Vulnerabilities - Portugal
Most studies on water supply and demand conclude that annual water availability would generally increase in northern and northwestern Europe and decrease in southern and southeastern Europe (17). In the agricultural sector, irrigation water requirements would increase mainly in southern and southeastern Europe (18). The overall balance between demand and supply under climate change suggests that water stress may occur in the Iberian peninsula (due to less supply), northwestern Europe (due to increasing demand) and eastern Europe (due to changes in demand and supply) (19).
Aquifers usually recharge slowly, and current abstraction levels may not be sustainable under future climate change scenarios. In some areas of southern Europe aquifers are already overexploited. When aquifers near the coast are overexploited, salt water may intrude, thus reducing water quality in the aquifer.
Many parts of Europe suffer water stress, and, as was seen in 2003, it is these areas that are most vulnerable to drought. Climate change modeling (20), using a range of climate scenarios, has predicted that droughts are likely to increase in frequency and intensity across most of Western Europe. Notwithstanding the severe impact of major droughts on the fabric of society, the institutional frameworks to cope with droughts at European level are poorly developed (21).
Continental Portugal is susceptible to droughts, usually associated to the blocking effects of the North Atlantic subtropical high pressure fronts, which impede polar fronts from reaching the Iberian Peninsula. Droughts are common in continental Portugal. However, its frequency and intensity have increased in the last decades of the 20th century (22). For the period 1971 - 2015, a clear drying trend was identified in most of the Iberian Peninsula, and this trend was related to the decreased precipitation and the increased reference evapotranspiration (26).
Drought was most severe in 1991/92, 1992/93, 1994/95, 1998/99, 1999/2000 and 2004/2005. The drought that began in late 2004 had impacted the whole country by the end of January of the following year. Precipitation values in January 2005 in central and southern regions were close to or lower than the minimum values previously observed, in some cases for as long as 100 years, as in the case of Lisbon and Evora which have not had a month of January without rain since 1901. The drought that began in November 2004 was, by the end of the hydrological year (September 2005), the most severe in the last 60 years in terms of land area affected (22).
Due to the 2004-2006 drought, Portugal spent 23.2 M€ in urban water supply. In 66 municipalities (100 500 inhabitants), urban water supply was supplemented by 22,850 water tank operations (23).
The definition of drought
Drought is a natural phenomenon defined as sustained and extensive occurrence of below average water availability. Drought should not be confused with aridity, which is a long-term average feature of a dry climate. It is also distinct from water scarcity, which constitutes an imbalance between water availability and demand (1).
Three general types of drought may be recognized (7):
- meteorological droughts – defined on the basis of rainfall deficiency;
- hydrological droughts – where accumulated shortfalls in river flows or groundwater replenishment are of primary importance;
- agricultural droughts where the availability of soil water through the growing season is the critical factor.
During lengthy droughts, all three categories may combine to increase water stress. High temperatures are not a necessary component of drought conditions, dry winters can lead to water resources stress in the following summer.
Droughts might manifest themselves either as short but extreme single season droughts (such as the hot summer of 2003) or longer-term, multi-season droughts, and they might be local or widespread in nature (7).
Vulnerabilities in Europe
The European Commission has estimated that at least 11 % of Europe's population and 17 % of its territory have been affected by water scarcity to date and put the cost of droughts in Europe over the past thirty years at EUR 100 billion (1).The drought of 2003 caused a total economic cost of over €13 billion in around twenty European countries (2,7).
Vulnerabilities – European trends in the past
In 2012 the IPCC concluded that there is medium confidence that since the 1950s in particular southern Europe has experienced a trend toward more intense and longer droughts (25). There is no evidence that river flow droughts have become more severe or frequent over Europe in general in recent decades (3), nor is there conclusive proof of a general increase in summer dryness in Europe over the past 50 years due to reduced summer moisture availability (4). Strong increases in the area of combined severe dry and wet conditions in Europe over the last three decades have also been identified, though, and it has been suggested that without global warming droughts would have been smaller and less pervasive (13).
