Another Mediterranean-Climate Mystery
Santiago and Central Chile
When it comes to water, go first to experience, then to reason. Leonardo da Vince There is the problem of having to scientifically prove the obvious. Millan Millan
When Mediterranean meteorologist Millan Millan solved the mystery of why the summer rains were vanishing throughout the Western Mediterranean Basin, showing how land disturbance there had destroyed the water cycles which the rains depended upon, he opened the door to other mysteries elsewhere, especially given the scale of land damage around the world. Where else, one has to wonder, are such things going on? It wasn’t long after publishing a series on Millan’s work that I received a note from a Chilean forester saying “Here in Chile we can find water cycle examples just as you describe. Andes Mountains affect.”
The forester, Diego Carvallo, was speaking from Santiago, Chile, which also has a Mediterranean-style climate. Santiago has become something of a climate poster-child, gripped like the rest of Central Chile in an enduring drought, with wells running dry, crops withering and its massive and much beloved Laguna de Aculeo drying up completely in 2018. Most commentators point to global warming (CO2) as the cause, others at overconsumption and corrupt distribution of water, but Carvallo sees a third thing going on. He sees water cycles dying, particularly in association with the massive sprawl around Santiago, Chile’s largest city. Since 1980 its population has more than doubled from 3.8 to 8 million people, it’s once green valley floor steadily covered over by homes, roads, stores and warehouses. From a hydrological standpoint, it’s like a vast horizontal dam spreading over the land, blocking the uprising flows of moisture from ground to atmosphere, along with associated cooling, both needed for the hydrological cycle. “There’s plenty of water,” Carvallo insists. And as we’ll see, he has some ideas about how to get it back.
The parallels between the Santiago region of Central Chile and the Western Mediterranean Basin, where Millan did his work are fairly striking. Both are Mediterranean, in that they inhabit mid-latitudinal zones characterized by hot dry summers and mild, wet winters. They also each face a large water body, the Pacific Ocean and the Mediterranean Sea, respectfully. Both are backed by a mountain range with an inland traverse of about 85 km. Santiago is backed by the Andes and Millan’s study area by the Cantabrian Mountains. And both have prevailing sea breezes that come in off the sea. Further, the lands of both are marked by long trajectories of degradation, involving deforestation, agriculture, grazing, industrialization and urban sprawl.
There are some differences, such as larger-scale weather patterns that are different for each region. Plus, for Santiago there’s a small mountain range running between it and the coast, producing its own effect on winds flowing in from the ocean. This range also creates a basin shape between it and the Andes, forming Chile’s Central Valley. Under natural conditions, such a basin, gathering water draining from two mountain ranges, would be wet, with lush meadows and marshlands, but that land is now buried under greater Santiago, a clue to the water problem there. Another important distinction: in the Western Mediterranean Basin Millan had twenty years of ongoing meteorological data to plumb, plus European Commission funding and a staff of nine scientists with which to answer the question of what was happening to the summer rains there. That sort of analysis won’t be repeated here. The emphasis, therefore, isn’t on answering questions but on asking them.
Perhaps the first question to ask is what the water cycle, and related climate, should be like in the Santiago region? What would be its natural-baseline condition? To answer that, we need to go back to 1540 when Pedro de Valdivia arrived in the area with a small contingent of conquistadors, on a southward march from Peru into Central Chile to expand the southern reach of the Spanish Empire. They came upon a long valley that stretched south before them and stopped to make camp at a large, fast flowing river. Valdivia liked what he saw, and wrote to Spanish King Charles of his desire to build a city there in the king’s honor, saying “It is rich in pasture and cultivated fields, in which all kinds of animals and plants can be bred and grown, there is plenty of beautiful wood for making houses…”
He named his city Santiago del Nuevo Extremo (Santiago of the New Frontier). The fast-flowing river he stopped at is now called the Mapocho, from the local indigenous term, Map Chuco, meaning “water that penetrates the land.” It seems the local indigenous understood something about rivers and aquifers that the later Spanish engineers didn’t, for those engineers quickly drained the river’s southern branch for a promenade which eventually became Santiago’s main thoroughfare. In 1888, the northern branch was channelized in concrete.
