Vulnerabilities Alps

Observed hydrologic regime changes of Alpine rivers

Global warming affects precipitation volumes in the Alps, the contribution of rain and snow to these volumes, and the timing of snowmelt. An overall decrease in snow cover is observed during the 20th century for low- and mid-elevations. Trends are less significant at higher elevations, and snowpack even increased due to higher precipitation totals. These changes affect stream flow of mountain catchments. These changes were investigated for a large number of catchments over the period 1961–2005 in six Alpine countries (Austria, France, Germany, Italy, Slovenia and Switzerland), with catchment size varying mainly between 100 and 1000 km2 (36).

Over the last decades, hydrologic regime of Alpine rivers has changed. These changes vary with the character of hydro-climatic regimes. During 1961–2005, all regimes show a consistent shift toward an earlier start of 
snowmelt flow, with a trend magnitude of 11 days, along with an increase of 18 days in the duration of the snowmelt season. Also, distinct differences have been observed between glacial- and snowmelt-dominated regimes, and mixed snowmelt–rainfall regimes (36):

• Pure glacial- and snowmelt-dominated regimes are found in the heart of the Alps. These hydrologic regimes are mainly controlled by the storage of precipitation as snow and ice during the cold months. Lowest flows occur between December and February, highest flows during spring and summer. For these regimes, winter droughts have become less severe: drought durations have decreased by an average of 25 days over 1961–2005 and volume deficits have decreased by an average of 47%. Glacial regimes, in particular, show a consistent behavior with a melting season shifted by a week earlier, an increase of 29% in the snowmelt volume, and an enhanced contribution of the glacier to the total stream flow of corresponding catchments.
• Mixed snowmelt–rainfall regimes are found in pre-alpine regions. They exhibit two low flow seasons: during the winter when part of the precipitation is stored as snowpack, and during the summer due to a combination of earlier snowpack shortage, lack of precipitation and high evapotranspiration. For these regimes, high flows are mainly driven by snowmelt during the spring and by abundant precipitation in autumn. For these regimes, winter droughts seem to have become more severe: volume deficit in the Southeastern Alps (mostly Slovenia) has increased by 10%.

Whether these trends are linked to climate change or to climate decadal variability remains an open question (36). 

Extremely low snow accumulation has been reported at all altitudes in the Italian Alps for the winters 2022 and 2023, compared with a long-term time series for the period 1930–2023, contributing to critical low-flow conditions in the Po and Adige rivers (38). 

Projections hydrologic regime changes of Alpine rivers

Global warming will have much more impact on droughts than on floods in the Alps. Simulated changes in flood magnitude are negligible whereas droughts will become more intense and last longer (39).

Climate change will have a much stronger effect on droughts than on floods in the Alps, scientists concluded in a recent study. They simulated discharge characteristics for 925 catchments in the Alps under future global warming levels of 1°C, 2°C, and 3°C. According to their results, river floods in the Alps will not change significantly in magnitude and will not last longer. The only change in floods they observed in their results is a change in seasonality: the timing of floods is expected to shift toward earlier in the year with increasing temperatures. Future droughts, on the other hand, are projected to become more intense, develop larger deficits, last longer, and become slightly more widespread with increasing temperatures (39).

These future projections of changes in floods and droughts align well with observations in the past. Observations so far do not show clear changes in flood magnitude (40) but do show earlier floods occurrences over the last decades (41) because of an earlier start of spring snowmelt season. Droughts have become more intense (42) because of decreased snowmelt and precipitation and increased evapotranspiration (43). In addition, these findings agree with the projections of other studies that show clear increases in streamflow drought deficits and intensities for the future for Central Europe and the Alps (44).

Fresh water resources in numbers - Italy

In Italy 100% of the urban population and 97% of the rural population have access to water. 20% of the bathing water does not satisfy bathing water standards. 70% of the population has access to sanitation. Water supply is becoming a social and economic emergency in Apulia, Basilicata, Sicily and Sardinia, primarily because of increasing water demand and lack of management practices. Further associated decreases in mean precipitation could aggravate this situation. Water stress might increase by 25% in this century (5).

In Italy, the total meteoric inflow is of about 300 billion m3/year (data of Regione Emilia Romagna). The highest percentage of these precipitations, a little more than 40%, is concentrated in the northern regions, 22% in the central ones, 24% in the southern regions and just 12% in the two largest islands, i.e. Sicily and Sardinia. The water resource availability, however, is estimated to be only 58 billion m3/year, 72% of which derivable from surface resources (springs, rivers, lakes), while 28% from underground resources (water tables close to the surface). Almost 53% of the utilizable surface resources are localized in northern Italy, 19% in central Italy, 21% in southern Italy, and 7% in the two largest islands (6).

