(*) Le changement climatique: Défis potentiels et adaptations pour l’ingénierie des ressources en eau du 21ème siècle

COMISSION INTERNATIONALE DES GRANDS BARRAGES

VINGT-QUATRIÈME CONGRÈS

DES GRANDS BARRAGES Hanoï, mai 2010

CLIMATE CHANGE: POTENTIAL CHALLENGES AND ADAPTATIONS FOR THE 21ST CENTURY WATER RESOURCES ENGINEER *

ICOLD Committee on Climate Change and Dams, Reservoirs

and the Related Water Resources

Committee Members include: Denis AELBRECHT*, Martin AIREY*, Claes-Olof BRANDESTEN*, Trevor JACOBS*, Ron LEMONS*, Amirhasan PAKDAMAN, Otto PIRKER, Pavel POPOV, Francisco Javier SÁNCHEZ CARO*, Guoqing WANG, Kyung Taek YUM; Corresponding Committee Members include: Se-Woong CHUNG, Andy HUGHES, Romas KAMANGA, Ick Hwan KO, Koichi

KUWABARA, Samuel OME, Tomonobu SUGIURA*; Paper Editor: Emily BAKER (*) denotes contributing author

1. WATER RESOURCES MANAGEMENT SOLUTIONS

Climate change concerns may include higher average temperatures; longer sustained periods of lower rainfall and hence reduced stream run-off; increased stress on river systems; higher water temperatures and increased evaporation; more severe and more frequent storm events1

. The global climate trend indicates that the majority of the world is vulnerable to the effects of climate change with extreme meteorological events potentially increasing the frequency of floods and droughts, which cause significant environmental consequences.

The impact of climate change on water resources and dam safety is complex and depends on the effects of local/regional precipitation, evaporation, snow 1 The ICOLD Committee on Global Climate Change and Dams, Reservoirs and the Associated Water Resources acknowledges that topics related to climate change causes are controversial from a scientific point of view. The Committee is aware of the scientific bases for climate change, but has elected to focus on the technical problems associated with climate change and responsible management solutions. The course of action set forth by the Committee is to protect human life, health and welfare while respecting a difficult and fragile balance with the planet.

accumulation and melt. In northern Europe, an increase in snow production and more unstable winters are predicted, but the situation varies in other parts of the world where trends indicate extreme flooding in higher latitudes and drought in lower latitudes [1]. Therefore effects of climate change on water resources, and specifically dam safety, cannot be generalized globally or even regionally. The effect of climate change on water resources is a situation that must be analyzed locally in site-specific studies.

The extent of adaptation measures to modify existing dams and reservoirs or to

change operational regimes in order to meet future requirements because of climate change is dependent upon the nature and scale of predicted impacts. This, of course, will vary from site to site and will be influenced by the climatic conditions that prevail. Suffice to say that there will not be one single solution or strategy to address climate change issues, and that the different impacts in different locations will need to be considered in different ways.

1.1 ROLE OF CLIMATE CHANGE COMMITTEE In 2008, at its annual meeting in Sofia, BGR, the International Commission on

Large Dams (ICOLD) created the Committee on Global Climate Change and Dams, Reservoirs and the Associated Water Resources in order to demonstrate the seriousness with which ICOLD approaches climate change and its effects on water resources. The Committee was formally constituted a year later in Brasilia, BRA, where its founding meeting took place with the mission to provide technical support to the international dam community by developing guidelines that support international climate change recommendations.

The current Committee chairman is Ron Lemons (USA). Five continents are

represented by the Committee of delegates from Australia, Brazil, Canada, China, Korea, France, Japan, Spain, Sweden, Turkey and United Kingdom. The Committee’s past meeting in Brasilia included observers from The Netherlands, Zambia and Nigeria, demonstrating an increasing interest in global climate change. At this meeting, the following main Committee objectives were set:

• Establishing a common view on issues, including avoiding a debate on the causes of climate change and focusing on its technical aspects and mitigating its consequences.

• Quantifying reservoir contributions to GHG2

• Evaluating additional contributing water quality issues related to climate change (thermal variations, overpopulation of plants, etc.).

emissions compared with other water supply infrastructure alternatives (groundwater utilization, desalinization, etc.).

2 GHG: Greenhouse Gas

• Evaluating the consequences of climate change on water resources systems including floods, droughts, de-freezing, etc. Identifying the key factors for proper water resources management especially in terms of planning for an uncertain future.

• Evaluating the consequences of climate change on desertization and erosion rates increments, potentially leading towards sediment management improvements.

• Identifying methodologies to transfer climatic and hydrological results from a global, to regional, to basin scale.

• Coordinating decision-making policies, as well as sharing practical experiences with other organizations.

Therefore, per ICOLD standards, the Committee is interested less in the climate

change debate and more in providing global solutions, a standpoint that requires a triple perspective:

1. Scientific or Understanding approach: understanding climate change processes and factors contributing to their proliferation; predicting scenarios at worldwide, regional and site-specific levels.

