Water Resources Management - Practices of Irrigation and On-farm Water Management - page 185

water sphere directly, they may originate independently from the water sphere.
Often, the problems in the economic and political spheres are caused by the lack
of detailed information on good management of water resources or by differences
in perception of a fair and equitable share of the water resources.
5.6 Impact of Climate Change on Water Resource
The potential impact of global climate change is one of the least addressed factors
in water resources planning. Dealing with the potential threat of global warming has
increased the complexity of water resources planning in arid and semiarid regions.
Very large uncertainties are associated with both the magnitude and rate of change
of climate associated with any future global warming.
5.6.1 Issues on Water Resources in Connection to Climate Change
In dealing with the impacts of climate change on water resources, there are
essentially three issues to be determined:
(i) the future availability of water (water supply)
(ii) future demand of water (water demand)
(iii) the consequences of both of these on the environment
The possible impacts of climate change on water resources are described below:
5.6.1.1 Impact on Water Supply
Climate change has impacts on water resources and subsequently on the sustain-
ability of our environment. Global warming would accelerate the hydrologic cycle,
increasing both precipitation and evapotranspiration rates (Waggoner, 1990 ) . The
excessive (especially high intensity) rain can cause flash flood. Melting of polar
ice caused by increase in temperature and thermal expansion may causes sea level
rise. On balance, renewable water supply is likely to decline under global warming,
but uncertainties as to the likelihood of global warming and its regional hydrologic
implications present a dilemma for water planners.
5.6.1.2 Impact on Agricultural Water Demand
Since about 70% of the world water use is for irrigation, a change in climate affect-
ing water resources will have the greatest impact upon this sector. Irrigation water
use is affected primarily by potential temperature changes. Ali and Adham ( 2007 )
showed that if all other elements of weather remain constant, a 10% increase in
maximum temperature would result in 7.3% increase in crop evapotranspiration