{"id":776677,"date":"2022-08-16T10:15:00","date_gmt":"2022-08-16T10:15:00","guid":{"rendered":"https:\/\/grist.org\/?p=584027"},"modified":"2022-08-16T10:15:00","modified_gmt":"2022-08-16T10:15:00","slug":"scientists-unravel-the-origins-of-the-southwests-monsoon","status":"publish","type":"post","link":"https:\/\/radiofree.asia\/2022\/08\/16\/scientists-unravel-the-origins-of-the-southwests-monsoon\/","title":{"rendered":"Scientists unravel the origins of the Southwest\u2019s monsoon"},"content":{"rendered":"\n

This story<\/em> was originally published by <\/em>High Country News<\/em><\/a> and is reproduced here as part of the<\/em> Climate Desk<\/em><\/a> collaboration. <\/em><\/p>\n\n\n\n

On an evening in late June, Alex Jimenez, Tucson Water\u2019s artist-in-residence, hosted an outdoor art installation designed to \u201ccall the rain through sound.\u201d <\/p>\n\n\n\n

The Santa Cruz Sound Experience, held underneath one of the bridges that crosses the dry Santa Cruz River, featured a three-hour sensory compilation of the region’s seasonal summer rains. Toward the end of the event, the skies answered the call, and attendees celebrated as raindrops fell.<\/p>\n\n\n\n

The monsoon season has come to the Southwest again. But this season is different from past monsoons: It\u2019s the first since scientists demonstrated that North America\u2019s monsoon \u2014 which drenches Sonora, northern Sinaloa and northeastern Chihuahua in Mexico, and the southern fringe of Arizona and New Mexico \u2014 differs from seasonal rains in the rest of the world. And, unfortunately for Southwesterners \u2014 who welcome the precipitation and need a break from the summer heat \u2014 the phenomenon is likely to weaken as the climate warms.<\/p>\n\n\n\n

Monsoons, which exist on every continent except Antarctica, are continental-scale wind patterns that transport water vapor and cause seasonal rains. In general, they occur when intense sunlight during summer causes the land to heat up. Warm air rises and draws in water vapor from the ocean, creating a \u201cthermal contrast between the land and the nearby ocean, and an air circulation between the two,\u201d William Boos, a climate scientist at the University of California, Berkeley, explained.<\/p>\n\n\n\n

Scientists and lay observers alike have long thought that the North American monsoon was also caused by this \u201cthermal forcing,\u201d with cooler water vapor being pulled in from the Pacific off the west coast of Mexico. To Boos, however, something about North America\u2019s monsoon, which is smaller and more oddly shaped than its peers, was \u201calways a little peculiar.\u201d<\/p>\n\n\n\n

In 2021, Boos and Salvatore Pascale, who researches climate dynamics at the University of Bologna in Italy, published an article in the journal Nature that showed that the Southwest\u2019s summer storms were not caused by the typical thermal forcing. Rather, they were caused by something that scientists call \u201cmechanical forcing,\u201d which has to do with terrain. When the mid-latitude jet stream \u2014 the band of eastward winds that circle the entire planet \u2014 collides with the Rocky Mountains, the range deflects the winds southward, to Mexico. As the winds move east, they push over Mexico\u2019s Sierra Madre, after collecting water vapor from the tropics of the eastern Pacific and Mexico. Then, when the jet stream lifts, forcing moisture-laden air up over mountainous terrain, the vapor condenses into \u201corographic rain\u201d that falls on the western side of the mountains, creating the monsoon.<\/p>\n\n\n\n

\u201cThe orographic effect is critically important, especially in terms of what\u2019s going to happen with climate change,\u201d said scientist Agustin Robles of the Technological Institute of Sonora’s Laboratory of Environmental Modeling and Sustainability. \u201cWe\u2019ll see the bulk of the changes there.\u201d<\/p>\n\n\n\n