2. Political or Precautionary approach: maintaining awareness of policies related to GHG emissions.

3. Technical or Mitigation approach: developing the infrastructures needed to ease the problems associated with climate change.

1.2 MODELING CHANGES IN CLIMATE When analyzing the impacts of climate change on river flow regimes, including

floods and droughts, and other water resources issues, the methodology is normally based on a complex chain of sequential GHG emissions scenarios; output from global climate models; a nested regional climate model to downscale global results and, finally, a locally adapted hydrological runoff model (Fig. 1). Unfortunately, existing regional climate scenarios vary considerably between different model settings, especially in the case of extreme precipitation within small areas such as catchments. New and refined climate scenarios will appear as science advances. Vested parties have to be aware that the target is moving as a new dimension arrives in water resources and dam safety work.

Global Modeling Regional Modeling Site-Specific Studies

Fig. 1 Schematic graphic of the production chain when analyzing regional impacts on extreme flood of global climate change.

But the picture is complicated. Many believe higher concentrations of GHG are

causing the changes, a problem that’s solution hinges upon the political success of international agreements to curb emissions, resulting in the current emission scenarios used in most climate change impact analyses. If other variables impact climate change, the analysis becomes even more complicated. While understanding climate change’s effects is a new challenge for dam owners, properly communicating the unknown is a new challenge for scientists who have to explain why and how the target is moving and why water managers cannot expect to obtain a single, lasting answer. Communication between managers and scientists has become crucial dam safety assessment’s future.

Because of the variability associated with climate change, planning and

maintaining infrastructures causes a scenario of uncertainty. Traditionally, dam and reservoir design has relied heavily upon historic observations. Scientists are beginning to realize that climate change may challenge this strategy. Past records are not comprehensive enough for accurate analysis of future conditions. Further, a new situation has arisen for dam owners. While significant investments are made to upgrade dams into compliance with new standards, including increased safety requirements, it is becoming apparent that climate change’s hazards cannot be ignored. In response to this new issue, dam owners are seeking practical advice from ICOLD for practical solutions.

1.3 EXPLORING OUR UNDERSTANDING Determining a path for the future in a time of uncertainty is not a new problem

for the power industry. About a century ago, many large-scale hydropower developments started in areas where little was known about river flow. Even mapping of water divides was incomplete. Nevertheless engineers managed to develop sustainable hydropower resources requiring adaptation to new conditions and data. Today dam owners face uncertainty as climate change impacts the future. While difficult in many respects, taking additional design measures and developing new methodology makes dam safety in response to climate change more manageable.

1.4 OUTLINING A RESPONSE In June 2009, civil engineers initiated a call to action with “Civil Engineering and

Climate Change Protocol,” submitted by the Institution of Civil Engineers (ICE), the American Society of Civil Engineers (ASCE), and the Canadian Society of Civil Engineers (CSCE) in an attempt to raise engineers’ awareness for the need

to adapt infrastructures to the anticipated results of climate change, including increased incidence and severity of storms, floods, droughts, sea level rise and storm surge. If the path of climate change continues, failure to modify critical infrastructures will lead to reduced access to drinking water supplies, increased exposure to flooding and threatened food security in large parts of Africa, Asia and Latin America.

With an increasing reliance on dams and reservoirs to eliminate the aftershock

of climate change, it is imperative that these projects become a primary investment. In particular, the public is increasingly charging dams and dam owners with providing sustainable development that offers two key societal contributions: guarantee and security. Social demand for guarantee simply means that we all want to turn on the tap and have water coming out. To dam owners, such a simple demand means increasing reservoir storage capacity, as well as providing a more efficient and abundant water supply system complemented with desalination plants and wells. In other words, the right of every human being to access drinking water must be guaranteed requiring rational and not opportunist management of this resource.

Despite less annual rainfall, flooding, already a hydrological extreme, is only

intensified by climate change resulting in increased discharge and larger volume floods. The most effective method for mitigating flood damage to both humans and property downstream from dams is by properly routing floods through reservoirs. Though stream bank protection and flood channels are complementary measures that must always be considered, reservoir routing is the best and most preventative measure. As safe infrastructures, our dams must protect citizens from floods, providing security and not generating incremental risks. Protection can only be achieved by setting higher flood control storages and incrementing discharge capacities. Dam safety must be reinforced by periodic and mandatory safety reviews, increased investment, and trained professionals devoted to dam inspection and surveillance.

The prospect of global warming and the ensuing uncertainty related to the

validity of dam safety criteria necessitates a new strategy in dam design where safety assessment is a critical component. Adding extra margins to design is more important than ever before. Adding extra margins to design is an additional cost but, when compared to the costs of making these adjustments after project completion, is more advantageous for all parties. Another key concept is flexibility. It is likely that future research on climate change will force scientists to reconsider the basis for specific site design. If deemed necessary, a project design with built-in flexibility can be technically modified without much effort.

