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Climate Change
CLIMATE
CHANGE AND THE WATER
The overwhelming scientific consensus is that
global warming - the rise in global temperatures caused by the buildup of
carbon dioxide and other emissions in the atmosphere that trap the sun's heat
like a blanket - poses a significant threat to our health, our economy, and our
environment.
Read on to learn what global warming means for
our rivers and water supply - and what steps we can take to meet the challenges
ahead.
Climate change is likely to have significant
impacts on the availability of fresh water.
Already in short supply throughout many parts
of the world, water for human consumption, agriculture, and industry will be a
major factor in economic growth, ecological sustainability, and global
conflict.
Research was undertaken to make initial
assessments of potential impacts of climate change on stream flow and water
balance in the western United States-a region characterized by the shortage of
water.
Additionally, research was conducted to
address the need for models, which account for the spatial magnitude and extent
of hydrologic processes.
The models need to handle key parameters such
as precipitation, soil moisture, and evaporation, in response to changing
climatic conditions.
The models must account for vegetation interactions
with soil moisture.
This is particularly important for simulating
regional vegetation response to climate change since vegetation distribution is
controlled in large part by the availability of soil moisture.
Research focused on developing and refining
detailed watershed scale hydrology models to address stream dynamics and water
storage.
Regional-scale modeling research was directed
toward developing physically and mechanically-based water balance models, which
can be spatially distributed at watershed, regional, and continental scales.
The research effort contributed to developing
methods for spatially distributing climatic data at scales appropriate for the
models, and providing these data bases to the climate change research
community.
This ORD project has been completed;
extensions of this research are continuing within the US Geological Survey.
So what does all this data and modeling mean?
The increasing demand for
water by population and industrial growth is creating chronic water shortages
throughout the world (Revenga
2000).
Add to this the potential impacts of global
climate change on water supplies and chronic shortages could reach crisis
levels.
Throughout much of the western United States
the supply of water for human consumption, agriculture, and industry depends on
snow pack and reservoir storage.
Most global climate warming scenarios suggest
warmer winters with more rainfall and less snowfall for much of the western
United States, which would substantially reduce snow accumulation and shift the
high flow season for many rivers from the spring to the winter (Lettenmaier et. al. 1992).
A substantial amount of the natural storage of
winter precipitation that presently occurs in the snow pack would be lost
resulting in increased spills in the winter and lower reservoir levels in the
summer and fall (Lettenmaier
and Sheer 1991).
A significant increase in flood hazard in the
western US could result from climate change, primarily due to an increase in
rain-on-snow events (Lettenmaier
and Gan Water 2 1990).
Such events occur when warm, wet storms move
over existing snow pack.
Rapid melting of the snow pack is the result
of a combination of warm air temperature, high wind and high humidity, which
cause significant condensation on the snow, and is particularly severe in
forest openings and forest clear-cuts (Marks et al. 1998).
This research suggests that some mitigation of
the adverse effects of global climate change may be achieved by adapting land
and water management practices to changes in runoff patterns and maximizing the
protective effects of natural vegetation.
Global climate changes are expected to be
regional in nature, and affect land cover and land use.
Key to understanding such regional effects on
water supplies is the response of vegetation. Plant communities play a
significant role in regional energy and water balance.
While hydrologic models designed to simulate
large river systems are good for operating reservoirs systems, they are not
adequate for predicting changes to regional water balance and, hence, changes
in regional vegetation (Marks
et al.1993).
Dolph et al. (1991) developed a spatially
distributed regional water balance model to evaluate the sensitivity of large
river basins to climate change.
The model was exercised for the Columbia River
Basin.
This research demonstrated that the existing
Historic Climate Network of climate monitoring stations underestimate
precipitation primarily because mountainous areas are underrepresented.
With climate warming, the model predicted increased
evaporative loss, decreased runoff and soil moisture.
These conditions could have profound effects
on vegetation distribution and subsequently regional water resources.
The ability to predict changes in regional
vegetation is necessary to evaluate the effects of climate change on forest
resources, agriculture, and water supplies.
Changes in soil moisture and
evapo-transpiration resulting from climate will have large impacts on water and
vegetation.
If changes in the regional water balance are
significant, major shifts in vegetation patterns and condition are a likely (Marks et al. 1993).
Neilson and Marks (1994) incorporated a
distributed water balance model with a vegetation model to produce a
biogeographic model, MAPSS (Mapped Atmosphere-Plant-Soil System).
This model was used to predict changes in
vegetation leaf area index, site water balance and runoff as well as changes in
biome boundaries.
When applied to potential climate change
scenarios, two areas exhibiting among the greatest sensitivity to drought-
induced forest decline were determined to be eastern North America and Eastern
Europe to western Russia.
How will global warming affect rivers in these
and other areas? Global warming is projected to have far-ranging effects on
rivers across the United States and worldwide.
Although these changes will vary from region
to region, scientists expect higher average global temperatures over the next
century to cause higher river temperatures, resulting in harm to freshwater
fish like salmon and bass and significant changes in aquatic plant and animal
habitat.
In addition, rainfall patterns will shift
-some areas will get more precipitation, some less.
Higher temperatures will cause mountain snowpack
to melt earlier in the year, causing significant changes to river flow patterns
- with less water available during the warmer and drier summer months.
Changing water levels in our rivers poses
greater challenges for farming, manufacturing, drinking water supplies and
wildlife habitat.
The supply of and demand for water will be
affected dramatically by these changes, as regions of the country that
currently have wet climates are expected to become drier and vice versa.
Some places may experience prolonged periods
of drought, while others could see a dramatic increase in rainfall and more
frequent flooding.
These changes will have significant
implications for a wide range of water uses, including agriculture, industry,
energy production, recreation, water infrastructure/storage, waste disposal,
and of course, healthy watershed functions.
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