Tag Archives: Precipitation

Climate change is making spring come earlier and earlier in the Northern Hemisphere

The declining number of rainy days in the Northern Hemisphere is making spring arrive earlier and earlier for plants in this half of the globe, new research reports.

Image credits Vinzenz Lorenz.

We have known that warmer average temperatures, a product of climate change, have been causing plants to sprout leaves earlier every year. A new study comes to add details to this picture, reporting that changes in precipitation patterns are also impacting this process.

According to the findings, the decrease in the number of rainy days every year has the second-greatest effect on plants, having quickened the emergence of leaves over the last few decades.

Springing early

“Scientists have looked mainly at how temperature affects when leaves first appear and, if they considered precipitation at all, it was just the total amount,” said Desheng Liu, co-author of the study and professor of geography at The Ohio State University. “But it isn’t the total amount of precipitation that matters the most — it is how often it rains.”

For the study, the team calculated that the decline in the frequency of rainfall in the Northern Hemisphere will cause spring (as defined by plants producing fresh leaves) to arrive sooner. The findings are based on datasets from the United States, Europe, and China, taken in points north of 30 degrees latitude (the northern third of the world). This data included the date each year when observers first note the presence of leaves on wild plants. The team also used satellite images from 1982 to 2018, which recorded when vegetation started to green.

Onset of leafing was then compared to data reporting on the frequency of rainy days each month at the investigated sites.

Overall, the team explains, the (steady) decline in rainy days over the years was associated with earlier onset of leafing in most areas of the Northern Hemisphere. The only exception were grasslands in predominantly semi-arid regions, where a decrease in precipitation (fewer rainy days) slightly delayed spring.

The results were used to create a model that estimates how much sooner spring would arrive in different areas of the Northern Hemisphere through to 2100. Current estimates place this figure at 10 days earlier than the calendaristic onset of spring by 2100. The team calculates that it will arrive one to two days earlier, on average, every decade through to 2100.

As to the link between rainfall and leafing, the team offers two main reasons. The first is that fewer rainy days means fewer overcast days in late winter and early summer. Due to this, plants receive more sunlight during this time, which stimulates the emergence and growth of leaves.

Secondly, more sunlight also means higher average air and soil temperatures during the day. At night, without clouds to reflect heat back down, temperatures will drop more rapidly.

“This contrasting effect earlier in the year makes the plants think it is spring and start leaf onset earlier and earlier,” said study co-author Jian Wang, a doctoral student in geography at Ohio State.

“We need to plan for a future where spring arrives earlier than we expected. Our model gives us information to prepare”.

The paper “Decreasing rainfall frequency contributes to earlier leaf onset in northern ecosystems” has been published in the journal Nature Climate Change.

Climate change is slowing down Europe’s storms, raising flooding risks

Europe should brace for more intense storms, new research reports, as climate change stands to power them up in the future.

Flooding in Sigonella, Sicily, Italy, in 2005. Image via Pixabay.

Intense, slow-moving rainstorms on the old continent will become more common in the future, according to experts at Newcastle University and the Met Office, UK. In absolute terms, we may see a 14-fold increase in their current frequency across dry land by the end of the century, they report. Such storms generally carry large amounts of precipitation which can cause extensive damage through flooding.

Slower storms tend to pose more of a risk because they dump precipitation on overall smaller areas, which means these are affected more strongly.

More of a bad thing

“With recent advances in supercomputer power, we now have pan-European climate simulations resolving the atmosphere in high detail as short-range weather forecasting models do,” explains lead author Dr. Abdullah Kahraman, of Newcastle University’s School of Engineering. “These models have grid spacing of approximately 2 km, which allows them to simulate storm systems much better, resulting in better representation of extremes”.

Although we’re already seeing flash floods across areas of Europe that traditionally never had to face them, such events will become even more common by the end of the century. Heating climate stands poised to make storms move slower over land, making them more likely to produce flooding through rainfall accumulation.

This, the team explains, is the first study to look at how the speed storms move at will be influenced by climate change. Most research regarding climate change and weather are focused on estimating the frequency and violence of freak or severe weather events to come.

“Using these state-of-the-art climate simulations, we have developed metrics to extract potential cases for heavy rainfall, and a smaller, almost-stationary subset of these cases with the potential for high rainfall accumulations. These metrics provide a holistic view of the problem, and help us understand which factors of the atmosphere contribute to heavy rainfall changes.

