6 research outputs found
Initial conditions of urban permeable surfaces in rainfall-runoff models using Horton’s infiltration
Abstract
Infiltration is a key process controlling runoff, but varies depending on antecedent conditions. This study provides estimates on initial conditions for urban permeable surfaces via continuous simulation of the infiltration capacity using historical rain data. An analysis of historical rainfall records show that accumulated rainfall prior to large rain events does not depend on the return period of the event. Using an infiltration-runoff model we found that for a typical large rain storm, antecedent conditions in general lead to reduced infiltration capacity both for sandy and clayey soils and that there is substantial runoff for return periods above 1–10 years.</jats:p
Comparison of the impacts of urban development and climate change on exposing European cities to pluvial flooding
The economic and human consequences of extreme precipitation and the related
flooding of urban areas have increased rapidly over the past decades. Some of
the key factors that affect the risks to urban areas include climate change,
the densification of assets within cities and the general expansion of urban
areas. In this paper, we examine and compare quantitatively the impact of
climate change and recent urban development patterns on the exposure of four
European cities to pluvial flooding. In particular, we investigate the degree
to which pluvial floods of varying severity and in different geographical
locations are influenced to the same extent by changes in urban land cover
and climate change. We have selected the European cities of Odense, Vienna,
Strasbourg and Nice for analyses to represent different climatic conditions,
trends in urban development and topographical characteristics. We develop and
apply a combined remote-sensing and flood-modelling approach to simulate the
extent of pluvial flooding for a range of extreme precipitation events for
historical (1984) and present-day (2014) urban land cover and for two
climate-change scenarios (i.e. representative concentration pathways,
RCP 4.5 and RCP 8.5). Changes in urban land cover are estimated using Landsat satellite imagery for the period 1984–2014. We
combine the remote-sensing analyses with regionally downscaled estimates of
precipitation extremes of current and expected future climate to enable 2-D
overland flow simulations and flood-hazard assessments. The individual and
combined impacts of urban development and climate change are quantified by
examining the variations in flooding between the different simulations along
with the corresponding uncertainties. In addition, two different assumptions
are examined with regards to the development of the capacity of the urban
drainage system in response to urban development and climate change. In the
stationary approach, the capacity resembles present-day design, while it
is updated in the evolutionary approach to correspond to changes in
imperviousness and precipitation intensities due to urban development and
climate change respectively. For all four cities, we find an increase in
flood exposure corresponding to an observed absolute growth in impervious
surfaces of 7–12 % during the past 30 years of urban development.
Similarly, we find that climate change increases exposure to pluvial flooding
under both the RCPÂ 4.5 and RCPÂ 8.5 scenarios. The relative importance of
urban development and climate change on flood exposure varies considerably
between the cities. For Odense, the impact of urban development is comparable
to that of climate change under an RCP 8.5 scenario (2081–2100), while for
Vienna and Strasbourg it is comparable to the impacts of an RCPÂ 4.5 scenario.
For Nice, climate change dominates urban development as the primary driver of
changes in exposure to flooding. The variation between geographical locations
is caused by differences in soil infiltration properties, historical trends
in urban development and the projected regional impacts of climate change on
extreme precipitation. Developing the capacity of the urban drainage system
in relation to urban development is found to be an effective adaptation
measure as it fully compensates for the increase in run-off caused by
additional sealed surfaces. On the other hand, updating the drainage system
according to changes in precipitation intensities caused by climate change
only marginally reduces flooding for the most extreme events
Influence of urban land cover changes and climate change for the exposure of European cities to flooding during high-intensity precipitation
The extent and location of impervious surfaces within urban areas due to
past and present city development strongly affects the amount and velocity
of run-off during high-intensity rainfall and consequently influences the
exposure of cities towards flooding. The frequency and intensity of extreme
rainfall are expected to increase in many places due to climate change and
thus further exacerbate the risk of pluvial flooding. This paper presents a
combined hydrological-hydrodynamic modelling and remote sensing approach
suitable for examining the susceptibility of European cities to pluvial
flooding owing to recent changes in urban land cover, under present and
future climatic conditions. Estimated changes in impervious urban surfaces
based on Landsat satellite imagery covering the period 1984–2014 are
combined with regionally downscaled estimates of current and expected future
rainfall extremes to enable 2-D overland flow simulations and flood hazard
assessments. The methodology is evaluated for the Danish city of Odense.
