Originally shared by John Baez
Floods and climate change
While Americans are watching Houston drown, floods are disrupting life for 20 million in India, Bangladesh and Nepal. So far they’ve killed at least 1,200 people. In India’s financial capital Mumbai, people are struggling to evacuate as transportation is paralysed and water has risen almost 2 meters in some parts of the city. Over in Bangladesh, 1/3 of the country is under water!
Of course flooding happens in South Asia every year during the monsoon season, June to September. But this year’s floods are much worse than usual. Why?
Are floods getting worse because of climate change? Hurricanes and monsoons start with the evaporation of warm ocean water. The Earth is the hottest it’s been in the last 100,000 years — and getting hotter. So it would be very strange if floods weren’t getting worse.
But let’s focus on a more specific question: why was Hurricane Harvey so intense?
Harvey benefited from unusually toasty waters in the Gulf of Mexico. As the storm roared toward Houston last week, sea-surface waters near Texas rose to between 2.7 and 7.2 degrees Fahrenheit above average. These waters were some of the hottest spots of ocean surface in the world. The tropical storm, feeding off this unusual warmth, was able to progress from a tropical depression to a category-four hurricane in roughly 48 hours.
“This is the main fuel for the storm,” says Kevin Trenberth, a senior scientist at the U.S. National Center for Atmospheric Research. “Although these storms occur naturally, the storm is apt to be more intense, maybe a bit bigger, longer-lasting, and with much heavier rainfalls [because of that ocean heat].”
This also suggests an explanation for one of Harvey’s strangest and scariest behaviors. The storm intensified up until the moment of landfall, achieving category-four strength hours before it slammed into the Texas coast. This is not only rare for tropical cyclones in the western Gulf of Mexico: It may be unique. In the past 30 years of records, no storms west of Florida have intensified in the last 12 hours before landfall.
Why do storms normally weaken — and why didn’t Harvey? As mentioned above, hurricanes feed and grow on warm ocean surface waters. But as they grow, their strong winds often pick up seawater, churning the oceans and moving the warmest waters deep below the surface. The same winds also bring newer, colder water closer to the atmosphere, which usually serves to drain energy and weaken the storm.
That didn’t happen with Harvey. The hurricane churned up water 100 or even 200 meters below the surface, said Trenberth, but this water was still warm — meaning that the storm could keep growing and strengthening. “Harvey was not in a good position to intensify the way it did, because it was so close to land. It’s amazing it was able to do that,” he told me.
This is from here:
For more on flooding in South Asia, try this: