The Uncertainty of Portugal's Storms and Droughts

The people of Ereira, in Montemor-o-Velho Municipality, on the Lower Mondego River, have been in isolation for 14 days, depending on amphibious vehicles of the Armed Forces to take them for groceries and voting in the national election on February 8, reported RTP (February 16). Today, it is also possible to reach Ereira by truck in addition to the military's land-and-water vehicles, reported CNN Portugal (February 17). (Photo from Lusa)

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Portugal faced drought in 2022. Since 2005, Portugal had not had so many regions in severe and extreme drought in the middle of winter, reported CNN Portugal (January 28, 2022).

The expansion of the Azores high-pressure system, which can block wet weather fronts to the Iberian Peninsula, caused the reduction in rainfall. The expansion was caused by the increase in greenhouse gas emission. It will cause more frequent droughts in Portugal and Spain, according to the Nature Geoscience article, Twentieth-century Azores High expansion unprecedented in the past 1,200 years (July 4, 2022).

No rain was in the forecast until at least February 15, 2022.

Today, four years later, successive storms led to declarations of a state of calamity in dozens of municipalities, caused power outages for hundreds of thousands, isolated populations into islands and caused widespread flooding, reported SIC Notícias (February 11).

Along with its role in droughts, the Azores high-pressure system also plays a fundamental role in the movement of storms which form in the Atlantic Ocean.

Jorge Ponte, a meteorologist at the Portuguese Institute of the Sea and Atmosphere (IPMA), explained that, since January, "we have had a relatively abnormal positioning of the Azores anticyclone, which has been farther south than normal", and this has allowed depressions to move farther south to the latitude of the Iberian Peninsula," according to SIC Notícias (February 11). What will happen over the weekend is that the anticyclone "will move up a bit in latitude and will cause an improvement in the weather".

Droughts

Droughts are still very much a part of Portugal's history and future.

"There has been a decrease in annual precipitation values in mainland Portugal, about -20 mm/decade (.8 inches), with the past 20 years having been particularly less rainy. Six of the driest years occurred after 2000, including 2005, the driest since 1931, 2007 the second driest and 2017 the third driest," according to Vanda Pires and Tânia Moura, both at the Portuguese Institute of the Sea and Atmosphere (IPMA), in Perspective Chapter: Droughts Risk in Portugal -- Past, Present and Future (September 17, 2025), Restoring Ecosystems and Assessing Drought Risk -- Approaches and Practices (2025).

"Some historical examples of drought in Portugal are the years 1354-1355, 1385-1398 (very long), 1504-1506 and 1733-1738."

Jet Stream Blockage

Filipe Duarte Santos, 83, Physics professor at the University of Lisbon, president of the National Council for the Environment and Sustainable Development (CNADS) and author of

Alteraçôes Climáticas, Climate Change, (2021) told Fundação Francisco Manuel dos Santos in Storms and Floods: 5 Questions for Filipe Duarte Santos (February 10):

"We have been experiencing a jet stream blockage in the North Atlantic Ocean, off the coast of the Iberian Peninsula. The jet stream consists of very intense westerly winds at an altitude of about 10,000 meters (6.2 miles), which drag along depressions (low-pressure atmospheric systems which cause rain and wind) and contribute to some of the turbulence we feel when traveling by plane.

"The jet stream separates the warm, humid air masses to the south from the cold, drier air masses to the north. It is located around the Arctic, like a necklace, but sometimes it meanders like rivers and comes farther south. In recent weeks, the jet stream has moved far south in the North Atlantic and has become stuck, almost motionless, pointing toward the Iberian Peninsula. Consequently, the storms (very deep depressions, i.e., with very low pressure at the center) that it drags along are hitting the coast of Portugal and affecting Spain and Morocco as well.

"We cannot predict when we will have another situation like this, with a "train" of successive storms, but we do know that the intensity of the storms is increasing, both in terms of wind speed and the amount of precipitation.

"This intensification is due to the increasing amounts of greenhouse gases (mainly carbon dioxide, methane and nitrous oxide), which are released into the atmosphere due to some human activities and which cause what we call anthropogenic climate change.

"Regarding precipitation, there is an increase in the intensity of tropical cyclones and the most intense extratropical cyclones. This increase in intensity manifests itself in increasingly faster winds and growing amounts of precipitation. There is no evidence of an increase in the frequency of these cyclones.

"On the other hand, in some regions of the world, such as the Mediterranean region and southern Europe, the frequency and duration of droughts are increasing.

"There is greater inter-seasonal and inter-annual variability, which, however, cannot be predicted with the climate models we have available."

Embracing Uncertainty in Climate Models

Computer models of the climate system, or Earth System Models (ESMs), are not equivalent to reality, according to David Stainforth, at the Grantham Research Institute on Climate Change and the Environment, said in Model of Catastrophe (November 11, 2025), Aeon.

"So, what can we do? One option is to make the models better. Make them more detailed and more complicated. That, though, raises an important question: when is a model sufficiently realistic to predict something as complex as climate change? . . .

"Earth System Models are fantastic achievements of modern computer-based science and tremendously useful tools for research. They break up the atmosphere and oceans into grid boxes -- typically with sides around 20 to 200 kilometers long, (12.4 to 124.3 miles) -- and, for each grid box, the computer code solves a set of well-founded and well-understood equations from classical physics, which describe how fluids, such as air and water behave. This is known as the 'dynamical core' of the model.

"But the dynamical core isn't enough to simulate Earth's climate system. That's because there are many critical processes which we don't fully understand and for which we don't have robust and well-tested mathematical representations, eg, the behavior of tropical and temperate forests. There are also many processes, such as clouds, atmospheric convection and ocean eddies, which take place on scales that are much smaller than the grid boxes. . . These processes need to be included in the models if they are able to simulate climate change. But we can't represent what is actually going on because we either don't know or it's computationally infeasible -- or both.

