A report released yesterday by the U.S. Climate Change Science Program (CCSP) - "Synthesis and Assessment Product 4.3: The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States" - shows that Arizona and adjacent areas of the Southwest and West will experience a 10-25% decrease in surface water runoff due to climate change, the worst in the nation. [below: median changes to runoff by USGS water resources regions. Numbers inside the regions are effectively a confidence measure. Fig 4.10 from the report]
Other impacts they report for this area include:
- Forests in the the Southwest are already being affected by climate change with increases in the size and frequency of forest fires, insect outbreaks and tree mortality. These changes are expected to continue.
- Increased drought conditions have occurred in the West and Southwest.
- Weeds grow more rapidly under elevated atmospheric CO2. Under projections reported in the assessment, weeds migrate northward and are less sensitive to herbicide applications.
- There is a trend toward reduced mountain snowpack and earlier spring snowmelt runoff in the Western United States.
- Invasion by exotic grass species into arid lands will result from climate change, causing an increased fire frequency. Rivers and riparian systems in arid lands will be negatively impacted.
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