Climate change with increasing temperature, and Spain, decreased precipitation will cause a decrease in water input and increased demand irrigation systems. The impacts of climate change on water resources, not only depend on the contributions yield the hydrological cycle, conditioned by the use and land cover, the temperature and time structure of precipitation, but is the system resources water available and how to handle a determining factor for the adequacy or shortage of water in front of global human needs. The water sensitivity to temperature increase and decrease in precipitation is very high, precisely in areas with high average temperatures and low rainfall. The most critical areas are the semi, which decreases contribution can be as high as 50% of the potential resources of the area. The temporal distribution of rainfall and temperature influences the generation of more body water, many times, that the same values ​​of these two climatic parameters.