Rainfall In Urban Areas Research Articles

An Urban Flood Model Development Coupling the 1D and 2D Model with Fixed-Time Synchronization

Due to climate change, the frequency and intensity of torrential rainfall in urban areas are increasing, leading to more frequent flood damage. Consequently, there is a need for a rapid and accurate analysis of urban flood response capabilities. The dual-drainage model has been widely used for accurate flood analysis, with minimum time step synchronization being commonly adopted. However, this method has limitations in terms of speed. This study applied the hyper-connected solution for an urban flood (HC-SURF) model with fixed-time step flow synchronization, validated its accuracy using laboratory observation data, and tested its effectiveness in real urban watersheds with various synchronization times. Excellent performance was achieved in simulating real phenomena. In actual urban watersheds, as the synchronization time increased, the errors in surcharge and discharge also increased due to the inability to accurately reflect water level changes within the synchronization time; however, overall, they remained minimal. Therefore, the HC-SURF model is demonstrated as a useful tool for urban flood management that can be used to advantage in real-time flood forecasting and decision-making.

Intensification and Changing Spatial Extent of Heavy Rainfall in Urban Areas

AbstractUrban areas have been shown to impact rainfall by altering both its intensity and spatial structure at sub‐hourly and sub‐kilometer scales. However, there is currently no clear understanding of the precise pattern of change and the mechanisms that drive these changes. Since the hydrological response in urban areas is highly sensitive to such rainfall properties, understanding these changes is critical to improving our ability to assess urban flood risk. We use 7 years of high‐resolution weather radar data (4‐ or 5‐min and 1 km) to analyze changes in patterns of rainfall intensity, spatial structure, and storm evolution across eight urban areas within Europe and the United States. The use of the same methodology across the different cities enables a consistent comparison among them. We track convective rainfall events using a storm tracking algorithm and assess changes in rainfall properties in the upwind, center, and downwind regions of each city. We also investigate changes in the frequency of storm initiations, terminations, splitting, and merging. Our results show that urban areas act to intensify rainfall—mostly over them, but sometimes on their peripheries. Overall, larger cities tend to show the largest rainfall enhancements. Our findings highlight that rainfall spatial structure is altered over the urban core; usually resulting in more spatially concentrated rainfall. We also observe increased storm initiations over most cities and increased storm splitting over one. Given that demographic projections show that future urban population will increase, our results point toward an increased future flood risk in growing cities.

Enhancing daily rainfall prediction in urban areas: a comparative study of hybrid artificial intelligence models with optimization algorithms

Forecasting precipitation is a crucial input to hydrological models and hydrological event management. Accurate forecasts minimize the impact of extreme events on communities and infrastructure by providing timely and reliable information. In this study, six artificial intelligent hybrid models are developed to predict daily rainfall in urban areas by combining the firefly optimization algorithm (FA), invasive weed optimization algorithm (IWO), genetic particle swarm optimization algorithm (GAPSO), neural network (ANN), group method of data handling (GMDH), and wavelet transformation. Optimization algorithms increase forecasting accuracy by controlling all stages. A variety of criteria are used for validating the models, including correlation coefficient (R), root-mean-square error (RMSE), mean absolute error (MAE), critical success index (CSI), probability of detection (POD), and false alarm ratio (FAR). The proposed models are also evaluated in an urban area in Ahvaz, Iran. The GAPSO-Wavelet-ANN model is superior to other models for predicting daily rainfall, with an RMSE of 1.42 mm and an R of 0.9715.

Characteristics of the temporal and spatial evolution of rainfall under the influence of urbanization: a case study of the Beijing–Tianjin–Hebei region

Abstract With rapid urbanization in recent years, the frequency of extreme rainfall events has increased in major cities around the world during the flood season, and the social and economic losses caused by heavy rainfall are becoming increasingly serious. The results show that (1) the overall duration of rainfall exhibits a downward trend, and the overall spatial performance gradually decreases from east to west. (2) The mountainous areas are prone to light and moderate rainfall events; the plains are more prone to rainfall events at levels above moderate rain, especially rainstorms and heavy rain events; the probability of light and moderate rainfall events in the suburbs is close to that of the urban areas, but the probability of rainfall events at levels above heavy rain is less than that of the urban areas; the probability of rainfall events of all levels in the outer suburbs is higher. (3) Increase in rainfall in urban areas compared to the southern suburbs is greater. (4) With increasing urbanization, the built environment in the mountainous areas and plains has continued to grow, and the original underlying surface conditions have changed.

