Changes in the climatology of precipitation, evapotranspiration, and soil m
oisture lead also to changes in runoff and streamflow. The potential effect
s of global warming on the hydrology of 23 major rivers are investigated. T
he runoff simulated by the Canadian Cetre for Climate Modeling and Analysis
(CCCma) coupled climate model for the current climate is routed through th
e river system to the river mouth and compared with results for the warmer
climate simulated to occur towards the end of the century. Changes in mean
discharge, in the amplitude and phase of the annual streamflow cycle, in th
e annual maximum discharge (the flood) and its standard deviation, and in f
low duration curves are all examined. Changes in flood magnitudes for diffe
rent return periods are estimated using extreme value analysis. In the warm
er climate, there is a general decrease in runoff and 15 out of the 23 rive
rs considered experience a reduction in annual mean discharge (with a media
n reduction of 32%). The changes in runoff are not uniform and discharge in
creases for 8 rivers (with a median increase of 13%). Middle- and high- lat
itude rivers typically show marked changes in the amplitude and phase of th
eir annual cycle associated with a decrease in snowfall and an earlier spri
ng melt in the warmer climate. Low-latitude rivers exhibit changes in mean
discharge but modest changes in their annual cycle. The analysis of annual
flood magnitudes show that 17 out of 23 rivers experience a reduction in me
an annual flood (a median reduction of 20%). Changes in now duration curves
are used to characterize the different kinds of behavior exhibited by diff
erent groups of rivers. Differences in the regional distribution of simulat
ed precipitation and runoff for the control simulation currently limit the
application of the approach. The inferred hydrological changes are, neverth
eless, plausible and consistent responses to simulated changes in precipita
tion and evapotranspiration and indicate the kinds of hydrological changes
that could occur in a warmer climate.