The climate and hydrology of the HKH region are changing. There are many important uncertainties about the current state of physical and social systems in the region in addition to the uncertainties about the future. However, not everything is uncertain or unknown. It is important to consider the impact of glacial retreat on regional water resources in the larger, hydroclimatic and social context of the HKH region. The effects of climate changes on glacier dynamics will affect both the supply and demand for water in the Himalayan region, and these changes will, in turn, affect the vulnerability of key populations to freshwater problems. Glacial retreat is only one factor that contributes to changes in the hydrological cycle, and the relative importance of glacial meltwater varies across the region and between seasons. In most instances, the contribution to surface-water discharge of snowmelt exceeds that of glacial melt. Glacial melt does contribute to the water flow in major rivers such as the Ganges and Indus, but for low-lying areas such as the Gangetic Plain, at much lower percentages than thought several years ago. The effect of glacial retreat will be most evident during the dry season, particularly in the west. In all seasons, changes in many regions are likely to be dominated by shifts in the location, intensity, and variability of precipitation (both rain and snow) rather than glacial retreat. Glacial meltwater is not a major contributor for river systems to the east but is more important for river systems to the west. Kaltenborn et al. (2010) conclude that,
In general, the impact of melting glaciers on the seasonal distribution of river flow is greatest where (i) ice melt occurs during a dry season; (ii) glacier meltwater flows into semi-arid areas; and/or (iii) small annual temperature cycles mean that there is little seasonal variation in snow cover. Conversely, the seasonal effect is smaller where there is significant precipitation during the melt season, such as the monsoonal central and eastern Himalaya.
Melting of glacial ice plays an important role in maintaining water security during times of drought or similar climate extremes. For example, in the European Alps during the drought year of 2003, glacial melt contributions to August discharge of the Danube River were about three times greater than the 100-year average (Huss, 2011). Thus, water stored as glacial ice is the region’s hydrological “insurance,” acting as a buffer against the hydrological impacts brought about by a changing climate, releasing the stored water to streams and rivers when it is most needed.
There may be normal, even increased, amounts of available meltwater to satisfy dry season needs because of the release of “insurance” water from storage in retreating glaciers for the next several decades (Barnett et al., 2005). To illustrate, the role of glacial wastage contributions to discharge under future warming scenarios was investigated for three highly glacierized catchments in the Alps that have long-term climate and discharge records (Huss et al., 2008). Annual runoff from the drainage basins shows an initial increase which is due to the release of water from glacial storage. After some decades, depending on catchment characteristics and the applied climate change scenario, runoff stabilizes and then drops below the current level. Retreating glaciers of the HKH in the short
term (decadal time frame) will subsidize surface flows by melting water held in storage, mitigating immediate losses to discharge by retreating glaciers (Kaser et al., 2010).
As noted in Chapter 2, paleoclimate records suggest a mixed record of wetness and dryness during the 20th century in the monsoon-dominated eastern HKH and hydrological modeling indicates that glacial melt is not a major contributor to river systems in the east (i.e., the Ganges, Yangtze, and Yellow). Thus, for the eastern HKH, these factors could result in little change to annual surface-water discharge, but could result in the loss of “insurance” water that glacial melt provides for water security during times of drought. In the western HKH, paleoclimate records indicate a trend toward wetter conditions in the 20th century and hydrological models indicate that glacial melt is much more important in the west (i.e., the Indus Basin). Thus, the consequences of climate change to water security could be large if a reduction in available surface water either annually and/or seasonally occurs in the western HKH. However, the trend toward wetter conditions in the western HKH confounds this assessment.
During situations such as these, groundwater, a significant amount of which is supplied to the major river plains of the region by the Himalayas, will be looked to as a source to offset water scarcity. Thus, water security issues for lowland populations over the next decade are more likely to come from overdrafting of groundwater resources than changes in discharge from retreating glaciers.
Although a greater understanding of the glaciers of the HKH region will inform knowledge about water security in the region, improved understanding of the science of the glaciers is itself not sufficient to answer all questions about the relationship between the hydrology, the population, and the policies and politics of the region. As discussed in Chapter 3, social changes are affecting water use at a greater rate than environmental factors are affecting the availability of water. For example, rising standards of living, including improving and changing diets and greater energy use, will have a significant effect on water-use patterns over the coming decades. Even if streamflow remains relatively stable in the short term, human factors could lead to water scarcity. Changing standards of living could also influence vulnerability to natural hazards.
