London scoping - ukcip

Final Report
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representing the unique ‘local’ climate of target sites (for a review see Wilby and Wigley,
1997). This enables the development of climate change scenarios of higher resolution than
available through UKCIP02, and at scales commensurate with many impact sectors. The
technique involves two main steps. Firstly, statistical relationships are established between the
target variable of interest (e.g., maximum daily temperatures in St James Park, London) and
indices of regional weather (e.g., wind direction, atmospheric pressure, etc., over southern
England) for the current climate (Figure 4.5). Secondly, the same statistical relationships are
employed to estimate the local variable for the future climate, using data supplied by a climate
model. SDS techniques are not computationally demanding and require orders of magnitude
less computer time than RCMs to produce equivalent scenarios. However, SDS scenarios are
dependent on the stability of the local–regional scale relationship(s), and on the choice of
predictor variable(s) used for downscaling future climate change (see Winkler et al., 1997).
Figure 4.5 The location and nomenclature of the nine climate model grid boxes used for
downscaling current and future climate scenarios to individual sites across the UK.
Downscaling for London was undertaken using climate information taken from the EE
and SE grid-boxes.
The local climate scenarios used for impacts assessment in subsequent sections of this report
were developed using the Statistical DownScaling Model (SDSM) version 2.2 (Wilby et al.,
2002). This software facilitates the rapid development of multiple, low–cost, single–site
scenarios of daily surface weather variables under current and future climate conditions. An
important feature of the SDSM package is the data archive: a set of daily climate variables
prepared for model calibration and downscaling to any site across the UK (Figure 4.5). This
archive contains variables describing atmospheric circulation, thickness, stability and moisture
content at several levels in the atmosphere, under climate conditions observed between 1961
and 2000. Equivalent predictor variables are provided for HadCM3 experiments of transient
climate change between 1961 and 2099, for the A2 (Medium-High Emissions) and B2