Assessing compound pluvial-fluvial flooding: Research status and ways forward

Compound weather and climate events have obtained increasing attention in recent years in the context of anthropogenic climate change. Compound pluvial-fluvial flooding (CPFF), usually referring to the superposition of heavy local rainfall in urban areas and riverbank overflow, is however rarely investigated. We perform a systematic literature review on this emerging topic and identify knowledge gaps. Major knowledge gaps concern the dependence between pluvial and fluvial flooding, and thus the co-occurrence probability, and its past and (possible) future changes. Although it is expected that CPFF increases in a warming world, we could not identify a single attempt to understand temporal changes. More systematic and comprehensive data collection and process documentation, particularly for pluvial and flash floods, are required to better understand and assess CPFF. Another major gap is the limitation of CPFF studies to hazard assessments. Implementing damage models would allow, with modest effort, to transfer hazard statements into risk statements. This would allow, in turn, to understand the scale of the problem in terms of societal relevance.

A simplified procedure to improve the usability of hydrodynamic modelling software in regenerative urban design

Densely urbanized areas are greatly exposed to the risks from climate change as reported by IPCC in 2018. In particular, compact urban settings afflicted by heavy storms and droughts, coupled with the intensification of the Urban Heat Island (UHI) effect and incremental heat waves require a requalification of the outdoor environment that accommodates for both strategic water management and enhanced microclimatic conditions. The present study proposes simplified procedures to enable the application of complex hydrodynamic modelling software (SWMM), by non-expert users (such as planners and designers), in the preliminary phases of an urban space project according to a water-sensitive urban design approach. In the paper, Italian multi-level regulations aimed at controlling the impacts of excessive rainfall in urban areas are taken into account as well as the integration of circular water management systems with evaporative cooling strategies. The proposed procedure is focused on two aspects: 1- to simplify the steps needed to convert the existing climatic data to provide a numerical sequence, to insert into the software; 2- to define a set of pre-compiled and multi-purposed solutions toolkits for the design of urban spaces that can be imported into the software through an external database.

Numerical analysis of aerosol direct and indirect effects on an extreme rainfall event over Beijing in July 2016

Impacts of aerosol direct (ADE) and aerosol indirect (AIE) effects on an extreme rainfall event over Beijing on 19–21 July 2016 were analyzed by conducting four numerical experiments with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The analysis shows that the ADE and AIE change the distribution of the rainfall centers and concentrate rainfall in urban areas. The ADE-induced hourly rainfall intensity increases by about 1 mm h−1, 10 mm h−1, and 5 mm h−1, whereas AIE-induced hourly rainfall intensity decreases by about 1.4 mm h−1, 10 mm h−1, and 3 mm h−1 in Beijing, central and eastern part of Beijing during 1200–1800 BJT on 19 July, respectively. The ADE has a slight impact (variation <0.3 mm h−1) on the hourly rainfall intensity, whereas the AIE increases the hourly rainfall intensity by about 1 mm h−1 in Beijing; the ADE and AIE increase the hourly rainfall intensity by about 12 mm h−1 and 20 mm h−1 in central part of Beijing while decrease by about 10 mm h−1 and 21 mm h−1 in eastern part of Beijing during 1200–1800 BJT on 20 July, respectively. The ADE destabilizes the atmosphere due to the increase in atmospheric diabatic heating, leading to an increase in rainfall in Beijing during 1200–1800 BJT on 19 July. The nucleation of more aerosols to cloud droplets, which decreases the size of the droplets and inhibits collision, decreasing the amount of rainfall. The impact of the ADE on rainfall is weakened due to the wet deposition caused by rainfall decreasing the aerosol concentration during 1200–1800 BJT on 20 July. The AIE increases the number of collisions and therefore increases the amount of rainfall. The difference in vertical speed is responsible for the difference in the local hourly rainfall intensity for central and eastern part of Beijing during 1200–1800 BJT on 20 July.

Characterization of an area susceptible to floods and inundations in a medium size city in Southern Brazil

The change in precipitation patterns that has occurred over the past decades establishes the discussion about the risks arising from rainfall in urban areas. These risks include floods, inundations and overflow, which are influenced by different conditions. The purpose of this work is to characterize a risk area, susceptible to inundations and floods, in the city of Passo Fundo, in the south of Brazil. In order to propose solutions aimed at mitigating risks for the area, a GIS (Geographic Information System) characterization was applied to prepare thematic maps to identify conditions of infrastructure networks, as well as other constraints of the built environment. The analysis showed that the area, predominantly residential, is currently susceptible to environmental risks, given the proximity to streams, the topography with slopes and impermeable surfaces, despite the existence of rain network infrastructure. Furthermore, the mitigation strategies were proposed, based on the concept of green infrastructure such as the implementation of draining surfaces, rain gardens and a linear park. The data collected in this study will provide subsidies to elaborate the risk maps of the area, deepening the analysis in future studies, assisting the decision making of the public power to prevent and mitigate risks such as floods, according to the identified vulnerability, as well as contribute to Goal 11 - Sustainable cities and communities on the United Nations Agenda 2030.

