35 research outputs found
The Influence of Rainfall and Catchment Critical Scales on Urban Hydrological Response Sensitivity
Interactions between spatial and temporal variability of rainfall and catchment characteristics strongly influence hydrological response. In urban areas, where runoff generation is fast due to high imperviousness degree, it is especially relevant to capture the high spatiotemporal rainfall variability. Significant progress has been made in the development of spatially distributed rainfall measurements and of distributed hydrological models, to represent the variability of catchment's characteristics. Interactions between rainfall and basin scales on hydrological response sensitivity, however, needs deeper investigation. A previous study investigated the hydrological response in the small urbanized catchment of Cranbrook (8 km2, London, UK) and proposed three dimensionless “scale factors” to identify if the available rainfall resolution is sufficient to properly predict hydrological response. We aim to verify the applicability of these scale factors to larger scales, with a distinct physiographic setting, in Little Sugar Creek (111 km2, Charlotte, USA), to identify the required rainfall resolution and to predict model performance. Twenty-eight events were selected from a weather radar data set from the National Weather Radar Network, with a resolution of 1 km2 and 15 min. Rainfall data were aggregated to coarser resolutions and used as input for a distributed hydrological model. Results show that scale factors and associated thresholds are generally applicable for characterization of urban flood response to rainfall across spatiotemporal scales. Additionally, application of scale factors in observation-based analysis supports identification of event characteristics that are poorly captured and critical improvements that need to be made before the model can benefit from high-resolution rainfall
The need for high resolution data to improve urban flood 1 risk assessment 2
Abstract 12 Cities are particularly vulnerable to rainfall-generated floods that are typically characterised 13 by their rapid onset and localised nature. This implies that precipitation and catchment 14 information need to be available at high resolution to reliably predict hydrological response 15 and potential flooding. On the contrary, urban areas constitute a major knowledge gap as most 16 flood risk studies have concentrated on natural basins and records of rain gauges and water 17 level gauges in cities are scarce. While increase in intense precipitation as a result of climate 18 change is expected in many areas around the world, it is at present not possible to assess how 19 this will affect urban pluvial flood risk. Collection of reliable, high resolution data in cities 20 needs to start urgently to build up datasets in support of urban flood risk assessment and to 21 enable detection of changes in flood risk whether these are induced by climate change, 22 urbanisation or other future developments. This study shows how implementation of 23 polarimetric X-band radar can contribute to filling the knowledge gap of flood risk 24 quantification in cities. 2
Sensitivity of urban drainage models to the spatial-temporal resolution of rainfall inputs: A multi-storm, multi-catchment investigation
Urban hydrological applications require high resolution precipitation and catchment information in order to well represent the spatial variability, fast runoff processes and short response times of urban catchments (Berne et al., 2004). Although fast progress has been made over the last few decades in high resolution measurement of rainfall at urban scales, including increasing use of weather radars, recent studies suggest that the resolution of the currently available rainfall estimates (typically 1 x 1 km2 in space and 5 min in time) may still be too coarse to meet the stringent requirements of urban hydrology (Gires et al., 2012). What is more, current evidence is still insufficient to provide a concrete answer regarding the added value of higher resolution rainfall estimates and actual rainfall input resolution requirements for urban hydrological applications. With the aim of providing further evidence in this regard, a collaborative study was conducted which investigated the impact of rainfall input resolutions on the outputs of the operational urban drainage models of four urban catchments in the UK and Belgium (Figure 1)
Holistic approach to flood risk assessment in areas with cultural heritage: a practical application in Ayutthaya, Thailand
Opportunities for multivariate analysis of open spatial datasets to characterize urban flooding risks
Cities worldwide are challenged by increasing urban flood risks. Precise and
realistic measures are required to reduce flooding impacts. However,
currently implemented sewer and topographic models do not provide realistic
predictions of local flooding occurrence during heavy rain events. Assessing
other factors such as spatially distributed rainfall, socioeconomic
characteristics, and social sensing, may help to explain probability and
impacts of urban flooding. Several spatial datasets have been recently made
available in the Netherlands, including rainfall-related incident reports
made by citizens, spatially distributed rain depths, semidistributed
socioeconomic information, and buildings age. Inspecting the potential of
this data to explain the occurrence of rainfall related incidents has not
