The Cloud Whisperers: The Quest to Bring the Rain
Guest Post by Judith D. Schwartz, author of Water in Plain Sight and The Reindeer Chronicles
Sixth-generation farmer Michael Thompson is not the sort to buck tradition. But when your living comes from the land, persistent drought can make a radical of you—at least by the standards of northern Kansas. Thompson shifted to planned rotational grazing and no-till crops on some lesser acreage his father offered him. The farm and ranch thrived while many in the region struggled through several low-rainfall years. The new practices improved the soil, which meant the operation made better use of the rain they got.
Thompson also feels they may actually have received more rain:
“I’m a firm believer that the more bare ground and bare fallow we see, it does affect our weather patterns. When we have more fallow in our area, we see the rain split and go around us. And I’m convinced that a lot of that is due to the reflectivity of all the heat being soaked up on bare soil or worked soil like this and reflected up into the sky.”
Now that he and some neighbors have turned to cover crops and rotational grazing, he says, “In our immediate area of our county we get more rainfall than other areas of the county that bare fallow and do a lot of tillage and overgraze.”
Though it may sound like an agrarian tall tale, Thompson’s impression that enhancing plant cover leads to more rain is being borne out by science—specifically the growing body of research that is linking precipitation to biological processes. With technologies that allow researchers to track and identify microorganisms and new protocols like NASA’s SMAP (Soil Moisture Active Passive), we’re able to zero in on what happens up in the clouds. And in the process, learning that our actions may control over what comes down from the sky more than we thought.
Clouds need plants to make rain just as plants need rain to live.
Enter: Bioprecipitation
Back in the late 1970s, Montana State University biologist David Sands was studying a pest that seemed to provoke frost damage in cash crops like wheat—a bacteria that caused ice-nucleation: the formation of ice crystals at temperatures that would not typically prompt freezing. When attempts to quell the troublesome microbe proved unsuccessful, he investigated to see how widespread it is, taking a small plane across agricultural fields. He collected samples amidst the clouds —holding a petri dish out the window—and found ample evidence of the same bacteria. Now why would the microbes be up there? He hypothesized that in promoting ice-nucleation, the bacteria also played a role in making rain. He coined the term bioprecipitation.
An intriguing aspect of rainfall is the centrality of ice: it happens that ice crystals are the ideal substance for moisture to cohere to, the perfect seed for a raindrop. But how do you get ice crystals to form? The obvious answer would seem to be freezing them, but, surprisingly, when it comes to extremely pure evaporated water lowering the temperature is no guarantee—even at 30 or 40 degrees below zero centigrade. Rather, specific bacteria promote the formation of ice at temperatures where ice would not necessarily form. These include the bacteria that wreaked havoc on David Sands’s crop, which has since been affectionately named “Sue” (for Pseudomonas syringae).
Water, plants, soil…and bacteria. The dance of life.
Decades later, in 2008, Sands and young colleagues Brent Christner and Cindy Morris published an article in Science presenting evidence that, throughout the world, airborne bacteria associated with plants play a pivotal role in precipitation. Thus vindicated, Sands notes the significance at a time when many regions are experiencing drought. He asks:
Might we be trying to extract too much biomass from the land? Might we be growing bacteria-resistant plants? We may really be affecting weather.
Cindy Morris, a microbial ecologist now based in Avignon France, was moved to write her own lyrics to Joni Mitchell’s song “Both Sides Now” (of the memorable line, “I really don’t know clouds at all”) from a scientist’s view. One stanza goes:
Particles and drops so small
That billow in the clouds so tall.
Nucleate and aggregate
Will make the great rains fall.
More prosaically, Morris calls crops “launch pads for microorganisms into the atmosphere.”
Plants Don’t Just Respond to Rainfall; They Generate Their Own
Rain requires nucleation—but there has to be moisture up there to nucleate. For this, forests are key. While all plants emit water vapor, a concentration of trees actively transpiring provides much the water that becomes our rain and snow. Thanks to transpiration, leaf resistance and other factors, forests help govern the flow of atmospheric moisture, determining where rain falls.
Research from WeForest, an international NGO, indicates that when areas are deforested, patterns in which forested areas “feed” precipitation to regions downwind are interrupted.