Since governments the world over have lagged behind on efforts to lower greenhouse gas emissions, there isn’t much we can do to avoid this increase in slow storms, according to the team. Under a RCP8.5 (business as usual) scenario, we can expect serious impacts throughout Europe, they add, from a combination of freak weather and more common storms, as well as the increase in slow-moving storms. The recent flooding seen in Germany and Belgium sadly underscores why such storms are dangerous to life and property, they add.

Europe itself is poorly suited to deal with slow-moving storms, as they are naturally very uncommon occurrences here, and generally confined to parts of the Mediterranean Sea. This means that predicting how they will evolve in the future, and which areas are likely to see the most of them, is vital to help people adapt and put systems in place to prevent loss of life due to flooding, as well as to limit the damage they can incur.

The paper “Quasi‐Stationary Intense Rainstorms Spread Across Europe Under Climate Change” has been published in the journal Geophysical Research Letters.

Wildfires could ‘seed’ new clouds with the particles they release

‘Ice’ is not the first thing that pops into your mind when thinking of wildfires, is it? And yet, new research is pointing to a link between such fires and the teeny tiny bits of ice that form clouds.

Image credits Sippakorn Yamkasikorn.

A new study is looking at the link between wildfires and ice-containing clouds like cumulonimbus or cirrus, the main drivers of continental precipitation. According to the findings, these clouds require microparticles to start forming — which a wildfire can supply in great quantities.

Ashes to rain

Cloud formation is a complex phenomenon, one that can shift quite significantly depending on conditions such as temperature or atmospheric dynamics. The clouds you’re used to seeing, for example, start their lives around very tiny particles, known as ice-nucleating particles (INPs). These can be anything from bacteria to minerals, just as long as they’re very tiny.

And that’s why the team was interested in studying how wildfires could influence the genesis of such clouds: wildfires can generate tons and tons of small particles. Because of this, they argue that wildfires could have a very important role to play in the dynamics of clouds, at least on a local level.

In order to find out, one study analyzed the plumes of the 2018 wildfires in California (western US) from samples taken at high altitudes, where the particles it contains might directly affect cloud formation. In very broad lines, this study found that INP quantities can become up to 2 orders of magnitude higher in a wildfire smoke plume compared to normal air. However, this didn’t account for the types of particles involved. Fires can produce a wide range of particles depending on the fuel they’re burning, their location, the specific conditions this burn is taking place in, and its temperature. One useful bit of information we can glean from this study is that the INPs were dominated by organic materials.

Spherical tar balls accounted for almost 25% of INPs in certain conditions, although this seems to vary widely with the type of fuel and the type of fire involved — understanding how they factor in is still “an open question,” according to the researchers.

Wildfires are predicted to become much more common in the future due to climate change, the team explains, so understanding how they can influence clouds (and thus, precipitation patterns) will do us a lot of good in the future. So far, the papers showcase that they can lead to very high levels of INPs accumulating in the troposphere, which could in turn influence how clouds and rain behave.

At this time, however, we need more modeling and sampling studies to understand these mechanisms in detail, and how they influence the world around us.

The paper “Observations of Ice Nucleating Particles in the Free Troposphere From Western US Wildfires” has been published in the journal Journal of Geophysical Research: Atmospheres.

Warming climates make hurricanes more dangerous and longer-lasting over dry land, a new study explains

Hurricanes are getting a boost from climate change and taking longer after making landfall to slow down and disperse. These changes are likely to mean that hurricanes in the future will affect communities farther inland.

Image via Pixabay.

A new study showcases how climate change is making hurricanes more dangerous and farther-reaching. Hurricanes that form above warmer waters in higher atmospheric temperatures can carry more moisture, the team explains, which allows them to keep raging stronger and for longer after reaching dry land. The problem is only going to get worse if climate change continues unabated and mean temperatures keep increasing.

Stormy futures

“The implications are very important, especially when considering policies that are put in place to cope with global warming,” said Professor Pinaki Chakraborty, senior author of the study and head of the Fluid Mechanics Unit at the Okinawa Institute of Science and Technology Graduate University (OIST).

