Setting the Scene for Flood Risk Management - Flood Risk Science and Management - page 9

Table 1.2 Summary of drivers of change in fluvial flooding systems (adapted from Hall et al. 2003b)

SPR
classi cation Driver set Drivers Explanation

Catchment
runoff

Precipitation Source Quantity, spatial distribution of rainfall and intensity. Rain/snow

proportion

Urbanization Pathway Changes in land surface (e.g. construction of impermeable surfaces and

stormwater drainage systems)

Rural land management Pathway In uences the function of surface and subsurface runoff. Changes include

the proportion of conservation/recreation areas and wetlands

Fluvial
processes

River morphology and
sediment supply

Pathway Changes in river morphology that in uence ood storage and ood

conveyance

River vegetation and
conveyance

Pathway Changes in river vegetation extent and type, e.g. in response to climate

change or due to changed maintenance or regulatory contraints

Societal
changes

Public behaviour Pathway Behaviour of oodplain occupants before, during and after oods can

signi cantly modify the severity of oods

Social vulnerability Receptor Changes in social vulnerability to ooding, e.g. due to changes in health

and tness, equity and systems of social provision

Economic
changes

Buildings and contents Receptor Changes in the cost of ood damage to domestic, commercial and other

buldings and their contents (e.g. due to increasing vulnerability of
domestic and commerical goods or increasing domestic wealth)

Urban vulnerability Receptor Changes in the number and distribution of domestic, commerical and

other buildings in oodplains

Infrastructure Receptor Systems of communication (physical and telecommunication), energy

distribution, etc.
Changes in the extent to which society is dependent on these systems

Agriculture Receptor Changes in the intensity and seasonality of agriculture, including removal

of agricultural land from production and hence changes in
vulnerability to ood damage

relative importance of different drivers of change
for flood managers in the future.
The implications of change within flooding
systems are profound. Milly et al. (2008) observe
that water management decisions - their discus-
sion was of water management in general rather
than flood risk management in particular - can no
longer proceed under the assumption that 'the idea
that natural systems fluctuatewithin an unchang-
ing envelope of variability'. The stationarity-based
assumptions that have underpinned engineering
design and, in our case, flood riskmanagement are
therefore no longer valid. Consequently there is a
need for adaptive policies that can deliver effective
riskmanagement without relying upon untenable
assumptions of an unchanging environment.

This implies a need for better models to repre-
sent these changing conditions and better obser-
vations with which to parameterize models. A
recent study for the UK Environment Agency
(Wheater et al. 2007) indicated that, to address
these processes of long-term change, a new holis-
tic modelling framework is needed, to encompass
the following:
. quantitative scenario modelling of the drivers
and pressures that impact upon flood risk, includ-
ing global climate and socioeconomic change;
. whole catchment and shoreline modelling of
flood and erosion risks under uncertain future
climatic and socioeconomic conditions, andunder
a wide range of policy and human response
options;