Extreme Hourly Precipitation Research Articles

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

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 72:239-249 (2017) - DOI: https://doi.org/10.3354/cr01469 Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling Aristita Busuioc*, Madalina Baciu, Traian Breza, Alexandru Dumitrescu, Cerasela Stoica, Nina Baghina 1National Meteorological Administration, Sos. Bucuresti-Ploiesti 97, Sect.1, Bucharest 013686, Romania *Corresponding author: busuioc@meteoromania.ro ABSTRACT: We propose a new index for quantifying the maximum rain intensity (IMAX) within a rainfall event. The goal of this paper is 2-fold: first, to analyse the characteristics of variability (trends, change points) for maximum values of this index calculated for spring (April-May), summer (June-August) and autumn (September-October) in comparison with other 2 precipitation indices (daily maximum and total amount). Secondly, to investigate the scaling of the IMAX high percentiles with temperature and compare the results to hourly precipitation extremes. The analysis was carried out at 6 Romanian stations over the period 1966-2007, extended over 1902-2007 for one station. Our results revealed a statistically significant increase of IMAX over the 20th century (intensified over the second half), in contrast with no significant trends in the other 2 precipitation indices. On the other hand, an opposite phase between IMAX variability and its corresponding duration (e.g. shorter durations correspond to higher intensities) was noted. Regarding the scaling behaviour of the IMAX percentiles, there was a difference between summer and spring/autumn. In summer, the 90th and 99th percentiles showed a Clausius-Clapeyron (CC) scaling for temperatures between 14 and 26°C and then a decrease, while the 99.9th percentile showed a super-CC scaling for temperatures lower than 18°C and then a decrease. The spring and autumn 90th and 99th percentiles showed an approximate 2CC scaling for temperatures ranging from 8-20°C. The 99.9th percentile exhibited a scaling close to the 2CC relationship for a temperatures range of 12-18°C (spring) and then a decrease, while the autumn 99.9th percentile exhibited a dependence close to 2CC scaling for temperatures <18°C and then a scaling close to CC. Comparing these results with those referring to hourly and daily precipitation extremes, we conclude that the magnitude of the CC scaling in Romania is mainly dependent on the temporal scale of the extreme precipitation event, storm intensity and season. The proposed index (IMAX) is more sensitive to temperature increases than the hourly and daily extremes, and therefore it is more appropriate to quantifying the climate signal related to intense precipitation events in a warmer climate. KEY WORDS: Extreme precipitation index · Temperature · Scaling · Clausius-Clapeyron relation · Trends · Romania Full text in pdf format Supplementary material PreviousNextCite this article as: Busuioc A, Baciu M, Breza T, Dumitrescu A, Stoica C, Baghina N (2017) Changes in intensity of high temporal resolution precipitation extremes in Romania: implications for Clausius-Clapeyron scaling. Clim Res 72:239-249. https://doi.org/10.3354/cr01469 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 72, No. 3. Online publication date: July 12, 2017 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2017 Inter-Research.

The long-term variation of extreme heavy precipitation and its link to urbanization effects in Shanghai during 1916–2014

Using the hourly precipitation records of meteorological stations in Shanghai, covering a period of almost a century (1916–2014), the long-term variation of extreme heavy precipitation in Shanghai on multiple spatial and temporal scales is analyzed, and the effects of urbanization on hourly rainstorms studied. Results show that: (1) Over the last century, extreme hourly precipitation events enhanced significantly. During the recent urbanization period from 1981 to 2014, the frequency of heavy precipitation increased significantly, with a distinct localized and abrupt characteristic. (2) The spatial distribution of long-term trends for the occurrence frequency and total precipitation intensity of hourly heavy precipitation in Shanghai shows a distinct urban rain-island feature; namely, heavy precipitation was increasingly focused in urban and suburban areas. Attribution analysis shows that urbanization in Shanghai contributed greatly to the increase in both frequency and intensity of heavy rainfall events in the city, thus leading to an increasing total precipitation amount of heavy rainfall events. In addition, the diurnal variation of rainfall intensity also shows distinctive urban-rural differences, especially during late afternoon and early nighttime in the city area. (3) Regional warming, with subsequent enhancement of water vapor content, convergence of moisture flux and atmospheric instability, provided favorable physical backgrounds for the formation of extreme precipitation. This accounts for the consistent increase in hourly heavy precipitation over the whole Shanghai area during recent times.