“We know that coastal areas need to ready themselves for more intense hurricanes, but inland communities, who may not have the know-how or infrastructure to cope with such intense winds or heavy rainfall, also need to be prepared.”

The link between climate change and more powerful hurricanes is already well documented, with previous research showing that they’re becoming more intense over the open ocean. This is the first study to look at how climate change makes these storms — also known as typhoons — behave after they reach dry land.

The team looked at hurricanes in the North Atlantic that made landfall throughout the last five decades. On the first day after reaching dry land, the storms weaken roughly twice as slowly today as they did 50 years ago, the team explains.

They further explored the mechanisms behind this behavior in a series of computer simulations of four hurricanes in different sea surface temperature contexts. Once these simulated hurricanes reached Category 4 strength, the team simulated their making landfall by turning off any upwelling moisture.

“When we plotted the data, we could clearly see that the amount of time it took for a hurricane to weaken was increasing with the years. But it wasn’t a straight line — it was undulating — and we found that these ups and downs matched the same ups and downs seen in sea surface temperature,” said Lin Li, first author and PhD student in the OIST Fluid Mechanics Unit.

Li adds that hurricanes are “heat engines, just like engines in cars”, where the fuel is moisture taken up from the surface of the ocean. The heat energy it carries intensifies and sustains the storm by powering winds. Once a hurricane reaches dry land, its fuel supply is cut, meaning it will eventually decay.

Although each hurricane in the simulation made landfall at the same intensity, those that formed over warmer oceans took more time to dampen down, the team explains. All in all, they write that “warmer oceans significantly impact the rate that hurricanes decay, even when their connection with the ocean’s surface is severed”.

Additional simulations showed that the moisture stored in each hurricane explained this inertia. They start weakening as this stored moisture starts depleting. Simulated hurricanes that weren’t allowed to store moisture showed no changes in their rate of decay relative to the surface temperatures of the water they formed over.

“This shows that stored moisture is the key factor that gives each hurricane in the simulation its own unique identity,” said Li. “Hurricanes that develop over warmer oceans can take up and store more moisture, which sustains them for longer and prevents them from weakening as quickly.”

More stored moisture also makes hurricanes “wetter”, meaning they release more rainfall over the areas they reach.

The authors explain that our current models don’t take into account hurricanes’ stored humidity, making them incomplete — which is why we haven’t yet understood the relationship between sea surface temperatures and the behavior of hurricanes over dry land.

The team is now working on studying hurricanes from other areas of the world to see whether climate change is impacting hurricane decay rates across the globe.

“Overall, the implications of this work are stark. If we don’t curb global warming, landfalling hurricanes will continue to weaken more slowly,” Prof. Chakraborty concludes. “Their destruction will no longer be confined to coastal areas, causing higher levels of economic damage and costing more lives.”

The paper “Slower decay of landfalling hurricanes in a warming world” has been published in the journal Nature.

The Great Plains could be drying down into a new Dust Bowl

A new study says we should get ready for a blast from the past — in all the wrong ways. According to its findings, America’s Great Plains risk turning back into the dustbowl of the 1930s.

Image via Pixabay.

The Great Plains area has become increasingly dry in the past 20 decades, the authors explain, with dust storms here becoming more common and more powerful over the same time. Such events are considerable health hazards, and threaten to decrease the area’s agricultural potential as they strip nutrients from soils.

Bad Lands

“Our results suggest a tipping point is approaching, where the conditions of the 1930s could return,” says lead author Gannet Haller, an atmospheric scientist at the University of Utah.

The main drivers of these changes are the expansion of agriculture and irrigation in the area alongside more common and intense droughts.

Andrew Lambert, a co-author on the study and a meteorologist at the U.S. Naval Research Laboratory in Monterey, California stumbled upon these findings while reviewing atmospheric haze data gathered by NASA satellites (such haze is caused by dust and smoke particles in the atmosphere). The team then confirmed these with records from local dust sensors over the last 20 years.

All in all, the team explains that there is two times as much dust being blown over the Great Plains as 20 years ago. Dust levels peak during spring and fall — planting and harvesting seasons — which point to the agricultural activity being a leading cause. Such dust depletes soils and contains ultrafine particles that can enter our bodies and cause lung and heart diseases.

