Published on July 31st, 2019 | by Jennifer Sensiba0
Southwest Monsoons Getting More Frequent & Intense
July 31st, 2019 by Jennifer Sensiba
For those of us living in the Southwest US, the seasonal monsoon thunderstorms aren’t a distant and hypothetical issue. If you live here or visit us in the late summer, they’re rather hard to miss! According to a group of Arizona scientists, it’s not just our imagination. They really are getting more extreme.
What They’re Like: Short, Intense Storms
Once last year I was charging my LEAF in Mesa, Arizona, right near the 101/202 interchange, just adjacent to some undeveloped tribal lands. I originally planned to charge for 30-40 minutes. 25 minutes into my charge, while checking Facebook, I noticed the light suddenly change. I looked back over my shoulder and saw the tell-tale sign of a severe storm there: a haboob. A wall of dirt, suspended in the air by high winds, was headed my way.
This was no time to leave my car, so I let the car keep charging.
As the dirt arrived, lights came on as if it was nightfall. First, I couldn’t see some stadium lights in the distance. Then, I couldn’t see the lights of the next parking lot. Then, I couldn’t see two cars over. Finally, I could scarcely see the charging station right in front of my car. Then the winds whipped up, pushing and pushing my car as a layer of thick sand and dust settled on the hood. After several minutes of this, the car started feeling like it was going to come off the ground. Just as I was wondering whether a rare southwest tornado was roaring up, the wind suddenly stopped, and was replaced by heavy, heavy rain that quickly flooded the parking lot. 20 minutes later, the storm disappeared almost as fast as it sprang up.
This time, unlike most, there was some real damage left in the wake of the storm. There were hundreds of downed trees, lots of pooled water, and a very unusual power outage. On the reservation land where the storm first started to kick up dust, many power lines fell. The Talking Stick Resort, with its vibrant and colorful lights everyone in the area is used to seeing, fell dark and stayed dark for several weeks. The repairs needed were extensive, and took a lot longer than anticipated.
Their Brief Lifespans Make Them Hard to Study
I’ve lived in the Southwest most of my life, usually in southern New Mexico. There is nothing new about these storms. I can remember several times as a kid when the storms were quite severe, washing away roads and flooding large areas. The very landscape in the Southwest, with many large riverbeds that lay dry most of the year, attests to all this. Measuring each storm is a challenge, though. They spring up, drench a small area, and then go away. Radar can only tell you so much.
Ask people who have lived in the southwest for decades, and they’ll usually tell you that the storms seem to be happening more often and with greater severity. It’s anecdotal, though. The memory of storms decades ago can be fuzzy, and some years are more severe than others. Complicating things further is that the experience of our neighbors, just a few hundred yards away, can differ. The storms are just that isolated.
A Different Approach To Studying Them
That’s what makes the recent article in the Phoenix New Times so important. A team of six scientists used data from dozens of rain gauges, placed in the Walnut Gulch Experimental Watershed. In the past, and in most other places, rainfall measurements haven’t been of high enough resolution (both in terms of time and space) to draw any solid conclusions about the southwest’s summer storms. Decades ago, they put gauges in much closer together and checked them much more often. Now, after decades of data collection, there’s something solid to report.
With this new data, the scientists found that, compared to 1970, storms are now producing 6-11% more rain per storm, while the time the storms last hasn’t changed. This means each storm is not only dumping more water, but is more intense, driving increased erosion.
Readers are probably wondering whether there is any evidence to tie this to global warming, and they were asked about this.
“This is really the one mechanism that helps explain why you get higher-intensity rains,” said Dave Goodrich, an engineer who worked on the study. “You can hold more water vapor in [a hotter] atmosphere, so when storms are triggered, you can release a lot more water.”
This Data is Very Important
While knowing whether summer storms are getting more intense may not seem like a big deal to many, it’s very important in the Southwest. That’s because we get half or more of our rainfall during the monsoon storms. More intense storms affects everything from ecosystems to infrastructure, and can have real life-or-death consequences.
One example is the various species of toad that live in the desert. They often hide deep in the ground or seek out moist places between storms, and hibernate in the ground during most of the year. More extreme storms can have a big effect on their mating habits, migrations, and whether that water will stick around for the toads to be able to come out of hibernation again at the end of the dry seasons. Beyond toads, many desert and mountain species depend on the rain, and can be either hurt or helped by them.
As the New Times article points out, infrastructure is often designed to last 50 or more years. Building a bridge for the flood environment that existed decades ago could mean that bridges could fail during late summer floods in just a few short years. Knowing flood data is also important for everything from store parking lots to houses, and getting it wrong could have expensive and/or deadly consequences if the future increases in rainfall aren’t accounted for.
Another promising thing is that the National Weather Service, universities, and volunteers everywhere are working to get finer rainfall measurements. The CoCoRaHS network uses a variety of volunteers to measure, map, and analyze rainfall in far more places than official rain gauges do. Seeing the effects of climate change everywhere will probably reveal much more in the coming years.
Hopefully this data and more can continue to help us plan for all of these changes, and maybe help do things to reduce the impact it has in even more places.
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