Moreover, about 70% of the underground resources is localized in the large flood plains of northern Italy. Not many underground resources are utilizable in southern Italy, being confined in the short stretches of coastal plains and in a few inner areas. These data confirm the uneven distribution between northern and southern parts of the country and the reduction trend caused by the concurrent decrease in precipitation and increase in evapotranspiration and water utilization (6).

Vulnerabilities - Italy

The expected impacts of climate change on water resources across southern European regions include further reductions in quantity, quality and availability, with increasing frequency and intensity of droughts, especially in summer. In particular, an increasing frequency and severity of river flow droughts could occur, with annual river flow decline and possible summer water flows reduction by up to 80%. Also, groundwater recharge shows a declining trend, with consequent shrinking of fresh groundwater resources, especially in coastal areas (26).

In many parts of Italy, particularly in the south, it has become ever more difficult to meet demand for water. The recent years of drought and the constant increase of water demand for the civil sector have made irrigation supply more problematic. Wastewater reuse could represent a viable solution to meet water demand. Several projects on wastewater reuse are currently in progress (18).

A higher frequency of dry periods is a phenomenon already well established. The economic damage to agriculture, particularly in the Po valley with its extensive irrigation, may become considerable (19).

Increased demand on water resources from new and diversified users is probably the main cause of reduced water availability in the northern Italy main basins. This reduction cannot be justified only on the basis of precipitation data that, especially in northern Italy, show a scarcely significant trend. During the summer season this situation gives rise to recurrent water resource allocation problems; for this reason, it is closely watched by the Dipartimento della Protezione Civile which, in collaboration with regional and water basin authorities, monitors hydropluviometric data and water availability at least once per month in order to foresee as soon as possible future water critical situations (6).

In particular, with reference to water stress, Italy might experience (25):

• water stress increase by 25% in the present century, with a growing demand for irrigation water;
• socio-economic emergency concerning safe water supply in several regions, such as Puglia, Basilicata, Sicilia and Sardegna, primarily because of increasing water demand and lack of management practices, aggravated by further decreases in mean precipitation;
• reduced availability of water resources affecting drinking water supply, water supply for irrigation and for hydropower generation in the Po river valley;
• increased soil dryness and increased frequency of droughts in the areas of plains;
• water quality depletion (26);
• increased seasonal water deficit due to significant pressures of summer tourism peaks on already scarce water resources, especially in small Mediterranean islands, which could become a major constraint to touristic supply in the future;
• intensification of conflicts among multiple uses of water resources;
• navigation of lakes and rivers impaired by a reduction of precipitation and water levels.

If the warming rate is constant, and if, as expected, glacier ice melting per unit area increases and total ice-covered area decreases, the total annual yield passes through a broad maximum: “peak meltwater”. Peak-meltwater dates have been projected between 2010 and 2040 for the European Alps (34), and for the second half of this century for the glaciers in Norway and Iceland (35).

Abstraction non-renewable groundwater reserves

‘‘Non-renewable groundwater’’ denotes groundwater gained by abstraction in excess of recharge. The amount of non-renewable groundwater abstraction that contributes to gross irrigation water demand has been calculated for a large number of countries, allowing for a global overview. The results of this study show that non-renewable groundwater abstraction globally contributes nearly 20%, or 234 km3 annually, to the gross irrigation water demand (for the reference year 2000) and has more than tripled in size since the year 1960. From 1960 to 2000 an increased dependency was shown of irrigation on non-sustainable groundwater with time. Thus, irrigation is more and more sustained by an unsustainable water source (25).

Country assessments reveal that non-renewable or non-sustainable groundwater supplies large shares of current irrigation water, particularly for semi-arid regions where surface freshwater and rainfall are very scarce: Pakistan, Iran, Saudi Arabia, Libya, UAE and Qatar. Much of current irrigation in these regions is sustained by non-sustainable groundwater (25).

For Europe, the contribution (%) of non-renewable groundwater abstraction to gross irrigation water demand was calculated for Italy (15%), Spain (7%), Turkey (7%) and Greece (2%) (25). Projected increases in irrigation demand in southern Europe will serve to stress limited groundwater resources further (30).

