A slow-moving storm system, fed by unusually warm seas in the Gulf of Mexico, began on August 7 to unleash heavy rains in the Southeastern United States.
From Tuesday, August 9 through Sunday, August 14 the storm inundated Louisiana, Mississippi, Alabama, Florida and Texas, killing three people.
Five cities in Louisiana have reported rainfall totals of over two feet.
On August 11, a measure of atmospheric moisture, precipitable water, was in historic territory at 2.78 inches, a measurement higher than during some past hurricanes in the region.
Increased moisture in the air and unusually heavy rainfall are classic signals of climate change.
As the world warms, storms are able to feed on warmer ocean waters, and the air is able to hold and dump more water.
These trends have led to a pronounced increase in intense rainfall events and an increase in flooding risk.
In the Southeastern US, extreme precipitation has increased 27 percent from 1958 to 2012.
Southeastern US sees extreme rainfall, a classic signal of climate change
Perry, Florida, saw 4.5 inches of rain in just two hours on August 8, and Hatch Bend, Florida, reported up to 12.4 inches of rain from Sunday until 9am on Monday.[1]
From Tuesday, August 9 through Sunday, August 14, the slow-moving storm inundated Louisiana, Mississippi, Alabama, Florida and Texas, killing at least three people.[2]
Five cities in Louisiana have reported over two feet of rain, with Watson, Louisiana, topping the list at 31.39 inches.[3]
The town of Lafayette, in the heart of the wettest part of the storm, reported 10.39 inches of rain on Friday, setting the town's record of wettest day until Saturday topped that at 10.40 inches.[4]
Record flooding has been observed on at nine river gauges in Louisiana.[12]
One of the clearest changes in weather globally and across the United States is the increasing frequency of heavy rain.[5]
A warmer atmosphere holds more water vapor. And like a bigger bucket, a warmer atmosphere dumps more water when it rains.
The storm in the Southeastern US was supercharged by running over a warmer ocean and through an atmosphere made wetter by global warming.
Climate change is now responsible for 17 percent of moderate extreme rainfall events, i.e. one-in-a-thousand day events.[6]
The more extreme the event, the more likely climate change was responsible, as climate change affects the frequency of the extreme events the most. In the instance of a one-in-a-thousand year event, the odds that climate change was responsible is dramatically higher.[6]
High sea surface temperatures feed moisture and energy into storms
On August 7, sea surface temperatures in the Gulf hovered near 90°F (32°C) at temperatures 3.6°F-5.4°F (2-3°C) above average.[7][8]
Along the central Gulf Coast, a measure of atmospheric moisture (from the surface up to the jet stream level) known as precipitable water is in the top percentile of historical values (3 to 3.5 standard deviations above normal).[9]
In New Orleans, the precipitable water was determined to be 2.78 inches Wednesday, which ranks among the top-five highest levels on record in August.[10]
As the world warms, storms are able to feed on warmer ocean waters, and the air is able to hold and dump more water.
Extreme rains and floods are consistent with climate change trends
Since the 1980s, a larger percentage of precipitation has come in the form of intense single-day events, and nine of the top 10 years for extreme one-day precipitation events have occurred since 1990.[11]
In the Southeastern US, extreme precipitation has increased 27 percent from 1958 to 2012.[5]
Discover how Climate Signals are related
This tree of climate signals illustrates factors that link this event to climate change.
Greenhouse Gas Emissions
Greenhouse gases from human activities—mainly the burning of fossil fuels like coal and gas—are likely responsible for all the observed warming since 1950. The fundamental physics of heat trapping greenhouse gases has been understood since the nineteenth century. Scientists have understood since the late 1970s that humans—by increasing the atmospheric concentration of greenhouse gases from 280 parts per million in preindustrial times to what is now over 400 ppm—have effectively wrapped the Earth in a thicker blanket, trapping more of the Earth’s infrared energy close to the surface.
Global Warming
From 1880 to 2012, the Earth warmed by 1.5°F (0.85°C) reversing a long term cooling trend. The physics behind the Earth’s temperature imbalance is simple. Scientists first realized that gases in the atmosphere cause a greenhouse effect in the 19th century and have known since the late 1970s that humans are now driving this effect, trapping more of the Earth’s infrared energy close to the surface through fossil fuel emissions. The atmospheric concentration of greenhouse gases has increased from 280 parts per million in preindustrial times to what is now over 400 ppm.
Increased Sea Surface Temperature
The amount of heat absorbed by the oceans has surged in the past few decades, contributing to more intense storms, sea level rise, sea ice melt, storm surge flooding and widespread ecosystem change.
Increased Atmospheric Moisture
A warmer atmosphere holds more moisture—about 7 percent more per 1°C of warming—and scientists have already observed a four percent increase in atmospheric moisture due to the air’s ability to hold more moisture as it warms. Storms supplied by climate change with increasing moisture are widely observed to produce heavier rain and snow. Increased atmospheric moisture content may also affect the El Niño Southern Oscillation, which is a major driver of interannual climate variability, by intensifying regional precipitation variability, and associated extreme precipitation and drought events. Research indicates that the increase in atmospheric moisture is primarily due to human-caused increases in greenhouse gases.
Increased Extreme Precipitation
Global warming leads to an increase in both ocean evaporation into the atmosphere and the amount of water vapor the atmosphere can hold. High levels of water vapor in the atmosphere in turn create conditions more favorable for heavy precipitation in the form of intense rain and snow storms.
Increased Flooding Risk
Heavy precipitation is contributing to increased flooding around the world. Flooding is worsened by regional climate trends such as increases in heavy rain and snow, early snowmelt, and increased seasonal precipitation. Flooding is also affected by non-climatic factors such as land development, deforestation, levee placement and local topography, making it challenging to determine an overarching climate signal in flood trends.
Gulf Storm August 2016
A slow-moving storm system, fed by unusually warm seas in the Gulf of Mexico, began on August 7 to unleash heavy rains in the Southeastern United States. From Tuesday, August 9 through Sunday, August 14 the storm inundated Louisiana, Mississippi, Alabama, Florida and Texas, killing three people. Five cities in Louisiana have reported rainfall totals of over two feet. On August 11, a measure of atmospheric moisture, precipitable water, was in historic territory at 2.78 inches, a measurement higher than during some past hurricanes in the region. Increased moisture in the air and unusually heavy rainfall are classic signals of climate change. As the world warms, storms are able to feed on warmer ocean waters, and the air is able to hold and dump more water. These trends have led to a pronounced increase in intense rainfall events and an increase in flooding risk. In the Southeastern US, extreme precipitation has increased 27 percent from 1958 to 2012.
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