Changing Precipitation Patterns - Drought and Wildfire
Global warming is also impacting drought and wildfire patterns around the world, with notable regional differences. The IPCC says that some regions of the world have experienced more intense and longer droughts (southern Europe and West Africa in particular) while other areas such as central North America and northwestern Australia have seen less frequent, less intense or shorter drought events.
Areas that see diminished precipitation will face water shortages. Other areas supplied from glacial sources will face the same problem to a greater severity. This has obvious implications on water resources management. For example, areas of the Colorado Basin are already facing water shortage issues. For some urban and suburban areas, the increasing footprint of the built landscape reduces the area of groundwater recharge zones, limiting the replenishment of aquifers coupled with decreasing annual precipitation.
Irrigation and agricultural interests face some particularly severe challenges and these issues will become more severe under global warming. The southern plains of the United States are at risk, and the threat is even higher for parts of Asia, including the Indian interior and parts of the China mainland. Viability of agricultural activity is and will be a concern for such areas by the 2050s.
Another hazard imposed by drought conditions is that of wildfire. With a longer growing season, diminished snowpack and less precipitation, the fire hazard will increase. Fire probability is enhanced by hot 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 under global warming. In fact the IPCC has noted that the wildfire season in western regions of the United States has increased by about 78 days in the last three decades. (1)
Under global warming, tropical cyclone frequency is projected to either remain unchanged or decline on a worldwide basis (including the Atlantic basin). Tropical cyclone intensities are projected to increase, however. The significant variability in tropical cyclone frequency and intensity will remain from year to year, making trend detection difficult.
Under global warming, the number of extratropical cyclones is expected to decrease. However, the intensity of these cyclones is likely to increase. There is evidence that Northern hemisphere mean storm tracks have already moved toward the poles. (2)
The incidence of severe convective storms is not expected to change under global warming and no observable trends have been detected in either tornado or hail climatology. The tornado events of 2011 are not attributable to climate change nor can they be identified as a trend. (3) In fact, the 2011 season was followed by one of the quieter seasons on record.
These IPCC assessments are at the forefront of scientific research and new advances are underway with the upcoming IPCC fifth assessment report, representing the consolidation and appraisal of climate change research from recent years.
1. IPCC AR4, 2007 - Working Group II, Section 14.2.2.
2. Ulbrich et al., 2009; IPCC AR4, 2007.
3. Doswell et al., 2012.