Substantial reduc­tions in potential groundwater recharge are projected for the 21st century in southern Europe (Spain and northern Italy) whereas increases are consist­ently projected in northern Europe (Denmark, southern England, northern France) (28). Along the southern rim of the Mediterranean Sea decreases in potential groundwater recharge of more than 70% by the 2050s have been simulated using output from two climate models (ECHAM4, HadCM3) under two emissions scenarios (A2, B2) (29).

Fresh water resources in numbers - Mediterranean basin

The Mediterranean basin is 3,800 km long and 400 to 740 km wide. It takes 90 years for the water in this sea to be completely renewed. Hence, it is especially susceptibility to pollution. The population is between 150 and 250 million depending on whether just the actual coastal strip is taken into account or the drainage basin of the Mediterranean (4).

Fresh water resources in numbers - Europe

By 2005 for Europe as a whole (including New Member States and Accession Countries) some 38% of the abstracted water was used for agricultural purposes, while domestic uses, industry and energy production account for 18%, 11%, and 33%, respectively (2). However, large differences exist across the continent.

In Malta, Cyprus and Turkey, for example, almost 80% of the abstracted water is used for agriculture, and in the southwestern countries (Portugal, Spain, France, Italy, Greece) still about 46% of the abstracted water is used for this purpose. In the central and northern countries (Austria, Belgium, Denmark, Germany, Ireland, Luxembourg, Netherlands, UK, and Scandinavia), to the contrary, agricultural use of the abstracted water is limited to less than 5%, while more than 50% of the abstracted water goes into energy production (a non-consumptive use) (2).

Southern countries use ca. three times more water per unit of irrigated land than other parts of Europe. The large amount of water dedicated to irrigation in the southern countries is problematic since most of these countries have been classified as water stressed, and face problems associated with groundwater over-abstraction such as aquifer depletion and salt water intrusion (3).

The total renewable freshwater resource of a country is the total volume of river run-off and groundwater recharge generated annually by precipitation within the country, plus the total volume of actual flow of rivers coming from neighbouring countries. This resource is supplemented by water stored in lakes, reservoirs, icecaps and fossil groundwater. Dividing the total renewable freshwater resource by the number of inhabitants leads to water availability per capita. Thirteen countries have less than 5,000 m3/capita/year while Nordic countries generally have the highest water resources per capita. The Mediterranean islands of Malta and Cyprus and the densely populated European countries (Germany, Poland, Spain and England and Wales) have the lowest water availability per capita. The water availability is an annual data which therefore does not reflect at all seasonal variations (23).

Vulnerabilities - Europe

Water availability in the Mediterranean is highly sensitive to changes in climate conditions. In the last century the Mediterranean basin has experienced up to 20% reduction in precipitation (2). Such a trend is expected to worsen with increasing demand for water and reduction in rainfall in the region (1,7). Future projection of this trend will reduce drastically water supplies in these areas, affecting considerably the population and economy of the Mediterranean countries (8).

In southeastern Europe annual rainfall and river discharge have already begun to decrease in the past few decades (9).

Water stress will increase over central and southern Europe. The percentage area under high water stress is likely to increase from 19% today to 35% by the 2070s, and the additional number of people affected by the 2070s is expected to be between 16 million and 44 millions. The most affected regions are southern Europe and some parts of central and eastern Europe, where summer flows may be reduced by up to 80%. The hydropower potential of Europe is expected to decline on average by 6% but by 20 to 50% around the Mediterranean by the 2070s (10).

Annual average runoff in southern Europe (south of 47°N) decreases by 0 to 23% up to the 2020s and by 6 to 36% up to the 2070s, for the SRES A2 and B2 scenarios and climate scenarios from two different climate models (10). Summer low flow may decrease by up to 80% in some rivers in southern Europe (11,5). Other studies (1) indicate a decrease in annual average runoff of 20–30% by the 2050s and of 40–50% by the 2075s in southeastern Europe.

Climate change must be seen in the context of multidecadal variability, which will lead to different amounts of water being available over different time periods even in the absence of climate change. … the average standard deviation in 30-year average annual runoff is typically under 6% of the mean, but up to 15% in dry regions (12).

Temperature rise and changing precipitation patterns may also lead to a reduction of groundwater recharge (13) and hence groundwater level. This would be most evident in southeastern Europe. Higher water temperature and low level of runoff, particularly in the summer, could lead to deterioration in water quality (14). Inland waters in southern Europe are likely to have lower volume and increased salinisation (15).

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 (1). In the agricultural sector, irrigation water requirements would increase mainly in southern and southeastern Europe (16). The risk of drought increases mainly in southern Europe. For southern and eastern Europe the increasing risk from climate change would be amplified by an increase in water withdrawals (17).