2. IMPACTS OF CLIMATE CHANGE ON DAMS, RESERVOIRS AND THE ASSOCIATED WATER RESOURCES

There is still considerable uncertainty regarding the science of the predictions

meaning it is extremely difficult to quantify the magnitude of these changes and, hence, the impact they will have on our reservoirs and water resources3

. Challenges include insufficient spillway capacity during flooding; revised flood control procedures; and inadequate storage functionality to sustain water demand during drought. However, it is widely accepted that these changes are taking place and need to be included in our planning and decision making so that future needs can be satisfied both with existing and new reservoirs.

In addition, the evolution of non-climate factors will have tremendous impacts on water resources management, particularly water shortage risks and spatial/temporal imbalances between water supply and water needs. Four main factors can be cited4

• Demographics: Population growth and migration in some areas of the world will dramatically affect water needs characteristics;

:

• Technology Development: Water use intensity, or the rate of water needed to produce a unit of goods or services, may evolve significantly while technology is improving; and additional water production technologies appear (e.g. desalination development);

• Economic Factors: New pricing frameworks for water consumption, withdrawals, cost of scarcity on water-based industry, and services;

• Regulatory Framework: Revision of water rights principles; new governance of water resources.

In some regions, these factors may evolve dramatically and have a significant impact on water resources system management and water needs. These evolutions, even without climate-driven change, may stand as either opportunities or threats to current dams and reservoirs depending on each situation, and will call for anticipation in adapting the operation and maintenance of existing structures, and adapting plans for future structures.

For example, in Japan the water supply largely depends on water resources

development structures, such as dams. In areas where people depend on snowmelt water for agriculture and other purposes, it is possible that people may suffer from serious impacts during and after spring because of decreased snow cover and early snowmelt. Extremely low precipitation will decrease river 3 The development of new and more robust methods for estimating dam design to accommodate extreme conditions may lead to dam and reservoir design safety revisions (especially of spillways), regardless of evidence indicating climate change-driven evolution of extreme hazards. 4 Care must be taken about risk increase perception, which may lead to confounding conclusions. Risk results from the combination of hazard occurrences as well as a system’s vulnerability response. Risk appears higher when vulnerability increases and hazard remains stable. A typical example is when perception of inundation risks due to urban areas extending into flood plains increases, while hydrological conditions remain the same. In other words, risk increase might be attributed to a climate change-driven evolution of hazard occurrences, when in reality only vulnerability exposure has increased.

discharge (Fig. 2) and dam storage volume, which pose a problem for securing necessary river discharge downstream. In addition, if snow falls less and melts earlier due to global warming, the timing of snowmelt will become earlier along with less river discharge, and thus dam storage volume will be low even in the soil-paddling season for rice fields. In general, water demand greatly changes as social conditions do. Drought risk should be assessed based on both climate change and changes in social conditions.

Fig. 2 Ratio of possible spring season average precipitation change in Japan (1979-1998 period and 2080-2099 future period).

2.1 DEFINING IMPACT ASSESSMENT SCENARIOS Impact assessment relies on the quantification of evolution between two

situations: a reference baseline case, to which a future situation is compared.5

Three main methods for performing climate change scenario analyses exist:

2.1.1 Deterministic “What If” Scenarios

Usually these scenarios are based on extrapolation of observed past climatic

data. Best case, worst case, and medium case scenarios can help determine bounds and range of potential future. No probability can be associated with this kind of scenario.

5 Key features of potential climate change patterns include: For Temperature – All GCMs corresponding to an increase in global average temperature, which may vary from one region to another. For Precipitation – Global trends depicting a world zonal distribution of possible precipitation changes. Uncertainties remain attached to change predictions at the regional or even site-specific level. GCM predictions may vary significantly from one to another, with one model depicting wetter conditions in a particular area and drier in another, while a different model produces reverse results.

Spring season (March-June)

F/P≧1.4

1.2≦ F/P＜ 1.4

1.0≦ F/P＜ 1.2

F/P＜ 0.8

0.8≦ F/P＜ 1.0

F/P: future/present

2.1.2 Deterministic Scenarios Based on GCM6 Outputs7

A climate change scenario based on a GCM is defined by the combination of: • A GHG emission scenario: In its Third Assessment Report [3] and

Assessment Report 4 [4], IPCC experts built four families of scenarios (A1, A2, B1, B2), each describing a plausible “demographic, politico-economic, societal and technological future,” roughly dependent on two parameters: (i) more or less environmental concern, and (ii) regional versus global solutions to social and economical issues. The four families are defined in IPCC (2001) and IPCC (2007).

• A GCM: IPCC projects gather results of approximately 10 GCMs selected from research organizations worldwide.

• A time horizon: climate models produce results for two or three decades around 2020, 2050, 2080, 2100 time horizons. GCM outputs are available as monthly average changes in temperature and precipitation referred to a baseline scenario. For the reference baseline scenario, IPCC recommends to use 1960-1990 as a sample 30-year period.

