Restoring Iberian rain

Forests and marshes, & the chimneys, cakes, and summer storms they create

I took off to Portugal this summer, with an idea stewing in my mind about restoring the watersheds in Iberia (the peninsula that Portugal and Spain co-inhabit), and honoring the legacy of Millan Millan, who had worked to restore the rains there.

In Southern Portugal, climbing to the top of a mountain, I stood on an ancient igneous rock, winds swirling around me. To the north, spread out below, was the region of Alentejo, with its olive groves, eucalyptus plantations, and cork oaks. To the south, below me was the region of Algarve, dry and hot, with its terra rosa soil and shrubs extending thirty kilometers out to the coastal cities and beautiful beaches.

A hundred kilometers away to the north, I could see a thunderous cloud formation rising like a sandstorm. I watched rapt as it raced across the landscape. It took fifteen engrossing minutes to reach me. When it arrived, the winds caused the eucalyptus trees to groan, and bend back and forth at precarious angles. Close up the clouds became patches of fog sprinting by. I could almost touch them. Then rushing a mile past the mountain top, the clouds began to vaporize, disappearing like a Cheshire Cat smile. The heat of Algarve was evaporating the clouds and their potential to create precipitation.

In winter though, it is cold enough that these Atlantic storms will sometimes make past these mountains and into the south to rain on the Algarve land.

Winds carry water all around Iberia. Below are two pictures of the winds at an altitude of 1600ft. The first one is on Sept 21st 2pm, 2024 where you can see the wind blowing into north eastern Spain from the Mediterranean Sea. The second one is Sept 24th 2pm, 2024 where you can see the wind blowing in from southwestern Portugal. Some of the wind then veers into central Spain, goes over the mountain range into the coastal regions of northeastern Spain, and then into the Mediterranean Sea. Some of the wind veers southeast into Andalusia, and then out to the Mediterranean Sea. (You can go onto Ventusky.com and explore wind profiles for different locations, altitudes and times)

[Sept 21st, 2024, 2pm. Wind at height 1600 ft.]

[Sept 24th,2024, 2pm. Wind at height 1600ft]

Portugal and Spain have been losing their rains over the past few decades. The loss is especially poignant in the coastal regions of southern Portugal, southern Spain and eastern Spain, where the weather is hotter, and the droughts more pronounced. The vanishing of the rains affects local residents, businesses and hotels who are experiencing increasing water stoppages. Andalusia, on the southern coast of Spain, produces tomatoes, peppers, cucumbers, artichokes, onions, lettuce, olive oil, and fresh fruit. Valencia on the eastern coast of spain, produces citrus, and produces rice, almonds, olives, avocados and a wide variety of vegetables. The loss of rains affects Spain food production, and its food exports to Europe.

[Regions of Spain]

In the 1990s the European Commission approached Millan Millan to look into why Spain was losing its rain. Millan was the head of the Center of Environmental Studies of the Mediterranean, an organization with 90 scientists and staff. He was a meteorologist who took pride in his observational skills, and his ability to read the clouds to discern an atmosphere’s history and future. In his detective work to solve the Riddle of the disappearing Spain rain, he walked around the local geographical areas, in the mountains with their maqui (shrubbery), and the marshes of the local area, to get a sense of what was causing the loss of the summer storms. He talked to a lot of locals who too had noticed the loss of the rain over the decades.

Millan put together a program to gather meteorological data from towers, tethered balloons, and aircraft. Then he ran various computer simulation models. Using this three pronged approach of observation, measurement, and simulation, Millan figured out the mystery that was causing the rains to disappear. The culprit was the draining of the marshes and the chopping down of the vegetation and the forests. This nature loss had led to reduced evapotranspiration and increased air temperature, which made it harder for clouds to form.

Having figured out the problem, Millan worked over the years to try convince the government to regenerate the land, so that the rain may return.

I connected with Millan and recorded this interview with him. Rob Lewis, author of the newsletter The Climate According to Life, also had a chance to correspond with Millan. He writes Millan “had to watch those summer storms he used to track as a boy with his father gradually disappear altogether.” Millan said to him “Those summer storms…are now totally gone.. The landscapes I loved, as they were, I now recognize as very downgraded ones. I can not stop thinking on how they must have been. My eyes can’t stop searching for the clues, all around, of Toba Rocks in the slopes. Rock created when limestone-enriched water flowed over mosses and other herbs in waterfalls and water oozing off the slopes. Now just rocky slopes.  It is all over the place here and there, where water flowed just a few years ago.” Millan passed away earlier this year.

