Wildfires following winter drought in Bolivia, September 2010
Source: NASA Earth Observatory
After three weeks in London where drought is not a problem at the end of the wet summer of 2010, late last week we returned to sere lawns and shriveled bushes and plants in Fairfax. 2010 was a wetter than normal year in northwestern and north-central Europe with above average rainfall in many places and flooding in several places in Poland and nearby countries even as it produced a severe drought in European Russia. The Russian drought has already been discussed here, and grain prices in world markets have escalated as a consequence. The mid-Atlantic Region, though at a much less severe level than European Russia, is in the midst of a drought.
Last Friday I got a weather advisory warning of the possibility of wildfires in the vicinity of Washington, DC. Over the past week a large wildfire has burned near Boulder, CO, destroying some houses and threatening to destroy others. One expects such fires in arid zones and especially in semi-arid zones like the eastern flank of the Front Range in Colorado where rainfall is adequate for the growth of forest but drought is common. Wildfires and drought are much rarer on the East Coast of the US. Subsequent rains and the cooler days of autumn have reduced the fire danger, but it is sobering to realize that drought-induced wildfires are possible anywhere, even in normally humid places.
Because much of its water supply is "run of river" rather than centered on storage reservoirs, the Washington, DC area is particularly susceptible to water shortages when rainfall is below average and the flow of the Potomac is low. A drought watch has been declared for the region following an abnormally hot and dry summer. Rainfall in July seemed to break the drought of early summer, but August was far below long-term average rainfall, and the year to date is well below the expected rainfall. High temperatures made the situation worse, for evaporation and transpiration rates rise with temperature. A drought watch is now in effect in the Washington area, and it could remain in place for the remainder of the summer and through the autumn, especially as October is normally a drier month than August or September.
Wildfires in south central South America, late August 2010
Source: NASA
A more interesting drought is the ongoing one in the Amazon basin, especially the southwestern edge of that Basin in Brasil and Bolivia. With normal rainfall of 100-400 cm or more per year, the area is too damp for large wildfires much of the time. There is a distinct dry season in the southern hemisphere winter, and some agricultural burning is normal toward the end of that season. In the abnormally dry winter of 2010 many of those agricultural fires grew to substantial size, and much of the south central portion of the Amazon basin has been plagued with a smoke pall since August. The dry weather has also resulted in reduced river flows in both the Amazonian and Paraná basins.
