London scoping - ukcip

Final Report
73
Figure 5.4 Number of days in the Thames Region with winter (left column) and summer (right
column) precipitation totals above 12.5 mm/d (Medium-High Emissions, and Medium-
Low Emissions, downscaled), with respect to the 1961 to 1990 average
Winter anomaly (days)
Winter anomaly (days)
10
8
6
4
2
0
-2
-4
1961 1981 2001 2021 2041 2061 2081
10
8
6
4
2
0
-2
-4
1961 1981 2001 2021 2041 2061 2081
Summer anomaly (days)
Summer anomaly (days)
5
4
3
2
1
0
-1
-2
-3
1961 1981 2001 2021 2041 2061 2081
5
4
3
2
1
0
-1
-2
-3
1961 1981 2001 2021 2041 2061 2081
Longer-duration precipitation totals are also of interest following the October/November 2000
flooding (CEH and Meteorological Office, 2001). The annual rise in the 30- and 60-day
duration autumn-winter totals is almost imperceptible under both the Medium-High Emissions
and Medium-Low Emissions scenarios (Figure 5.5). However, beyond the 2050s, extreme
precipitation events of 30- and 60-day duration do increase in magnitude (Table 5.6). For
example, by the 2080s the 60-day precipitation event that occurs on average 1 in 10 years (i.e.,
probability 0.10) increases in magnitude by 10%, whereas the 1 in 20 year event (probability
0.05) increases by 16%. For both the 30- and 60-day events, the rarer the event (i.e., lower
probability of occurrence) the greater the magnitude change. These results suggest that extreme
precipitation events of the type experienced in late-2000 will become more common in the
future – a result that is entirely consistent with UKCIP02 scenarios (Hulme et al., 2002).