Now in Iberia, I wanted to restore the rain, to honor Millan’s legacy. Restoring the rain will entail restoring marshes, shrubbery, forests, rivers, and aquifers, utilizing the local dehesas (the agroforestry lands), shifting to regenerative agriculture practices, rewilding, and using a variety of water earthworks practices.

I met up with water cycle restorationist Nick Steiner (who I had recently recorded a podcast with) and some other amazing folk in Spain. We began working on a plan. I’ll discuss more of it, as it unfolds over the next few months.

I’ve also been talking to a lot of people from many different backgrounds with a diversity of skills interested in the project. Multi-stakeholder dialogs in different regions of Iberia between regenerative farms, local businesses, hotels, local government, can help us build partnerships that work together to regenerate watersheds. Commonland is an example of an organization doing this kind work, as they work to bring multi-stakeholders together. They are partnering with AlVeLal on a project to bring together local farmers, conservationists, government, and entrepreneurs, in the provinces of Almeria, Granada and Murcia in southeastern Spain to vision and work together how to restore ecosystems at landscape scale (which means one hundred thousand hectares or more).

An idea that has emerged through our discussions is to shift a segment of the tourism industry into eco-tourism. Costa Rica is an example of a country that managed to save a lot of its forests by taking an ecotourism approach starting in the 1970s. As a result they have much more nature than neighboring countries in the Central America. Italy is an example of country where agritourism took off. We have been discussing how we can create a regenerative water eco-tourism movement.

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For more detailed clues to how we can restore the rain, lets take a deeper dive into Millan’s research into the rain in Spain. I’ll discuss here results from his paper “Extreme hydrometeorological events and climate change predictions in Europe” [2013].

Millan researched what was happening in the region of Valencia, which is on the eastern coast of Spain. Valenica is sandwiched by mountains on its west and the Mediterranean sea on the east. In many ways Valencia’s storm issues are similar to other Iberian coastal regions, like Andalusia and Algarve, who are also bordered by mountains and the coast.

Millan delineated three types of wind systems that bring rain to Valencia. First, there are winds that comes from the Atlantic ocean, blowing into Portugal, across central Spain and then into Valencia. Those storms happens in non-summer months. During the summer the mountains stop the clouds travelling across the Iberian peninsula from reaching Valenicia. (This is the kind of effect I had noticed when the mountains stopped the clouds from travelling into the Algarve region.) See A below. Second, there are the summer storms that come in from the Mediterranean Sea. See B. Third, there is rain that comes from what are called backdoor cold fronts or levanters blowing in from the Mediterranean Sea in the east. These back door fronts are produced by anticyclones moving from the Atlantic to Siberia in early fall until late winter spring, an anticyclone being a high pressure system with a center where colder air sinks and then spreads outwards in a clockwise spiral.

[Map of Valencia. Fig A. shows rain brought by Atlantic fronts. Fig B shows rain brought from summer sea breezes. Fig C shows rain brought by backdoor fronts/ Levanters. The curvy lines show amount of rainfall. Last figure bottom right shows how much rainfall a month comes from each type of rain]

The key cause of summer storms are the sea-breezes of B.

Why do sea breezes blow inland? Because of temperature gradients. Lets illustrate this with a fish tank. Imagine putting blue dye and ice on one side of the tank, and putting red dye while shining a heat lamp on the other side. You will see the the blue dye sink and flow towards the hot side, while the red dye will flow at a higher height to the cold side. The temperature gradients creates a circulation of the water. The same thing happens with air. During the day in summer, the air will at flow at lower heights from the colder ocean to the warmer land, and flow back at higher heights from the land to the ocean. At night the land cools off, and the wind flows reverse.

The sea breezes combine with upslope winds as they blow inland. Upslope winds happen when the land heats up, causing the air to rise up the side of a mountain, thus creating a wind.