Relative contributions of weather systems to mean and extreme global precipitation

AbstractThis study presents the first global estimates of the relative contributions of different weather systems, i.e., tropical cyclone, center and front of extratropical cyclone, and others, to mean and extreme precipitation. An objective method of classification of the precipitating weather systems was used with a reanalysis data set and a satellite‐based precipitation product for 2001–2010. Tropical cyclones, extratropical cyclones with associated fronts, and other weather systems contribute about 4%, 37%, and 59%, respectively, of the global (60°S–60°N) mean precipitation. The relative contributions of the weather systems were found to be different both in terms of the different classes of precipitation intensity and in terms of the different temporal scales of precipitation. Tropical cyclones and extratropical cyclones produced greater contributions to extreme hourly precipitation than to annual precipitation in most of the oceanic regions of their activity. The contributions of tropical cyclones to extreme precipitation showed clear peaks on temporal scales of 24–72 h. The contributions of extratropical cyclones showed less dependence on the temporal scale than tropical cyclones. Consideration of combinations of multiple weather systems revealed that in eastern North America and East Asia, substantial portions (22% and 19%, respectively) of the extreme 24 h precipitation related to tropical cyclones are contributed by the coexistence of tropical cyclones and fronts. However, such contributions were found rarely in other land regions. On most temporal scales, fronts at locations remote from the centers of extratropical cyclones were found to contribute to extreme precipitation as much as the centers of extratropical cyclones.

Synoptic Situations of Extreme Hourly Precipitation over China

Abstract In this study, synoptic situations associated with extreme hourly precipitation over China are investigated using rain gauge data, weather maps, and composite radar reflectivity data. Seasonal variations of hourly precipitation (&amp;gt;0.1 mm h−1) suggest complicated regional features in the occurrence frequency and intensity of rainfall. The 99.9th percentile is thus used as the threshold to define the extreme hourly rainfall for each station. The extreme rainfall is the most intense over the south coastal areas and the North China Plain. About 77% of the extreme rainfall records occur in summer with a peak in July (30.4%) during 1981–2013. Nearly 5800 extreme hourly rainfall records in 2011–15 are classified into four types according to the synoptic situations under which they occur: the tropical cyclone (TC), surface front, vortex/shear line, and weak-synoptic forcing. They contribute 8.0%, 13.9%, 39.1%, and 39.0%, respectively, to the total occurrence and present distinctive characteristics in regional distribution and seasonal or diurnal variations. The TC type occurs most frequently along the coasts and decreases progressively toward inland China; the frontal type is distributed relatively evenly east of 104°E; the vortex/shear line type shows a prominent center over the Sichuan basin with two high-frequency bands extending from the center southeastward and northeastward, respectively; and the weak-synoptic type occurs more frequently in southeast, southwest, and northern China, and in the easternmost area of northeast China. Occurrences of the weak-synoptic type have comparable contributions from mesoscale convective systems and smaller-scale storms with notable differences in their preferred locations.

Peak precipitation intensity in relation to atmospheric conditions and large‐scale forcing at midlatitudes

AbstractResearch on relations between atmospheric conditions and extreme precipitation is important to understand and model present‐day climate extremes and assess how precipitation extremes might evolve in a future climate. Here we present a statistical analysis of the relation between large‐scale conditions and hourly precipitation at midlatitudes, by using observations of the Netherlands combined with a regional reanalysis. The aim is to gain a better understanding of the typical large‐scale atmospheric conditions and large‐scale forcing associated with extreme hourly precipitation and determine the typical differences between cases of extreme precipitation and weaker events. To avoid double counting, we perform an event‐based analysis and consider the hourly peak intensity, rather than all hourly data. Atmospheric large‐scale profiles consistently show a clear separation between precipitation deciles, characterized by increasing instability and moisture content of the atmosphere for more extreme precipitation. Furthermore, stronger events are characterized by larger atmospheric forcing preceding the event, which primarily relates to vertical motions. Based on these results, four atmospheric parameters, describing atmospheric moisture, stability and large‐scale convergence, are analyzed as potential indicators of strong precipitation events. Despite positive relations between these parameters and the peak intensity, their correlations are found to be weak.

