OR/17/026 Appendix 4 - Change factors
| Mansour, M M, and Hughes, A G. 2017. Summary of results for national scale recharge modelling under conditions of predicted climate change. British Geological Survey Internal Report, OR/17/026. |
To summarise the plethora of results produced by the 11 ensembles, the results for each groundwater body have been summarised by choosing an extreme value (minimum or maximum) or median for monthly values for each ensemble (see Groundwater bodies for details). The aim is to present the minimum, maximum of the change factors for each ensemble for both the historic simulation and future climate scenarios. To demonstrate the baseline conditions the monthly minimum, maximum and media are presented for the historical simulation (Figure A15). Two sets of monthly summary plots are presented for the 2050s (Figure A16) and the 2080s (Figure A17).
A4.1 - Historical simulation
Figure A15 shows that there is a distinct recharge season within the historical simulation: for all three sets of plots (minimum, maximum and median) April to October show a significant proportion of England and Wales with very low or zero recharge. The recharge season can be thought of, therefore, November through to March. In general very little difference can be observed for each month between the minimum, maximum and the median values. This is understandable given that the aim of the historical simulation for each ensemble is to produce very similar rainfall and PE for the period between 1951 and 2009. This appears to be reflected in the recharge calculation.
A4.2 - Change factors for 2050s
Compared with the baseline, the plots for the 2050s (see Figure A16) show much more variation between minimum, maximum and median, which given that they represent a future predicted climate is understandable. The minimum change factor for the ensembles shows that the likely percentage change will occur between May to September, the months that for the historical simulation (Figure A15) show the lowest recharge. Of more interest are January and December where the minimum change factors are positive (light blue on the plots). This means that recharge is predicted to increase in some parts of the country whatever ensemble is chosen.
The maximum plots are mostly all positive values, again as would be expected, however May, June, August and September show negative values as their maximum which indicates that recharge is predicted to decrease whatever ensemble is chosen. However, these months have a very low recharge anyway and for only selected geographical areas.
The median percentage change values show three categories of responses: January, February, November and December are predominantly positive; May to September are predominantly negative and February, March and October as geographically mixed.
A4.3 - Change factors for the 2080s
The plots for the 2080s (Figure A17) shows a response that is very similar to that displayed for the 2050s (Figure A16). There are variations in geographical extent of the changes, reflecting subtle changes in rainfall patterns. Particularly for the median case January, February, November and December show a more definite positive signature.
