There are apparent trends in streamflow volumeboth increases and decreasesin
many regions. These trends cannot all be definitively attributed to changes
in regional temperature or precipitation. However, widespread accelerated glacier
retreat and shifts in streamflow timing in many areas from spring to winter
are more likely to be associated with climate change.
The effect of climate change on streamflow and groundwater
recharge varies regionally and between scenarios, largely following projected
changes in precipitation. In some parts of the world, the direction of change
is consistent between scenarios, although the magnitude is not. In other
parts of the world, the direction of change is uncertain.
Peak streamflow is likely to move from spring to winter
in many areas where snowfall currently is an important component of the
Glacier retreat is likely to continue, and many small glaciers
Water quality is likely generally to be degraded by higher
water temperature, but this may be offset regionally by increased flows.
Lower flows will enhance degradation of water quality.
Flood magnitude and frequency are likely to increase in
most regions, and low flows are likely to decrease in many regions.
Demand for water generally is increasing as a result of
population growth and economic development, but it is falling in some countries.
Climate change is unlikely to have a large effect on municipal and industrial
demands but may substantially affect irrigation withdrawals.
The impact of climate change on water resources depends
not only on changes in the volume, timing, and quality of streamflow and
recharge but also on system characteristics, changing pressures on the system,
how the management of the system evolves, and what adaptations to climate
change are implemented. Nonclimatic changes may have a greater impact on
water resources than climate change.
Unmanaged systems are likely to be most vulnerable to climate
Climate change challenges existing water resources management
practices by adding additional uncertainty. Integrated water resources management
will enhance the potential for adaptation to change.
Adaptive capacity (specifically, the ability to implement
integrated water resources management), however, is distributed very unevenly
across the world.