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Meteorological processes over islands with complex orography could be better simulated by Convection Permitting Regional Climate Models (CP-RCMs) thanks to an improved representation of the orography, land–sea contrasts, the combination of coastal and orographic effects, and explicit deep convection. This paper evaluates the ability of the CP-RCM CNRM-AROME (2.5-km horizontal resolution) to simulate relevant meteorological characteristics of the Mediterranean island of Corsica for the 2000–2018 period. These hindcast simulations are compared to their driving Regional Climate Model (RCM) CNRM-ALADIN (12.5-km horizontal resolution and parameterised convection), weather stations for precipitation and wind and gridded precipitation datasets. The main benefits are found in the representation of (i) precipitation extremes resulting mainly from mesoscale convective systems affected by steep mountains during autumn and (ii) the formation of convection through thermally induced diurnal circulations and their interaction with the orography during summer. Simulations of hourly precipitation extremes, the diurnal cycle of precipitation, the distribution of precipitation intensities, the duration of precipitation events, and sea breezes are all improved in the 2.5-km simulations with respect to the RCM, confirming an added value. However, existing differences between model simulations and observations are difficult to explain as the main biases are related to the availability and quality of observations, particularly at high elevations. Overall, better results from the 2.5-km resolution, increase our confidence in CP-RCMs to investigate future climate projections for Corsica and islands with complex terrain. [ABSTRACT FROM AUTHOR]

The spatiotemporal characteristics of subdaily extreme precipitation over the Tibetan Plateau (TP) have undergone significant changes due to global warming. In this study, we employed the high‐resolution Weather Research and Forecasting regional climate model to conduct a series of historical and projection simulations under representative concentration pathways (RCPs), especially RCP4.5 and RCP8.5. The aim was to investigate the past and future climatologies and spatiotemporal evolution of subdaily precipitation extremes using newly proposed subdaily extreme precipitation indices (EPIs). The results show that projected changes in precipitation amount, particularly during wet hours, exhibit spatial disparaties. Notably, there are significant decreases along the southern border of the TP and over the western TP, while obvious increases are observed over the inner TP. The southeastern TP, western TP, and southern border of the TP are expected to experience less frequent, shorter duration, and more intense precipitation on an hourly basis. The TP, as a whole, has demonstrated significantly increasing trends in moderate‐to‐heavy precipitation frequencies, along with consistent decreasing trends in precipitation events with short, medium, and long durations. Furthermore, it is predicted that the relationship between extreme precipitation and temperature will deviate from the Clausius‐Clapeyron (C‐C) relationship toward the double C‐C relationship in the far‐future under RCP8.5, particularly over the southeastern TP. Additionally, there are robust correlations between the intensity‐related EPIs and elevation. This indicates that, at the local scale, the complex topography of the region may play a crucial role in shaping the nonuniform distribution of precipitation extremes by modulating associated upward motion. Plain Language Summary: The Tibetan Plateau (TP) has experienced substantial warming during the past decades, at a rate twice that of the global average due to its unique location and elevated terrain. Warming has significantly changed the amount, intensity, frequency, and extremes of precipitation over the TP. The changes in precipitation would influence the stability of the local ecoenvironment and the development of agriculture and industry directly. Previous studies have shown the big picture of daily precipitation extremes in the future, but the characteristics of precipitation extremes at hourly timescale are unclear. This study simulates the changes in subdaily precipitation extremes in the historical (1980–2005) and future (2006–2099) periods under different climate scenarios (RCP4.5 and RCP8.5). Our results show that the spatiotemporal changes and variability over the western TP, the southern border of TP and the southeastern TP are more dramatic than that over the central TP. The southeastern TP shows higher sensitivity and vulnerability to subdaily precipitation extremes and may experience less frequent precipitation lasting for a shorter duration, but with stronger intensity at hourly timescale. The results of this study can guide adaptive measures and be helpful for long‐term water resource management over the TP. Key Points: The simulated hourly precipitation over the Tibetan Plateau (TP) is characterized by heterogeneity and spatially disparate changesLess frequent, shorter duration, and more intense precipitation over the southeastern and the southern border of the TP are projectedThe distributions of the intensity‐related indices exhibit a dependency on elevation [ABSTRACT FROM AUTHOR]

