Number Of Heavy Rainfall Events Research Articles

Evaluating the response and adaptation of urban stormwater systems to changed rainfall with the CMIP6 projections

Climate change is altering urban rainfall characteristics, leading to extreme urban stormwater and, particularly, more frequent flooding. Due to the uncertainty of climate change, the responses of urban drainage systems to climate change are becoming more complicated. This complexity makes it difficult for decision makers to assess whether urban infrastructure is sufficiently resilient to cope with flood risks. In this study, the Xiao Zhai area, a high-density urban area of China, was used as an example. A quantitative method for assessing these risks and the resilience of urban drainage systems to future urban stormwater was developed. First, based on the Coupled Model Intercomparison Project Phase 6 (CMIP6), the variation and uncertainty of future rainfall in the study area were analysed. A high-fidelity hydro-hydraulic model was developed to analyse the influence of climate change on future urban stormwater. Finally, the relationship between urban flood risk and the resilience of urban drainage systems was evaluated. The results show that the temporal distribution of future rainfall from 2023 to 2100 is relatively uniform. However, the number of heavy rainfall events increases significantly during this period. The flood risk caused by future rainfall was one level higher than the historical flood risk. For example, the flood risk caused by future 5a rainfall is equal to the flood risk from historical 10a rainfall. The correlations between the spatial distributions of flood risk and resilience are 0.49–0.63. Urban drainage systems urgently need to be improved and refined in areas with flood risk and low resilience to become more resilient to climate change. Rational planning of grey-green rainwater facilities in flood risk and low resilience areas can improve the rainwater system's resilience to 0.67–0.95 for climate change.

Features of weather types involving heavy rainfall along the southern Spanish Mediterranean

Heavy rainfall events in the Mediterranean can be of high intensity, commonly exceeding 100 mm day-1, and have irregular spatio-temporal distribution. Such events can have significant impacts both on soils and human structures. The aim of this paper is to highlight a systematic comparison of synoptic conditions with heavy rainfall events in Mediterranean Southern Spain, assessing the weather types responsible for meteorological risk in specific locations of this mountainous region. To do this, we analyzed the maximum intensity of rainfall in observational periods ranging from 10 min to 24 h using a database from 132 rain gauge stations across the study area since 1943; then, the heavy rain has been associated with the weather type which triggers it. This analysis identified a pattern of heavy rainfall which differs from that previously reported in the Mediterranean area. Thus, in this research, the maximum number of heavy rainfall events uses to come from a dominant pattern of low pressures associated to front systems and East-Northeast winds; but the maximum volumes use to be associated to Cold Drops and the same winds; in addition, there are differences throughout the territory, showing several patterns and seasonal incidence when analyzing sub-zones, which may be related with different erosive conditions according to its position with respect to Atlantic or Mediterranean sea, and the entity of its relief.

The Impact of Modified Fractional Cloud Condensate to Precipitation Conversion Parameter in Revised Simplified Arakawa‐Schubert Convection Parameterization Scheme on the Simulation of Indian Summer Monsoon and Its Forecast Application on an Extreme Rainfall Event Over Mumbai

AbstractThe impact of modified fractional conversion parameter (from cloud condensate to precipitation) in the revised simplified Arakawa‐Schubert (RSAS) convection scheme in Climate Forecast System version 2 on the simulation of Indian summer monsoon (ISM) is examined. While the default fractional conversion parameter is constant in RSAS, the modified parameter has the form of an exponential function of temperature above the freezing level, whereas below the freezing, level it is kept constant. The model simulation indicates RSAS with modified conversion parameter (RSAS_mod) shows a better fidelity in capturing the mean monsoon features over the ISM region. The spatial distribution of precipitation shows notable improvement over the ISM region. Most of the global general circulation models has a tendency to grossly overestimate (underestimate) the convective (large‐scale) rainfall over the ISM region, which has somewhat improved in RSAS_mod simulation. It is suggested that reduced rate of conversion of cloud condensate to convective precipitation above the freezing level leads to suppression of convective precipitation, which further increases the detrained moisture from the upper‐level, resulting enhancement in large‐scale precipitation. Further, improvement has been noted in outgoing longwave radiation, wind circulation, total cloud fraction, and dynamical and thermodynamical processes in RSAS_mod simulation. The modified conversion parameter helps in improving the feedback between moisture and convective processes through better lower tropospheric moistening. In addition to mean summer monsoon, the RSAS_mod indicates its potential in predicting an extreme rainfall event over Mumbai in high‐resolution global forecast system at T1534 horizontal resolution. However, its fidelity needs to be further tested for more number of heavy rainfall events.