Grid-based Traffic Vulnerability Analysis by Using Betweenness Centrality

We propose a technique to measure the impact of loss of traffic function in a particular area to surrounding areas. The proposed method is applied to the city of Seoul, which is the capital of South Korea with a population of about ten million. Based on the actual road network in Seoul, we construct an abstract road network using 1 km × 1 km grid cells. The link weight of the abstract road network is re-adjusted considering traffic volume measured at several survey points. On the modified abstract road network, we evaluate the traffic vulnerability by calculating a network measure of betweenness centrality for every single grid cell. This study analyzes traffic impacts caused by road dysfunction due to heavy rainfall in urban areas.

Impacts of Urbanization on the Precipitation Characteristics in Guangdong Province, China

With the development of urbanization, whether precipitation characteristics in Guangdong Province, China, from 1981 to 2015 have changed are investigated using rain gauge data from 76 stations. These characteristics include annual precipitation, rainfall frequency, intense rainfall (defined as hourly precipitation ⩾ 20 mm), light precipitation (defined as hourly precipitation ⩽ 2.5 mm), and extreme rainfall (defined as hourly rainfall exceeding the 99.9th percentile of the hourly rainfall distribution). During these 35 years, the annual precipitation shows an increasing trend in the urban areas. While rainfall frequency and light precipitation have a decreasing trend, intense rainfall frequency shows an increasing trend. The heavy and extreme rainfall frequency both exhibit an increasing trend in the Pearl River Delta region, where urbanization is the most significant. These trends in both the warm seasons (May−October) and during the pre-flood season (April−June) appear to be more significant. On the contrary, the annual precipitation amount in rural areas has a decreasing trend. Although the heavy and extreme precipitation also show an increasing trend, it is not as strong and significant as that in the urban areas. During periods in which a tropical cyclone makes landfall along the South China Coast, the rainfall in urban areas has been consistently more than that in surrounding areas. The precipitation in the urban areas and to their west is higher after 1995, when the urbanization accelerated. These results suggest that urbanization has a significant impact on the precipitation characteristics of Guangdong Province.

Glyphosate and atrazine in rainfall and soils in agroproductive areas of the pampas region in Argentina

The presence in the atmosphere of glyphosate (GLP) and atrazine (ATZ) was investigated—those pesticides dominating the market in Argentina—through rain, as the main climatic phenomenon associated with wet deposition, both through analyzing source-receptor relationships with soil along with the climatic influences that may condition that transport and through estimating the annual deposition on the surface of the Argentine pampas. Rainwater samples (n = 112) were collected throughout each rainfall in urban areas of the pampas having different degrees of land use and with extensive crop production plus subsurface-soil samples (n = 58) from the relevant periurban sites. The herbicides—analyzed by liquid-chromatography–mass-spectrometry—were detected in >80% of the rain samples at median-to-maximum concentrations of 1.24–67.3 μg·L−1 (GLP) and 0.22–26.9 μg·L−1(ATZ), while aminomethylphosphonic acid (AMPA) was detected at 34% (0.75–7.91 μg·L−1). In soils, GLP was more frequently registered (41%; 102–323 μg·kg−1) followed by ATZ (32%; 7–66 μg·kg−1) and then AMPA (22%; 223–732 μg·kg−1). The maximum GLP concentrations quantified in rainwater exceeded the previously reported levels for the USA and Canada. No associations were observed between soil and rainwater concentrations in the same monitoring areas—despite the soil's action as a source, as evidenced through the AMPA present in rainwater. Median GLP concentrations were significantly associated with isohyets, in an increasing gradient from the east to the west—as such in an inverse pattern to that of the annual rainfall volumes; whereas ATZ-rainwater levels exhibited no characteristic spatial configuration. The estimated annual deposition of GLP by rainfall indicated that more than onc source of a herbicide can lead to its presence in the atmosphere and points out the relevance of rainfall's contribution to the surface levels of a pollutant.