The Dust Bowl of the 1930s was likely caused by a combination of climate and agricultural drivers, the team explains. These draw their roots in the massive expansion of farmland in the area in the 1920s as mechanization allowed farmers to work more land than ever before. An extended drought in the following decade (with record-breaking heatwaves in 1934 and 1936), dried the plains out completely.

Climate change is also drying out the area and is likely to make heat waves much more common and intense occurrences, potentially leading to a megadrought worse than anything in the last 1000 years. New farmland in the area — most of it aimed at producing corn for biofuel refineries — is amplifying the problem. The study found a strong correlation between new cropland and downwind areas where dust levels are growing the fastest.

“Much of the [recent agricultural] expansion has been on less suitable land,” Lambert says. “It’s particularly ironic that the biofuel commitments were meant to help the environment.”

Lambert is particularly worried that the same feedback loops that created the dust bowl may be forming again. Wind-borne dust can lead to crop losses by removing nutrients from the soil. This then prompts farmers to plow more terrain, which restarts the cycle.

The worry is the potential for a repeat of the 1930s feedback loops, where the wind-borne dust carried away vital nutrients from the soil, leading to crop losses and the need to plow up more terrain—thereby removing stabilizing ground cover and adding to the supply of dust. The fact that local weather and precipitation patterns are likely to shift due to climate change could also contribute to the issue. It also makes it harder for us to estimate exactly how the situation will evolve.

The paper “Dust Impacts of Rapid Agricultural Expansion on the Great Plains” has been published in the journal Geophysical Research Letters.

Climate warming changed rainfall patterns across the Northern Hemisphere

Winter precipitation patterns across the Northern Hemisphere are shifting due to climate heating, a new paper reports.

A team led by researchers at the National Center for Atmospheric Research (NCAR) has isolated the effect of man-made climate change on winter precipitation across the Northern Hemisphere. They report that our lifestyle has significant impacts on wintertime rain and snowfall.

When it rains it pours

“I thought this was quite revealing,” said NCAR senior scientist Clara Deser, a co-author of the study. “Our research demonstrates that human-caused climate change has clearly affected precipitation over the past 100 years.”

The team used a novel approach to tease apart artificial and natural elements that affect the patterns of precipitation and their effects. The researchers drew on records and observations of precipitation and large-scale atmospheric circulation patterns, along with statistical techniques and computer climate simulations. In the end, they identified the amount of average monthly precipitation in specific regions of North American and Eurasia that fell as a result of human impact on the climate, rather than natural variability.

Rises in mean temperatures associated with human-caused emissions of greenhouse gas have noticeably increased wintertime precipitation over wide swathes of northern Eurasia and eastern North America since the 1920s, the team reports.

The findings can help to improve our understanding of how climate change can impact precipitation across the globe. Globally, precipitation is projected to increase by an average of 1-2% for each additional degree Celsius of increase in mean temperatures, because a warmer atmosphere holds more water vapor. Local changes, however, may make some regions become drier and others far wetter than they are today.

It’s not easy teasing apart man-made from artificial elements when it comes to precipitation, as this is affected by many local factors and conditions that can vary from day to day or year to year. In this chaotic setting, it’s virtually impossible to establish reliable long-term trends.

Previously, scientists relied on large numbers of climate model simulations to determine the influence of a changing climate on precipitation. In this present study, however, the team started with observed data. In essence, their approach can be summed up as: if you take away the precipitation caused by natural factors, and then compare that to what was recorded on the ground, you can tell how much of it can likely be attributed to human-driven changes in climate.

A) Observed precipitation trends overall; B) Dynamical contribution to A. C) A-B.
Image credits Ruixia Guo et al., 2019, AGU.

The approach used by the team is known as dynamical adjustment. It’s based on statistical techniques applied to observed data — the team used observations of large-scale circulation patterns in the atmosphere for every winter month from 1920 to 2015. Such circulation patterns occur independently of atmospheric greenhouse gas levels.

After crunching all the data, the team could estimate the average amount of precipitation that would be produced by a particular circulation pattern. They then compared these results to measured levels of precipitation to reveal the influence of climate change.

Northeastern North America, as well as a small part of northwestern North America, has experienced more precipitation due to man-made climate change, the team reports. Much of northwestern and north-central Eurasia fares similarly.

In contrast, parts of central and southwestern North America may have experienced drying, although not enough to offset natural variability, they add. Much of southern Eurasia is also experiencing drying as a result of climate change. However, the authors cautioned that their results for those regions were less pronounced and not statistically significant.