Experimental study on the hydraulic capacity of grate inlets with supercritical surface flow conditions.

Due to an increasing number of heavy rainfall events, the managing of urban flooding requires new design approaches in urban drainage engineering. With bidirectional coupled numerical models the surface runoff, the underground sewer flow and the interaction processes between both systems can be calculated. Most of the numerical models use a weir equation to calculate the surface to sewer flow with unsurcharged flow conditions, but uncertainties still exist in the representation of the real flow conditions. Street inlets, existing in different types, are the connecting elements between the surface and the underground system. In the present study, an empirical formula was developed based on physical model test runs to estimate the hydraulic capacity and type-specific efficiency of grate inlets with supercritical surface flow. Influencing hydraulic parameters are water depth and flow velocity upstream of the grate and, in addition, different geometrical parameters are taken into account, such as the grate dimensions or the orientation of the bars (transverse, longitudinal or diagonal). Good agreement between estimated and measured results could be proven with relative deviations less than 1%.

Automatic segmentation of 3D point clouds of rubble masonry walls, and its application to building surveying, repair and maintenance

Abstract Changing climatic conditions are contributing to faster deterioration of building fabric. Increasing number of heavy rainfall events can particularly affect historic and Cultural Heritage (CH) buildings. These evolving and uncertain circumstances demand more frequent survey of building fabric to ensure satisfactory repair and maintenance. However, traditional fabric surveys have been shown to lack efficiency, accuracy and objectivity, hindering essential repair operations. The recent development of reality capture technologies, together with the development of algorithms to effectively process the acquired data, offers the promise of transformation of surveying methods. This paper presents an original algorithm for automatic segmentation of individual masonry units and mortar regions in digitised rubble stone constructions, using geometrical and colour data acquired by Terrestrial Laser Scanning (TLS) devices. The algorithm is based on the 2D Continuous Wavelet Transform (CWT), and uniquely it does not require the wall to be flat or plumb. This characteristic is important because historic structures, in particular, commonly present non-negligible levels of bow, waviness and out-of-verticality. The method is validated through experiments undertaken using data from two relevant and highly significant Scottish CH buildings. The value of such segmentation to building surveying and maintenance regimes is also further demonstrated with application in automated and accurate measurement of mortar recess and pinning. Overall, the results demonstrate the value of the automatic segmentation of masonry units towards more comprehensive and accurate surveys.

Impacts of future climate change (2030-2059) on debris flow hazard: A case study in the Upper Minjiang River basin, China