2.1.3 Probabilistic Approaches Based on GCM Outputs Probabilistic Approaches are an attempt to overcome the limitations that

deterministic scenarios might raise, in particular due to remaining uncertainty in precipitation change patterns in GCM climate projections. The perspective of increasing change in climate and climate variability might enhance our water resources systems exposure beyond known variation bounds scientists expect.

The following examples illustrate the variety of climate change-induced impacts

that may affect dams, reservoirs and associated water resources systems.

Example Scenario One: Deterministic “What If” Scenarios Study One: Les Bois Hydropower Station, Mer de Glace Glacier, FRA

At the Les Bois hydropower station in the French Alps, the intake structure that collects melting water under the glacier has been adapted to the Mer de Glace glacier front retreat. The glacier front retreated approximately 350m in 40 years. A new intake works design was based on optimistic and pessimistic scenarios for the next 20 years, as shown in Fig 3.

6 GCM: Global Climate Model or General Circulation Model 7 Assessment Report 4 from IPCC emphasizes the complexity of deriving predictions pertaining to extreme hydrological events evolution’s frequency and intensity from GCM simulations stating: “The resolution of global models precludes their simulation of realistic circulation patterns that lead to extreme events” [4] [2]).

Fig. 3 Optimistic (left) and pessimistic (right) 2008-2028 Mer de Glace glacier (FRA) front

evolution scenarios. From LGGE (source: EDF)

Example Scenario Two: Deterministic Scenarios Based on GCM Outputs Study Two: Navajo Reservoir, New Mexico and Colorado, USA

Weintraub et al. (2005) [5] simulated “what if” scenarios of a Navajo reservoir in New Mexico and Colorado, USA assessing depletion risk assuming that drought conditions were extended three-to-five years beyond those already experienced, with dry years chosen at random from past years and combined with an incremental change in air temperature (+0°C; +1°C; and +2°C). In the pessimistic scenario, results showed that reservoir releases should be reduced by 70% to maintain the minimum elevation criterion needed to ensure gravity water supply for downstream irrigation.

Study One: San Joaquin River System, California, USA

Brekke et al. (2004) [6] investigated the impact of 2025 and 2065 time horizon climate change scenarios on the San Joaquin River System for wet, dry and normal years based on 73 years of past observations. The two scenarios are based on the same GHG emission hypothesis, combined with (i) a “wet” GCM – Hadley model HadCM2, and (ii) a “dry” GCM – NCAR-PCM. Hydrological responses have been coupled with a reservoir system management tool called CALCIM. This tool integrates long-established California state water rights and optimizes allocation of water and tradeoffs between releases and storage estimating bounds of climate change’s potential impacts on river systems.8

Study Two: Columbia River System Hydropower, Washington, USA Payne et al. (2004) [7] developed a comprehensive analysis of climate change

impact evaluation and mitigation to the Columbia River System hydropower operation in Washington, USA, and its increasing competition with other water

8 The authors, however, recognize the analysis’s limitations, which are restricted to two scenarios that do not allow for a comprehensive evaluation of the water shortage risk; compared with present climate baseline conditions the “wetter” GCM depicts a significant water delivery improvement, while “drier” GCM depicts water shortage intensification. Due to variance, impact’s breadth is considered too incoherent to guide relevant mitigation measures. Further, it is explicitly noted that “non uniform probability

needs, especially instream flow requirements for fish habitat quality. The analysis uses output from both NCAR-PCM global and RCM regional climate models, to allow for a comparison between direct downscaling of NCAR-PCM outputs with dynamic downscaling through RCM, the nested models approach.9

Example Scenario Three: Probabilistic Approaches Using GCM Outputs Study One: Irrigation Water System, Victoria, AUS

Jones (2000) [8] developed a probabilistic approach to evaluate the impact of climate change on a farm’s irrigation water system. The physical model is simple, but is embedded into a general risk analysis framework that can be transposed to other water resources systems. Jones suggests splitting a probabilistic climate impact assessment in two independent parts10

1. Map the intrinsic climatic sensitivity of the water resources system to arbitrary incremental changes in air temperature and precipitation. This sensitivity mapping is quantified through the probability that an annual water supply is below a minimum threshold.

:

2. Combine the above sensitivity mapping with estimates of probability density functions for air temperature (T) and precipitation (P) changes at the time horizon of interest resulting in probability quantification that a given risk threshold might be exceeded at the given time horizon.

Fig. 4 Water shortage / hydropower reduction probabilistic risk curve for Navajo reservoir, USA [9]

9 Again, only one GHG emission scenario is considered, and impacts are assessed at three different typical time horizons. A VIC hydrological model of the Columbia River System is coupled with the CALCIM reservoir operation optimization and planning tool. CALCIM optimizes water resources management in reservoirs, accounting for different water uses and related priorities including flood control, hydropower needs, and environmental constraints such as instream flow targets. The authors tested possible mitigation measures to limit hydropower production losses induced by a shift of higher system inflows due to snowmelt. The study illustrates an ensemble of methods and tools that are required to achieve a whole climate change impact evaluation and to test mitigation projects. Again, however, restriction of the analysis to only one GCM and one GHG emission scenario is a limitation. 10This method is a simplified alternative to a Monte-Carlo analysis as illustrated in Fig. 4.

