One Million Years of Data Predict Worsening Monsoon Seasons

core samples of mud warn of climate change exacerbating seasonal winds

By Jonny Lupsha, Wondrium Staff Writer

A study looking back a million years warns of severe upcoming monsoon seasons. Predictive data used in the study is based on core samples of mud drilled from the northern Indian Ocean. Monsoons are powerful seasonal winds that bring heavy rain.

Huge rain cloud from monsoon season
Large geographic areas are affected by alternating wet and dry monsoon seasons, with winds seasonally blowing from cold to warm regions. Photo By Jewelzz / Shutterstock

South Asia is home to the biggest monsoon system on Earth. Every year, harsh seasonal winds bring torrential rainfall to the area, including up to 425 inches of rain in certain parts of India alone—which is more than 13 times the average annual rainfall in the United States. According to a new study that drilled core samples of mud from the Bay of Bengal, climate change is about to make monsoon season get worse.

Where do monsoons come from? In his video series Oceanography: Exploring Earth’s Final Wilderness, Dr. Harold J. Tobin, Professor in the Department of Earth and Space Sciences at the University of Washington in Seattle, said monsoons are almost like a macrocosm of daily coastal breezes.

Day In, Night Out

Dr. Tobin said that there’s a differential amount of temperature change in the land and in the sea in coastal areas, even though the same amount of sunlight is hitting them. This is due to the composition of soil versus sea water, among other things, leading to the land heating up more than the water and that hot air rising, which pulls in cooler sea air to replace it.

“At night, the whole process reverses itself,” Dr. Tobin said. “The sea is warm; the cool air sinks off of the land, flows down off the land, and moves back out to sea and flows out over the ocean where that cool, relatively dry air that’s come from the land interacts with the warm air from over the ocean, which then is rising offshore and putting the water vapor in the atmosphere that ultimately turns back into fog for the next day.”

If we adjust our scope to seasonal instead of daily, he said, nearly the same thing happens with monsoons.

Monsoon Season

According to Dr. Tobin, the Himalayas are a region of both high altitude and large land area. In the summer, the Sun warms up areas of land, causing air to flow upward over India and over the mountains, rising high into the atmosphere.

“That rising warm air from the land is drawing in air from offshore,” he said. “Now, the ocean offshore in this subtropical region is relatively warm and certainly very moist—it carries a lot of water vapor. It’s being pulled in and then rising up the mountain front where it’s expanding, due to the decrease in pressure as you go to higher elevation, and dumping those torrential rainfalls.”

Much like the nighttime turnaround for coastal breezes, the winter tells a very different story for monsoons. As the landscape becomes cooler, Dr. Tobin said, the ocean is still retaining warmth, so the rising air over the ocean carries everything back out. The air flow essentially reverses.

“Dry winters happen as dry air sinks off the Himalayan Mountains and the Tibetan plateau,” Dr. Tobin said. “The whole monsoon season then just varies back and forth, but [is] essentially the exact same process of differential thermal inertia between the water and the landscape.”

Edited by Angela Shoemaker, Wondrium Daily