Downturn in scaling of UK extreme rainfall with temperature for future hottest days

Extreme daily precipitation is thought to increase with warming at a rate of 6.5% per K. High-resolution simulations for the southern UK show this scaling for present conditions, but above 22 °C this scaling fails owing to changes in dynamics. Extreme daily precipitation is thought to increase with temperature at a rate of 6.5% per K according to the Clausius–Clapeyron relationship between temperature and saturation vapour pressure1. A wide range of scaling relationships has been observed globally for extreme daily and hourly precipitation, with evidence of scaling above 6.5% per K for sub-daily extreme precipitation in some regions2,3,4. Only high-resolution climate models can simulate this scaling relationship5. Here we examine the scaling of hourly extreme precipitation intensities in a future climate using experiments with a model for the southern UK with kilometre-scale resolution6. Our model simulates the present-day scaling relationship at 6.5% per K, in agreement with observations. The simulated overall future increase in extreme precipitation follows the same relationship. However, UK extreme precipitation intensities decline at temperatures above about 22 °C—a temperature range that is not well sampled in the present-day integration—as a result of a more frequent occurrence of anticyclonic weather systems. Anticyclones produce more days with strong daytime heating, but are not favourable to the development of deep intense convective storms. We conclude that future extreme hourly precipitation intensities cannot simply be extrapolated from present-day temperature scaling, and demonstrate the pitfalls of using regional surface temperature as a scaling variable.

Changes in the large‐scale thermodynamic instability and connection with rain shower frequency over Romania: verification of the Clausius–Clapeyron scaling

The goal of this article is twofold: first, changes in the spring and summer thermodynamic instability over the North Atlantic European region and the connection with frequency of rain showers at 81 locations across Romania for the period 1961–2010 are analysed; second, the relationship between hourly precipitation extremes and air temperature with respect to the validity of Clausius–Clapeyron (CC) scaling is investigated. The Best Lifted Index (lftx4) has been selected to quantify the thermodynamic instability. The mechanisms responsible for the rain showers' variability in Romania were analysed using the canonical correlation analysis (CCA). Results show that the regional distribution of the lftx4 changes is quite similar in the two seasons, with a transition towards thermodynamic stability over most of Mediterranean regions – central Europe and instability in northern Europe, Black Sea, North Atlantic (summer), southern North Atlantic (spring). The frequency of rain showers in Romania exhibits a significant increasing trend in both seasons, which is in agreement with the increase in frequency of Cumulonimbus clouds. In contrast, the frequency of rainfall days does not exhibit any significant trend that shows a shift in the nature of precipitation towards more showers. The CCA shows that the optimum large-scale mechanisms responsible for this behaviour are given by the first CCA pair with the lftx4 pattern represented by a dipole structure with a nucleus of thermodynamic instability centred over Romania. The dynamic factor is an additional ingredient for spring, as precipitable water is for summer. The extreme hourly rainfall intensities reveal a similar behaviour over the entire country: the 90th percentile shows dependence close to the CC relation for all temperatures; the 99th and 99.9th percentiles exhibit rates close to double the CC rate for temperatures between ∼10 and ∼22 °C and negative scaling rates for higher temperatures. The daily intensities have a less clearly defined scaling behaviour.

Relationship between Interannual Variations of Extreme Hourly Precipitation and Air/Sea-Surface Temperature in Japan

Long-term changes in extreme hourly precipitation in Japan were examined using data at 983 stations for 1979 to 2013, with relation to the variations in air temperature (AT) and sea-surface temperature (SST). According to the statistics over the whole country, annual maximum and 95 percentile precipitations show increasing trends of 2-4%/decade, whereas AT and SST have risen at a rate of 0.2-0.3°C/decade. Analysis for each region and season indicates that the increase in extreme precipitation is a nation-wide feature and is not limited to a single season. Moreover, year-to-year variations in extreme precipitation tend to be in phase with those of AT and SST, with a correlation coefficient of 0.5-0.6 on the annual basis, although negative correlation is found for the summer season in western Japan and the Nansei Islands.

Bayesian hierarchical modeling of extreme hourly precipitation in Norway

Spatial maps of extreme precipitation are a critical component of flood estimation in hydrological modeling, as well as in the planning and design of important infrastructure. This is particularly relevant in countries, such as Norway, that have a high density of hydrological power generating facilities and are exposed to significant risk of infrastructure damage due to flooding. In this work, we estimate a spatially coherent map of the distribution of extreme hourly precipitation in Norway, in terms of return levels, by linking generalized extreme value (GEV) distributions with latent Gaussian fields in a Bayesian hierarchical model. Generalized linear models on the parameters of the GEV distribution are able to incorporate location‐specific geographic and meteorological information and thereby accommodate these effects on extreme precipitation. Our model incorporates a Bayesian model averaging component that directly assesses model uncertainty in the effect of the proposed covariates. Gaussian fields on the GEV parameters capture additional unexplained spatial heterogeneity and overcome the sparse grid on which observations are collected. Our framework is able to appropriately characterize both the spatial variability of the distribution of extreme hourly precipitation in Norway and the associated uncertainty in these estimates. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Automatic threshold and run parameter selection: a climatology for extreme hourly precipitation in Switzerland