Based on the observations of hourly precipitation for 131 years from Hong Kong Observatory Headquarters, this study examined the long-term changes in the characteristics of hourly precipitation extremes in terms of intensity, total precipitation amount, duration, and frequency. Results show that the hourly precipitation extremes have significantly intensified by 29%–38% from 1885 to 2022. The 131-year observations evidence that the more extreme the hourly precipitation is (i.e. higher percentiles), the faster the increasing rate it has. Specifically, the magnitudes of hourly precipitation with the 95th, 97.5th, 99th, and 99.9th percentiles increased by rates of 0.03 mm, 0.05 mm, 0.07 mm, and 0.12 mm per year, respectively. Through the secular trend analysis, we found that only the maximum intensity of extreme precipitation events (i.e. events with maximum intensity exceeding the 95th percentiles) shows a significant increasing trend during 1885–2022, while the trends in the total precipitation amount, duration, and mean intensity are not significant. However, by comparing the percentile bin values between three sub-periods of the 131-year record, we found a significant rise over time in the total precipitation amount, mean intensity, and maximum intensity of extreme precipitation events with different intensities (i.e. 95th, 96th, 97th, 98th, and 99th percentiles), while the change in the duration is not significant. The analysis of the frequency of precipitation events shows significant increases in the proportion of extreme precipitation events during 1885–2022. The observations of 53 stations across Hong Kong from 1986 to 2022 show significant intensification and increasing frequency in the hourly precipitation extremes in most areas of Hong Kong. Meanwhile, the precipitation duration shows a decreasing tendency, which may explain the insignificant changes in the total precipitation amount. These findings provide important insights into the longer-term variations in the characteristics of hourly precipitation extremes.

Hourly precipitation extremes are crucial in hydrological design. Their frequency and magnitude is encapsulated in the probability distribution tail. Traditional extreme-analysis methods rely on theorems, like the Pickands-Balkema-de Haan, indicating specific type of tails assuming asymptotic convergence—a questionable assumption for real-world samples. Moreover, popular stochastic models for hourly precipitation presume light-tailed distributions to facilitate their mathematical formulation. In practice, limited information on hourly precipitation extremes makes identifying and quantifying their tail highly uncertain, especially on a station-by-station basis. Yet no comprehensive regional analysis of tails has been undertaken to quantify a climatology of tails for diagnostic and prognostic purposes. Here we undertake such an analysis for the conterminous United States. We introduce a novel Bayesian-adjustment approach to assess the best model between power-type and stretched-exponential tails showing that the latter performs better. We present climatology of the tail and quantify its heaviness in over 4,000 hourly precipitation records across the United States and present three main conclusions. First, we show that hourly precipitation tails are heavier than those commonly used with important implications including underestimation of extremes. Second, we provide spatial maps of the tail behavior which reveal some strikingly coherent spatial patterns that can be used for inference in the absence of local observations. Third, we find a nonlinear increase in the tail heaviness with elevation and we formulate parametric functions to describe this law. These results can improve the accuracy of frequency analysis, probabilistic prediction, rainfall-runoff modeling, and downscaling of historical observations and climate model projections.

