London scoping - ukcip

Final Report
69
Figure 5.3 Changes in maximum soil moisture deficits (SMDs) and length of recharge season in
the River Loddon catchment (Medium-High Emissions, and Medium-Low Emissions,
downscaled), with respect to the 1961 to 1990 average
Max SMD Anomaly (mm)
Max SMD Anomaly (mm)
100
80
60
40
20
0
-20
-40
-60
1961 1981 2001 2021 2041 2061 2081
80
60
40
20
0
-20
-40
-60
1961 1981 2001 2021 2041 2061 2081
Recharge anomaly (days)
Recharge anomaly (days)
60
40
20
0
-20
-40
-60
-80
1961 1981 2001 2021 2041 2061 2081
60
50
40
30
20
10
0
-10
-20
-30
-40
-50
1961 1981 2001 2021 2041 2061 2081
Drier soils at the end of the water year also mean that more precipitation is required for rewetting
to saturated conditions under which groundwater recharge or surface runoff is assumed
to occur. As a consequence, the length of the recharge season declines by up to 8 days in the
2050s and by as much as 14 days by the 2080s, compared with an average recharge season of 60
days between 1961 to 1990. In the River Loddon, autumn and winter recharge declines by 4 to
6% by 2050s, and by 3 to 10% by 2080s. The change for the River Kennet is not so consistent
with a 7% increase in recharge with little or no apparent change in the annual precipitation
under the Medium-Low Emissions scenario, suggesting that there has been a greater
concentration of precipitation during the active recharge period. In contrast, the 8% decline in
precipitation under the Medium-High Emissions scenario nets a 10% reduction of recharge by
the 2080s.
Finally, although runoff was not explicitly modelled in either case study it approximates
recharge in the long-run (assuming zero abstraction), suggesting that the annual resource might
change by between +7% (Kennet, Medium-Low Emissions) and –10% (Kennet and Loddon,
Medium-High Emissions) by the 2080s.