Despite the absence of a general trend in Europe, there have been distinct regional differences. In particular, more severe river flow droughts have been observed in Spain, the eastern part of eastern Europe and large parts of the United Kingdom (3). However, in the United Kingdom there is no evidence of a significant increase in the frequency of occurrence of low river flows (5).
Increasing drought deficits were observed in Spain, eastern Europe and large parts of central Europe with changes in precipitation cited as a major explanatory factor (11). Others (12) have indicated that the proportion of Europe experiencing extreme and/or moderate drought conditions has changed significantly during the twentieth century with fewer droughts over Scandinavia, Netherlands and the Ukraine and more in areas of eastern Europe and western Russia.
Water extraction as well as water management across catchments and changes in land use and management also make it very difficult to attribute changes in average water discharge, floods and droughts to climate-change forcing (8).
Changes in drought severity for western Europe have been attributed to a changing climate but for eastern European countries the increased extraction of water for economic expansion is also a significant factor (15). It has been suggested that the influence of increases in water consumption on future droughts may even be of the same magnitude as the projected impact of climate change (16).
Vulnerabilities – Future projections for Europe
In 2012 the IPCC concluded that there is medium confidence in a projected increase in duration and intensity of droughts in some regions of the world, including southern Europe and the Mediterranean region, and central Europe (25).
River flow droughts are projected to increase in frequency and severity in southern and south‑eastern Europe, the United Kingdom, France, Benelux, and western parts of Germany over the coming decades. In snow-dominated regions, where droughts typically occur in winter, river flow droughts are projected to become less severe because a lower fraction of precipitation will fall as snow in warmer winters. In most of Europe, the projected decrease in summer precipitation, accompanied by rising temperatures which enhances evaporative demand, may lead to more frequent and intense summer droughts (9).
As a result of both climate change and increasing water withdrawals, more river basins will be affected by severe water stress, resulting in increased competition for water resources. The regions most prone to an increase in drought risk are the Mediterranean and south-eastern parts of Europe, which already suffer most from water stress (10).
According to research based on six regional climate models, there is not a simple north–south pattern of decreased–increased drought, with models projecting fewer events for parts of the Iberian Peninsula and parts of the Mediterranean. Considerable uncertainty exists at the regional scale. For example, for Britain and northern Spain, different models project both increases and decreases. … All models project longer and more severe droughts in the Mediterranean and shorter, less severe, events for Scandinavia with greater uncertainty as to the direction of change for the rest of Europe (14).
The use of six regional climate models has demonstrated the range of uncertainty in future projections of even mean precipitation across Europe, but also enables some generalizations to be made. Increases in precipitation are likely during winter and these are likely to be largest and most persistent for northern Europe. In contrast, large decreases in precipitation are likely during summer, these being largest in southern Europe (14).
For longer-duration droughts there is a clearer spatial pattern, which indicates fewer droughts in northern Europe due to larger increases in winter precipitation and more droughts of increasing severity in the south (14).
Droughts may strongly affect biodiversity all across Europe. Some examples (8):
- The environmental impacts of droughts can be exacerbated by unsustainable trends in water use. The worst combination appears when drought strikes freshwater ecosystems already weakened by excessive water withdrawals. For example, Lake Iliki, some 100 km northeast of Athens, has been reduced to a third of its original size, partly by a severe drought in 2000 but also as a result of increasing drinking water demand. Likewise, Lake Djoran, located between Greece and the Former Yugoslav Republic of Macedonia, is at risk of drying up, thus threatening one of the richest inland fishing stocks in Europe.
- Wetlands are particularly vulnerable to drought. The drought that affected Spain in the first half of the 1990s reduced by 97 % the flooded area of the Natural Park of the ‘Tablas de Daimiel’, the most important wetland area in the interior of the Iberian peninsula. Here too, water withdrawals, in this case for agricultural purposes, contributed to the loss.
- Droughts can cause the deterioration of water quality in rivers, lakes and reservoirs by exacerbating algal blooms that reduce the oxygen available for aquatic species. In the summer of 1999, for instance, these processes affected many lakes in Finland.