Water shortages due to extended droughts will also affect tourism flows, especially in southeast Mediterranean where the maximum demand coincides with the minimum availability of water resources (4).

Fresh water resources in numbers - Wordwide

In the absence of climate change, the future population in water-stressed watersheds depends on population scenario and by 2025 ranges from 2.9 to 3.3 billion people (36–40% of the world’s population). By 2055 5.6 billion people would live in water-stressed watersheds under the A2 population future (The A2 storyline has the largest population), and ‘‘only’’ 3.4 billion under A1/B1 (1).

Climate change increases water resources stresses in some parts of the world where runoff decreases, including around the Mediterranean, in parts of Europe, central and southern America, and southern Africa. In other water-stressed parts of the world— particularly in southern and eastern Asia—climate change increases runoff, but this may not be very beneficial in practice because the increases tend to come during the wet season and the extra water may not be available during the dry season (1).

Europe: five lake categories

There are almost one and a half million lakes in Europe, if small water bodies with an area down to 0.001 km2 are included. The total area of lakes is over 200,000 km2; in addition the manmade reservoirs cover almost 100,000 km2. The response of European lakes to climate change can be discussed by dividing the lakes into five categories (22):

Deep, temperate lakes

Typical representatives of this class are e.g. Lakes Maggiore, Ohrid, Geneva and Constance with mean depths of 177, 164, 153 and 90 meters, respectively. Due to the great depth and relatively mild winters, there is usually no ice cover. The future climate change in Europe may suppress the turnover in deep lakes. This implies the enhancement of anoxic bottom conditions and an increased risk of eutrophication. The oxygen conditions can also be anticipated to deteriorate due to increased bacterial activity in deep waters and surficial bottom sediment.

Deep subalpine lakes in Europe, like Lake Maggiore, are experiencing a decrease in the frequency of winter full turnover and an intensification of stability. As a result, hypolimnetic oxygen concentrations are decreasing and nutrients are accumulating in bottom water, with effects on the whole ecosystem functioning (58).  A reversion in the increasing thermal stability would be possible only if global GHG emissions started to be reduced by about 2020, allowing an equilibrium mixing regime to be restored by the end of the twenty-first century. Otherwise, persistent lack of complete mixing, severe water warming and extensive effects on water quality are to be expected for the centuries to come (37). 

Shallow, temperate lakes

Balaton (600 km2, 3 m) in Hungary and Müritz (114 km2, 8 m) in Germany belong to this class. Increasing water temperatures may result in intensified primary production and bacterial composition. The probability of harmful extreme events, e.g. mass production of blue-green algae, will increase. The impacts may extend to fish life; changes in species composition and reduced fish catches will be anticipated. The use of the expression 'thermal pollution' is well justified for these lakes.

Boreal lakes

Ladoga (17 670 km2, 51 m), Onega (9670 km2, 30 m) and Vänern (5670 km2, 27 m) are the largest in this class, being also the three largest lakes in Europe. This group includes about 120 lakes with an area exceeding 100 km2. Most lakes of the boreal zone mix from top to bottom during two mixing periods each year. Shortening of the ice cover period will be the most obvious consequence of climate change in these lakes. This could improve the oxygen conditions in winter and spring.

Arctic lakes

These are mainly small water bodies in northern Scandinavian mountains and in the tundra region. Arctic lakes are generally considered to be particularly sensitive to environmental changes. Melting permafrost may seriously threaten the ecosystems of arctic lakes. In some cases the whole lake may disappear as a consequence of ground thaw and enhanced evaporation.

Mountain lakes

To this class belong all high altitude lakes in central Europe and also those located in southern Scandinavia. Even if mountain lakes were connected by channels, physical and ecological constraints limit species migration between them. In a warming climate, there is no escape route; the only possibility for survival is adaptation.

Adaptation strategies - EU

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 strategies - Southern Europe

In southern Europe, to compensate for increased climate related risks (lowering of the water table, salinisation, eutrophication, species loss), a lessening of the overall human burden on water resources is needed. This would involve stimulating water saving in agriculture, relocating intensive farming to less environmentally sensitive areas and reducing diffuse pollution, increasing the recycling of water, increasing the efficiency of water allocation among different users, favouring the recharge of aquifers and restoring riparian vegetation, among others (20).