Although economic development could reduce adverse outcomes, including loss of life, monetary loss could increase.
When considering the link between humans and the environment in the context of water security in the HKH region, four themes emerge: (1) there is significant variability in the climate, hydrology, and glacier behavior as well as the demographics and water-use patterns of the region; (2) uncertainties exist and will continue to exist in both the physical and social systems; (3) to reduce and respond to this uncertainty there is a need for improved monitoring of both the physical and social systems; and (4) in the face of uncertainty, the most compelling need is to improve water management and hazards mitigation systems.
Theme 1: There is significant variability in the climate, hydrology, and glacier behavior in the region as well as the demographics and water-use patterns within the region. The retreat rates of Himalayan glaciers vary over time and space, with the rate of retreat being higher in the east than the west. There are confounding factors such as dust and black carbon that will affect glacial melt and in some cases increase glacial wastage. Changes in the monsoon will probably be more important than changes in glacial wastage at lower, downstream elevations. Rates of urbanization vary across the region, as does the portion of the population with access to improved water and sanitation.
Theme 2: Uncertainties exist and will continue to exist in both the physical and social systems. The impact of future climate change is uncertain but will probably accelerate rates of glacial retreat. Accelerated glacial retreat rates will have significant impacts in local, high-mountain areas but will probably not be very important downstream. As the region’s population becomes more urbanized and standards of living change, water-use patterns will also change in ways that will be difficult to predict. Existing demographic methods to not allow for projections at sufficient spatial resolution to determine whether, for example, certain basins and elevation zones will experience higher rates of population growth than others and how the demographic composition of those specific areas will change. In both the physical and social systems, stationarity—the assumption that
the systems will fluctuate within a known range of variability—will no longer apply. In other words, the past is not a good basis for prediction, and past trends in the climate, hydrology, glaciers, and population of the region will not be a viable guide for the future (e.g., Milly et al., 2008).
Theme 3: To reduce and respond to this uncertainty, there is a need for improved monitoring of both the physical and social systems. Monitoring will need to occur on a more extensive and consistent basis. Without enhanced monitoring, the information needed to respond to changing environmental and social conditions will be unavailable. Monitoring and research will further understanding of both the physical and human systems in the region, and identify the various options available to respond to change in the face of uncertainty.
Theme 4: In the face of uncertainty, the most compelling need is to improve water management and hazards mitigation systems. Existing patterns of water use and water management need improvement. As discussed in Chapter 3, some progress has been made in improved assessments in the recent past. Going forward, improved implementation of lessons from these assessments in water policies and programs will be necessary. Options for adapting to climate change are discussed in greater detail in the next section. However, the people most likely to be affected by changing water security in South Asia are the rural and urban poor who have the least capacity to adapt to changing environmental and social conditions and hazards. Management of groundwater and demand-side management are among the areas where improvements can be made.
Anticipating future conditions in the HKH region is hindered by an incomplete understanding of current conditions and of both the extent to which natural feedback mechanisms will generate new equilibria and human systems will adapt to signals of stress and change. As discussed throughout the report, many open scientific questions remain about the physical and social systems of the region, which, if addressed, could lead to a greater understanding. These research and data needs are presented in roughly the same order as the topics appeared in the report, and the order does not indicate priority. These needs are critical to more fully address the questions in the Committee’s charge.
The HKH is one of the least-observed regions on Earth. Currently available data lack the necessary spatial and temporal resolution, as well as quality, to fully understand the region. There is a need for carefully designed surface observing systems (including temperature, precipitation amount and type, streamflow, glacial mass balance, glacier albedo, groundwater, paleoclimate proxies) that are integrated with satellite observations to provide comprehensive monitoring of the region. In addition to new data, pooling of existing data and resources, including release of relevant classified or restricted satellite imagery or water data, and sustained international cooperation and data sharing are critically important to advance understanding and reduce uncertainties. Comprehensive monitoring and data sharing would help answer the following questions:
• Climate, meteorology, and aerosols: What are the effects of greenhouse gas warming and black carbon radiative forcing on winds, temperature, precipitation variability, and trends in the summer monsoon and mid-latitude westerlies? How much of the regional atmospheric aerosol loading is driven by local emissions compared with transport from remote sources? How do black carbon deposition, snowfall, and snow turnover processes combine to affect the albedo of glaciers and snowpack? How has the temperature in the mid and lower troposphere changed? How do current changes in the regional climate compare to natural climate changes that occurred in the past? How will the monsoon change in the future?