Compared to singular hot or wet extremes, their occurrence in close sequence might cause larger impacts, because the initial hazard either increases exposure/vulnerability of affected communities to the next or physically worsens the second hazard. Heatwave‐preconditioned hourly precipitation extremes in the Yangtze River Valley are typical of the latter situation. Fueled by soaring convective energy after heatwaves' passage, hourly precipitation extremes are heavier, intensifying faster, and more concentrated during afternoon to evening, compared to those not proceeded by heatwaves. Consequently, flash flood‐producing events (e.g., 50 mm/hr or stronger) account for larger fractions in preconditioned events than in the non‐preconditioned group, with the spectrum difference further exaggerated by warming. This drives the frequency increase in potentially high‐impact events several‐fold larger than expected from the widely‐adopted univariate perspective. These results point to heatwave‐preconditioned hourly precipitation extremes as an emerging hazard of climate change carrying greater flash flood risks. Plain Language Summary: Despite plentiful knowledge on heatwaves' impacts on human health, little has been known about heatwaves' implication for extreme rainfall and the resulting floods. After experiencing sustained sweltering weather, people are sometimes eager for cooling brought about by heavy precipitation; however, subsequent rainfall, if intensified by the heat into an exceptional level, introduces uncharted risks of flash floods. Hourly precipitation extremes in the Yangtze River Valley are a case in point. Within 3 days after the passage of a heatwave, hourly precipitation extremes in the region are more torrential than those not preceded by heatwaves. These heatwave‐preconditioned events are also intensifying faster with climate warming. In this context, heavier events, such as those stronger than 50 mm/hr, are more prevalent in preconditioned events than in the non‐preconditioned group. Namely, once an hourly precipitation extreme occurs in the wake of a heatwave, the chance of it evolving into a flood‐causing one is higher. So, to better evaluate risks of flash floods, a more holistic view is needed, by not only considering precipitation itself but also factoring into its temporal proximity to heatwaves. Key Points: Rigorously sticking to the impact‐centric principle, heatwave‐preconditioned hourly precipitation extremes are defined and analyzedIn the Yangtze River Valley, heatwave‐preconditioned hourly wet extremes are heavier and intensifying faster than non‐preconditioned onesPreconditioned and non‐preconditioned hourly precipitation extremes differ not only in intensity spectrum but also in diurnal cycle [ABSTRACT FROM AUTHOR]

It is widely recognized that future rainfall extremes will intensify. This expectation is tied to the Clausius-Clapeyron (CC) relation, stating that the maximum water vapour content in the atmosphere increases by 6–7% per degree warming. Scaling rates for the dependency of hourly precipitation extremes on near-surface (dew point) temperature derived from day-to-day variability have been found to exceed this relation (super-CC). However, both the applicability of this approach in a long-term climate change context, and the physical realism of super-CC rates have been questioned. Here, we analyse three different climate change experiments with a convection-permitting model over Western Europe: simple uniform-warming, 11-year pseudo-global warming and 11-year global climate model driven. The uniform-warming experiment results in consistent increases to the intensity of hourly rainfall extremes of approximately 11% per degree for moderate to high extremes. The other two, more realistic, experiments show smaller increases—usually at or below the CC rate—for moderate extremes, mostly resulting from significant decreases to rainfall occurrence. However, changes to the most extreme events are broadly consistent with 1.5–2 times the CC rate (10–14% per degree), as predicted from the present-day scaling rate for the highest percentiles. This result has important implications for climate adaptation. This article is part of a discussion meeting issue 'Intensification of short-duration rainfall extremes and implications for flash flood risks'. [ABSTRACT FROM AUTHOR]

Short duration extreme precipitation has devastating impacts on city area. Local urbanization effects, superimposed upon regional climate change, complicate examination of long‐term changes in short duration precipitation extremes in urban areas. Based on high‐quality rain gauge observations of summer time hourly precipitation in Beijing Region over 1977–2013, this study reveals that despite the general drying tendency for North China, the urban area of Beijing has experienced more hourly precipitation extremes (HPE) than the suburban area since 2004, coinciding with the surge in the growth of urban built‐up areas. These hourly urban precipitation extremes are increasingly inclined to occurring during night‐time, especially during 1800 LST to 0200 LST (UCT+8). On the one hand, the amplified urban heat inland effect, which was more significant at night‐time, seems to have facilitated formation of more intense small scale thermal‐low and resultant ascending branch; on the other hand, it has favoured to establishing unstable stratification in the lower level. This possible mechanism explains the preference of HPE in urban areas during night‐time and climate change diversity under the influence of megacity superposition. [ABSTRACT FROM AUTHOR]

Midlatitude synoptic weather regimes account for a substantial portion of annual precipitation accumulation as well as multi-day precipitation extremes across parts of the United States (US). However, little attention has been devoted to understanding how synoptic-scale patterns contribute to hourly precipitation extremes. A majority of 1-h annual maximum precipitation (AMP) across the western US were found to be linked to two coherent midlatitude synoptic patterns: disturbances propagating along the jet stream, and cutoff upper-level lows. The influence of these two patterns on 1-h AMP varies geographically. Over 95% of 1-h AMP along the western coastal US were coincident with progressive midlatitude waves embedded within the jet stream, while over 30% of 1-h AMP across the interior western US were coincident with cutoff lows. Between 30-60% of 1-h AMP were coincident with the jet stream across the Ohio River Valley and southeastern US, whereas a a majority of 1-h AMP over the rest of central and eastern US were not found to be associated with either midlatitude synoptic features. Composite analyses for 1-h AMP days coincident to cutoff lows and jet stream show that an anomalous moisture flux and upper-level dynamics are responsible for initiating instability and setting up an environment conducive to 1-h AMP events. While hourly precipitation extremes are generally thought to be purely convective in nature, this study shows that large-scale dynamics and baroclinic disturbances may also contribute to precipitation extremes on sub-daily timescales. [ABSTRACT FROM AUTHOR]