Managed aquifer recharge

Comprehensive management approaches to water resources that integrate ground water and surface water may greatly reduce human vulnerability to climate extremes and change, and promote global water and food security. Conjunctive uses of ground water and surface water that use surface water for irrigation and water supply during wet periods, and ground water during drought (31), are likely to prove essential. Managed aquifer recharge wherein excess surface water, desalinated water and treated waste water are stored in depleted aquifers could also sup­plement groundwater storage for use during droughts (32,33). Indeed, the use of aquifers as natural storage reservoirs avoids many of the problems of evaporative losses and ecosystem impacts asso­ciated with large, constructed surface-water reservoirs.

Adaptation strategies - Italy

Adaptation strategies in Italy include (6,26):

• the promotion of water labelling of goods and products;
• water emergencies regulations in order to address water crises, providing both technical and financial support for emergency measures;
• ad hoc organizations for crisis management, (like a “Drought control room” for drought events in the Po river basin, and a “Coordination Unit for the management of water resources” shared between Puglia and Basilicata regions) in order to regulate the use of water and take the necessary measures to prevent water crises;
• a number of structural funds include irrigation networks as well as drinking-water distribution networks, not only for water emergencies; in terms of cohesion funds, Italy has a water programme, useful for water crisis prevention too;
• a National Plan for irrigation that involves water management, and allocated specific funds to tackle the effects of extreme events (including droughts). Measures include voluntary actions for water economies in agriculture through a pact with agriculture organizations, and avoiding the exploitation of waterbeds in the neighbourhood of wetlands of high natural value;
• plans to combat drought and desertification.

Water pricing policy

In Italy, according to a report of 2007, incentives to ensure an efficient use of water resources were not adequate by 2007 and water pricing policy was not completed yet (23).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Italy.

1. Arnell (2004)
2. Eisenreich (2005)
3. EEA (2003); EEA (WQ03b), both in: Eisenreich (2005)
4. European Environment Agency (EEA) (2005)
5. WHO (2007)
6. Ministry for the Environment, Land and Sea of Italy (2007)
7. Rosato and Giupponi (2003), in: European Environment Agency (EEA) (2005)
8. Trigo et al. (2004), in: Eisenreich (2005)
9. Hulme (1999); UNEP/MAP/MED/POL (2003), both in: European Environment Agency (EEA) (2005)
10. Alcamo et al. (2007)
11. Santos et al. (2002), in: Alcamo et al. (2007)
12. Arnell (2003), in: Arnell (2004)
13. Eitzinger et al. (2003), in: European Environment Agency (EEA) (2005)
14. Mimikou et al. (2000), in: European Environment Agency (EEA) (2005)
15. Williams (2001); Zalidis et al. (2002), both in: Alcamo et al. (2007)
16. Döll (2002), in: European Environment Agency (EEA) (2005)
17. Lehner et al. (2006), in: Alcamo et al. (2007)
18. Barbagallo, Cirelli and Indelicato (2001), in: WHO (2007)
19. Swedish Commission on Climate and Vulnerability (2007)
20. Alvarez Cobelas et al. (2005), in: Alcamo et al. (2007)
21. APAT (2006), in: Ministry for the Environment, Land and Sea of Italy (2007)
22. Kuusisto (2004)
23. European Commission (DG Environment) (2007)
24. Commission of the European Communities (2007)
25. Wada et al. (2012)
26. Ministry for the Environment, Land and Sea of Italy (2009)
27. Portoghese et al. (2009), in: Ministry for the Environment, Land and Sea of Italy (2009)
28. Hiscock et al. (2011), in: Taylor et al. (2012)
29. Döll (2009), in: Taylor et al. (2012)
30. Falloon and Betts (2010), in: Taylor et al. (2012)
31. Faunt (2009), in: Taylor et al. (2012)
32. Scanlon et al. (2012), in: Taylor et al. (2012)
33. Sukhija (2008), in: Taylor et al. (2012)
34. Huss (2011), in: IPCC (2014)
35. Jóhannesson et al. (2012), in: IPCC (2014)
36. Bard et al. (2015)
37. Fenocchi et al. (2018)
38. Colombo et al. (2023)
39. Brunner and Gilleland (2024)
40. Bertola et al. (2020); Blöschl et al. (2019), both in: Brunner and Gilleland (2024)
41. Blöschl et al. (2017); Fang et al. (2022), both in: Brunner and Gilleland (2024)
42. Brunner et al. (2023); Scherrer et al. (2022), both in: Brunner and Gilleland (2024)
43. Duethmann and Blöschl (2018); Moraga et al. (2021), both in: Brunner and Gilleland (2024)
44. Forzieri et al. (2014); Baronetti et al. (2022), both in: Brunner and Gilleland (2024)