Note the mention of pastures and cultivated fields. Tending those pastures and cultivating those fields would have been indigenous Picunches, growing crops like potatoes, beans and maize and shepherding camelids similar to Alpacas. They weren’t working purely for themselves, but also for the Inca, under whose domination they had lived for a hundred years, an arrangement about to change for both cultures as they were each to be overrun by Spanish expansion.
The land was also about to be overrun. Valdivia had a city to build, and as he noticed, there was “plenty of beautiful wood” around, such the native puemo, a kind of oak. Researchers examining the land use histories of the Central Valleys of both California and Central Chile depict a mosaic of native oak woodlands, matorral (shrubland) and grasslands occupying the vast valley and surrounding hills, along with the crops and pasturage of the Picunches. The first thing Valdivia did, they note, was clear those forests. The “scattered trees were evidently quickly harvested in the initial settlement. Fire was used to clear the lowland matorral so that the land could be used for agriculture.”1 Others write, “During the colonization of Chile, Spaniards cleared vast areas of forest for agriculture and pasture, mainly those located in the Central Depression (Valley) of Chile.”2
After the land was cleared by axe and fire, cattle were brought in, from Peru and Panama, and huge cattle ranches quickly developed, along with export driven dryland wheat cultivation. By the mid 1800’s Chile’s wheat harvest was feeding the California gold rush along with the Viceroyalty of Peru. Impoverished indigenous were driven to the hills, forced to subsist on already degraded landscapes. The comparison study points out, “All of this intensive land use utilization in Chile was concentrated in the central valley in the Santiago region,” adding “today the northern valley is virtually treeless.”1
By 1930 Central Chile faced a severe erosion crisis, with industrialization soon on its heels. Meanwhile, Santiago continued to expand, becoming not only Chile’s most populous city, but it’s center for industry and railroads. Then in 1974, under the Pinochet regime, the government began subsidizing the conversion of native forests to pine and eucalyptus plantations, especially along the coastal range.
As can be seen, the Santiago region has a long and mostly brutal history of human occupation, but if a hydrological baseline could be determined, a “natural condition,” it would have to be what Valdivia encountered when he entered the lands of the Picunches: a valley rich in life, with “plenty of beautiful wood.” Whatever modifications the indigenous and Incan presence had made to the landscape, they were apparently done in a way that maintained a plentiful water cycle. Though there are no meteorological records from that time, early building records of Santiago note a water table depth of 8 meters. It’s since dropped to nearly 80 meters.
Below is an image Millan produced to illustrate the situation he observed in the Western Mediterranean Basin. The top figure represents the original, healthy water cycle, the bottom the damaged one. Notice at the right edge of both images an arrow enters representing moisture flowing in from the Mediterranean Sea, the sea breeze, and is the same for each. In the top image it’s joined by another arrow of moisture off some swamps, and then some more off upland vegetation and then low mountain trees, resulting in a thunderhead and rain. Millan calls this a “combined breeze,” because it combines moisture from both sea and land.
He refers to the sea portion as the “carrier” component and the land portion as the “trigger” component. The sea carries the main moisture in and the land triggers it with further moisture, or not. Trigger is a good word, because the vegetation isn’t only contributing moisture, it’s also contributing microscopic bits of biota, such as spores, bacteria, and chemicals that provide ideal nuclei for water vapor to condense and freeze around, greatly improving the likelihood of rain.
However, in the bottom image, the damaged watershed, we see that while the sea breeze still carries moisture in, the land contribution is reduced. It can’t provide enough to trigger a rain-producing storm. Note also what happens with the airmass. In the healthy system, it is lifted 12 km high, where the released heat can escape the region, some out to space in an “open” system, but in the damaged one it only travels 5 km high, with the humid, warm, polluted air folding back over the region. Then notice a third thing. In the top image, heavy dark arrows show significant amounts of water seeping down and recharging the aquifer and lowland marshes. On the damaged land, not so much. Notice also there is still some vegetation in the bottom image, meaning the landscape may look OK, with shrubs around, but a critical level, or threshold level, of transpiration is no longer there. The result is a downward cycle of drought, fires, floods and erosion in what water-restoration expert Zach Weiss refers to as the “hydrologic death spiral.”
Now let’s imagine these images representing the area around Santiago. In the lower right of each we would make some small rises to represent the coastal range. This would drop down again to form the basin that in the top image would historically be filled with meadow, marsh and woodland, and in the bottom is filled by Santiago, which we might represent with a thick grey line rising just up the foothills of the Andes.
