Water is a critical resource, exerting fundamental influences on many dimensions of human activities and ecosystems. In response to issues of climate change and how the climate changes may influence human activities and ecosystems, most people are no longer asking ‘is climate change occurring?’ but instead, are asking ‘by how much? ’.
One of the challenges we are facing is to understand how climate change will influence the hydrologic cycle and, ultimately, influence human activities and ecosystems. We expect significant increases in average air temperatures, increased intensities and frequencies of flood occurrences, and declines in low seasonal river flows and lake levels are considered likely, all of which may translate to widespread implications to humans and the environmental ecosystem impact.
This paper describes various types of evidence that are already available, and adds to the evidence from historical/measured trends, some indications as to the nature of predicted changes that are likely to evolve over time. Specific examples of the climate change impacts that are evident include:
a) trends of increasing temperatures are widespread and pervasive
b) increasing trends of precipitation are evident
c) for some locales, the impact will be increasing desertification whereas for others, more flooding
A number of case studies are used to demonstrate historical evidence and computer model projections demonstrate that historical trends will likely continue.