• Glaciers: What is the relationship between climate changes and the mass balance of the HKH glaciers? What is the response time of individual glaciers to climate forcing, and how does this response time vary among glaciers in the region? Have temperature changes in the mid and lower troposphere affected the equilibrium line altitude or the ratio of snow to rain? How does snow cover change seasonally?
• Hydrology: What is the relative contribution, seasonally and annually, of glacial wastage and melt-water to total streamflow in the major rivers of the
HKH region? What are the surface water-groundwater recharge mechanisms in the region? How will climate change affect groundwater supply? How can hydrological data become more widely accessible to the science and management communities? How can remote sensing be used in conjunction with well data to increase understanding of groundwater in the region?
Currently available demographic compositional data do not conform to geophysical parameters and lack the necessary spatial resolution to determine whether, for example, certain basins and/or elevation zones will experience higher rates of population growth than others. Current understanding of water usage is poor because of a lack of regional datasets. Remote sensing advances may address some of these deficiencies, particularly in the plains. Improved measurement of water withdrawals from surface water, and even more so groundwater pumping, will be crucial for developing, monitoring, and managing regional water budgets, hazards, and stresses. As lowland water and energy scarcity may increase demand for mountain water storage, advances in water use analysis will have increasing importance. Improved datasets and monitoring would help answer the following questions:
• Demographics: How will populations change in areas with water scarcity as compared with areas with sufficient water supplies?
• Water-use patterns: How can major improvements in water-use data collection, access, and utilization be accelerated? How do changing lifestyles, standards of living, and demographic trends affect water supply, demand, and management?
• Water management: What dams are planned in the region, and how will they affect water management and hydrology? How can the results of international- and national-level climate assessments be incorporated into water management and policy at the subnational level?
Environmental Risk and Security
Hazard datasets remain inconsistent and not coded in ways that enable causal analysis of large-N samples of floods, droughts, heat waves, and secondary impacts associated with climate variability. Although deaths and numbers of persons affected are regularly reported, and to a lesser extent physical damages (e.g., houses and infrastructure destroyed), rigorous economic damage and need estimation are a priority for policy research. Disaster resilience, recovery, and reconstruction processes are less well documented than initial impacts, in part because they occur when postdisaster attention wanes. The human dimensions of loss and reconstruction require intensive field research, and strong relationships between research and practice. New methods of postdisaster mobile phone survey data transfer and mapping have considerable promise for advancing socioeconomic lines of research on a regional scale. Improved economic, social, and political datasets would help answer the following questions:
• Natural hazards and vulnerability: Which populations in the region will be most vulnerable to a changing climate? What are the proximate and root causes of vulnerability in the HKH region? How do alternatives for secure and sustainable livelihoods differ for populations in the mountains more dependent on glaciers and larger downstream populations on the plains? How can the results of collaborative research on exemplars of disaster-resilient settlement, infrastructure, and housing in mountain environments of the HKH region complement initiatives to increase collaboration on climate change, glaciology glacial lake outburst flood monitoring, and flood warning—and help increase the prospects for successful adaptation to changes in climate and hydrology in the region? How can early-warning systems be used to minimize deaths from hazards such as GLOFs?
• Security dynamics and water conflict: What is the current and future institutional capacity to absorb change at the local, national, and international levels? How can the research community design appropriate metrics to monitor the capacity of governmental institutions to address water stress? Does water stress, among other stressors, affect state stability? Through what mechanisms? What are the possibilities for better incorporation of scientific information about glaciers, hydrology, and climate change into international water-sharing treaties? Will climate change impacts on glacial melt and hydrology be severe enough to
constitute a threat to water and food security and/or political stability?
