Regional climate modeling using convection‐permitting models (CPMs; horizontal grid spacing <4 km) emerges as a promising framework to provide more reliable climate information on regional to local scales compared to traditionally used large‐scale models (LSMs; horizontal grid spacing >10 km). CPMs no longer rely on convection parameterization schemes, which had been identified as a major source of errors and uncertainties in LSMs. Moreover, CPMs allow for a more accurate representation of surface and orography fields. The drawback of CPMs is the high demand on computational resources. For this reason, first CPM climate simulations only appeared a decade ago. In this study, we aim to provide a common basis for CPM climate simulations by giving a holistic review of the topic. The most important components in CPMs such as physical parameterizations and dynamical formulations are discussed critically. An overview of weaknesses and an outlook on required future developments is provided. Most importantly, this review presents the consolidated outcome of studies that addressed the added value of CPM climate simulations compared to LSMs. Improvements are evident mostly for climate statistics related to deep convection, mountainous regions, or extreme events. The climate change signals of CPM simulations suggest an increase in flash floods, changes in hail storm characteristics, and reductions in the snowpack over mountains. In conclusion, CPMs are a very promising tool for future climate research. However, coordinated modeling programs are crucially needed to advance parameterizations of unresolved physics and to assess the full potential of CPMs.

The uncertainties in current global and regional climate model integrations are partly related to the representation of clouds, moist convection, and complex topography, thus motivating the use of convection-resolving models. On climate time scales, convection-resolving methods have been used for process studies, but application to long-term scenario simulations has been very limited. Here we present a convection-resolving simulation for a 10 yearlong period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) integrated with the Consortium for Small-Scale Modeling in Climate Mode model. Two one-way nested grids are used with horizontal resolutions of 2.2 km for a convection-resolving model (CRM2) on an extended Alpine domain (1100 km × 1100 km) and 12 km for a convection-parametrizing model (CPM12) covering Europe. CPM12 is driven by lateral boundary conditions from the ERA-Interim reanalysis. Validation is conducted against high-resolution surface data. The CRM2 model strongly improves the simulation of the diurnal cycles of precipitation and temperature, despite an enhanced warm bias and a tendency for the overestimation of precipitation over the Alps. The CPM12 model has a poor diurnal cycle associated with the use of parameterized convection. The assessment of extreme precipitation events reveals that both models adequately represent the frequency-intensity distributions for daylong events in summer, but large differences occur for hourly precipitation. The CPM12 model underestimates the frequency of heavy hourly events, while CRM2 shows good agreement with observations in the summer season. We also present results on the scaling of precipitation extremes with local daily mean temperatures. In accordance with observations, CRM2 exhibits adiabatic scaling for intermediate hourly events (90th percentile) and superadiabatic scaling for extreme hourly events (99th and 99.9th percentiles) during the summer season. The CPM12 model partly reproduces this scaling as well. The excellent performance of CRM2 in representing hourly precipitation events in terms of intensity and scaling is highly encouraging, as this addresses a previously untested (and untuned) model capability.

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.

The importance of soil moisture anomalies on airmass convection over semiarid regions has been recognized in several studies. The underlying mechanisms remain partly unclear. An open question is why wetter soils can result in either an increase or a decrease of precipitation (positive or negative soil moistureprecipitation feedback, respectively). Here an idealized cloud-resolving modeling framework is used to explore the local soil moisture-precipitation feedback. The approach is able to replicate both positive and negative feedback loops, depending on the environmental parameters.The mechanism relies on horizontal soil moisture variations, which may develop and intensify spontaneously. The positive expression of the feedback is associated with the initiation of convection over dry soil patches, but the convective cells then propagate over wet patches where they strengthen and preferentially precipitate. The negative feedback may occur when the wind profile is too weak to support the propagation of convective features from dry to wet areas. Precipitation is then generally weaker and falls preferentially over dry patches. The results highlight the role of the midtropospheric flow in determining the sign of the feedback. A key element of the positive feedback is the exploitation of both low convective inhibition (CIN) over dry patches (for the initiation of convection) and high CAPE over wet patches (for the generation of precipitation).

The daytime heat transfer mechanisms over mountainous terrain are investigated by means of large-eddy simulations over idealized valleys. Two- and three-dimensional topographies, corresponding to infinite and finite valleys, are used in order to evaluate the influence of the along-valley wind and the valley surroundings on the heat transfer processes. The atmosphere is coupled to an interactive land surface, allowing for dynamic feedback on the surface fluxes. The valley heat budget is analyzed both from a local and bulk perspective, and the flow is Reynolds decomposed into its mean and turbulent component. The analysis clarifies recent issues of contention regarding the heating of the valley atmosphere. The flow decomposition allows one to clearly distinguish between the different heating processes: those associated with the mean flow, such as advection-induced cooling by the upslope flows and the warming induced by the compensating subsidence, and those associated with the turbulent motions. The latter include the warming of the mixed layer due to the convergence of the turbulent heat flux and cooling in the capping inversion due to overshooting thermals. The analysis from the bulk perspective confirms that the net effect of the thermally induced cross-valley circulation is to export heat out of the valley and away from the mountain ridge. The valley-volume effect is confirmed as the primary cause of enhanced diurnal temperature amplitudes in valleys. The results are robust with regard to the different topographies studied.