Jones et al 2010, Westra et al 2014, season (Ban et al 2015, storm type , Molnar et al 2015, microphysics (Singh & O'Gorman 2014), regional atmospheric stability (Loriaux et al 2013) and large-scale circulation . In some areas, a strong difference between coastal (showing dependence close to CC scaling) and inland regions (showing a super-CC scaling) has been found (Panthou et al 2014).…”

Relevance of the correlation between precipitation and the 0 °C isothermal altitude for extreme flood estimation

“…Similarly, Wasko et al (2015) showed in a study conditioning the scaling on precipitation event duration that, in Australia, moisture availability limitations cannot be found for short events (1 h-2 h). In Switzerland, Molnar et al (2015) concluded that there could be limitations of moisture availability. However, this conclusion was drawn without discussing its dependence on the precipitation duration.…”