The team focused on winter because winter precipitation is driven by broad atmospheric patterns that are easier to see in the data than localized conditions that affect summer precipitation (such as soil moisture and individual thunderstorms), the team explains. The Northern Hemisphere simply has more and better-quality precipitation recordings, so they focused the study here.

The results fit with climate model simulations of human-caused changes in precipitation, which helps verify the models.

“Scientists previously turned to climate models for answers. Here, the climate models come in only at the end to confirm what we teased out of observations independently,” said NCAR scientist Flavio Lehner, a co-author of the study.

“I think this is the major scientific breakthrough of this work.”

Lehner and Deser used the same technique in a separate study published in Geophysical Research Letters last year, to show that recent drying in the U.S. Southwest is largely attributable to natural variability.

The paper “Human Influence on Winter Precipitation Trends (1921–2015) over North America and Eurasia Revealed by Dynamical Adjustment” has been published in the journal Geophysical Research Letters.

Climate change may bring “megadroughts” back to the US Southwest

Researchers are trying to figure out what caused the megadroughts of yore — and whether they could happen again.

Arid ground.

Image credits Mathias Beckmann.

The American Southwest was left bone-dry between the 9th and 15th centuries by about a dozen megadroughts — severe droughts that last for decades at a time. But it mysteriously changed to the climate we know today around the year 1600. Curious to see what caused this series of megadroughts and whether they could happen again, a team of scientists at Columbia University’s Lamont-Doherty Earth Observatory analyzed how elements of the global climate system come together to generate such events.

Climate warming, they report, creates the conditions in which such megadroughts flourish.

Heating up, drying down

The authors report that higher mean ocean temperatures, combined with a high radiative forcing rate played an important part in generating these megadroughts. High radiative forcing means that the Earth absorbs more energy from sunlight than it radiates back into space. Severe and frequent La Niña events sealed the deal. La Niña makes large swathes of the Pacific surface cool down, which has powerful effects on worldwide weather patterns.

The team reached these findings by reconstructing aquatic climate data and sea-surface temperatures from the last 2,000 years. The increase in radiative forcing seen between the 9th and 15th centuries in the American Southwest were likely the product of an increase in solar activity (i.e. more incoming energy) and a decrease in volcanic activity (which generates particles that can reflect incoming sunlight) at the time. The end result was higher mean temperatures, which increased evaporation rates.

At the same time, warmer sea-surface temperatures in the Atlantic combined with unusually strong and frequent bouts of La Niñas reduced precipitation levels throughout the (already dried-out) area.

Of the three factors, the team estimates that the La Niña conditions had the largest impact — more than twice as important in causing the megadroughts as the others combined.

The team explains that while they were able to identify the causes of these megadroughts in much better detail than any researchers before them, they caution that it’s hard to accurately predict them in the future. We have reliable projections of how temperatures, aridity, and sea surface temperatures will evolve, but La Niña and (its counterpart) El Niño activity remain difficult to simulate.

However, one thing they could say for sure is that man-made climate warming is creating the conditions necessary for more megadroughts in the future. The megadroughts the team investigated were caused by natural climate variability that increased radiative forcing. Today, the main driver of dryness in many areas around the globe is human activity — and this paves the way for more megadroughts.

“Because you increase the baseline aridity, in the future when you have a big La Niña, or several of them in a row, it could lead to megadroughts in the American West,” explained lead author Nathan Steiger, a Lamont-Doherty Earth Observatory hydroclimatologist.

The paper “Oceanic and radiative forcing of medieval megadroughts in the American Southwest,” has been published in the journal Science Advances.

Rain.

Water from thin air: a look at how rain and precipitation forms

When it rains, it pours — but why does it rain in the first place?

Rain.

Image via Pixabay.

Water is a vital part of life on Earth and, luckily for us, it always keeps moving around. There’s always a bit of it floating around in the air as vapor, for example. If enough of it builds up in the atmosphere, it falls as precipitation — most commonly as ‘rain’. It sounds simple enough, but the mechanisms that generate precipitation are actually very complex and finely-tuned. So let’s break them down and see how each part works, and how they fit together.