Return period assessment of urban pluvial floods through modelling of rainfall–flood response

AbstractIntense rainfall in urban areas can often generate severe flood impacts. Consequently, it is crucial to design systems to minimize potential flood damages. Traditional, simple design of urban drainage systems assumes agreement between rainfall return period and its consequent flood return period; however, this does not always apply. Hydraulic infrastructures found in urban drainage systems can increase system heterogeneity and perturb the impact of severe rainfall response. In this study, a surface flood return period assessment was carried out at Lystrup (Denmark), which has received the impact of flooding in recent years. A 35 years' rainfall dataset together with a coupled 1D/2D surface and network model was used to analyse and assess flood return period response. Results show an ambiguous relation between rainfall and flood return periods indicating that linear rainfall–runoff relationships will, for the analysed case study, be insufficient for flood estimation. Simulation-based mapping of return periods for flood area and volume has been suggested, and moreover, a novel approach has been developed to map local flood response time and relate this to rainfall characteristics. This approach allows to carefully analyse rainfall impacts and flooding response for a correct flood return period assessment in urban areas.

Quantitative Assessment on the Radar Rainfall of KICT X-band Daul-polarization Radar

Korea Institute of Civil Engineering and Building Technology (KICT) introduced X-band dual-polarization radar (KICT hydrological radar) in September 2013 to observe the heavy rainfall in urban area. It has been known that X-band dual-polarization radar is good for the observation of the heavy rainfall because the radar can provide data with high spatial-temporal resolution. This study estimated the radar rainfall by using the specific differential phase (KDP) from KICT hydrological radar and quantitatively assessed the radar rainfall. Forty two rain events were applied and eighty AWSs within the radar observational range were used for the assessment. As a result, there was no bias in the radar rainfall estimated by KDP. The accuracy of the radar rainfall was more than 50 % and the accuracy on the close range from 5 to 20 km was more than 60 %. Also, it has found that X-band dual-polarization radar was useful for the observation of the heavy rainfall than the small rainfall because the accuracy increased as the radar rainfall increase. Keywords: KICT Hydrolgocal Radar, X-band Dual-polarization Radar, Radar Rainfall, Heavy Rainfall

DEVELOPING A SPATIAL PROCESSING SERVICE FOR AUTOMATIC CALCULATION OF STORM INUNDATION

Abstract. With the increase in urbanization, the surface of earth and its climate are changing. These changes resulted in more frequent floodingand storm inundation in urban areas. The challenges of flooding can be addressed through several computational procedures. Due to its numerous advantages, accessible web services can be chosen as a proper format for determining the storm inundation. Web services have facilitated the integration and interactivity of the web applications. Such services made the interaction between machines more feasible. Web services enable the heterogeneous software systems to communicate with each other. A Web Processing Service (WPS) makes it possible to process spatial data with different formats. In this study, we developed a WPS to automatically calculate the amount of storm inundation caused by rainfall in urban areas. The method we used for calculating the storm inundation is based on a simplified hydrologic model which estimates the final status of inundation. The simulation process and water transfer between subcatchments are carried out respectively, without user’s interference. The implementation of processing functions in a form of processing web services gives the capability to reuse the services and apply them in other services. As a result, it would avoid creating the duplicate resources.

Fine-scale evaluation of rainfall from TV-sats: A new method for water monitoring and flash flood prevention

In this paper we present a method for rebuilding rainfall maps at high resolution (500 m × 500 m, 1 min). This method is based on the assimilation of opportunistic measurements of the attenuation that affects the signals coming from TV satellites in a model of spatiotemporal advection of rainfall fields. At the frequencies used (Ku band), the attenuation affecting the signals in the atmosphere is mainly due to rain. We set a sensor (field analyzer) on the ground, and then measured the mean rainfall over the link. This method was applied to a simulated network of sensors. These simulated sensors were realistically set over the Paris area, on a zone assumed to be typical of an area with high socio-economic issues (flood prevention, water resources management). We compared the simulated rainfall maps with the maps rebuilt by our algorithm. We then showed the feasibility of our approach for measuring the rainfall in urban areas with high resolution.

Effect of Mineralogy on Durability and Strength of Hornfelsic Rocks under Acidic Rainfall in Urban Areas

In order to assess mineralogical composition influence on durability and strength of rocks, four samples of hornfelsic rocks were selected from southern and western parts of the city of Hamedan, west of Iran. These rock samples were subjected to mineralogical, physical and mechanical tests in the laboratory. Also, they were evaluated in 15 cycles of slake-durability testing in different pH of sulfuric acid solutions and XRD analysis. Based on the results, the type and amount of minerals, their density and hardness had an influence on the uniaxial compressive strength and the slake durability index of tested rocks. That means, presence of non-dissolved minerals such as graphite in studied rocks, decreases Unconfined Compressing Strength (UCS) but increases the slake durability index. The results of slake-durability test indicated that weight loss of the samples at initial cycles was found to be higher than the end cycles. Also, in these samples, initial minerals in the fresh samples were not exchanged by secondary minerals such as clay minerals. Therefore Hamedan hornfelsic rocks are approximately resistant when were put under accelerated chemical weathering and degradation in the laboratory and natural chemical weathering.

