An Analysis of (Sub-)Hourly Rainfall in Convection-Permitting Climate Simulations Over Southern Sweden From a User’s Perspective

Abstract

To date, the assessment of hydrological climate change impacts, not least on pluvial flooding, has been severely limited by i) the insufficient spatial resolution of regional climate models (RCMs) as well as ii) the simplified description of key processes, e.g., convective rainfall generation. Therefore, expectations have been high on the recent generation of high-resolution convection-permitting regional climate models (CPRCMs), to reproduce the small-scale features of observed (extreme) rainfall that are driving small-scale hydrological hazards. Are they living up to these expectations? In this study, we zoom in on southern Sweden and investigate to which extent two climate models, a 3-km resolution CPRCM (HCLIM3) and a 12-km non-convection permitting RCM (HCLIM12), are able to reproduce the rainfall climate with focus on short-duration extremes. We use three types of evaluation–intensity-based, time-based and event-based–which have been designed to provide an added value to users of high-intensity rainfall information, as compared with the ways climate models are generally evaluated. In particular, in the event-based evaluation we explore the prospect of bringing climate model evaluation closer to the user by investigating whether the models are able to reproduce a well-known historical high-intensity rainfall event in the city of Malmö 2014. The results very clearly point at a substantially reduced bias in HCLIM3 as compared with HCLIM12, especially for short-duration extremes, as well as an overall better reproduction of the diurnal cycles. Furthermore, the HCLIM3 model proved able to generate events similar to the one in Malmö 2014. The results imply that CPRCMs offer a clear potential for increased confidence in future projections of small-scale hydrological climate change impacts, which is crucial for climate-proofing, e.g., our cities, as well as climate modeling in general.

Characteristics of precipitation extremes over the Nordic region: added value of convection-permitting modeling

“…HCLIM3 also overestimates the precipitation events of more than 5 mm (R5mm) by around 60 % (5 % over Sweden), while HCLIM12 underestimates these events by 43 %-69 %. Also, Lind et al (2020) and Olsson et al (2021a) found mostly positive biases for hourly values over the 95th percentile in HCLIM3 and underestimation of the percentile values by HCLIM12.…”

“…HCLIM12 and ERA5 also underestimate the observed intensities of the 99.9th percentile events throughout the day. Previously, Belušić et al (2020), Lind et al (2020), andOlsson et al (2021a) have shown that HCLIM3 improved the representation of the diurnal cycles of mean precipitation as well as the 90th and 99th percentiles compared to HCLIM12.…”

“…1), the high grid resolution combined with the 21-year-long simulation period allows for a robust assessment of the added value in simulating precipitation extremes over the Nordic countries. The simulations have been evaluated and presented in previous studies by Lind et al (2020) and Olsson et al (2021a). However, Lind et al (2020) focused mainly on general model evaluation, while Olsson et al (2021a) evaluated heavy-and extreme-precipitation events only over the southern part of Sweden.…”

“…The simulations have been evaluated and presented in previous studies by Lind et al (2020) and Olsson et al (2021a). However, Lind et al (2020) focused mainly on general model evaluation, while Olsson et al (2021a) evaluated heavy-and extreme-precipitation events only over the southern part of Sweden. Both studies found an added value of the convection-permitting HCLIM38 model setup in simulating the intensities and frequencies of mean-and heavyprecipitation events at sub-daily timescales.…”

“…Previously, Lind et al (2016) showed an added value of the high-resolution HCLIM model with the previous cycle 37 in representing precipitation extremes over the Alps. The current study deepens the understanding of the benefits of convectionpermitting climate modeling over northern Europe by extending the analysis by Olsson et al (2021a) over the whole model domain and by studying extreme-precipitation events with generalized extreme value (GEV) theory. 2 Model and observations…”