There are some potential adaptations that governments, communities, or individuals may consider in response to climate change’s effects on the hydrologic system. Even with significant international progress toward mitigating greenhouse gas emissions, with current levels of carbon dioxide and other greenhouse gases in the atmosphere, there will be significant climate change over the next few decades, and thus some adaptation, particularly to strengthen water management systems, will be necessary.
It can be difficult to make decisions about which adaptation strategies to pursue in the face of uncertainty about the magnitude of climate change’s hydrological impacts. Also, there are significant uncertainties about the effectiveness of various adaptation options. Some adaptation options have been shown to be effective in adapting to variability under current climatic conditions, but it is not known whether they will hold up under a changing climate (NRC, 2010a). Additionally, implementation of adaptation strategies can be challenging in developed countries:
Numerous attempts have been made to develop and implement adaptive management strategies in environmental management, but many of them have not been successful, for a variety of reasons, including lack of resources, unwillingness of decision makers to admit to and embrace uncertainty; institutional, legal, and political preferences for known and predictable outcomes; the inherent uncertainty and variability of natural systems; the high cost of implementation; and the lack of clear mechanisms for incorporating scientific findings into decision making. Despite all of the above challenges, often there is no better option for implementing management regimes…. (NRC, 2011b)
And developing countries are likely to face as many challenges.
Good first adaptation strategies to pursue are generally flexible (i.e., they do not lock a country or other entity into a long-term commitment to the strategy), are relatively low-cost and are “no regret” strategies (i.e., they would be good strategies to take regardless of how severe climate change’s impacts become). In general, many strategies that encourage good management of water resources under current climate could serve as useful adaptation strategies in a world with altered climate. Similarly, because people with fewer resources are often more vulnerable to climate change disruptions, many strategies that promote sustainable economic development could also be useful adaptation strategies in the face of climate change.
There is a large literature on the topic of adaptation, and the Committee can only briefly describe a few potential adaptation options in this section. Adaptation was discussed previously in the context of water management institutions and disaster agencies in Chapters 3 and 4, respectively. Here, the Committee describes options that affect the supply or timing of water available to users, followed by options that affect the demand of water by users. Then the Committee discusses integrated watershed management and river basin management, which often consider both supply and demand. Finally, the Committee discusses adaptation options to decrease the risk of negative impacts from flooding.
Adapting Under Uncertainty: The Need to Monitor
As discussed above, and throughout this report, lack of understanding and a paucity of data about current and emerging conditions of glacial melt and the hydrological system more generally are major sources of uncertainty in the region. Adaptive management1 of water resources depends critically on observations of changes that are occurring. Therefore, adaptation options will rely on expanding the monitoring programs in the region, including increased hydrometeorological data; measurements of glacial mass balances, seasonal snow cover, black carbon on snow and ice; assessment of GLOF risks; streamflow data (i.e., discharge); water quality; and demographic patterns of water use. Both remotely sensed and in situ data are valuable for such monitoring programs (USAID, 2010).
1 Adaptive management is a flexible approach designed to meet management goals under a variety of future climate conditions and requires a nonstationary view (e.g., Milly et al., 2008; NRC, 2010a, 2012b).
In addition to uncertainties in the physical systems of the region, there are also uncertainties in the social systems. Adaptive management of the region’s water resources will require a greater understanding of how each option will affect downstream users, the potential negative consequences of each option, and whether an option may prove to be maladaptive. In addition, it will be necessary to monitor the impacts of adaptation policies, and make adjustments to the policy as required. Interventions that can be repurposed and customized are especially desirable when operating under conditions of uncertainty and change. The capability to support and integrate interventions into local innovations that are effective is also of great value. Effective program evaluation, something that is often overlooked, is especially important when designing and implementing interventions under conditions of uncertainty. A central concern with adaptation strategies is their potential for changing power relationships and introducing conflict, and for creating unrealistic expectations that can become difficult to manage and a source of significant social tension. Some management and adaption options in the face of hydrological change may themselves detrimentally affect water availability for downstream riparians, possibly sparking or exacerbating water conflicts or political tensions. In other words, the rational pursuit of otherwise reasonable adaptation options (e.g., the construction of more water storage or the expansion of irrigation) as insurance against prospective climate-induced shortfalls or volatility in future supply could have negative consequences.
