15rsta.royalsocietypublishing.orgP h i l .T r a n s .R .S o c .A376:20160452 ........................................................
IPSL-CM5A-LR GFDL-ESM2M HadGEM2-ES
IPSL-CM5A-MR
–75 –50 –10 –1 0 1 10 50 75
%
ensemble mean
MIROC-ESM-CHEM ACCESS1-0
Figure9. Changesinrun-offformeanflowssimulatedbytheJULESecosystem–hydrologymodelundersixclimatesimulations
at2°Cglobalwarming.( a)Ensemblemeanand( b)percentageofmodelsagreeingonincreasedflow.
and 75%, especially in the Iberian Peninsula. Southern Africa also sees a decrease in low ﬂows
where changes in mean ﬂows were small. Changes in high run-off show similar patterns and
magnitudes to those in mean run-off.
The simulated changes in both mean and low run-off ﬂows show substantial differences
among the six simulations (ﬁgures 10 and 11). In most basins examined here, the range of
outcomes include both increases and decreases in mean and low ﬂows for any particular basin,
but generally with the largest proportion simulating increases in both mean and low ﬂows. In a
few cases, notably the Lena in northeast Asia and Ganges in southeast Asia, the ensemble agreed
entirely or almost entirely on increased ﬂows. Even here, the range of outcomes is large, with the
projected ﬂow increases in the Ganges for 2°C global warming ranging from approximately 30%
to more than 110%.
Exceptions to the general picture of consensus on increasing ﬂows are seen in the Amazon,
Orange, Danube and Guadiana basins where the range of projected extends more towards
decreased mean ﬂows. Mean ﬂows in the Amazon are projected to decline by up to 25% for 2°C
global warming. For low ﬂows, the ensemble of projections entirely gives decreased ﬂows at 2°C
global warming for these basins.
The signal of decreased ﬂows was stronger for low ﬂows than mean ﬂows, and indeed in the
Niger, the range of mean ﬂow changes extended more towards increases whereas the range of
low ﬂow changes extended more towards decreases.
(b) Impactsat1.5°Cglobalwarmingcomparedto2 °C
For almost all quantities and simulations examined here, global-scale changes in extremes and
run-off at 1.5°C global warming ( table 6 ) are smaller than those compared to 2°C ( table 5 ;
ﬁgures 12 and 13). The exceptions to these are mean and low run-off which each show one
instance of a smaller change at 2°C than 1.5°C, but still with a majority of simulations showing
larger changes at 2°C (ﬁgure 13). For temperature-related indices, the ranges of change at the two
GWLs do not overlap—the change at 2°C in all members is larger than the change at 1.5°C in