Trees are also sources of precipitation nuclei. Says Cindy Morris, also affiliated with WeForest: “Trees and forests release ‘ice nuclei’ into the atmosphere including certain fungal spores, pollen and bacteria that can initiate rainfall at much warmer temperatures, sometimes as warm as -4 °C. This means that rain initiation can take place more readily in low altitude clouds.”
Low clouds nourish a myriad of rare orchids in a cloud forest.
Research on forests and rainfall has yielded concepts like “rainbow water” (the blend of ocean- and plant-derived water that becomes rain); “ecological rainfall infrastructure” (a fancy way of saying “trees”); “precipitation sheds” (land areas that contribute evaporated water that downstream becomes precipitation); and “biological rainfall generation."
In Australia, the North East Forest Alliance published a review of 150 scientific papers called “Clearing Our Rainfall Away”—the title a warning of what removing forests could mean.
Clouds Prefer Natural Vegetation
Australian scientists have this nifty, if unintended, research vehicle called the “rabbit-proof fence”, a 6,000 kilometer barrier created more than a century ago to stop rabbits and other pests from encroaching into then-wild Western Australia. This conveniently draws a 3,000 kilometer line that divides land covered with native vegetation and cultivated cropland. What we learn is that the otherwise identical types of land have different precipitation patterns: the natural land gets more rain while the agricultural land tends to dry out and bake.
The late scientist Tom Lyons wrote an article with the evocative title, “Clouds Prefer Native Vegetation”. He found that due to factors including transpiration rates, reflectivity, canopy resistance and surface roughness, the unplowed land sees more cloud cover and thus more rain. Photos show clouds hovering over the native brush and grasses while the agricultural land has clear skies—this in a country plagued by heatwaves, wildfire and drought. This is particularly the case in Western Australia, the site of the fence, which has seen dramatically less rainfall over the past 25 years.
A group of Australian scholars posit that “the combined effects of burning to remove fuels (organic matter) and clearing of native vegetation has removed patches of moisture and altered microclimates throughout, thereby cumulatively altering regional climates and delivering more severe seasonal droughts and more intense fires.”
Plants and clouds. So happy together.
However, they say that accumulating organic matter maintaining soil moisture will create a beneficial feedback loop whereby plant litter is incorporated into the soil rather than lying around as fuel for fires. How to get the cycle spinning in the right direction? Said Tom Lyons:
a belt of re-vegetated country 20 kilometers wide would be adequate to change cloud cover and rainfall.
Understanding the biological root of rainfall can help us restore the hydrological cycle and therefore the vitality of our landscapes. There are direct climate implications as well. University of Montana researcher Paul Stoy has described the “Fallow Reduction Phenomenon”: large areas of the Northern Great Plains, where the use of cover crops has increased, are experiencing cooler temperatures—in contrast to other regions that are warming.
NASA’s SMAP program has revealed how “soil memory”, or moisture that remains in the soil after weather events, plays a role in weather patterns, including amplifying floods or droughts. In addition, our growing understanding of the aerosols—dust, soot, pollen, salts—that lurk in air we might otherwise consider “clean”, and their relevance to climate and weather. Until now, this has been difficult to model and observe.
As Gail Fuller, another Kansas farmer, says,
We know we can screw the weather up the wrong way, so it does make sense we can cause more precipitation if we do it the right way.
Judith D. Schwartz is an author who tells stories to explore and illuminate scientific concepts and cultural nuance. She takes a clear-eyed look at global environmental, economic, and social challenges, and finds insights and solutions in natural systems. She writes for numerous publications, including The American Prospect, The Guardian, Discover, Scientific American, and YaleE360. Her latest book, “The Reindeer Chronicles”, is a global tour of earth repair, featuring stops in Norway, Spain, Hawai’i, New Mexico, and beyond.
“JUDITH SCHWARTZ PROVES, ONCE AGAIN, THAT SHE IS ONE OF ECOLOGY’S MOST INDISPENSABLE WRITERS.”
—Ben Goldfarb, PEN America Literary Award-winning author of Eager
For more information about Judith and to order her grounded-but-optmistic books, visit her website.
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At Sueño de Vida we work in a meaningful way to heal land ravaged by deforestation. How meaningful? According to a recent UN Foresight Brief on climate change,
--It is of the utmost importance to stop deforestation and to increase reforestation efforts around the world. Agricultural practices should focus on soil building and the use of agroforestry methods.
That is exactly what we do here at SdV. You can help by helping us do what we do every day: plant forests that nurture soil, people, and local community.