Rainfall Change (%)

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3. THE ROLE OF DAMS AND RESERVOIRS IN A BALANCED AND FLEXIBLE, ADAPTIVE APPROACH TO MEET FUTURE WATER NEEDS

The impacts of climate change on reservoirs will vary depending upon each

reservoir’s purpose. For instance, at water supply, irrigation or hydropower generation reservoirs the reduced run-off from catchments during longer periods of drought, will deplete stored water resources and will clearly affect the availability, reliability and long-term security of the supply to be abstracted. For water supply reservoirs, higher water temperatures, reduced stream discharge and increased sedimentation will also cause deterioration in the quality of stored water, which will inevitably result in increased water treatment requirements. For irrigation reservoirs in an arid climate setting, the consequences of depleted water resources will be a reduction in water allocations for farmers with the inevitable loss of efficiency, reduction in crop yields and failure of harvests.

During the past several decades, clean energy sources such as solar power,

wind power and hydropower, have become world priorities. While these energy sources have increased in efficiency and power over time, each is limited in a certain capacity. For instance, their efficiency is aleatory as it is not always possible to produce energy since the origin of their energy sources is dependent on meteorological conditions. Conversely, when ideal meteorological conditions are present, there is a potential for energy produced to exceed what can be absorbed by demand. In the case of a hydropower reservoir, the loss of generation capacity may mean that additional fossil fuels have to be consumed in order to meet electricity demand, which, in turn, would cause a further adverse impact on the situation through the release of GHG into the atmosphere. In this case, the only effective and efficient competitive storage system is found in reversible hydropower plants.

For reservoirs that are used solely for flood alleviation, conditions are likely to

be quite different. These reservoir basins often remain mostly drawn down or empty. Higher temperatures and reduced run-off may mean that the periods of drawdown are even longer and that lake levels are lower. However, the extreme floods to be captured and attenuated by the reservoirs will be of greater volume and with higher peaks, such that the temporary storage volume available and/or the capacity of the overflow works may no longer be adequate. This shortfall in capacity could potentially impact reservoir safety as uncontrolled overtopping of the dam could cause a breach that would lead to failure.

In modern society, it is increasingly likely that our reservoirs have a significant

amenity value. Whilst this is rarely the reservoir’s sole purpose, it has become an important factor and any changes that impact the reservoir’s operational regime or the reservoir’s levels so that the amenity value is reduced, will also need to be acknowledged when considering adaptation.

Whatever the impact, it is clear that modifications and improvements are likely to be needed at dams and water supply facilities to meet future needs and to ensure the safety of our reservoirs. Societal changes in water and energy consumption will also need to run in parallel, but with an increasing world population the need for reservoirs is clear. Hence climate change impacts must be included within the management and adaptation of existing reservoirs, as well as for the planning and development of new water resources.

3.1 POSSIBLE SOLUTIONS There are likely to be a range of adaptive solutions that will need to be

considered. Water supply and irrigation reservoir solutions include: • Modifications to draw-off arrangements so water can be abstracted

from lower levels in the reservoir during periods of prolonged drought; • Improved water treatment capabilities to take account of a reduced

water quality and higher water temperatures; • Introduction of check dams and regulation structures on streams to

give greater flexibility and controllability for incoming flow; • Modifications to spillway structures and/or raising the dam crest to

account for higher magnitude floods; • Raising dams to increase live storage that might be available so as to

counter the effects of ongoing and increasing sedimentation rates; • Improvements around reservoir shores so that the adverse impacts of

prolonged periods of reduced water levels can be mitigated, and so that, as far as possible, the amenity value can be retained.

In the UK, where limited water resources are not generally perceived as a

problem, there are predictions that abstractions from water supply reservoirs will need to increase. These increases combined with reduced inflows will mean that the reservoirs will be drawn down to below average levels. This will result in a loss of amenity around the margins of the reservoir and at one such reservoir the water company is constructing small dams within the upper reaches of the main reservoir so as to retain higher water levels and thus create lagoons and wetland habitats around the shoreline.

For the River Murray System in southeast Australia, climate change is not a

‘future scenario’ as circumstances have already changed particularly regarding inflows, temperatures and losses. The Murray-Darling Basin has been experiencing drought for over a decade and unprecedented severe drought for the past three years, with the last large flood in 1996. The consequences of the recent unprecedented drought have been widespread, and include severe stress on floodplain ecology, including some wetlands that have been deliberately cut off from the river to reduce evaporation losses, and on communities. Under these severe circumstances, Australian authorities have had to respond quickly with a range of adaptive measures including changing inter-state water sharing

arrangements, operational changes of the river system, prioritizing both permanent and temporary drought contingency measures, reduced water allocations and abstractions. A recent response has been to institute the “Basin Plan,” which integrates planning across state and federal governments. This plan includes provisions for setting and implementing “sustainable diversion limits” and provisions for critical human water needs of communities dependent on the Murray-Darling Basin water resources.