been done yet. Multivariate analysis tools for describing communities and
environmental patterns have been previously developed and used in the field
of study of ecology. The objective of this paper is to outline opportunities
for these tools to explore urban flooding risks patterns in the mentioned
datasets. To that end, a cluster analysis is performed. Results indicate
that incidence of rainfall-related impacts is higher in areas characterized
by older infrastructure and higher population density
Effects of different spatial and temporal rainfall data resolution on hydrological response in flat urban catchments
Flooding in urban areas is one of the main weather-related risk problems of the last decades. It is due to the fact that the population is growing and moving from the rural areas to the cities, which become more urbanized and densely populated. This phenomenon is combined with the climate changes of the last years, that present an increase of short but quite intense rainfall events. These conditions determine a fast and short-time response of the catchments, which increases the probability of flooding
On the occurrence of rainstorm damage based on home insurance and weather data
Rainstorm damage caused by the malfunction of urban drainage systems
and water intrusion due to defects in the building envelope can be
considerable. Little research on this topic focused on the
collection of damage data, the understanding of damage mechanisms
and the deepening of data analysis methods. In this paper, the
relative contribution of different failure mechanisms to the
occurrence of rainstorm damage is investigated, as well as the
extent to which these mechanisms relate to weather variables. For
a case study in Rotterdam, the Netherlands, a property level home
insurance database of around 3100 water-related damage claims was
analysed. The records include comprehensive transcripts of communication
between insurer, insured and damage assessment experts, which
allowed claims to be classified according to their actual damage
cause. The results show that roof and wall leakage is the most frequent
failure mechanism causing precipitation-related claims, followed by
blocked roof gutters, melting snow and sewer flooding. Claims
related to sewer flooding were less present in the data, but are
associated with significantly larger claim sizes than claims in the
majority class, i.e. roof and wall leakages. Rare events logistic
regression analysis revealed that maximum rainfall intensity and
rainfall volume are significant predictors for the occurrence
probability of precipitation-related claims. Moreover, it was found
that claims associated with rainfall intensities smaller than
7–8 mm in a 60-min window are mainly related to failure
processes in the private domain, such as roof and wall leakages. For
rainfall events that exceed the 7–8 mm h−1 threshold,
the failure of systems in the public domain, such as sewer systems,
start to contribute considerably to the overall occurrence
probability of claims. The communication transcripts, however,
lacked information to be conclusive about to which extent
sewer-related claims were caused by overloading of sewer systems or
failure of system components
On the sensitivity of urban hydrodynamic modelling to rainfall spatial and temporal resolution
Cities are increasingly vulnerable to floods generated by intense rainfall,
because of urbanisation of flood-prone areas and ongoing urban
densification. Accurate information of convective storm characteristics at
high spatial and temporal resolution is a crucial input for urban
hydrological models to be able to simulate fast runoff processes and enhance
flood prediction in cities. In this paper, a detailed study of the
sensitivity of urban hydrodynamic response to high resolution radar rainfall
was conducted. Rainfall rates derived from X-band dual polarimetric weather
radar were used as input into a detailed hydrodynamic sewer model for an
urban catchment in the city of Rotterdam, the Netherlands. The aim was to
characterise how the effect of space and time aggregation on rainfall
structure affects hydrodynamic modelling of urban catchments, for
resolutions ranging from 100 to 2000 m and from 1 to 10 min.
Dimensionless parameters were derived to compare results between different
storm conditions and to describe the effect of rainfall spatial resolution
in relation to storm characteristics and hydrodynamic model properties:
rainfall sampling number (rainfall resolution vs. storm size), catchment
sampling number (rainfall resolution vs. catchment size), runoff and sewer
sampling number (rainfall resolution vs. runoff and sewer model resolution
respectively).
Results show that for rainfall resolution lower than half the catchment
size, rainfall volumes mean and standard deviations decrease as a result of
smoothing of rainfall gradients. Moreover, deviations in maximum water
depths, from 10 to 30% depending on the storm, occurred for rainfall
resolution close to storm size, as a result of rainfall aggregation. Model
results also showed that modelled runoff peaks are more sensitive to
rainfall resolution than maximum in-sewer water depths as flow routing has a
damping effect on in-sewer water level variations. Temporal resolution
aggregation of rainfall inputs led to increase in de-correlation lengths
and resulted in time shift in modelled flow peaks by several minutes.
Sensitivity to temporal resolution of rainfall inputs was low compared to
spatial resolution, for the storms analysed in this study