Dams. From abundant rain to drought, everything is cyclical

Dams.  From abundant rain to drought, everything is cyclical


March brought relief to Portugal, with the country benefiting from greater water availability due to heavy rain brought by storms Mónica and Nelson. The statistics reveal a positive general scenario: 68% of the 81 monitored dams have more than 80% of their volume stored. A detailed analysis shows that Portuguese reservoirs, by river basin, also reflect this positive trend. Regions such as Tejo, Douro, Alentejo, Vouga and Cávado record volumes above 90%, while some, such as Mira, Arade, Ribeiras do Barlavento and Ribeiras do Sotavento, are slightly below the historical average.

Overall, March had a positive balance in total storage volume (86%), with some reservoirs approaching their maximum quotas. The Alqueva Dam deserves to be highlighted, being just 1.5 meters from its maximum capacity, which is crucial for human, agricultural and energy supply. Despite the good news, the south of the country still faces challenges. On the Alentejo coast, Barlavento and Sotavento Algarvio, water continues to be a scarce resource. To resolve these regional disparities, there are proposals under debate, such as the “water highway”, with the aim of transferring water from the North to the South, and investments in infrastructure, such as the construction of new dams. But none of this is new, as many of the phenomena are cyclical. For example, two years ago, abundant rain in March significantly improved the drought situation in Portugal. Most reservoirs recovered their water levels and only 16% of the country was facing a severe drought.

According to a report from the Reservoir Management Commission at the end of 2015, for example, during the hydrological year 2014/15, which comprised the days between October 1, 2014 and September 30, 2015, Portugal faced a situation of severe drought. The hydrological year began with above-average rainfall in October and November, with November being particularly rainy, with monthly rainfall approximately twice as high as normal. However, in the following months, especially between December and May, precipitation levels were consistently below average, with monthly amounts generally below 80% of normal. The months of December, February and March stand out, which recorded very low precipitation values, less than 40% of the average.

The lack of rain led to a meteorological drought across the country from March 2015, intensifying until July and persisting until August. Only at the end of the hydrological year, in September, was there an improvement, especially in the northwest region of the country, due to the abundant rains that occurred that month in the North and Center regions. If we go back even further in time, we realize that in March 2006 Portugal saw a significant improvement in the drought situation, with dams reaching storage levels that had not been seen since 2004, according to the Water Institute (Inag). Of the 57 reservoirs monitored, 23 had more than 80% of storage capacity and only two had less than 40%.

Compared to the previous year, the situation was much more favorable, approaching that observed in 2004. Two years earlier, in March, 32 dams were above 80% and only two were below 40%. Already in 2005, the country was facing a severe drought, with only nine reservoirs with more than 80% water and 12 below 40% by the end of the month. For some river basins, such as the Tagus, the situation was relatively comfortable, with 82% of total storage capacity. The Castelo de Bode reservoir, which supplies the Lisbon Metropolitan Area, was almost full, with 91% water.

Furthermore, five basins, including those of Arade, Ave, Cávado and Lima, had storage levels above the 1990/2000 average, while those of Douro and Mondego were practically at the average level. The Sado basin still faced challenges, with five dams with less than half their capacity, with the Roxo reservoir being the most affected, with only 25% of water. The recovery in dam levels in 2006 was a direct result of a very rainy March, with accumulated precipitation exceeding the historical average. However, despite the improvement, the distribution of rain still showed disparities, with more rain in the South and less in the North of the country.

Between abundant rain and drought Floods represent the most impactful natural disasters in Portugal, with serious social and material consequences. On average, they constitute around 80% of compensation for natural disasters in the country. One of the most catastrophic events was the flood that occurred on November 25th and 26th, 1967 in the metropolitan region of Lisbon, caused by a cold depression with subtropical characteristics. The depression caused intense precipitation, resulting in flash floods and flash floods.

The greatest damage occurred due to inadequate construction in flood-prone areas, the coincidence with high tide and the fact that it occurred at night when many people were sleeping. Precarious housing along rivers and streams was particularly affected, resulting in thousands of people being displaced and hundreds of deaths. The Salazar government minimized the impacts of the floods, hiding the real number of deaths and the damage caused. It is estimated that more than 700 people died during the event, but official data points to only 250 victims. The lack of aid and the poverty of local populations worsened the situation.

Despite the regime’s censorship, news about the floods triggered an international solidarity movement. Several countries, including the United Kingdom, Italy and France, offered donations and health support to help Portugal deal with the consequences of the disaster. In February 2010, many years later, a sudden storm devastated Funchal, Madeira, leaving 47 dead, 4 missing, 600 homeless and 250 injured. The floods resulted in cars washed away, parking lots submerged and homes destroyed. The hospital was overwhelmed and psychological support teams were set up to help victims and families affected by the trauma.

Many areas were isolated, with concerns that more victims could be in remote villages. Damage was widespread, with roads cut, electricity and water outages, and a widespread sense of fear among the population. The president of the Regional Government requested assistance from the European Union and spoke with Durão Barroso, while José Sócrates traveled to the island to find out about the damage. The causes of the tragedy were torrential rains, resulting in flash floods and destruction throughout the city.

On the other hand, mainland Portugal has faced droughts over the centuries, with devastating impacts on agriculture, water resources and people’s well-being. In the years 1354-55, 1385-98, 1504-06, 1733-38 and 1753 the population witnessed the recurrence of these droughts. In the 19th century, there was a particularly long and severe period between 1873 and 1878, especially dramatic for the Algarve. So much so that in 1875 the newspaper Gazeta do Algarve read: “There is no hope that agriculture will produce enough to support the inhabitants of the province, nor will there be enough pasture to feed livestock”. In recent decades, there has been an increase in the frequency of meteorological droughts, covering large areas of the country. Since 1980, there have been eight severe droughts, including the 2004/2006 drought, the most intense in 90 years. Recently, the droughts of 2011/2012 and 2017/2018 affected almost the entire territory, highlighting Portugal’s vulnerability to these extreme weather events.


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