The operation of hydropower reservoirs at lower levels, and hence the greater

exposure of the reservoir margins, will probably provide less of a problem than for water supply reservoirs. By their very nature, these reservoirs are normally subjected to wider variations in levels over shorter periods of time. Improvement options might include:

• Lower power intakes to compensate for lower headpond water levels; • Modifications to screening arrangements to take account of higher

sediment loads that could have an adverse impact on turbines and hydro-mechanical equipment performance and design life;

• Operational changes to meet different power demands with an emphasis on meeting only peak demand and efficiently storing water;

• Greater use of pumped storage for hydropower generation in conjunction with thermal power plants providing further potential for better efficiency.

The need for increased spillway capacity or the need to provide additional temporary flood storage so as to obviate the need for spillway improvements is likely to be the main thrust of modifications to flood storage reservoirs, as they are more likely to be empty for longer periods of time and subjected to higher temperatures. This could mean reservoir basins and embankment structures will dry out, which in turn might dictate a changed maintenance regime to ensure that the works remain fully operational and effective when they are called upon to capture and attenuate extreme flood flows.

One common theme of the adaptations is the need to ensure adequate spill

capacity to handle extreme flood flows. As a result of climate change impacts this might involve peak discharges that are higher than those of the original design flood. To some extent, these types of problems have already been addressed over the last 30 years with a move towards probable maximum flood (PMF) as the design standard, and greater emphasis on estimation of precipitation methods and hence prediction of PMF. As a consequence, many of the larger reservoirs in Europe have already been designed and/or modified to cope with increased flood flows.

In Sweden, the latest research into flood flow estimation using flow data from

1990 onwards indicates that design flood peaks could increase by up to 15%, although in some parts of the country the predicted increases are less than 5%. In these ‘cold climate’ conditions the impact of increasing snowmelt contribution induced by rising winter temperatures is another factor to be taken into account when re-estimating flood discharge. Increases of this order are not likely to be so

significant as to warrant a radical re-think of the overflow works at a reservoir. Moreover it seems that the relatively low percentage increases in peak floods that might be attributed to climate change are only of the same order as the degree of certainty within estimation procedures.

That is not to say that the possible need to increase spill capacity can be

ignored, although it is probable that the scale of modifications required will be of a similar nature to the works that have already been executed and with which the dam engineering industry is very familiar. These modifications have typically involved increasing the overflow weir length minimizing any increase in flood surcharge combined with relatively modestly raising embankment or dam wall crests to prevent overtopping. The additional of auxiliary spillways or fuse plug type spillways to meet the needs of higher but very rare flood flows has also been a feature of improvements to date. Modest increases in the discharge capacities of spillway channels and stilling basins have been realized by channel widening or by raising side walls. The challenge facing dam engineers is whether a further round of spillway improvements to satisfy climate change requirements, even if they are of a modest scale, is at all practical and viable for existing reservoirs that may have already been the subject of modification.

Beyond excessive flooding, higher air temperatures are likely to be another

aspect of climate change. It is thought that this will be a lesser impact than stream flow changes for reservoir engineering other than in extreme heat. Temperature changes are unlikely to affect the overall structural integrity or performance of dam walls, which will have been designed to accommodate a wide range of temperature variations. However, increased temperatures could impact some ancillary works such as steel access bridges, free-standing valve towers, exposed pipelines and roadways.

In addition to the physical improvements that might be introduced to meet

climate change needs, it is also probable, and in some parts of the world highly likely, that operational changes in the way we manage our water resources and reservoirs will be essential. Typical operational adaptation could include:

• Increased over-year storage to compensate for longer term droughts; • Increased storage to capture a larger proportion of extreme floods; • Greater range of reservoir operation to fully utilize available storage; • Reduced water allocations for irrigation to minimize evaporation

losses and reduce environmental stress on ‘low flow’ river systems; • Greater use of inter-watershed transfer projects to move water

between different river basins and thus give greater flexibility to the resources’ use, which could help mitigate effects of localized micro-climatic impacts.

3.2 GENERAL OBSERVATION

Many of the potential modifications outlined are aimed at single-purpose reservoirs. Where one utility is responsible for water supply, another for power generation and yet another organization has the responsibility for flood control, it is inevitable that reservoirs have been developed and are operated with that main purpose in mind. The same could be said for the adaptation measures that might now be needed to meet the challenges of climate change.

However the potential for increased use of multi-purpose reservoirs should not

be over-looked. This approach may be more suited to the planning and development of new reservoirs rather than to the modification of existing works. The multi-purpose reservoir with a flexible approach to operation could offer great benefits to meet society’s differing needs including secure water supplies, peak power demands, long term sustainability of river basins and flood protection, while taking on board the impacts of climate change as they might affect each of these fundamental needs.

