London scoping - ukcip

Final Report
14
3.3 Precipitation (including snowfall)
Individual precipitation records are particularly susceptible to local conditions, instrumentation
and observer practices. The detection of precipitation trends at single stations is also
confounded by inter-annual variability (i.e., there is a high level of ‘noise’ relative to ‘signal’).
Therefore, recent precipitation trends for the Thames Region were analysed using a composite
record of 12 gauges from 1883 (Davis, 2000). This data set also better reflects the Thames-wide
water resource context of London.
Annual water year precipitation totals (October through following September) for the Thames
region indicate a slight but statistically insignificant increase since the 1880’s. However,
relative to the 1880’s winter precipitation has increased by 11% and summer has declined by
10% over the same period (Figure 3.3). The largest changes in monthly precipitation totals have
occurred in January (+28%), April (+27%), September (+36%), and July (-26%), but much of
the apparent increase is due to the cluster of dry winters and springs in the first few decades of
the record (see Brugge, 1993).