"So, they are included in the models through pieces of code called 'parameterization schemes'. These parameterization schemes aren't representations of the physics of what's happening but statistical characterizations of how each process affects and interacts with the rest of the model. Clouds, ocean eddies and many land surface systems are examples of processes represented this way.

"This difference between physics-based 'dynamical core' and the statistically fitted parameterizations may seem a rather dry and uninteresting issue, best left to the specialists. In practice, this difference is central to debates over what climate science can tell us about the future.

"Nevertheless, changing the way we use ESMs could provide a different and better way to generate the local climate information we seek. Doing so involves embracing uncertainty as a key part of our knowledge about climate change. It involves stepping back and accepting that what we want is not precise predictions but robust predictions, even if robustness involves accepting large uncertainties in what we can know about the future.

"We should not only make plans based solely on our best estimate of what might happen. We also should consider the range of plausible outcomes we foresee. . . . Uncertainty, therefore, needs to be at the core of adaptation planning while also being the lens through which we judge the value of climate policy and the energy transition."

Flood Risk Areas

Filipe Duarte Santos was asked how flooding may have been mitigated this year. He said that the dissemination of information regarding flood risk areas, a monitoring network of sensors measuring water levels in dams and rivers, and flood-resistant infrastructure could have made a difference.

"Detailed flood risk maps, both river and coastal, exist and are produced in both the public and the private sectors, particularly in the insurance industry. However, these public maps are not properly disseminated, and the legislation stemming from them is sometimes not enforced. The capacity for 'law enforcement', that is, the ability to ensure compliance with the law, is still relatively low in our country."

Geographer António Bento Gonçalves said that flooding in the Lower Mondego River region is neither an unexpected nor exceptional phenomenon. It has been recurring for centuries. He advocates for structural change in land-use planning and criticizes construction on floodplains, even where there is critical infrastructure, reported SIC Notícias (February 13).

"We cannot continue to authorize people to set up shop, whether individuals or businesses, warehouses, factories or houses in floodplains because no matter how much is done, no matter how much work is carried out, this will always happen.

"And not only can we not authorize it, but the municipalities have to set an example, and they, themselves, cannot install too much infrastructure on floodplains."

António Bento Gonçalves said that in 1464, a royal charter from King Afonso V already prohibited burning on the riverbanks of the Mondego River to prevent erosion and silting.

"We are in the 21st century and, in the 15th century, we already had this notion, which, however, we have been losing," said the geographer, adding that wildfires exacerbate the problem."

Sensor Monitoring of Water Levels

Filipe Duarte Santos said that losses from floods can be reduced with a "national monitoring network with sensors which measure water levels in dams and rivers, and river flows, operating effectively and providing data. With this data, timely warnings of increased risk can be issued, which are essential for alerts and for taking actions that reduce or avoid risks."

Infrastructure

"The occurrence of extreme meteorological and climatic phenomena (floods and droughts) affects Portugal with severe socioeconomic impacts which depend, to a large extent, on the degree of development and the organization of infrastructures to minimize their effects," according to Perspective Chapter: Droughts Risk in Portugal -- Past, Present and Future.

Duarte Santos also said that certain measures adapting to extreme events can reduce deaths and property losses.

"One successful example of these adaptation measures was implemented on the island of Madeira after the extreme precipitation event -- a flash flood -- on February 20, 2010 (at the Bica da Cana weather station, 268 millimeters (10.6 inches) of rain fell in 24 hours), which resulted in 47 deaths and approximately 600 displaced people.

"A set of adaptation measures were studied, planned and implemented, including investments in flood-resistant infrastructure."

The Autonomous Region of Madeira now has flood-resistant infrastructure thanks to the European Union's Solidarity Fund, European Regional Development Fund (ERDF) and Cohesion Fund, and to the speedy response of citizens and municipalities, reported El País (June 28, 2018).

"Retention dams are located on the three valleys which run through the island from north to south, and act as filters to stop trees, rocks and sediment from falling at full speed on the towns below. The distance between the cement blocks, which make up the dam, decreases as the blocks reach the sea. This means that the biggest dangers are trapped first," explained Sérgio Lopes, a geographer at the island's Regional Secretary of Teams and Infrastructure.

Pine trees on the mountain tops are being replaced by nearly two million endemic species which are more resistant to forest fires and better at storing water. Canals have been built on the river basins, and the riverbanks have been cleaned up, reported El País.

On June 6, 2023, there was a more intense downpour than the one in 2010. The more recent storm caused 349 millimeters (13.7 inches) of precipitation in Bica da Cana in 24 hours, but there were no deaths and only 38 displaced people, said Filipe Duarte Santos.

"Adaptation is not a simple process because it involves various socioeconomic sectors and bio-geo-physical systems: water resources, agriculture, forests, ecosystems, human health, coastal zones, fisheries, population centers and cities, housing, infrastructure, the economic and financial sector, and others.

"This means that it involves multiple ministries and their respective agencies, authorities, institutes and directorates-general, municipalities and non-governmental organizations.

"The success of adaptation depends on effective, science-based adaptation measures, adequate and timely funding, and a culture of planning and active cooperation among all institutions involved in the process. It depends on good governance, planning and multi-level organization, that is, between the local level of municipalities, which is extremely important, the level of government and its institutions, and the level of the European Union, which has provided significant economic, financial and legislative support."

However, if the goal is a common one of reducing the the loss of life and property, then the work will be successful.

At the moment, everyone is at risk in an uncertain scenario, which only will become more dangerous over time meaning that reacting to catastrophe, and not planning for it, will become less and less effective.