An increase in extreme precipitation events due to future climate change will have a decisive influence on the formation of debris flows in earthquake-stricken areas. This paper aimed to describe the possible impacts of future climate change on debris flow hazards in the Upper Minjiang River basin in Northwest Sichuan of China, which was severely affected by the 2008 Wenchuan earthquake. The study area was divided into 1285 catchments, which were used as the basic assessment units for debris flow hazards. Based on the current understanding of the causes of debris flows, a binary logistic regression model was used to screen key factors based on local geologic, geomorphologic, soil, vegetation, and meteorological and climatic conditions. We used the weighted summation method to obtain a composite index for debris flow hazards, based on two weight allocation methods: Relative Degree Analysis and rough set theory. Our results showed that the assessment model using the rough set theory resulted in better accuracy. According to the bias corrected and downscaled daily climate model data, future annual precipitation (2030-2059) in the study area are expected to decrease, with an increasing number of heavy rainfall events. Under future climate change, areas with a high-level of debris flow hazard will be even more dangerous, and 5.9% more of the study area was categorized as having a high-level hazard. Future climate change will cause an increase in debris flow hazard levels for 128 catchments, accounting for 10.5% of the total area. In the coming few decades, attention should be paid not only to traditional areas with high-level of debris flow hazards, but also to those areas with an increased hazard level to improve their resilience to debris flow disasters.

Mobilisation of microbial indicators, microbial source tracking markers and pathogens after rainfall events

Climate change is expected to affect the Mediterranean region by causing an increase in the number of heavy rainfall events. The aim of this study was to assess the effect of extreme river flow variations due to rainfall on the persistence and mobilisation of various microorganisms. These included faecal pollution indicators (Escherichia coli (EC), somatic coliphages (SOMCPH) and sulphite reducing clostridia spores (SRC)), microbial source tracking indicators (Bacteroides thetaiotaomicron GA17 strain phages (GA17PH) and sorbitol fermenting bifidobacteria (SFBIF)), and two pathogens (Salmonella spp and Enterovirus). Water and sediment samples were taken at different distances from the river before and after heavy rainfall events. The microbial load was higher in sediment samples closer to the river course. The concentration of some faecal indicators (EC and SFBIF) increased in sediments and river water after rainfall events, whereas the most conservative parameter (SRC) showed almost no variation. After rainfall, the indicators persisted at a different rate. Salmonella spp and Enterovirus were detected in some samples but always at lower concentrations than the microbial indicators. In conclusion, sediments are reservoirs of faecal and MST indicators and pathogens and could therefore pose a risk of pathogen dissemination.

Projected changes of rainfall event characteristics for the Czech Republic

AbstractProjected changes of warm season (May–September) rainfall events in an ensemble of 30 regional climate model (RCM) simulations are assessed for the Czech Republic. Individual rainfall events are identified using the concept of minimum inter-event time and only heavy events are considered. The changes of rainfall event characteristics are evaluated between the control (1981–2000) and two scenario (2020–2049 and 2070–2099) periods. Despite a consistent decrease in the number of heavy rainfall events, there is a large uncertainty in projected changes in seasonal precipitation total due to heavy events. Most considered characteristics (rainfall event depth, mean rainfall rate, maximum 60-min rainfall intensity and indicators of rainfall event erosivity) are projected to increase and larger increases appear for more extreme values. Only rainfall event duration slightly decreases in the more distant scenario period according to the RCM simulations. As a consequence, the number of less extreme heavy rainfall events as well as the number of long events decreases in majority of the RCM simulations. Changes in most event characteristics (and especially in characteristics related to the rainfall intensity) depend on changes in radiative forcing and temperature for the future periods. Only changes in the number of events and seasonal total due to heavy events depend significantly on altitude.

The Effects of Typhoon Initialization and Dropwindsonde Data Assimilation on Direct and Indirect Heavy Rainfall Simulation in WRF model

A number of heavy rainfall events on the Korean Peninsula are indirectly influenced by tropical cyclones (TCs) when they are located in southeastern China. In this study, a heavy rainfall case in the middle Korean region is selected to examine the influence of typhoon simulation performance on predictability of remote rainfall over Korea as well as direct rainfall over Taiwan. Four different numerical experiments are conducted using Weather Research and Forecasting (WRF) model, toggling on and off two different improvements on typhoon in the model initial condition (IC), which are TC bogussing initialization and dropwindsonde observation data assimilation (DA). The Geophysical Fluid Dynamics Laboratory TC initialization algorithm is implemented to generate the bogused vortex instead of the initial typhoon, while the airborne observation obtained from dropwindsonde is applied by WRF Three-dimensional variational data assimilation. Results show that use of both TC initialization and DA improves predictability of TC track as well as rainfall over Korea and Taiwan. Without any of IC improvement usage, the intensity of TC is underestimated during the simulation. Using TC initialization alone improves simulation of direct rainfall but not of indirect rainfall, while using DA alone has a negative impact on the TC track forecast. This study confirms that the well-suited TC simulation over southeastern China improves remote rainfall predictability over Korea as well as TC direct rainfall over Taiwan.