In the upper image, water flowing down from the Andes and Coastal Range gathers in soils and feeds bottomland vegetation, cooling air and transpiring moisture that joins and triggers the sea breeze rising up the mountains on what Carvallo calls the “water train.” In the lower image, water is sluiced away with modern engineering, while the bottomland soils and vegetation are replaced by man-made, heat-absorbing materials, like roofing tiles, sidewalks and roads. The sea breeze is not only deprived of moisture but is heated, thus needing even more moisture to reach critical saturation for precipitation. The water train is derailed.
So to our main question—is a water cycle collapse occurring in the Santiago region similar to what Millan observed in the Western Mediterranean Basin?—one could answer, “it sure looks like it.” But “it sure looks like it,” is not a very scientific answer, and raises the problem identified by Millan, of “having to scientifically prove the obvious.” It would certainly make sense for people in the region to put it to a scientific test, but Millan’s experience in local, provincial, national and international government was that “civil engineers, agriculture, meteorological and watershed authorities do not seem to question how the resource (water) is generated. All they do is say ‘it is scarce.’ The fact that many management practices kill said resource does not seem to face them.”
Such a water-scarcity mindset is also the norm in Chile, as in the US by the way. Recently a golf course owner contacted Carvallo regarding pressure from city officials to replace the grass fairways with artificial turf, to save water. But Carvallo says that’s the opposite of what we need to do, resulting in only more impenetrable, non-respiring surface, parching the water cycle that bit more. Carvallo also points to drip irrigation as having unintended consequences. By focusing water only on the agricultural product, the soil around it is dried out and the soil-organisms die, depriving the atmosphere of moisture in the summer and hardening the soil against absorption during the winter rains. Further, herbicides are sprayed against weeds that would compete for water, harming the soil even more. Though it seems like water is scarce, Carvallo says what’s really scarce is healthy soil and vegetation.
Which brings us to perhaps the most important question, what to do about it? How does one revive the ancient water cycles that once richly greeted Valdivia and his conquistadors? Perhaps not surprisingly, in peering for the answer Carvallo looks back as much as forward, to techniques developed over 1,400 years ago by pre-Incan cultures to the north, in the Peruvian Andes. These people, the Wari, confronted a high desert climate with long, rainless dry periods punctuated by torrential rains in the brief winters, the water flowing mostly away over the rocky desert terrain, while often sending huaicos, stone laden mud-floods, careening down the valleys. They needed a way to hold on to the water, to slow it’s tumult down the land, for which they used the land itself, with a system called amunas. These were canals, ponds and sink holes, built to direct water high onto hillsides and ridges where it’s allowed to slowly sink into the soil and subsoil, appearing again weeks and months later in downslope springs, during the height of the dry. The huaicos were tamed, the springs and aquifers replenished, the soil hydrated. Amunas are now being rejuvenated in the hills above Lima, Peru, with studies suggesting that dry season flows can be increased by up to 33% there.3
Carvallo envisions applying the principle to the area around Santiago, using the extensive canal system already in place. Currently, with farming done in the summer, most of the canals are left empty in the rainy winter, missing the opportunity to gather and soak water into the land, hydrate the subsoil and replenish aquifers. Carvallo would also soak parks and greenspaces, anywhere to keep the precious winter gift of rain from flowing away. Coupling this hydration with land restoration and regenerative agriculture could provide considerable moisture and cooling to the atmosphere.
This still leaves Santiago though, heating the sea breeze and breaking the water train, for which Carvallo also looks back, though not quite as far. At one time almost all dwellings in the region had parrones, essentially grape arbors, strung on wires over outdoor patios, providing shade and transpirational cooling in the hot summers, not to mention grapes to make wine from and songs from the birds overhead. In winter, after the leaves fall, the solar warmth is allowed back in, when it’s wanted. Carallo wants to bring the parrones back, but on a much larger scale. Cooling not only yards but houses, not only houses but buildings.
