2. Potential impacts of Climate change on water resources
a. Melting glaciers
As the increasing greenhouse gases emission in the global world, the global warming is predicted to raise
continuously in the future. Between1901 to 2005, global annual temperature has sown an increase in 0.3
to 0.5°C per decade (Trenberth et al, 2007). As a result of the warming world, the consequent ice melting
and rising sea level may impact the global water resources in both supply and demand sides.
In a warmer environment, the precipitation as snow may decrease and the winter snow may melt earlier in
spring in snow-dominated regions (Barnett et al, 2005). Glaciers is sensitive to the temperature. As the
temperature drop as the latitude increase. In tropical area, accumulation of snow may occur in mountain.
In these mountains, there are two parts- accumulation zone (higher latitude) and ablation area (lower
latitude). The accumulation area is the major zone of glacier build-up while the snow accumulated in
ablation area would turn to be source of melt water in summer and autumn (Chevallier et al, 2010). These
two areas are separated by equilibrium line. As the temperature increase, the equilibrium line may
increase; as a result, melting water from accumulation area may be the additional water discharge into the
river (Chevallier et al, 2010). The additional water may increase the water supply in the short run, but not
in the long run. In the long term, the melt water discharge into the river basin may gradually decrease
while the water reservoir represented by the glaciers become empty, the discharge of the whole basin may
decrease and water supply may decrease as a result (Barnett et al. 2005). The flow of river channels from
glaciers dominated into rain and snow dominated (Chevallier et al, 2010).
Climate change may lead to a shifting peak of river runoff to winter and earlier spring while initially in
summer and autumn which are the period that water demand is the highest (Barnett et al, 2005).
However, the earlier influx of water discharge may exceed the reservoir volume and ultimately the water
may pour to the ocean (GRACE Communication Foundation, 2018). For instance, in the western USA, the
reduction in mountain snow pack and shift in seasonable stream-flow by 2050, the spring river runoff
maximum may come one month earlier in the year; However, capacity of the reservoir storage would not
be able to handle the amount of the sifting maximum runoff and this water may end up going to ocean
(Chevallier et al, 2010).
While uncertainty of precipitation under climate change, there are still negative impacts. If less rain falls
occurs, water availability may decrease. If more rain falls and the reservoir storage capacity is much less
than the annual runoff, the excessive runoff may enter to the ocean ultimately (Barnett et al, 2010). Also,
according to the figure one, surface runoff and snow of all given snow-dominated regions are estimated to
decrease. These suggest that climate change may increase the water supply in the short term and it will
turn to a decrease trend in the long term. It shows a long-terms water stress in these areas.
b. Rising sea level
According to the figure 2a and 2d, from 1990 to 2000, the
Arctic summer sea ice extent has been declining while the
global average sea level has been increased for 175mm.
the rising global temperature provide a warmer
environment which restrict the formation of sea ice
content and also the temperature have led to the melting
of ice sheets and glaciers. These increase the sea level.
Referring to the figure 2, the global average upper ocean
heat content has been increased significantly. While the
particle density may decrease while the temperature
increase, therefore, the increase in surface ocean
temperature may lead to the ocean expansion. Rising sea
level is the consequence of these two factors (NASA,
2018). The sea-level-rise may lead to the intrusion of sea
water in the coastal area while the sea level is higher than
the land water table. Also, when the sea level is higher
than river level, the intrusion of sea water may also occur.
Which salinized the ground water resources and the river
water and decrease the fresh water supply.
c. Accelerating spatial variability of precipitation
Referring to the figure 3, there is an inconsistent
distribution of change in precipitation globally. Some of
the regions are estimated a decrease in precipitation but
some are estimated an increase in precipitation. A
significant increase in precipitation is predicted in nearpolar
latitude. These show a spatial variability of
precipitation. Projected 1.5°C to 4.5°C increase in global
mean temperature would result in 3% to 5% increase in
global mean precipitation while which is expected to
occur in higher latitudes, especially in winter. However,
even higher precipitation input, decline in runoff may
occur due to higher evaporation rates. Increased
evaporation and decreased precipitation may give rise to run off reduction in some lower latitude basins.
For instance, referring to the table 1, there are five river basins in semiarid regions, even though all of
these rivers have no change in precipitation, the mean annual runoff still present a decline trend. Also, a
majority of semiarid basin show the decline in annual runoff. In these semiarid and some arid area, as the
precipitation is estimated to decline and the evapotranspiration is estimated to increase, the severity and
frequency of drought may be expected to increase as a result. Therefore, these regions are sensitive to the
3. Potential impacts of human activities on water resources
a. Construction of dams and reservoirs
b. Ground water extraction
c. Land use change (Agriculture)
d. Water transfer projects
(GRACE Communication Foundation, 2018)