Hydroclimatic Aspects of the 2011 Assiniboine River Basin Flood

Abstract In the spring and early summer of 2011, the Assiniboine River basin in Canada experienced an extreme flood that was unprecedented in terms of duration and severity. The flood had significant socioeconomic impacts and caused over $1 billion (Canadian dollars) in damage. Contrary to what one might expect for such an extreme flood, individual precipitation events before and during the 2011 flood were not extreme; instead, it was the cumulative impact and timing of precipitation events going back to the summer of 2010 that played a key role in the 2011 flood. The summer and fall of 2010 were exceptionally wet, resulting in above-normal soil moisture levels at the time of freeze-up. This was followed by record high snow water equivalent values in March and April 2011. Cold temperatures in March delayed the spring melt, resulting in the above-average spring freshet occurring close to the onset of heavy rains in May and June. The large-scale atmospheric flow during May and June 2011 favored increased cyclone activity in the region, which produced an anomalously large number of heavy rainfall events over the basin. All of these factors combined generated extreme flooding. Japanese 55-year Reanalysis Project (JRA-55) data are used to quantify the relative importance of snowmelt and spring precipitation in contributing to the unprecedented flood and to demonstrate how the 2011 flood was unique compared to previous floods. This study can be used to validate and improve flood forecasting techniques over this important basin; the findings also raise important questions regarding floods in a changing climate over basins that experience pluvial and nival flooding.

Characteristics of rainfall-induced landslides in Miocene formations: A case study of the Shenmu watershed, Central Taiwan

Fractured and high-permeability Miocene formations, exhibiting shallow soil layers and dense faults, and an increasing number of heavy rainfall events have caused severe and frequent landslides in the Shenmu watershed of Central Taiwan. The Shenmu watershed exhibited a landslide ratio that was typically greater than 1.0% during heavy rainfall events between 1996 and 2009, and can be considered one of the most landslide-prone areas in Taiwan. The landslide ratio in the lower hillslopes is approximately 2.8 to 43.3 times greater compared with that in the upper hillslopes. Analyzing based on a self-organized criticality (SOC) perspective indicated that the β value of the Shenmu watershed (1.24–1.26) was the lowest among landslide-prone areas, implying that small landslides dominated the distribution of landslides documented in available records. The six large landslides that occurred include four shallow landsides and two deep-seated landslides (with a landslide depth greater than 10m). Approximately 82.3% of the small landslides constituted bank-erosion landslides in the downstream watershed, whereas 96.2% of the large landslides occurred in upstream areas with dense faults. Large landslides occurred during only heavy rainfall events in which the accumulated rainfall was greater than 1000mm in fractured and high-permeability strata with dense faults. The large landslides deposited considerable amounts of sediment into streams, inducing significant bank-erosion landslides in the downstream watershed. Bank erosion in the downstream watershed caused additional small landslides along the river. Large landslides were typically caused by a fault density of 693.6m/km2, fractured strata with a permeability of 10−3 to 10−4m/s, and high levels of accumulated rainfall exceeding 1000mm. The apparent increase in bank erosion, which increased from 103% to 136% between 1996 and 2009, resulted from an increasing number of heavy rainfall events and the amount of sediment deposition caused by major landslides. Frequent landslides result from the increasing number of heavy rainfall events, fractured rock exhibiting dense faults, and steep and shallow-soil morphology in the Shenmu watershed.