Abstract Extreme value analyses of a large number of relatively short time series are in increasing demand in environmental sciences and design. Here, we present an automated procedure for the peaks-over-threshold (POT) approach to extreme value theory and use it to provide a climatology of extreme hourly precipitation in Switzerland. The POT approach fits the generalized Pareto distribution (GPD) to independent exceedances above some high threshold. To guarantee independence, the time series is pruned: exceedances separated by less than a fixed interval called the run parameter are considered a cluster, and all but the cluster maxima are discarded. We propose the automation of an existing graphical method for joint selection of threshold and run parameter. Hourly precipitation is analyzed at 59 stations of the MeteoSwiss observational network over the period 1981–2010. The four seasons are considered separately. When necessary, a simple detrending is applied. Results suggest that unnecessarily large run parameters have adverse effects on the estimation of the GPD parameters. The proposed method yields mean cluster sizes that reflect the seasonal and geographical variation of lag dependence of hourly precipitation. The climatology, as represented by the return level maps and Alpine cross-section, mirror known aspects of the Swiss climate. Unlike for daily precipitation, summer thunderstorm tracks are visible in the seasonal frequency of events, rather than in the amplitude of rare events.

Indirect downscaling of hourly precipitation based on atmospheric circulation and temperature

Abstract. The main source of information on future climate conditions are global circulation models (GCMs). While the various GCMs agree on an increase of surface temperature, the predictions for precipitation exhibit high spread among the models, especially in shorter-than-daily temporal resolution. This paper presents a method to predict regional distributions of the hourly rainfall depth based on daily mean sea level pressure and temperature data. It is an indirect downscaling method avoiding uncertain precipitation data from the GCM. It is based on a fuzzy logic classification of atmospheric circulation patterns (CPs) that is further subdivided by means of the average daily temperature. The observed empirical distributions at 30 rain gauges to each CP-temperature class are assumed as constant and used for projections of the hourly precipitation sums in the future. The method was applied to the CP-temperature sequence derived from the 20th-century run and the scenario A1B run of ECHAM5. For the study region in southwestern Germany ECHAM5 predicts that the summers will become progressively drier. Nevertheless, the frequency of the highest hourly precipitation sums will increase. According to the predictions, estival water stress and the risk of extreme hourly precipitation will both increase simultaneously during the next decades. However, the results are yet to be confirmed by further \\mbox{investigation} based on other GCMs.

Spatial patterns of seasonal scale trends in extreme hourly precipitation in South Africa

Hourly precipitation data from 1998 to 2007 spread across 102 stations in South Africa were analyzed for trends in extreme hourly precipitation events. The analyses were conducted at the seasonal scale for summer and winter for nine different variables. The results of our analysis showed predominantly positive trends during summer, with the strongest trends concentrated in the coastal areas in the southeast. The spatial variations in the trends were reversed during the winter season, with negative trends observed in the coastal areas and positive trends occurring in the interior. The summer patterns also overlap with areas experiencing overall increasing trends in annual extreme precipitation as well as a stronger diurnal cycle identified in recently published literature.

Scaling and trends of hourly precipitation extremes in two different climate zones – Hong Kong and the Netherlands

Abstract. Hourly precipitation extremes in very long time series from the Hong Kong Observatory and the Netherlands are investigated. Using the 2 m dew point temperature from 4 h before the rainfall event as a measure of near surface absolute humidity, hourly precipitation extremes closely follow a 14% per degree dependency – a scaling twice as large as following from the Clausius-Clapeyron relation. However, for dew point temperatures above 23 °C no significant dependency on humidity was found. Strikingly, in spite of the large difference in climate, results are almost identical in Hong Kong and the Netherlands for the dew point temperature range where both observational sets have sufficient data. Trends in hourly precipitation extremes show substantial increases over the last century for both De Bilt (the Netherlands) and Hong Kong. For De Bilt, not only the long term trend, but also variations in hourly precipitation extremes on an inter-decadal timescale of 30 yr and longer, can be linked very well to the above scaling; there is a very close resemblance between variations in dew point temperature and precipitation intensity with an inferred dependency of hourly precipitation extremes of 10 to 14% per degree. For Hong Kong there is no connection between variations in humidity and those in precipitation intensity in the wet season, May to September. This is consistent with the found zero-dependency of precipitation intensity on humidity for dew points above 23 °C. Yet, outside the wet season humidity changes do appear to explain the positive trend in hourly precipitation extremes, again following a dependency close to twice the Clausius-Clapeyron relation.