Water vapor and clouds

Water in puddles, rivers, lakes, or oceans evaporates constantly and builds-up in the atmosphere as vapor. However, there’s only so much water that air can hold, which we call its ‘saturation value’. This value fluctuates with changes in temperature; the warmer the air, the more water it can hold.

Air tends to be warmest near the surface of the Earth and cools down when it rises. As it cools down, its water saturation value drops progressively. At a certain point, it drops enough that the air has to shed water, at which point the vapor starts to condense. This temperature is known as the ‘dew point’. Further cooling will cause excess vapor to condense onto solid surfaces (i.e. dew), or onto condensation nuclei (this forms droplets). These condensation nuclei, or ‘aerosols‘ are tiny particles of various origins (such as dust, fog, pollen, or pollution).

The water droplets formed as air reaches its dew point clump together and scatter incoming sunlight. Our eyes perceive this as white, diffuse clouds. Air masses with little buoyancy relative to the surrounding atmosphere don’t rise very fast, and generate ‘fair wind’ clouds. Air that’s very buoyant compared to its surrounding atmosphere rises rapidly and much higher, forming thick clouds that produce heavy rains. Clouds can also form from the cooling and condensation that occurs as air flows over physical obstructions like mountain ranges.

So around this point, we have our clouds all ready to go. Let’s see how it all comes down.

Precipitation

The droplets that create clouds are really, really tiny — about one-hundredth of a millimeter in diameter. They’re so small that they can just remain suspended in the air, essentially floating around freely. However, they’re not motionless: they do move when pushed by air currents. As they do, some collide, growing larger and heavier and start a slow descent through the cloud. They collide with even more droplets on the way, which makes them grow even heavier.

Meteorologists define rain as liquid water drops that have a diameter of at least 0.5 millimeters when they reach ground level. Drops smaller than this are considered drizzle. Drizzle is generally produced by low-level clouds (Stratus clouds) in temperate areas. It’s very thin — drizzle feels like a mist — and forms when there aren’t enough rising air currents to keep small droplets within the cloud.

If the cloud is dense enough that droplets grow to over one-tenth of a millimeter in diameter, they will survive all the way to the ground despite evaporation. This forms ‘warm rain’, which in temperate zones are thin rains. In the tropics, this process leads to heavy rainfall from clouds lower than 5km above ground level.

Clouds.

Image credits Engin Akyurt.

In temperate areas, heavy rains tend to be generated by a process that involves frozen particles. Temperatures at cloud level tend to be below 0ºC, but the droplets remain liquid. However, they do feel the temperature and spend their time in a state known as ‘supercooling‘. In such a state, even a slight disturbance, such as a collision or contact with an aerosol particle causes them to freeze solid almost instantly.

Water vapor condenses faster onto solid ice particles than it does on liquid droplets, so these little bits of ice grow much faster than surrounding drops and fall sooner. They also grow more as they fall. Warmer masses of air closer to the surface melts the ice as it’s falling, and they reach the ground as rain.

Very thick clouds, however, can create hail. The process is largely similar to the one above, with the exception that the ice particles they form are so large that they can’t melt before reaching the ground. Powerful storms can also generate upward winds that yank these falling bits of ice back into the cloud and re-freeze them. The process is repeated several times as the particles fall, grow larger, and are pulled back up. Eventually, they grow too heavy for the wind to affect them any more and fall to the ground as large, layered hailstones.

How air temperature influences things

Hailstones.

Image credits Etienne Marais.

Drizzle can also be produced by thick clouds if the drops that fall out of them go through a very dry and warm layer of air and evaporate until they are less than 0.5mm in diameter. If drops pass through a layer of cold air, you get snow. If the layers of air within the cloud and those between the cloud and the ground alternate between below and above freezing, you get all kinds of precipitation.

Hail, as we’ve seen, can form when drops go through a succession of warm-cold layers. Freezing rain forms in a similar fashion. If a droplet or ice particle falls through a moderate or warm layer of air (enough to make it fully liquid) but hits a very cold layer right above the ground, it becomes supercooled — and freezes right as it hits the cold ground. This coats everything in a thin layer of ice that becomes progressively ticker as more drops fall down. Frozen rains have been known to snap tree limbs and down power lines with the weight of the ice coat.