Extreme value modelling of daily areal rainfall over Mediterranean catchments in a changing climate

AbstractHeavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks‐over‐threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100‐year quantiles. Copyright © 2011 John Wiley & Sons, Ltd.

Standard years for large-scale hydrological scenario simulations

Scenario analyses are regularly characterised by a large number of degrees of freedom. It is usually unfeasible to perform sophisticated hydrological simulations with continuous long-term meteorological time series for all combinations of scenarios and adaptation strategies. To reduce computation time while retaining sufficient degrees of freedom, a so-called “standard year” has been developed. Average hydrological conditions according to simulations driven by this standard year should optimally resemble results from full 30-year simulations. Therefore, the standard year should optimally represent intra-annual variability. The objective of this paper is to explore how the errors, introduced by using standard years compare to natural variability. In addition, the standard year was also tested for future climate scenario simulations. The standard year was constructed by perturbing meteorological quantities recorded during a selected meteorological year. The selection of this year was based on precipitation ( P) and reference crop evapotranspiration ( E ref) in 1967, due to the good resemblance of the potential cumulative precipitation deficit in the Netherlands ( E ref − P) during April–September in this year with the mean climatology. Subsequently, the 1967 precipitation and reference crop evapotranspiration was modified such that the standard year optimally captured intra-annual modes of variability. This is done by the application of spatially varying correction factors, which set the 2-monthly precipitation and reference crop evapotranspiration sums equal to climatology. As a standard year only contains one year of meteorological data, it has no interannual variability by construct. As a consequence, extreme daily events are biased and small but systematic errors are simulated in the major hydrological budget terms. Surface runoff appeared oversensitive to the underestimated number of heavy rainfall events and was considerably underestimated by standard year simulations. The simulated climate change response of the major hydrological terms was reproduced very well and the error introduced by the standard year methodology appeared much smaller than the climate change signal.

Fluvial transport during thermally and pluvially induced peak runoff events in a glacier‐fed mountain catchment in western norway

.Results compiled after three years of process monitoring and analysis in the glacier‐fed Erdalen catchment, situated in the steep fjord‐landscape of western Norway, indicate that there are significant intra‐ and inter‐annual variations with respect to fluvial sediment transport rates and sediment yields. Three different periods with a high frequency of major discharge events can be identified over the year, with these three periods showing a significant inter‐annual variability. High runoff in spring (April–June) is mainly caused by snowmelt whereas major discharge events in summer (July–August) are due to thermally caused glacier melt. In autumn (September–November), major discharge events are associated with heavy rainfall events. Autumn is the most important period with respect to fluvial sediment transport and fluvial sediment yields. Fluvial sediment transport and fluvial sediment yields in Erdalen are altogether supply‐limited. The intensity of fluvial transport in autumn and over the entire year depends strongly on the number of heavy rainfall events that trigger transfers of sediments from slopes into channels via saturation overland flow with connected slope wash and debris flow events. Annual suspended sediment yields are about two times greater than annual solute yields corrected by atmospheric inputs. Suspended sediment concentrations in glacier melt water during summer and annual sediment yields in Erdalen are both lower than in many other glacierized catchments worldwide. Because of the quantitative importance of single meteorological events for fluvial sediment transport and yields, and the high intra‐ and inter‐annual variability of sediment yields in Erdalen, process monitoring and analysis will be continued to be able to calculate more reliable annual sediment yields and denudation rates.