Results suggest that the past 30 years of urban development alone has
increased the city's exposure to pluvial flooding by 6% for 10-year
rainfall up to 26% for 100-year rainfall. Corresponding estimates for
RCP4.5 and RCP8.5 climate change scenarios (2071–2100) are in the order of
40 and 100%, indicating that land cover changes within cities can
play a central role for the cities' exposure to flooding and conversely also
for their adaptation to a changed climate
Influence of urban land cover changes and climate change for the exposure of cities to flooding during high-intensity precipitation
The extent and location of impervious surfaces within urban areas due to
past and present city development strongly affects the amount and velocity
of run-off during high-intensity rainfall and consequently influences the
exposure of cities towards flooding. The frequency and intensity of extreme
rainfall are expected to increase in many places due to climate change and
thus further exacerbate the risk of pluvial flooding. This paper presents a
combined hydrological-hydrodynamic modelling and remote sensing approach
suitable for examining the susceptibility of European cities to pluvial
flooding owing to recent changes in urban land cover, under present and
future climatic conditions. Estimated changes in impervious urban surfaces
based on Landsat satellite imagery covering the period 1984–2014 are
combined with regionally downscaled estimates of current and expected future
rainfall extremes to enable 2-D overland flow simulations and flood hazard
assessments. The methodology is evaluated for the Danish city of Odense.
Results suggest that the past 30 years of urban development alone has
increased the city's exposure to pluvial flooding by 6% for 10-year
rainfall up to 26% for 100-year rainfall. Corresponding estimates for
RCP4.5 and RCP8.5 climate change scenarios (2071–2100) are in the order of
40 and 100%, indicating that land cover changes within cities can
play a central role for the cities' exposure to flooding and conversely also
for their adaptation to a changed climate
Efficient Hydrodynamic Modelling of Urban Stormwater Systems for Real-Time Applications
Urban water drainage systems represent complex networks with nonlinear dynamics and different types of interactions. This yields an involved modeling problem for which different off-line simulation approaches are available. Nevertheless, these approaches cannot be used for real-time simulations, i.e., running in parallel to weather now- and forecasts and enabling the monitoring and automatic control of urban water drainage systems. Alternative approaches, used commonly for automation purposes, involve parameterized linear delay systems, which can be used in real-time but lack the necessary level of detail, which, in particular, is required for adequate flood risk prognostics. Given this setup, in the present paper, an approach for the effective modeling of detailed water drainage systems for real-time applications implemented with the open-source Storm Water Management Model (SWMM) software is addressed and exemplified for a part of the water drainage system of the city of Flensburg in northern Germany. Additionally, a freely available early-warning system prototype is introduced and used to combine weather forcast information on a 2-h prediction horizon with the developed model and available measurements. This prototype is subsequently used for data assimilation using the ensemble Kalman filter (EnKF) for the considered area in Flensburg
Efficient Hydrodynamic Modelling of Urban Stormwater Systems for Real-Time Applications
Urban water drainage systems represent complex networks with nonlinear dynamics and different types of interactions. This yields an involved modeling problem for which different off-line simulation approaches are available. Nevertheless, these approaches cannot be used for real-time simulations, i.e., running in parallel to weather now- and forecasts and enabling the monitoring and automatic control of urban water drainage systems. Alternative approaches, used commonly for automation purposes, involve parameterized linear delay systems, which can be used in real-time but lack the necessary level of detail, which, in particular, is required for adequate flood risk prognostics. Given this setup, in the present paper, an approach for the effective modeling of detailed water drainage systems for real-time applications implemented with the open-source Storm Water Management Model (SWMM) software is addressed and exemplified for a part of the water drainage system of the city of Flensburg in northern Germany. Additionally, a freely available early-warning system prototype is introduced and used to combine weather forcast information on a 2-h prediction horizon with the developed model and available measurements. This prototype is subsequently used for data assimilation using the ensemble Kalman filter (EnKF) for the considered area in Flensburg