Fun facts about rain

  • Although raindrops are depicted in the classic teardrop shape, they’re actually dome-shaped as they fall; the bottom is flat due to air resistance.
  • The USGS estimates that one inch of rain per acre is equal to roughly 27,000 gallons (102,206 liters) of water.
  • Mawsynram, a village in Meghalaya, India, receives the most annual rainfall — about 10,000 millimeters of rain per year on average; most of it falls during the monsoon season.
  • Yungay, Chile, is the driest village on Earth, by comparison — around 0.1 mm each year on average.
  • Acid rain forms when pollutants such as sulfur dioxide and nitrogen oxide (some are natural but mostly man-made) bind with water vapor in the atmosphere. The mix is acidic enough to damage organic material, but can also corrode steel and weather stone.
  • While Earth’s rains are made of water drops, other planets have much more exotic rains — boiling sulfuric acid, sideways glass rains, and diamond hailstones are just a few.
Sahara desert.

Clean energy could make the Sahara green

Installing solar and wind power in the Sahara would have benefits for both the region and the world’s grids, a new paper concludes.

Sahara desert.

Image via Pixabay.

The Sahara may be a deserted place, but according to the new study, green energy could also help the desert itself become greener: filling in all that empty space with solar and wind farms would help liven up the place — all while supplying ample green energy. Researchers from the University of Illinois at Urbana-Champaign (UI) found that such installations would increase local precipitation levels, which in turn would lead to increased vegetation.

The paper also reports that such power plants would also increase local temperatures under current conditions. However, this effect would likely be ‘very different’ in the field, due to the shift in vegetation patterns associated with changes in precipitation.

Greening Sahara

“Previous modeling studies have shown that large-scale wind and solar farms can produce significant climate change at continental scales,” says lead author Yan Li, a postdoctoral researcher in natural resources and environmental sciences at the UI.

“But the lack of vegetation feedbacks could make the modeled climate impacts very different from their actual behavior.

The team focused on the Sahara for several reasons: for starters, it’s the largest desert in the world. It’s also sparsely inhabited, and “highly sensitive to land changes”, Li explains. Furthermore, its geographical position — in Africa, but fairly close to both Europe and the Middle East — would also make it an ideal place to build plants that cater to these areas’ large (and growing) energy markets.

Li and colleagues simulated the effects of wind and solar farms covering in excess of 9 million square kilometers (roughly 3.5 million sq miles). On average, the simulated wind plants would churn out 3 terawatts, and solar ones 79 terawatts, of electrical power per year. Needless to say, that is a lot of powerplants: global energy demand in 2017 totaled about 18 terawatts, making the team’s scenario a tad overkill.

But what the team really wanted to see was what environmental effects solar and wind installations would have on the desert — as such, they needed to model the plants on a huge scale.

Their work revealed that wind farms do indeed increase near-surface air temperatures. Changes in minimum temperatures were greater than those seen in maximum temperatures, the team adds — i.e. wind farms increase minimum temperatures more than maximum ones.

“The greater nighttime warming takes place because wind turbines can enhance the vertical mixing and bring down warmer air from above,” the authors wrote.

Precipitation levels also increased by as much as 0.25 millimeters per day on average in regions with wind farm installations. The Sahel region saw the largest increases in average rainfall — 1.12 millimeters per day where wind farms were present.

Sahara changes.

Impacts of wind and solar farms in the Sahara on mean near-surface air temperature (in Kelvin) and precipitation (millimeters per day).
Image credits Li // Nature.

Overall, the increase in precipitation levels was double “that seen in the control experiments,” Li said. Such levels of precipitation would, in turn, lead to increased vegetation cover, he adds, “creating a positive feedback loop”.

“The rainfall increase is a consequence of complex land-atmosphere interactions that occur because solar panels and wind turbines create rougher and darker land surfaces,” says study co-author Eugenia Kalnay from the University of Maryland.

Solar farms had a similar effect on temperature and precipitation. Unlike the wind farms, solar installations had almost no effect on wind speeds.

Put together, the changes seen in the team’s model could have a very positive effect on the economic and social well-being in the Sahara, Sahel, Middle East, and other nearby regions, the team writes. The combination of clean (and cheaper) energy and increased rainfall and vegetation would also help boost local agriculture, they add.

The paper “Climate model shows large-scale wind and solar farms in the Sahara increase rain and vegetation” has been published in the journal Nature.