rainfall

Spin Cycle: Attributing Louisiana Floods to Global Warming

The Spin Cycle is a reoccurring feature based upon just how much the latest weather or climate story, policy pronouncement, or simply poobah blather spins the truth. Statements are given a rating between 1-5 spin cycles, with fewer cycles meaning less spin. For a more in-depth description, visit the inaugural edition.

In mid-August a slow moving unnamed tropical system dumped copious amounts of precipitation in the Baton Rouge region of Louisiana. Reports were of some locations receiving over 30 inches of rain during the event. Louisiana’s governor John Bel Edwards called the resultant floods “historic” and “unprecedented.”

Some elements in the media were quick to link in human-caused climate change (just as they are to seemingly every extreme weather event). The New York Times, for example, ran a piece titled “Flooding in the South Looks a Lot Like Climate Change.”

We were equally quick to point out that there was no need to invoke global warming in that the central Gulf Coast is prime country for big rain events and that similar, and even larger, rainfall totals have been racked up there during times when there were far fewer greenhouse gases in the atmosphere—like in 1979 when 45 inches of precipitation fell over Alvin, TX from the slow passage of tropical storm Claudette, or in 1940 when 37.5 in. fell on Miller Island, LA from another stalled unnamed tropical system.

But we suspected that this wouldn’t be the end of it, and we were right.

Six Decades of Temperature and Precipitation in Kentucky

Air temperature and precipitation, in the words of Chattopadhyay and Edwards (2016), are “two of the most important variables in the fields of climate sciences and hydrology.” Understanding how and why they change has long been the subject of research, and reliable detection and characterization of trends in these variables is necessary, especially at the scale of a political decision-making entity such as a state.

A Century of Precipitation Trends in Victoria, Australia

In the debate over CO2-induced global warming, projected impacts on various weather and climate-related phenomena can only be adjudicated with observed data. Even before the specter of dreaded global warming arose, scientists studied historical databases looking for secular changes or stability. With the advent of general circulation climate models, using historical data, scientists can determine whether any observed changes are consistent with the predictions of these models as atmospheric carbon dioxide increases.

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