One potential impact of climate change on the region’s hydrology is to increase the frequency of both high-flow events and low-flow events. One adaptation option is to try to increase storage, so that water can be stored during wet periods for use during dry periods. Three approaches to this effort are improved water supply forecasting, dams, and catchment systems. In each approach, the need for flexible systems that can adapt in a range of uncertain futures suggests that small-scale and low-cost systems may be the best options for at least the planning horizon of most countries and donors.
New dams, either at a large or a small scale, are one way to increase hydropower and/or storage in both the Indus and the Ganges/Brahmaputra, although any new dam construction would likely be a politically controversial decision, both within a country and between countries. Because climate will be changing over the long term, dam planning needs to include multiple scenarios over the projected life of the dam to ensure its usefulness under climate change. As well as the potential for being maladaptive over time, dam construction could also have unintended and cumulative negative consequences on the regional ecology, settlements, and downstream sediment supply (e.g., NRC, 2011a). Additionally, geological instability limits the stability of major dams and reservoir development in the region and adds risk from dam failure. In any event, dam management regimes at existing dams will need to be altered, so that, rather than being operated on the basis of historical distribution of streamflow events, dam operation is based on the current (altered) climate. Because changes in dam management will affect the availability of water to downstream users, either in the same country as the dam or a different one, such changes may have the potential for conflict if decisions are not made cooperatively with all affected parties.
More local-scale catchment systems can store water in wet seasons for use in dry seasons. Catchments are often constructed and managed at the local level. They are relatively less expensive, lower impact, and easier to change than large dams.
Another adaptation option sometimes used in the face of water shortages is to construct a system for interbasin water transfers, moving water from a relatively wet place to a relatively dry place. Such systems are often extremely expensive to construct, such as the Chinese plan to divert water from south China to the north, the South-North Water Diversion Project, which is estimated to cost around $62 billion dollars (Wong, 2001). Moreover, any plan by upstream countries for an interbasin transfer in the Ganges/Brahmaputra Basin would likely have international political repercussions and could be the basis for a conflict. Interbasin water transfer is further complicated by the lack of understanding of the impact of climate changes on the hydrology of the region. Changes in the flow of rivers in the relatively wet areas could impair their ability to adequately provide water for the dry areas, decreas-
ing the effectiveness of a very expensive project. For these reasons, proposals for interbasin water transfers are generally controversial among hydrologists, policy analysts, NGOs, and the courts.
Usually, climate change adaptation is considered a separate topic from climate change mitigation (i.e., the reduction in emissions of pollutants that cause climate change). Greenhouse gas emission mitigation is by necessity a global challenge, because most greenhouse gases are well mixed in the atmosphere. However, for South Asian countries the control on the emission of aerosols and particulate matter could help mitigate the regional pattern of climate change, because these pollutants play an important regional role in, respectively, the monsoon cycle and the rate of snowmelt and icemelt. Although the exact scientific relationship between these pollutants and regional climate is still an area of active scientific exploration, there is potential that countries could cooperate to maintain traditional climate patterns to some extent by limiting emissions of aerosol and particular matter. Because actions by a small set of countries could significantly change the regional concentration of these pollutants, such an agreement could avoid the problem facing many global agreements about greenhouse gas pollutants, where there are many actors who have to approve an agreement. Reducing aerosol emissions is also a resilience-building strategy, in that it has the co-benefit of reducing respiratory diseases and premature deaths, especially among women and children (NRC, 2010b).