Such cooling is becoming critical in certain parts of the city, where extreme heat, dryness and stagnation has resulted in “climate sacrifice territories,”4 barely livable places where the poor and marginalized are crowded. Carvallo thinks government and business should prioritize these areas to provide both immediate relief to the most vulnerable and to demonstrate the concept. Once people see the lived experience of others improving, the demand for such greening would likely grow. He has discussed the concept with architects who say such a vine-draping approach is far more feasible than green roofs, which due to the weight of soil and moisture, require extensive upgrades in roof support and drainage. And while draping a city in vines might be hard to imagine, some sort of vegetative presence there is more natural than the current architecture of inanimate structures, built at great effort and expense. Short of removing the city, option are pretty limited.
So amunas in the hills and parrones on the houses! But would it be enough to rehabilitate the water train? That is admittedly hard to say. We do know that summer daytime humidity has dropped from 80% to 50% since the 1980’s, so whether or not we can quantitatively make such predictions, it qualitatively makes sense to try and cool and hydrate a place that’s drying out. Here we might want to consider Da Vinci’s counsel when dealing with water, and “go first to experience.” The experience of the region, as in so many places around the world, appears to be pretty consistent: desiccation follows degradation. Here’s what the great naturalist Alexander Von Humloldt wrote in1800 upon witnessing the effects of deforestation and water diversion upon a much-diminished Lake Valencia in Venezuela. “When forests are destroyed, as they are everywhere in America by the European planters, with an impudent precipitation, the springs are entirely dried up, or become less abundant. The beds of the rivers remaining dry during a part of the year are converted into torrents whenever great rains fall on the heights. The sward and moss disappearing from the brush-wood on the sides of mountains, the waters falling in rain are no longer impeded in their course: and instead of slowly augmenting the level of the rivers by progressive filtrations, they furrow during heavy showers the sides of the hills, bear down the loose soil, and form those sudden inundations that devastate the country.”
It’s the same thing Millan saw in the Western Mediterranean Basin. And when Millan presented his work in San Diego, also a Mediterranean climate, it’s what the district Forest Service chief saw when he walked up to Millan after the presentation and said “If what you say is true, we’re in a lot of trouble here in 20-25 years.” The year was 1999.
The patterns and cycles are in fact not hard to see; they’re inscribed in the landscapes around us. Our ability to not see them is perhaps a vision impairment common to this and any civilization. But not seeing comes with risk, as Millan warned when I relayed Carvallo’s description of his situation. ”Once a critical threshold is crossed the system drops to a new state very quickly, and it seems to me that Diego is now at that stage, observing the results.”
This rather ominous observation is one of the last comments Carvallo and I received from Millan. Sadly, he caught COVID in the middle of our correspondence and passed away due to complications. I think he would want his comments to us known, and seemed to recognize in the Santiago region a coastal/mountain storm relay as he experienced, and spent a good part of his life trying save, in his own Mediterranean maqui. There were oaks there once too. “Everything fits with his observations,” he wrote. “Even if the coastal air comes into the city, it’s now overheated along its path, the evapotranspiration component, required to trigger the precipitations has also been altered.”
Millan said something else that seems particularly poignant in view of the tragic fires that recently engulfed the coastal hills outside Valparaiso, killing 112 people. “From my observations of the maps, I would guess that there were summer storms in the mountain ranges located between the coast and Santiago, that may have disappeared as soon as the original land layout was changed. There are far too many places where all this is happening, I am afraid.”
Mooney, et al, 1972, Land-use history of California and Chile as related to the structure of the sclerophyll scrub vegetations. Vol. 21, No. 5, Part One of Two, JANUARY 1972, pp. 305-319
Salas, et al, 2016, The Forest Sector in Chile, And Overview and Current Challenges. http://dx.doi.org/10.5849/jof.14-062
Ochoa-Tocachi, B.F., Bardales, J.D., Antiporta, J. et al. Potential contributions of pre-Inca infiltration infrastructure to Andean water security. Nat Sustain 2, 584–593 (2019). https://doi.org/10.1038/s41893-019-0307-1
Mendez, et al, 2020, Adverse Climate Change caused by urbanization without planning or environmental evaluation in Santiago, Chile. Norte Grande Geography Magazine.
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Another great addition to this series Rob. Nothing could better honour Dr Millan and his legacy than continuing to explore the questions that were so central to his life's work. Thank you.
Add California, parts of Pacific Mexico, Panama and Peru, to it, the coast of Oman, the coast of Pakistan, parts of coastal Australia, some Carirbbean islands, a lot of places have seen similar damage and similar results.