Lakshmi: Why is it raining so much?

Guest ColumnistFebruary 11, 2010 

Over the past few months, we in South Carolina have witnessed above normal rainfall. It rained 17 inches in October, November and December - twice the climate average. The rain has come down for days at a stretch and been a big factor in replenishing water stores in the state. Lakes and ponds are full, and rivers and streams are flowing fast.

We are in the middle of an El Nino. El Nino (Spanish for child Jesus) is the name given to a phenomenon that occurs every three to four years. It begins as warm waters appear off the coast of Peru during Christmas. This ocean warming impacts atmospheric convection and precipitation in many areas around the world. The rainfall follows the location of warmer waters, and there is an increased precipitation in the western coasts of North America, accompanied by lower precipitation in South East Asia and India. The sea level falls in the western tropical Pacific with the warmer water flowing eastwards. Coral reefs in the western tropical Pacific are exposed and subject to damage, and in the eastern tropical Pacific Ocean the lack of the upwelling water results in loss of nutrients off the coasts of Chile, damaging the fishing industry.

In the United States, El Nino results in above normal rainfall in the Southeast, Southwest and the Midwest and lower than normal precipitation in the Pacific Northwest. The West coast of United States suffers from torrential downpours like the ones seen in the Los Angeles area last week resulting in mudslides and flash flooding. The Pacific Northwest has not had much snowfall, which is forcing the Olympics organizers to alternate plans to make snow for some of the outdoor events in Vancouver.

In South Carolina, this excess wintertime precipitation will not only replenish the surface stores of water - lakes, ponds and rivers - but also add to the groundwater via infiltration. During winter there is less evaporation of water from the land surface and hence greater availability of this water for the spring growing season.

This El Nino closely resembles the 2002-2003 El Nino, which resulted in above normal rainfall for most of the 2003 calendar year except for the month of January. If this holds good, we will see more rain in February through May this year as compared to last year and the climate average.

In the past few years, South Carolina and the entire Southeast have suffered from multiple years of lower than normal rainfall, which had left large water storage bodies such as Lake Lanier at one point with less than a few weeks of water supply to the city of Atlanta. The shortage of water had resulted in legal disputes between Georgia, Alabama and Florida regarding water sharing, with Alabama and Florida contending that the state of Georgia and the city of Atlanta withdraw more than their share of water from Lake Lanier and thereby release less water into the Apalachicola River, which forms the Apalachicola-Chattahoochee-Flint river system. As El Nino results in an increase in the amount of water in the system, everyone will have more water, and this will lead to decrease in arguments in the courtroom!

Dr. Lakshmi chairs the Department of Earth and Ocean Sciences at the University of South Carolina.

The State is pleased to provide this opportunity to share information, experiences and observations about what's in the news. Some of the comments may be reprinted elsewhere in the site or in the newspaper. We encourage lively, open debate on the issues of the day, and ask that you refrain from profanity, hate speech, personal comments and remarks that are off point. Thank you for taking the time to offer your thoughts.

Commenting FAQs | Terms of Service