Rainwater harvesting as source control option to reduce roof runoff peaks to downstream drainage systems

The objective of the paper is to evaluate the potential of tank-based rainwater harvesting systems in free standing houses as the source control method to mitigate peak roof runoff due to rainfall in urban areas. To this aim, the water balance simulation of the rainwater tank was carried out using both high resolution rainfall series and toilet water demand data extracted from the database of results built in a previous field campaign involving six experimental households in southern Italy. Simulations show that significant potential for runoff peak reduction exists, basically depending on the rainwater tank size and on the characteristics of the water demand in the house.

The influence of rainfall on road accidents in urban areas: A weather radar approach

This paper presents a novel and rigorous approach to the analysis of the impact of rainfall on road traffic accidents in urban areas. It is argued that previous approaches to rainfall quantification for accident analysis, primarily using a representative surface meteorological station to represent an urban area, may not give an accurate record of the conditions across the city in question. Using an innovative city-wide weather radar approach to rainfall quantification and matched-pairs analysis, road accidents in the UK cities of Manchester and Greater London are examined over a 3-year baseline period (2008–2011). A comparative study is made over the same period used a traditional station-based approach. The resulting relative accident rates demonstrate divergence between the two cities and the two approaches. Although the stricter criteria for a rain event under the weather radar approach gives an increased RAR in Manchester, the RAR observed under these conditions decreases in Greater London. Reasons for the variation in RAR are explored and include traffic volume and speed, other coincident weather conditions and driver behaviour, in accordance with Elvik’s (2006) laws of accident causation. It is argued that the approach described in this study offers significant improvements to the analysis of current weather-related accidents by giving a more representative measure of rainfall in urban areas.

Gastrointestinal Illness among Triathletes Swimming in Non-Polluted versus Polluted Seawater Affected by Heavy Rainfall, Denmark, 2010-2011

Recent years have seen an increase in the frequency of extreme rainfall and subsequent flooding across the world. Climate change models predict that such flooding will become more common, triggering sewer overflows, potentially with increased risks to human health. In August 2010, a triathlon sports competition was held in Copenhagen, Denmark, shortly after an extreme rainfall. The authors took advantage of this event to investigate disease risks in two comparable cohorts of physically fit, long distance swimmers competing in the sea next to a large urban area. An established model of bacterial concentration in the water was used to examine the level of pollution in a spatio-temporal manner. Symptoms and exposures among athletes were examined with a questionnaire using a retrospective cohort design and the questionnaire investigation was repeated after a triathlon competition held in non-polluted seawater in 2011. Diagnostic information was collected from microbiological laboratories. The results showed that the 3.8 kilometer open water swimming competition coincided with the peak of post-flooding bacterial contamination in 2010, with average concentrations of 1.5x104 E. coli per 100 ml water. The attack rate of disease among 838 swimmers in 2010 was 42% compared to 8% among 931 swimmers in the 2011 competition (relative risk (RR) 5.0; 95% CI: 4.0-6.39). In 2010, illness was associated with having unintentionally swallowed contaminated water (RR 2.5; 95% CI: 1.8-3.4); and the risk increased with the number of mouthfuls of water swallowed. Confirmed aetiologies of infection included Campylobacter, Giardia lamblia and diarrhoeagenic E. coli. The study demonstrated a considerable risk of illness from water intake when swimming in contaminated seawater in 2010, and a small but measureable risk from non-polluted water in 2011. This suggests a significant risk of disease in people ingesting small amounts of flood water following extreme rainfall in urban areas.

기후변화 영향을 고려한 도시지역의 확률강우량 전망

Recent inundation damage has frequently occurred due to heavy rainfall in urban area, because rainfall has locally occurred exceeding the capability of a flood control plan by the exiting design rainfall from the data of Seoul weather station. Accordingly the objective of this study is to predict new design rainfall in order to make a future flood control plan considering climate change. In this study, for considering spatial characteristics of rainfall in urban area, data of AWS was used and for retaining insufficient rainfall data, WGR model was estimated the application of target area. The results were compared with the observation data and consequently show reasonable results. In addition, to prepare for climate change, design rainfall was calculated by applying for various climate scenarios and the result would be used in order to establish future flood control plan.