The sea breezes are affected by the land cover, topography and the slope of the land. Millan’s paper references the work of Jianwei Miao. Miao and his colleagues simulated the winds coming in southeastern Spain along the coast, and looked at scenarios when the coastal areas and mountains were all forests, and scenarios when the area was all desert. What they found was that in the all-forest case the winds move at 2.7 meters a second and reach 25km inland. In the all-desert case the winds move at 9 meters a second and reach 75 km inland.( Not noted by Millan or Miao, when winds slow down they can lead to the water vapor molecules being more likely to find each other, and nucleate into rain. [Eiras-Barca 2020, Zhao 2019, and see my previous article on Francina Dominguez’s research]

Lets follow a time sequence for how these sea breezes blow inland. Measurements show that in the mornings the winds will blow a certain distance inland, and then start ascending into an updraft, into what Millan terms a chimney. This wind formation stays for about a half hour to an hour, and then the breeze blows even further inland, and creates another chimney. The wind moves in this start and stop rhythm as it penetrates further inland. A number of updrafts/chimneys form in the range between 60-100km. You can see this in the diagram below. The sea is on the right in the figures. The winds blow inland towards the left. Red arrows indicate where the chimneys form. At 10am (fig b) and at noon (fig c) a number of chimneys are forming. It takes about 4-6 hours for the breeze to work its way inland all the way up the mountain (fig d)

[Figures from Millan 2013. Red arrow shows wind blowing inland. Blue arrows show wind blowing back out to sea. Each frame is a particularly time of day from 2:00 hrs to 22:00 hrs]

There are two key variables that affect whether the water vapor in the chimneys then turn into clouds. The first variable is the amount of water vapor that the evapotranspiration adds to the chimneys. When forests and coastal marshes disappear, so does the evapotranspiration. When Millan did his research, the coastal plains were by then only evapotranspiring 5 to 7 liters per square meter, and the maqui (the shrubbery) of the mountains were only evapotranspiring 1 to 3 liters per square meter.

The second variable that affects whether the water vapor in the chimneys turn into clouds is how much the air heats up. At the coast the percentage of water in the atmosphere is 14 grams of water for every kilogram of dry air (14 g/kg). If the breeze heated up an extra 16 degrees Celsius at it moved inland, then the water vapor in the chimneys would need to reach a ratio of 21 g/kg to be able to form clouds at 2000 meters altitude (which is a little higher the mountain ranges in Valencia). However if the breeze heated up an extra 19 degrees Celsius as it moved inland, as was sometimes measured by Millan, then it would need to reach a ratio of 25 g/kg for clouds to form. With the loss of coastal marshes and forest, there was more bare land which heated up the breezes more. According to Millan these two variables, the loss of evapotranspiration, and the heating of the sea breezes, is why most of the summer storms have disappeared over the last 50 years.

If you would like a slightly more technical version of this explanation, Millan writes “The number of steps that the combined breeze takes to reach the mountain ridges inland and, thus, the number of chimneys, and layers, formed during its development depend on the lay of the slopes around the Western Mediterannean Basin. During this process, storms can develop whenever the Convective (-orographic) Condensation Level (CCL) of the incoming air mass is reached within the chimney at the leading edge of the combined breeze. This can trigger deeper (moist) convection and the development of convective showers or a storm. If storms do develop, the air mass becomes mixed all the way up to the tropopause, and the closed-loop coastal wind system becomes ‘‘open’’. That is, it ends up behaving like a small monsoon...However, the airmass coming inland from the sea sustains heating as it moves inland along the warm surface. Thus, the formation of a storm requires the addition of water vapour to offset its heating, and keep the CCL of the incoming airmass below its height of injection into the return flows aloft. For example, by evaporation from: the surface, coastal wetlands, vegetation, forests, irrigated crops, etc. Otherwise, heating prevails and the CCL of the incoming airmass will keep on rising”. If the CCL, which is the level/height at which the water vapor condenses, is higher than the chimneys, then no clouds form.

What happens if the water vapor does not condense into clouds? The wind at higher altitudes will then carry that water vapor back out to the edge of the ocean. There it hovers in the air, and forms a number of layers, like a cake, with each layer containing the water vapor and the pollution. Reading Millan’s paper, I pondered why the layers do not mix as Millan does not go into details of this. My guess it is probably because the pollution absorbs the radiation and thus heats up that layer. When a layer is warmer than layer below it, it will not mix as warm air wants to rise, not sink.

