Water Resources impacted by Climate Change?

Implications of climate change on the Earth's Hydrologic Cycle are slowly coming into focus but the underlying phenomenon are still not well understood. Any assessment of climate change impact on water supplies are, thus, only our attempt to err on the 'safe' side for humanity and nature's ecosystems.


The Greenhouse Effect

Source - ucar.edu

If the greenhouse effect can be attributed to a single event, this event happened in 1988. Scientists, seeking to explain a series of unusually warm years, were able to link for the first time in 1988, the increase in atmospheric temperature to the retention of long-wave radiation (received in sunlight) in the atmosphere. Further research linked this increase in retention to an increase in greenhouse gasses that include Carbon dioxide, water vapor, nitrous oxide, methane and chlorofluorocarbons.
(As addition of carbon dioxide fuels increase in all the greenhouse gases, we are developing ways to reduce human carbon dioxide emissions)
Predicting Climate
We all know too well how difficult it still is for us to predict tomorrow's weather. 
Our difficulty is simply due to our lack of understanding on how the vast number of processes and their feedback cycles, come together to make the weather we experience.
Climate Change
As we don't really know how to predict the impacts of climate change, we have developed the approach of trying to understand (and model) historical data on temperature rises and the amount of greenhouse gases in the atmosphere. So, using the historical record as a 'given' we are measuring the increase in amount of greenhouse gases to assess what climate we should expect
Pinpointing Impacts of Climate Change
Climate change is expected to cause rapid changes in temperature, precipitation and concentrations of greenhouse gases (water and Carbon Dioxide). To predict the direction of these changes (i.e. will the result be a flood or a drought?) we make models to represent nature's complex ecosystems. The conclusions we reach are only as good (i.e. as closely representing the functioning of the ecosystem) as the models we can make.
Keeping in mind that our conclusions on the impact of climate change on water resources is only as good as the models we make, 

Rainfall is THE Concern

Source - loadstorm.com

Numerous computer model-based assessments have raised concerns of BIG changes in the amounts of rainfall.

• In high latitudes areas (in equatorial Africa and Asia, in Southeast Asia) annual rainfall is projected to dramatically increase, while in mid-latitudes and in most subtropical regions rainfall is expected to decrease. 
• A general reduction in precipitation of snow is expected to reduce the amount and duration of snow cover

Additional implications of reduced or unanticipated rainfall can also be postulated:

• If we pollute more and more water, less rainfall implies that the concentration of pollutants in our water supply will remain higher longer
• As we use an enormous volume of water to generate electricity and cool thermal power plants, any reduction in rainfall will only increase pressure on water supplies
• Current levels of irrigated food production will have inadequate amounts of irrigation water (for example, in the dry US West) leading to reduction in food supplies - some studies predict a drop in USfood production by 30% for a 3 Degree Centigrate increase in air temperature.
• And ..........

Maybe, the solution is to develop ways to extract both water vapor and carbon dioxide from the atmosphere!!