What causes a drought like the exceptional Southeastern Drought of 2007?
Droughts are not headline grabbers like tornadoes, blizzards, hurricanes, heat waves, etc. They are slowly building events that will make the news once water levels reach critical levels or farmers suffer crop losses. Droughts can have more of an overall impact since they last so much longer than the other events. There are several reasons why a drought occurs. Iím going to describe the drought of the Southeastern United States which has peaked in 2007. The Southeast normally receives some of its yearly rainfall from tropical cyclones or the remnants of these storms. During 2006 and 2007, very little rainfall was attributed to tropical cyclones. More importantly, a persistent high pressure ridge has been present over the Southeast. This ridge has several names. Iíve seen it referred to as the Great Smokies Ridge, The Southeastern Ridge, for example. This high pressure ridge has caused subsidence in the atmosphere and has prevented widespread, frequent rainfall which normally occurs over the Southeastern states. It has also prevented low pressure areas from approaching the Southeast and has steered them west up through the Mississippi Valley. Alabama has been especially hard hit as well as Georgia, North Carolina, Virginia and Tennessee. Another reason for the drought is the lack of low pressure storms (or extra-tropical cyclones) during the colder months of the year. Normally, low pressure areas develop near the Gulf States and they move eastward or northeastward through the Southeast dumping huge amounts of rain. There havenít been many such storms during 2006 and 2007. La Nina plays a role in the dry weather pattern as it changes the weather patterns across North America. La Nina is a term used for the unusually cold water temperatures of the Eastern Pacific near the Equator. Some effects of the drought are as follows: Lake levels have dropped drastically, river levels have dropped to record lows, water supplies are threatened, trees are suffering, wells dried up, crops have failed, etc, etc. Is this drought caused by global warming? That is a question that really cannot be answered right now.