Figure 3-5: Projected changes
in average annual water runoff by the year 2050, relative to average runoff for
the period 1961-1990, largely follow projected changes in precipitation.
Changes in runoff are calculated with a hydrologic model using as inputs climate
projections from two versions of the Hadley Centre AOGCM for a scenario of 1%
per year increase in effective CO2 concentration in the atmosphere:
(a) HadCM2 ensemble mean and (b) HadCM3. Projected increases in runoff in high
latitudes and southeast Asia, and decreases in central Asia, the area around the
Mediterranean, southern Africa, and Australia are broadly consistent across the
Hadley Centre experiments, and with the precipitation projections of other AOGCM
experiments. For other areas of the world, changes in precipitation and runoff
are scenario- and model-dependent.