The objective in developing a future climate series is to choose the set of global climate model (GCM) seasonal scaling factors that give the median change in mean annual precipitation in the Galilee subregion. There are 15 available GCMs as presented in Table 3 with seasonal scaling factors for each of the four seasons: summer (December–February), autumn (March–May), winter (June–August) and spring (September–November).
For each GCM the change in mean seasonal precipitation that is associated with a 1 degree global warming is calculated. These seasonal changes are then summed to give a change in mean annual precipitation.
The resulting changes in mean annual precipitation for a 1 degree global warming in the Galilee subregion are shown in Table 3 for each GCM. The 15 GCMs predict changes in mean annual precipitation ranging from –7.3% (i.e. a reduction in mean annual precipitation) to 6.4% (i.e. an increase in mean annual precipitation). The GCM with the median change is GFDL2.0. The corresponding projected change in mean annual precipitation per degree of global warming is a reduction of 3.1%, or about 17 mm. The seasonal scaling factors for GFDL2.0 are +6.0%, –10.4%, – 13.0% and –13.8% for summer, autumn, winter and spring, respectively. In other words, projected increases in precipitation in the wettest season, summer, are offset by projected decreases in the other three seasons.
Table 3 List of 15 global climate models (GCMs) and their predicted change in mean annual precipitation across the Galilee subregion per degree of global warming
The seasonal scaling factors associated with GFDL2.0 are used to generate trended climate inputs for the years 2013 to 2102. The trends assume global warming of 1 degree for the period 2013 to 2042, compared to 1983 to 2012. The global warming for 2043 to 2072 is assumed to be 1.5 degrees and the corresponding scaling factors for this period are therefore multiplied by 1.5. The global warming for 2073 to 2102 is assumed to be 2 degrees.
Scaling factors are applied to scale the daily precipitation in the climate input series that is generated for 2013 to 2102. The resulting annual precipitation time series for the Galilee subregion is shown in Figure 6. It depicts a cycle of 1983–2012 climate that is repeated a further three times but with increasingly trended climate change scalars. It can be seen that the decrease in precipitation from 2013 to 2102 is less than the typical interannual variability (Figure 6).