- Droughts may also weaken the resistance of certain plant species to plagues and increase their susceptibility to forest fires, as happened in the Greek island of Samos in the summer of 2000.
- Finally, drought can threaten the very survival of species in certain areas. The prolonged drought that affected southern Spain in the mid 1990s caused a high mortality rate among maritime pines and severely withered green oak and cork oak forests.
Droughts may also trigger soil erosion, mainly in Mediterranean areas. One way this happens is through a reduction in vegetation cover caused by forest fires or by increased plant mortality due to water stress. In addition, when the soil is very dry, the water infiltration rate decreases. Consequently, if a period of drought is followed by heavy storms, erosion is triggered by surface runoff. The problem is especially acute in the arid and semi-arid Mediterranean areas where the process may lead to desertification (8).
Europe should view 2003 as a wake-up call. The 2003 drought should be the catalyst for actions aimed at reducing drought impacts across all relevant sectors (7). Drought is not mentioned in European energy policies. Similarly European transport navigation policy makes no reference to low flow conditions, whereas health policies make few provisions for reduced water supplies and deteriorating water quality. Drought is one criterion for exemption to the requirements of the Water Framework Directive – an increasingly likely situation. It makes no provision for managing biodiversity protection during severe droughts (7).
In contrast to internal policy, drought is addressed as a real issue in EU development policies. Drought is seen as a threat to sustainable development, a humanitarian issue and a driver of mass migration and political instability (7).
EU policy orientations for future action
According to the EU, policy orientations for the way forward are (24):
- Putting the right price tag on water;
- Allocating water and water-related funding more efficiently: Improving land-use planning, and Financing water efficiency;
- Improving drought risk management: Developing drought risk management plans, Developing an observatory and an early warning system on droughts, and Further optimising the use of the EU Solidarity Fund and European Mechanism for Civil Protection;
- Considering additional water supply infrastructures;
- Fostering water efficient technologies and practices;
- Fostering the emergence of a water-saving culture in Europe;
- Improve knowledge and data collection: A water scarcity and drought information system throughout Europe, and Research and technological development opportunities.
Adaptation activities currently seem to be focused on flood management and defence, while adaptation measures related to the management of water scarcity and drought, although recognized as equally damaging, do not yet seem to be widespread (2).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Portugal.
- EC (2007a), in: EEA (2009)
- Anderson (ed.) (2007)
- Hisdal et al. (2001), in:EEA, JRC and WHO (2008)
- Van der Schrier et al.(2006), in:EEA, JRC and WHO (2008)
- Hanneford and Marsh (2006), in:EEA, JRC and WHO (2008)
- Van Lanen et al. (2007), in: EEA (2009)
- Eisenreich (2005)
- EEA, JRC and WHO (2008)
- Douville et al. (2002); Lehner et al. (2006); Feyen and Dankers (2008), in:EEA, JRC and WHO (2008)
- Alcamo et al. (2003); Schröter et al. (2005), in: EEA, JRC and WHO (2008)
- Demuth and Stahl, 2001, in: Blenkinsop and Fowler (2007)
- Lloyd-Hughes and Saunders (2002), in: Blenkinsop and Fowler (2007)
- Dai et al. (2004), in: Blenkinsop and Fowler (2007)
- Blenkinsop and Fowler (2007)
- Lehner et al. (2006), in: Blenkinsop and Fowler (2007)
- Lehner and Döll (2001), in: Blenkinsop and Fowler (2007)
- Arnell (2004), in: European Environment Agency (EEA) (2005)
- Döll (2002), in: European Environment Agency (EEA) (2005)
- European Environment Agency (EEA) (2005)
- Arnell (1999), in: Eisenreich (2005)
- Vogt and Somma (2000), in: Eisenreich (2005)
- Portuguese Environment Agency with the cooperation of Ecoprogresso – Environment and Development Consultants, SA (2006)
- European Commission (DG Environment) (2007)
- Commission of the European Communities (2007)
- IPCC (2012)
- Páscoa et al. (2021)