Appropriate planning of adaptive arrangements is essential to deal with the

wide range of climate change issues. The impacts of climate change are already affecting water resources in dry, arid climates. While increased storage in the form of new reservoirs can provide a buffer for resisting climate change, this will only be the case if catchments’ long-term yields are sufficient to fill reservoirs. Hence adaptation needs to be incorporated into reservoir planning and design from now on. The works may involve new dams or modifications to existing facilities. This adaptive management needs to be sufficiently flexible so as to accommodate the uncertainties that surround climate change predictions and it must be developed using a risk-based approach in order to prioritize projects, while not precluding further future intervention should the need arise.

4. PREPARATIONS AND ADAPTATIONS FOR CLIMATE CHANGE Because climate change is affecting the world differently, solutions are based

on regional adaptation. Though many adaptations are site-specific, common approaches exist across the globe. By sharing these adaptations with each other, water resources managers will be in the best position to responsibly manage climate change both now and in the future. The following is a list of possible climate change impacts that may require adaptation.

• Streamflow o Decreased and increased runoff o Greater extremes (larger flood flows and longer droughts) o Larger flood peaks o Runoff timing o Decreased runoff from snow o Reduced glaciers

• Evapotranspiration

o Increased evaporation o Less net evaportaion

• Water Quality o Runoff from larger wildfire zones o Higher water temperatures o More evaporation concentrating reservoir dissolved solids o Greater precipitation increasing point and non-point pollution

• Reservoirs o Increased flood control ability

Adaptation is exhibited in systems as they adjust to change, variability and extremes; mitigate against hazards and reduce vulnerability; capitalize on opportunities; and cope with consequences. In the case of ICOLD, Committee members are experiencing climate change with varied effects.

4.1 ADAPTATION PATHWAYS Adaptation to changing climatic conditions is occurring through advanced

engineering solutions. However, many regions report that the real challenge with climate change lies less in finding technical solutions and more in finding new ways of doing things and of thinking. These new ways for adapting to the effects of climate change include instituting a risk management approach to manage storage facilities and sustain minimum flows; balancing water rights with the needs for water for the environment, recreation, irrigation, municipalities, power and other uses; using adaptive governance and adaptive management to build in flexibility to deliver more appropriate adaptations; and planning ahead even if ideal information is not available.

4.1.1. Adapting for Wetter Conditions ICOLD members from Japan and Sweden, where regions are experiencing

wetter conditions, report the response to climate change has resulted in upgraded facilities, infrastructure, and operations. General upgrades include increasing dam height; improving rainfall and discharge forecasting through storage management; improving ability to remove sediment deposits; grouping and coordinating operations of multiple dams in a river system; upgrading dam spillways to accommodate surplus snow melt and seasonal changes; updating design flood guidelines to account for climate change; revising calculations where necessary; using climate scenarios for sensitivity analyses and, based on results, building in flexibility and extra margins.

In order to institutionalize these adaptations, it is imperative to develop new

approaches to regional development by placing additional emphasis on preventative measures that improve crisis management. These efforts include improving forecasting and warning systems for floods and sediment-disasters resulting in disaster resistance and establishing emergency water supply and distribution systems for human water needs. Further, by raising public awareness

and developing incentives, regions can make saving water, reducing carbon emissions, and river environment conservation and management a priority resulting in effective flood control management and land use regulations.

4.1.2. Adapting for Drier Conditions Conversely, ICOLD members from Australia and Spain, where conditions are

considerably drier, report infrastructure adaptations focused on water conservation and securing water supplies. These efforts include an increase in piping projects, desalination facilities and water tanks, which are furthered through temporary and permanent water restrictions and conservation. Decision making and planning based on science that illustrates climate change scenarios, information relevant to water infrastructure, and research on rainfall and runoff changes allows dam owners to find better ways to manage rivers at the national, state and local levels. Crisis management is invaluable during dry times when water supplies are regulated to human consumption, essential services such as energy generation, and the riverine environment. 4.1.3 Adapting for Variable Conditions

For some, the effects of climate change are increasingly varied bringing both

wetter and drier, though still extreme, conditions. Adaptations for these environments include upgraded and expanded infrastructures to protect people and property; increased supplies and supply reliability by upgrading water intake structures to accommodate glacial retreat; and decreased demands on water for energy generation particularly in the hottest summer months. These efforts are initiated based on research focused on structural fatigue and movement due to the effects of extreme events; flooding intensity and frequency; changes in hydrologic extremes; and historical droughts.

4.2 BUILDING OUR CAPACITY

In addition to technical adaptations, additional universal adaptation pathways

are emerging across regions no matter the climate challenge. Researchers are studying the historic record to learn about the climate and determine what can be learned from the past. Conducting research on climate change now and making careful observations, projections, and assessing impacts and vulnerability will inform future planning for flood control, water use and environmental conservation, efforts that will directly influence rivers, ecosystems and water and material (such as carbon and salt) cycles.

