Risk Analysis, Vol. 38, No. 6, 2018 DOI: 10.1111/risa.12930
A Probabilistic Analysis of Surface Water Flood Risk
and Chris Kilsby
Flooding in urban areas during heavy rainfall, often characterized by short duration and high-
intensity events, is known as “surface water ﬂooding.” Analyzing surface water ﬂood risk is
complex as it requires understanding of biophysical and human factors, such as the localized
scale and nature of heavy precipitation events, characteristics of the urban area affected (in-
cluding detailed topography and drainage networks), and the spatial distribution of economic
and social vulnerability. Climate change is recognized as having the potential to enhance the
intensity and frequency of heavy rainfall events. This study develops a methodology to link
high spatial resolution probabilistic projections of hourly precipitation with detailed surface
water ﬂood depth maps and characterization of urban vulnerability to estimate surface water
ﬂood risk. It incorporates probabilistic information on the range of uncertainties in future
precipitation in a changing climate. The method is applied to a case study of Greater London
and highlights that both the frequency and spatial extent of surface water ﬂood events are
set to increase under future climate change. The expected annual damage from surface water
ﬂooding is estimated to be to be £171 million, £343 million, and £390 million/year under the
baseline, 2030 high, and 2050 high climate change scenarios, respectively.
KEY WORDS: Climate change; economic damage; surface water ﬂood risk
Flooding (including coastal, riverine, and ﬂash
ﬂooding) is one of the most frequent and damag-
ing natural disasters in terms of number of people
affected and economic damage.
As such, effec-
tive long-term ﬂood risk management is an increas-
ingly critical issue for many governments around the
Flooding in urban areas during heavy rainfall is
known as surface water ﬂooding, pluvial ﬂooding, or
Environmental Change Institute (ECI), School of Geography
and the Environment, University of Oxford, Oxford, UK.
School of Civil Engineering and Geosciences, Newcastle Univer-
sity, Newcastle, UK.
Address correspondence to Katie Jenkins, Environmental
Change Institute (ECI), School of Geography and the Envi-
ronment, University of Oxford, Oxford OX1 3QY, UK; katie.
storm water ﬂooding.
Surface water ﬂooding oc-
curs due to a complex interplay of factors, includ-
ing the precise location, intensity, and duration of
rainfall, the characteristics of urban land surfaces,
and the engineering design of the surface drainage
and sewer system. Surface water ﬂooding tends to be
most severe during intense rainfall downpours, which
are often, but not exclusively, associated with convec-
tive rainfall events. Rainfall may be inﬁltrated into
the ground, but in urban areas with impermeable sur-
faces rainfall will ﬂow on the surface in directions
modiﬁed by the form of buildings and streets and will
accumulate at locations with low topographical ele-
vation. These processes are modiﬁed by drains that
are designed to convey water away from urban areas
on the surface or in pipes.
The scale and severity of economic impacts will
be dependent on the characteristics of the event, the
vulnerability of the area and population exposed to
2017 Society for Risk Analysis