Changing weather patterns will cause changes to precipitation characteristics worldwide. According to the IPCC (IPCC SREX, 2012), “there is medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions, droughts have become less frequent, less intense, or shorter, for example, in central North America and northwestern Australia.”
By the end of the century, GCM projections indicate that the number of days between precipitation events will increase for the broader areas of:
• Southern Australia
• Southeast Asia and India
• Asia Minor
• Southern Europe
• Northern, west-coastal and southern Africa
• Northeastern South America and coastal west South America
• Central America and western North America
The effects on soil moisture could be particularly acute in the U.S. south central plains as well as southern Europe, raising significant issues for agricultural interests in these areas by the 2050s. Increasing periods between rainfall events places stress on soils, limiting the capacity for agricultural activity. In extreme cases, affected areas can essentially become deserts.
Areas that see diminished annual precipitation will face water shortages. Other areas with water supply mainly from glacial sources will face the same problem to a greater severity due to glacial retreat. This has impacts for water resources management. For example, areas of the Colorado Basin in the United States and some Himalayan watersheds are already facing water shortage issues. For urban and suburban areas, the increasing footprint of the built landscape reduces the area of groundwater recharge zones, limiting the replenishment of aquifers. This compounds the problem for areas affected by decreasing annual precipitation.
Another hazard imposed by drought conditions is that of wildfire. With a longer growing season, diminished snowpacks and diminished precipitation, the wildfire hazard will increase. Fire probability is enhanced by warmer temperatures, lower relative humidities and greater wait times between rainfall events. As vegetation becomes dry under these conditions, it is more prone to ignition by random sources and more likely to spread with an increase in surrounding dry fuels. The wildfire hazard in areas already facing such a threat will see an increase in severity of this threat under global warming. In fact, the IPCC has noted that in the last three decades, the wildfire season in the western United States has increased by about 78 days (IPCC AR4, 2007 - Working Group II, Section 14.2.2).
Long-term adaptation strategies for the drought hazard include land-use planning that permits rainwater catchment, and preserves groundwater recharge zones and the deployment of sustainable agricultural practices. Under extreme cases, agricultural interests may be forced to relocate if soils no longer permit a viable growing season. The wildfire threat can be reduced by housing modification, increased separation distance between the home and adjacent forests and thinning of fuels on the property itself.