One common adaptation strategy used to address short-term water shortages is to withdraw ground-water. Groundwater is a form of water storage, and can be sustainably used as long as withdrawal rates do not exceed recharge rates of the aquifer. However, changes in the regional hydrology could affect the recharge rate, leading to uncertainties in the amount of water that can be sustainably withdrawn. Increased use of groundwater may be one adaptation to climate change, but some major aquifers are already being depleted by excess withdrawals, so there are (often uncertain) limits to how extensively increasing withdrawal from ground-water can be a long-term adaptation to climate change. In addition, groundwater withdrawal in delta regions could lead to increased subsidence, which in turn leads to increased sea level rise. Increased use of the traditional karez or qanat system of channeling groundwater (Box 3.1) may serve as a climate change adaptation, but success depends on the level of community cohesion and will be limited unless enough groundwater is available for the system. Because available data indicate the groundwater is currently being used unsustainably in the region, this adaptation option, by itself, is likely not realistic; however major advances in conjunctive management of surface and groundwater will be a high priority
There are also options for local water storage. For instance, some high-altitude communities in the HKH region have experimented with building small ponds that freeze in the winter into miniglaciers (ICIMOD, 2000b). These miniglaciers then melt slowly over the growing season, providing farmers and towns with water. Larger reservoirs could potentially become a hazard due to earthquake-induced failure, or change the energy balance of snow-covered basins. Additionally, there are emerging technologies that harvest water from humid air (ICIMOD, 2000a). An increasing number of cities in South Asia are adopting harvesting requirements in building and development codes (Agarwal et al., 2001). Another way to increase water supply at the local level is to reuse treated wastewater (e.g., Kumar et al., 2005), particularly for irrigation.
Given the uncertainty in the future magnitude of climate change impacts, one general adaptation option is to expand the diversity of techniques that are used to obtain water. The idea is that instead of just one source, which could be critically affected by climate change, multiple sources would be relatively less sensitive to disruption by climate change, unless climate change were to impact all the sources simultaneously and synchronously.
Any strategy that increases water-use efficiency can serve as a potential climate change adaptation, but can also increase a population’s vulnerability if users do not see the value in using less water. Because users sometimes expand their use to take advantage of increased water availability, efficiency gains do not always translate into reductions in total water use. These gains may still increase the productivity of a given water use per unit of water withdrawn and hence a sector’s resiliency to climate change. The agricultural sector is the biggest
user of water, and the one with the greatest potential for increases in water-use efficiency to serve as an adaptation. For instance, cotton, rice, and sugarcane irrigation in the Indus Basin use a large volume of water, and small reductions in the amount of water used per hectare could significantly reduce water use by these crops. Another sector where gains in water-use efficiency may be helpful in adapting to climate change would be the energy sector. Thermoelectric power plants that use once-through cooling systems withdraw significantly more water than recirculating cooling systems. Although most of this water is discharged to the stream after use, there can be local thermal impacts. A switch from once-through cooling to recirculating cooling can significantly reduce water withdrawals by the sector. However, recirculating systems have higher consumptive use than once-through systems, so trade-offs are necessary (NREL, 2003). Municipal water systems also could improve technological efficiency, perhaps as part of extending their coverage to growing populations. Such adaptation strategies require large infrastructure investments, which affect their feasibility.
There are a number of tools available to affect demand management. Some of these are technology based and include flow restrictors, low-flush toilets, closed conduit irrigation systems—sprinkler and drip systems—and water metering, either by itself or in connection with rational regimes of water pricing. In general, the relatively high capital costs of these technologies make their adoption prohibitively expensive for much of the water-using population in the region. More decentralized demand management techniques include water pricing and water rationing. Shah (2009) describes how the availability of complementary inputs such as energy for pumping groundwater have been used successfully to manage demand for irrigation water in some areas. This is accomplished by making energy available only during certain periods of the day. These decentralized demand management techniques have the advantage of allowing each user to adjust consumption according to their circumstances.
More significant climate change impacts on hydrology might necessitate changes in land use over time. For instance, farmers might adapt to climate change by shifting from a water-intensive crop that requires significant irrigation to a less intensive, perhaps rainfed, crop. Such a strategy would require periodic adjustments to account for further changes in precipitation patterns. The focus of adaptation strategies might also be how to reduce irrigation demands during extreme low-flow periods of the year. Although forgoing irrigation during low-flow events imposes an economic cost on farmers, it may leave enough water in surface water and groundwater for downstream users. However, this may have a negative impact on regional food security, again demonstrating the complexities of adaptation options.
River Basin Management
The ideal model for river basin management and the processes its development, management, and maintenance have been given considerable thought and have evolved through time (Molle et al., 2010; NRC, 2010c). Embedded within this discussion is the concept of environmental flow (EF) that describes the water regime (quantity, timing, and quality) within a system that is required to maintain the surrounding ecosystem and human livelihood. Most EF assessments have been developed and performed in developed countries. Yet assessment of EFs in developing countries, such as those in the HKH region, is a necessary step toward successful river basin management, and some progress has been made (Smakhtin et al., 2006).