There\u2019s a simple reason why scientists hadn\u2019t already figured out geology\u2019s role in creating the monsoon: The technology to do so didn\u2019t exist. Whereas the Tibetan Plateau is so large that it could be modeled for its effect on climate starting in the 1980s, the Sierra Madre was too small and too fine for computers to render accurately until recently. Boos and Pascale used a cutting-edge supercomputer to compare a model of the region’s topography with a version in which they set all the landscape\u2019s elevations to zero. Since that version in effect flattened Mexico, they called it \u201cFlatMex.\u201d In FlatMex, the monsoon all but disappeared, leading to their conclusion that the North American Monsoon is created by wind going over the Sierra Madre.<\/p>\n\n\n\n

The recent research built on previous studies of the North American monsoon. A few years ago, Pascale, Boos and six other collaborators published a study that challenged the idea that climate change will increase precipitation across North America.<\/p>\n\n\n\n

\u201cThere\u2019s a classic idea that as the air gets warmer, it can hold more water vapor, so it will deliver more water to the continent,\u201d said Boos. While that may be true for other monsoons \u2014 including the southeast Asian monsoon, which has already become wetter \u2014 it\u2019s different in regions like the Southwest, where most of the rainfall comes from thunderstorms and the cumulus clouds associated with them. <\/p>\n\n\n\n

Thunderstorms are caused by a difference in the temperature and humidity of the air near ground level and the air higher up in the atmosphere. Once the difference between the two air temperatures reaches a certain level, they turn over, switching places. The hotter, less dense air rises and the colder, denser air sinks, because of gravity. But as the upper levels of the atmosphere warm, there is less of a difference between the two temperatures \u2014 and that means fewer thunderstorms and a weaker monsoon.<\/p>\n\n\n\n

Communities in the Southwest, which is already facing increasing aridity and extreme heat, will need to improve both air quality and the infrastructure that ensures their access to water, and they\u2019ll also have to find ways to cope with more days at high temperatures. Unfortunately, there \u201caren\u2019t a lot of options\u201d to address the declining summer rainfall, said Dan McGregor, natural resources services manager for Bernalillo County, New Mexico. His agency mainly encourages water users to conserve water, maintain their wells and to harvest rainwater.<\/p>\n\n\n\n

In the Southwest, these effects will disproportionately affect those who rely directly on the rains. Sheryl Joy, Acting Seed Bank Manager at the organization Native Seeds\/SEARCH in Tucson, said that for Indigenous communities in Arizona who have developed agricultural systems organized around the summer rains, \u201ccontinued declines in monsoon rainfall could have devastating effects\u201d on the communities who continue to use these practices.<\/p>\n\n\n\n

In Sonora, Mexico, where most of the monsoon\u2019s precipitation falls, there is less infrastructure in place to address water shortages than there is in the U.S. Southwest. \u201cUnlike Arizona or California, which have long-term planning and responses such as the Tier 1 shortage announcements, here our institutions have not anticipated the effects of the weaker monsoon,\u201d said Robles. \u201cThey tend to blame drought, when it\u2019s really a modification of the monsoon over the last 30 or 40 years.\u201d<\/p>\n\n\n\n

Jonah Ivy of Tucson\u2019s Watershed Management Group focuses on helping residents use the water that falls, rather than waste it as runoff. \u201cWhat does a weaker monsoon matter if right now we\u2019re pushing all the water off our landscapes?\u201d he said. \u201cEven with a weaker monsoon, we still live in the wettest desert in the world. We still live in abundance.\u201d<\/p>\n

This story was originally published by Grist<\/a> with the headline Scientists unravel the origins of the Southwest\u2019s monsoon<\/a> on Aug 16, 2022.<\/p>\n

This post was originally published on Grist<\/a>. <\/p>","protected":false},"excerpt":{"rendered":"

But just as their understanding of the phenomena becomes more clear, it\u2019s starting to disappear.<\/p>\n","protected":false},"author":21278,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8923,553],"tags":[],"_links":{"self":[{"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/posts\/776677"}],"collection":[{"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/users\/21278"}],"replies":[{"embeddable":true,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/comments?post=776677"}],"version-history":[{"count":1,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/posts\/776677\/revisions"}],"predecessor-version":[{"id":776682,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/posts\/776677\/revisions\/776682"}],"wp:attachment":[{"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/media?parent=776677"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/categories?post=776677"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/radiofree.asia\/wp-json\/wp\/v2\/tags?post=776677"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}