All insights

Riding the Atmospheric Rivers into April

Hu Yoshida Hu Yoshida
CTO Emeritus, Hitachi Vantara

April 03, 2023

Having suffered through drought in California these last 10+ years, I never heard of an Atmospheric River Storm. Today, however, we are once again huddling in our homes waiting for the power to be restored while we endure the 12th atmospheric river storm to hit since late December. Along with bomb cyclones and tropical storms, atmospheric rivers have been in the news with greater frequency over the last few years, as intensifying weather events affect more of the public.

Known in pop culture as the Pineapple Express, these storms have apparently been an important part of California’s climate for thousands of years. As warm air rises it creates low air pressure at Earth’s surface. Surrounding air rushes in to fill the low-pressure space and spins counterclockwise due to the rotation of the Earth. As the air moves, it creates a current near the surface of the Earth that pulls hot, wet air from the tropics towards the continent. The low ‘river’ of atmospheric water from the Pacific hits our coastal and Sierra Mountain ranges and is driven upwards, releasing its moisture as rain or snow.

These heavy vapor streams have a flow similar to the Mississippi River at 500,000 ft³/s. That’s close to 6 Olympic swimming pools per second and 25 times the average flow of the Sacramento River. Typically, we would get about 2 or 3 of these a year in California, but nothing like the pounding we are getting this year. While the East Coast has it’s hurricanes, due to its warm coastal waters, we now have our west coast equivalent in these atmospheric rivers.

At first this was a welcome relief from the drought we have been suffering from, which has led to wildfires, power outages, and water restrictions. But now the reservoirs are full and spilling over, the ground is saturated, and the hillsides are sliding. Drought-weakened trees are falling over taking out power lines and smashing houses and cars. As spring comes and the snow in the Sierras melt, California is bracing for more flooding and all around us the vegetation is exploding which will be a challenge when the summer fire season starts.

According to Scientists at the Scripts Institute climate change, due to the warming of the earth’s temperature, is to blame for this increase and intensity of atmospheric rivers. As the earth’s temperature rises, more moisture evaporates into the atmosphere from lakes and rivers and oceans, and that moisture adds to the intensity of atmospheric rivers. Studies show, atmospheric rivers will be more intense and interspersed with extreme drought in the years to come. Studies also show that as the climate warms, these atmospheric rivers will get warmer, meaning less snow and more rain which will be harder to manage. Snow melt is easier to manage than a heavy rain that dumps its moisture in a few days or hours.

As we enter the month of April and approach Earth Day, the temperature’s rising. There is little we can do to change the physics except to address one of the prime causes for the dramatically changing climate. And that we can only do indirectly through our efforts large and small to reduce the emissions of CO2 and other greenhouse gases. Till then, we can add atmospheric rivers to the growing list of damaging effects of climate change. Let’s use it as another reason to  renew our efforts to reduce the use of fossil fuels.


Hu Yoshida

Hu Yoshida

Hu Yoshida spent 24 years at Hitachi Vantara helping define technical direction and enabling customers to address their digital transformation needs. He is widely known in the industry and was instrumental in evangelizing Hitachi's unique approach to storage virtualization.