Stagnant Storm Drains
Over the last 40 years in the eastern U.S., there has been an increase in the frequency during warm months of 30-day periods when there is no rain. These dry spells now occur about twice as often as they did in the 1960′s. Rainfall events push water through municipal sewer and storm water systems. During dry spells, standing water sits in these systems and provides the ideal breeding ground for southern house mosquitoes, which carry West Nile Virus. Less rain, however, generally means fewer small plots of standing water (such as in used tires), where the Asian tiger mosquito, which probably only occasionally carries West Nile Virus, breeds.
(Source: Kaiser, Jocelyn. Drought Portends Mosquito Misery.”" Science 301 (2003): 04 and Omahen, Sharon. “Drought drives mosquito numbers high.” Online posting, 3 October 2007. Georgia Faces: The University of Georgia College of Agricultural and Environmental Service. 17 June 2008 and Groisman, PY and Knight RW. “Prolonged Dry Episodes over the Conterminous United States: New Tendencies Emerging during the Last 40 Years.” Journal of Climate 21 (2008): 1850-1862 .)