Magnification of Flood Disasters and its Relation to Regional Precipitation and Local Human Activities since the 1980s in Xinjiang, Northwestern China

Analyses of flood disasters were conducted using 1950–2001 data on the flood-damaged areas of cropland, the annual number of flood disasters and the direct economic losses in Xinjiang. There is an increasing trend in flood disasters in Xinjiang during the second half of the 20th century, especially since the mid-1980s. Results of a non-parametric Mann–Kendall test on the cropland-flooded index time series revealed an abrupt change in the mid-1980s. The reasons are discussed with respect to changes in annual precipitation and regional human activities, by correlating cropland-flooded area to annual precipitation and three socio-economic parameters (population, cropland area and GDP). The correlation coefficients between the flood-damaged area and the annual precipitation during the periods 1961–1998 and 1987–1998 were substantially higher than during the period of 1961–1986. The correlation coefficients between the flood-damaged area and the three human activity parameters, however, were relatively high for the whole period of 1961–1998, but generally not significant for the 1961–1986 and 1987–1998 periods, separately. These suggest that the occurrence of flood disasters could be mainly induced by local human activities before the mid-1980s, and thereafter mainly by abnormal precipitation in Xinjiang. Meteorological and hydrological records showed that the number of heavy rainfall events and the frequency of rainstorm flood disasters increased since the 1980s. In addition, siltation of reservoirs and loss of flood control structures are partly responsible for the increase of flood-damaged area. These results suggest that the increasing trend in flood disasters in Xinjiang since the middle 1980s could be attributed, at least in part, to an increasing trend in annual precipitation.

Observed coherent changes in climatic extremes during the second half of the twentieth century

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 19:193-212 (2002) - doi:10.3354/cr019193 Observed coherent changes in climatic extremes during the second half of the twentieth century P. Frich1,*, L. V. Alexander1,**, P. Della-Marta2, B. Gleason3, M. Haylock2, A. M. G. Klein Tank4, T. Peterson3 1Met Office, Hadley Centre for Climate Prediction and Research, London Road, Bracknell RG12 2SY, United Kingdom 2Bureau of Meteorology (BoM), GPO Box 1289K, Melbourne, Victoria 3001, Australia 3National Climatic Data Centre (NCDC), 151 Patton Avenue, Asheville, North Carolina 28801, USA 4Royal Netherlands Meteorological Institute (KNMI), Postbus 201, 3730 AE De Bilt, The Netherlands *Present address: National Environmental Research Institute (NERI), Postboks 358, Frederiksborgvij 399, 4000 Roskilde, Denmark. **Corresponding author. E-mail: lisa.alexander@metoffice.com ABSTRACT: A new global dataset of derived indicators has been compiled to clarify whether frequency and/or severity of climatic extremes changed during the second half of the 20th century. This period provides the best spatial coverage of homogenous daily series, which can be used for calculating the proportion of global land area exhibiting a significant change in extreme or severe weather. The authors chose 10 indicators of extreme climatic events, defined from a larger selection, that could be applied to a large variety of climates. It was assumed that data producers were more inclined to release derived data in the form of annual indicator time series than releasing their original daily observations. The indicators are based on daily maximum and minimum temperature series, as well as daily totals of precipitation, and represent changes in all seasons of the year. Only time series which had 40 yr or more of almost complete records were used. A total of about 3000 indicator time series were extracted from national climate archives and collated into the unique dataset described here. Global maps showing significant changes from one multi-decadal period to another during the interval from 1946 to 1999 were produced. Coherent spatial patterns of statistically significant changes emerge, particularly an increase in warm summer nights, a decrease in the number of frost days and a decrease in intra-annual extreme temperature range. All but one of the temperature-based indicators show a significant change. Indicators based on daily precipitation data show more mixed patterns of change but significant increases have been seen in the extreme amount derived from wet spells and number of heavy rainfall events. We can conclude that a significant proportion of the global land area was increasingly affected by a significant change in climatic extremes during the second half of the 20th century. These clear signs of change are very robust; however, large areas are still not represented, especially Africa and South America. KEY WORDS: Observed climatic extremes · Derived indicators · Temperature · Precipitation · Climate monitoring · Global change Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 19, No. 3. Online publication date: January 16, 2002 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2002 Inter-Research.