As awareness increases and public interest piques, climate change gains

visibility. It is our job as engineers to guide the public by providing accurate and

detailed information. If we understand the effects of climate change globally, regionally and locally, and if we consider the influences on stakeholders as they make decisions towards adaptation, engineers can inform communities on the best ways to address climate change effects.

The most fundamental facet of adaptation is collaboration. Collaboration allows

engineers to underpin concepts and knowledge that will inform constructive debates leading to a universal language for describing climate change minimizing misunderstanding. Further, sharing source information, tools and methods allows engineers to assess the efficacy of adaptation pathways and focus less on vulnerability caused by climate change. Ultimately, these actions will provide enough commonality that engineers can set goals, assign roles and responsibilities that will improve policy planning and development.

Despite our best efforts, engineers will never fully understand climate change.

We can, however implement strategies to overcome a lack of information and to enhance our capacity to adapt. One way we can adapt is by supporting ownership of adaptation requirements across regions since uncoordinated or poorly targeted policies and actions create inefficiencies that exacerbate risks and are costly. In the absence of complete knowledge, we also need to shift away from a prescriptive approach, in particular, for sustainable long-term planning and policy development. Whereas a prescriptive approach may limit opportunities, adaptive governance and management approaches open up opportunities as water resources managers adapt to changing circumstances and demands and share responsibilities across communities and governments.

Though uncertainty surrounds the effects of climate change on water resources

management, water resources managers must consider three criteria while planning: water availability limitations, occurrence of extreme events and methods for sustainability. This is not to say that planning for climate change will not come with its own struggles. The climate is changing and will continue to change forcing researchers to continually adapt. Water is limited in availability, and our human needs must be balanced with those of the environment. All of this requires social and material as well as financial capital, which in the upcoming years will cost several percent of a nation’s GDP. In addition to the adaptive efforts required on a national level, progressive water resources managers will consider new urban development concepts that focus on low carbon emissions, water saving and river environment conservation and management. Adaptive practices include shifting the focus of policy away from technical prescriptive approaches and towards flexible approaches that attempt to balance social, economic and environmental objectives.

5. FUTURE COMMITTEE ACTIVITIES

Most of the activities outlined in the Committee’s terms of reference have been completed. While in Hanoi and over the following year, the Committee will coordinate with other ICOLD technical and national committees. Final bulletin preparations will begin, with the Committee expected to formally adopting them in 2011. Remaining activities include:

• Contact and interact with the Environmental Committee on possible GHG effects from reservoirs;

• Contact and interact with ICOLD committees on potential structural effects associated with changed load conditions;

• Contact and interact with ICOLD sediment management committees; • Review of advances to down-scale GCM results to basins; and • Prepare a final bulletin.

SUMMARY

The ICOLD Committee on Global Climate Change and Dams, Reservoirs and

the Associated Water Resources was formed in 2008 and met for the first time in 2009 when delegates from Australia, France, Japan, Spain, Sweden and USA presented their research on the possible effects of climate change on water resources. Findings were similar across presentations and are outlined here. Additionally, representatives from Korea, The Netherlands, Nigeria and Zambia attended and provided comments.

Here the common issues, approaches, experiences and preliminary

conclusions are summarized including topics surrounding stream flow, evapotranspiration and water quality. The Committee gives consideration to the evolving role of dams and reservoirs in a balanced, flexible, adaptive approach to meeting the future water needs of the environment, recreation, irrigation, population and power generation, providing recommendations for dam owners and those with vested interests in water resources.

Le Comité technique de la CIGB sur le changement climatique et les barrages, réservoirs et ressources en eau associées, a été créé en 2008 et s'est réuni pour la première fois en 2009 en présence de représentants d'Australie, de France, du Japon, d'Espagne, de Suède et des Etats-Unis, qui ont chacun présenté un aperçu des recherches sur les impacts possibles du changement climatique sur leurs systèmes de ressources en eau respectifs. Les approches et préoccupations des différents pays présentent de grandes similarités, décrites dans le présent document. Des participants de Corée, des Pays-Bas, du Nigéria et de la Zambie ont également contribué aux échanges.

Cette communication dresse un panorama synthétique des enjeux, approches,

expériences et premières conclusions partagés entre les membres du Comité, relativement aux évolutions possibles des apports et des régimes hydrologiques,

et de la qualité d'eau dans un contexte climatique instationnaire. Le Comité s'attache à examiner, selon une approche équilibrée, ouverte et adaptative, l'évolution du rôle que devront assurer les barrages et réservoirs pour répondre aux différents besoins: qualité des milieux aquatiques et de l'environnement, usages récréatifs, irrigation, eau potable et autres usages domestiques, et production d'électricité. Cette analyse débouchera à terme sur des recommandations à l'attention des gestionnaires d'ouvrages et de tous ceux qui sont investis d'une mission particulière dans la gestion des ressources en eau.

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