The layered cake now has a huge amount of water vapor in it. Millan’s simulations then showed, as did other researchers, that large winds will come along and take that massive layered cake and blow it into Europe, causing large storms and floods there. In meteorology phenomena can be connected in unexpected ways. The loss of coastal marshes and forests in Spain, can lead to floods in France, Germany, Belgium, Switzerland and Italy.

Its normal for there to be treaties between countries up and down river of each other, because water use upriver affects water availability down river. What research like that of Millan and others show, is that we may also need treaties between countries upwind and downwind of each other, because land use upwind affects floods and droughts downwind. Jessica Keune and Diego Miralles, of Ghent University in Belgium have been proposing that the European countries come together to form a watershed precipitation recycling network where they can make upwind and downwind treaties [Keune 2019]

Regions in Portugal and Spain might also find it beneficial to make legislation and partnerships with each other, as land use in one region affects rain and drought in another eg. land use in Portugal’s central region and Spain’s Extremadura region will affect the amount of winter rain Spain’s Andalusia region gets.

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Others since Millan Millan have also been studying the loss of rain in Spain.

Monica Garcia is part of the Spanish National Research Council. Their Desertification Research Centre - CIDE is devoted to researching the causes, factors and processes of desertification. She worked with Yubo Liu, from Beijing who had been studying where the rain came from in the Huai He River Valley, China, finding that 40% of Huai He’s rain came from the small water cycle.

They studied the change in Spanish rain and wrote a paper with their colleagues called “Recent decrease in summer precipitation over the Iberian Peninsula closely links to reduction in local moisture recycling." [Liu 2022] The average summer precipitation decreased from 34.89 mm per month during the 1980-1997 period to 27.17 mm per month during the 1997-2019 period, a decrease of 22%. Winter rains are made largely from moisture from external areas to Iberia, while summer rains are made more from the Iberian small water cycle (aka moisture recycling). They found that the Iberian small water cycle has significantly decreased.

In the figure below we can see the loss of summer rain in the Iberian Peninsula. In some places the loss is up to 17.5mm. In the Valenicia region, the rain decrease ranged from 2.5 to 7.5 mm. Today Valencia is left with only 18mm of summer rain. In Malaga, in the Andalusia region of Spain there has been a loss of about -5 to -7.5mm of summer rain. Nowadays Malaga is left with only 10mm of summer rain.

[Summer rain in IP (Iberian Peninsula). Liu 2022]

“Water begets water, soil is the womb, vegetation is the midwife” Millan eloquently once pronounced. If we can begin to restore enough of the soil and the vegetation in Iberia, it will bring back some rain, which will then enable even healthier soil and more vegetation to grow, which will in turn bring back even more rain.

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If you ideas or skills to contribute to the restore Iberian rain project, or want to get involved, feel free to share below in the comment section, and to connect with each other.

This is a reader-supported and rain-powered publication.

References

Eiras-Barca, J., Dominguez, F., Yang, Z., Chug, D., Nieto, R., Gimeno, L. and Miguez-Macho, G. (2020), Changes in South American hydroclimate under projected Amazonian deforestation. Ann. N.Y. Acad. Sci., 1472: 104-122. https://doi.org/10.1111/nyas.14364

Keune, Jessica, and D. G. Miralles. "A precipitation recycling network to assess freshwater vulnerability: Challenging the watershed convention." Water Resources Research 55, no. 11 (2019)

Liu, Yubo, Monica Garcia, Chi Zhang, and Qiuhong Tang. "Recent decrease in summer precipitation over the Iberian Peninsula closely links to reduction in local moisture recycling." Hydrology and Earth System Sciences 26, no. 8 (2022): 1925-1936 https://hess.copernicus.org/articles/26/1925/2022/hess-26-1925-2022.pdf

Miao, J.-F., Kroon, L.J.M., Vilá-Guerau de Arellano, J., Holtslag, A.A.M., 2003. Impacts of topography and land degradation on the Sea Breeze over Eastern Spain. Meteorol. Atmos. Phys. 84 (3–4), 157–170.

Millán, Millán M. "Extreme hydrometeorological events and climate change predictions in Europe." Journal of Hydrology 518 (2014): 206-224

Yang, Zhao, and Francina Dominguez. "Investigating land surface effects on the moisture transport over South America with a moisture tagging model." Journal of Climate 32, no. 19 (2019): 6627-6644.