• Scaling relationship of hourly precipitation extremes with air temperature and DPT. • Scaling coefficients during monsoon are negative and have dropped post 1975. • Scaling coefficients during non-monsoon are close to CC scaling rate. • Super-CC scaling rates for some locations using DPT as the scaling variable. • Probability of monsoon extremes is higher when conditioned on higher temperatures. This study presents a scaling analysis of extremes in hourly precipitation with coincident temperature in 14 urban locations across India for monsoon as well as non-monsoon seasons, and examines the probabilistic association through bivariate copula. Using gridded hourly rainfall and dew point temperature (DPT) datasets from ERA5 Reanalysis and daily maximum temperature from the India Meteorology Department (IMD), it examines how far the scaling relationships of sub-daily precipitation extremes with temperature deviate from the Clausius-Clapeyron (CC) scaling across different climatic regimes in India. Pre- and post-1975 analyses were conducted to evaluate if the scaling relationships have altered in line with the global climate shift of the 1970s. Findings from the study indicate that during the monsoon, the scaling relationship was negative in all the cities except Pune (PNQ) during the post-1975 period. In fact, in most of the locations (e.g., Bhopal (BHO), Jaipur (JAI) and Mumbai (BOM)), the scaling coefficient for monsoon rainfall extremes decreased after the 1975 global climate shift. During the non-monsoon season, the scaling coefficient was slightly positive almost everywhere and approximately equal to the CC scaling rate, both pre- and post-1975; the only exception being in PNQ, where a negative scaling was observed. The joint probabilistic distributions for BOM showed that the non-exceedance probability of extreme rainfall was higher when conditioned on higher temperatures in the monsoon season; however, the opposite was observed in the non-monsoon season pre-1975. A similar distinct seasonal feature was noticed in a few other locations including New Delhi (DEL). Using DPT as the scaling variable, Chennai (MAA), Guwahati (GAU) and Tiruchirappalli (TRZ) showed positive scaling in both pre- and post-1975 in both monsoon and non-monsoon seasons. Unlike with maximum air temperature, super-CC scaling was observed with DPT in the monsoon season for TRZ (pre-and post-1975) and for MAA and GAU (pre-1975) and also in the non-monsoon season for MAA (pre-and post-1975) and for GAU and BOM (post-1975). This analysis is expected to provide useful insights into the regional and seasonal distribution of hydrological extremes for a subsequent assessment of their impacts on the design of urban infrastructure. [ABSTRACT FROM AUTHOR]

Summary: Hourly precipitation extremes in the Netherlands in eight transient (1951–2099) and five ERA40 driven (1961–2000) regional climate model (RCM) simulations were analyzed. Generalized extreme value (GEV) distributions were fitted to the annual maximum amounts. Large differences were found between the estimated GEV parameters for the RCM simulations and those for an 11-year (1998–2008) high-quality radar data set. There were also large differences between the GEV parameters for different RCM simulations. The influence of the boundary conditions (ERA40 or a global climate model simulation for the present climate) on the extreme value distributions was in most cases small. A similar analysis for the daily precipitation extremes revealed much smaller differences between RCM simulations and a much better agreement with the results for the radar data. The increase in large quantiles of the daily maxima at the end of the 21st century in the transient RCM simulations was much smaller than that in the quantiles of the hourly maxima. For the latter, large differences were found between the changes from different RCM simulations, partly resulting from an increase in the GEV shape parameter in a number of RCM simulations. This increase in the shape parameter also largely explains the differences between the changes in large quantiles of the hourly and daily precipitation extremes. [ABSTRACT FROM AUTHOR]