Behold the Hetao Irrigation District
How can a tiny oasis in a vast desert spawn some of the strongest storms on Earth?
The Yellow River runs mostly east-west through the vast Gobi and Inner Mongolian deserts in China. It is an important water source for people, animals, and plant life in the region. Over 2000 years ago, humans began using the river to irrigate local flat lands for agricultural use.
The Hetao Irrigation District just happens to be located to the right of a massive arrow-shaped feature in the desert.
Nestled in Inner Mongolia, this agricultural marvel turns the arid Yellow River plains into a lush, green checkerboard of productivity. Imagine ancient dynasties wielding shovels and smarts to create a snaking network of canals and dams. It's not just a triumph of old-school engineering; it's an ongoing tango with the elements, where climate meets agriculture. Today, the Hetao dances to the rhythm of seasonal rains and river flows, spinning wheat, rice, and sunflowers out of what was once unforgiving land.
This irrigation district is so massive that it influences the skies above it. We know that borders between land and water influence weather patterns, but most of our studies involve the atmospheric impact of the boundaries between land and water (or ice). Less is known about the effects of stark and sudden differences in vegetation.
Compared to a dusty desert landscape, substantial plant life absorbs and radiates heat differently, and reduces soil erosion/dust in the air. Among other things, this leads to decreased temperature and increased humidity compared to dryer, arid land.
A team of scientists presented new research on this area at last summer’s 32nd Conference on Weather Analysis and Forecasting, the 20th Conference on Mesoscale Processes, and the 28th Conference on Numerical Weather Prediction. Yes, it was a supergroup of conferences that combined, much like Voltron, to become bigger than the sum of its parts. The acronym is officially 32WAF/20Meso/28NWP. Who knew weather conferences could make such terrific password generators?
When the dry, warm winds from the northwest blow toward the cooler, more humid air to the southeast, a unique type of boundary layer forms. Researchers monitoring the area report that, on average, such layers produce storms about 26 days out of the year. These storms can be intense, even forming tornadoes (though there are no reports of raining frogs yet).
A tornado in Hetao documented by the DECODE research team.
Video still courtesy of Yijing Liu.
This research is important because there are many places on Earth where desert and vegetation quickly give way to each other. Just look at any large map.
I used to work in an ancient building with an HVAC system built before the Big Bang. I once measured one person’s office temperature to be 22 degrees F warmer (5.6 C) than the person next door, thanks to an out-of-control radiator that the facilities team said would never be repaired. I whimsically wondered why wonderful wind storms didn’t form in the hallway. Perhaps we needed more greenery.
Read more about this phenomenon, with some cool radar imagery, in A Research Spotlight from 32WAF/20Meso/28NWP from the AMS’ Front Page Blog.
Next week: Thunderstorm Tracking
Acknowledgements to Dr. Chad Kaufman for contributions to this post.