Temporal and spatial characteristics of extreme hourly precipitation over eastern China in the warm season

Based on hourly precipitation data in eastern China in the warm season during 1961–2000, spatial distributions of frequency for 20 mm h−1 and 50 mm h−1 precipitation were analyzed, and the criteria of short-duration rainfall events and severe rainfall events are discussed. Furthermore, the percentile method was used to define local hourly extreme precipitation; based on this, diurnal variations and trends in extreme precipitation were further studied.

Long-term precipitation change by hourly data in Haihe River Basin during 1961–2004

Hourly summer precipitation data recorded at 21 stations during 1961–2004 in the Haihe River Basin in North China were analyzed. The results show that the precipitation frequency and amount and the morning peak mainly relating to long-duration rainfall events decreased during this period, whereas the normalized afternoon peak mainly relating to short-duration events increased, which may suggest that the proportion of short-duration rainfall has increased as the total summer rainfall has decreased. For short-duration events, the mean intensity and peak intensity increased at most stations and the time to peak intensity decreased, which may be attributable to the higher thermal contrast between the warmer lower surface and cooler upper level. In the case of long-duration events, the total amount was significantly correlated with the East Asian summer monsoon index for the period 1961–2001 (correlation coefficient of 0.63). Although the total amount of rainfall in long-duration events decreased in the basin, the mean intensity and peak intensity, as well as the extreme hourly precipitation, increased in the western basin and decreased in the eastern basin.

The Relationship between Extreme Hourly Precipitation and Surface Temperature in Different Hydroclimatic Regions of the United States

Abstract In a changing climate, there is an interest in predicting how extreme rainfall events may change. Using historical records, several recent papers have evaluated whether high-intensity precipitation scales with temperature in accordance with the Clausius–Clapeyron (C–C) relationship. For varying locations in Europe, these papers have identified both super C–C relationships as well as a breakdown of the C–C relationship under dry conditions. In this paper, a similar analysis is carried out for the United States using data from 14 weather stations clustered in four different hydroclimatic regions: the coastal northeast, interior New York, the central plains, and the western plains. In all regions except interior New York state, 99th percentile 1-h precipitation generally followed the C–C relation. In interior New York, there was evidence that intensity scaled with a super C–C relationship. For the 99.9th percentile precipitation, interior New York displayed some moderate evidence of a super C–C relationship, the western plains showed little relation between precipitation and temperature, and the remainder of sites generally scaled with the C–C relationship. Also, if only July, August, and September precipitation is considered, all stations except those in interior New York have little relation between temperature and precipitation, suggesting that precipitation intensity during summer months may not be well constrained by the C–C relationship. Overall, the C–C relationship (or a variation thereof) does not appear to constrain extreme precipitation in all regions and in all seasons, and its ability to aid in constraining future predictions of extreme precipitation may only be relevant to certain locales and time periods.

On the value of hourly precipitation extremes in regional climate model simulations

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.

A spatial analysis of extreme hourly precipitation patterns in India

AbstractStation level hourly precipitation data from 1980 to 2002 spread across the Indian subcontinent were analysed for trends in extreme hourly precipitation events. The analyses were conducted for the main seasons of winter, dry‐summer, and wet‐summer monsoon seasons, respectively. The results of the study indicated rising trends in extreme heavy precipitation events, mostly in the high‐elevation regions of the northwestern Himalaya as well as along the foothills of the Himalaya extending south into the Indo‐Gangetic basin. In general, the lowest positive trends to slightly neutral to negative trends in extreme precipitation events were observed during the winter season, while stronger positive trends were found for both dry‐summer and wet‐summer monsoon seasons. Along the west coast, the southern part experienced a declining trend, whereas the northern section of the coast experienced an increasing trend of extreme precipitation events. Most of Deccan Plateau extending towards south central coastal regions of the subcontinent also experienced a positive trend in the occurrence of extreme heavy precipitation events. Furthermore, the trends affecting large, million‐plus‐population urban agglomerations were examined separately, and these trends were found to be pre‐dominantly positive during dry‐summer and wet‐summer monsoon seasons, but showed neutral to negative trends during the winter season. Copyright © 2008 Royal Meteorological Society