Often, water managers implement minimum EF requirements based on system objectives such as maintaining populations of fish at a given level or supplying local communities and/or agriculture with a given volume of water (NRC, 2010d). When a river basin is at the point where there is no more utilizable flow in a given year, the basin is said to be “closed” (Falkenmark and Molden, 2008). If a basin is closed and utilization continues, an unsustainable situation ensues. The waters of the Indus and the Ganges are already said to be overallocated or nearing overallocation, thus “closed” basins (Falkenmark and Molden, 2008; Smakhtin, 2008).
Efforts to effectively manage river basins attempt to avoid this type of situation and the associated impacts such as a decrease in water quality or inequitable sharing of the resource. It is increasingly being realized that the biological and social systems supported by water are not adequately described by a single minimum flow requirement or a set of flow requirements, but a more
comprehensive assessment of water management is needed that accounts for hydrological change (NRC, 2012b). This would include, for example, basic strategies such as demand management, increased storage, establishment of EFs, and operational flexibility (NRC, 2012b).
One option, integrated watershed management (IWM), attempts to consider both demand- and supply-side strategies for managing water in a basin to find a solution to any water problems in the basin. Although definitions of IWM vary, the general focus of management is on looking at all uses of water simultaneously when making policy decisions. For the Ganges/Brahmaputra and the Indus, there is a clear need, for example, to link management of surface-water resources more closely with management of ground-water resources. There is also a need for management decisions to be made that consider the needs of water users in different countries. This is often a difficult task politically, but the existing international agreements (e.g., Indus Water Treaty) illustrate that agreements about water allocations can be achieved.
Many of the international agreements in the region are not yet fully integrating climate change considerations into their decision making, and any progress on this front could serve as a climate change adaptation, by ensuring that basin water resources are managed efficiently and equitably in a changing climate. Climate change planning at the national level is important. Even if many national hydrological agencies are considering the potential impacts of climate change, many other national government agencies are not. If, for instance, agencies deciding on the construction of new irrigation systems are not adequately considering the effect of climate change in their decisions, then countries may commit significant resources to irrigation that will not be useful in a future climate.
At national and subnational levels, opportunities exist to provide knowledge and assistance to farmers in efficient water use, especially as regards irrigation systems. Local or subnational organizations, networked for greater impact, can develop farm-level and cooperative strategies for both groundwater and surface-water use. Another adaptation option includes establishing or strengthening community-based water user associations (WUAs) and forest user groups (FUGs), with better coordination links to national policy frameworks for water management and health (clean water and sanitation) (USAID, 2010).
Managing Flood Risks
The first step in reducing potential flooding impacts from climate change is to map which communities are at risk (NRC, 2009). The primary risk of flooding from glacial melt per se is GLOFs, which are mostly a risk to high-elevation communities along rivers and streams, but similar phenomena can pose risks at lower elevations when debris or ice jams dam water that then bursts out. In contrast, the risk of downstream flooding may be increased by climate change, depending on a number of factors including the rate and timing of snowmelt and the magnitude of monsoonal rains. Because there are many large settlements near rivers in the lower floodplains of the Ganges/Brahmaputra and Indus basins, if climate change increases the risk of downstream flooding events, it could significantly affect hundreds of millions of people.
Once communities at risk from flooding are identified, there are various options that can be used to minimize risk, although many are very difficult to implement. New development can be limited in flood-plains or other sensitive areas, or existing homes and infrastructure in floodplains at risk of flooding can be decommissioned. Vegetation, including forests, can be restored where needed to retain water and thus mitigate flooding. Governments can offer flood insurance programs, as the Federal Emergency Management Agency’s National Flood Insurance Program does in the United States, both mandatory in high-risk areas and nonmandatory in low-risk areas. Alternatively, new infrastructure can be built to protect areas at risk of floods (e.g., dams, pumping stations, or storage basins). Sometimes this infrastructure is traditional “gray” infrastructure, such as levees. However, levees are often considered to be maladaptive, because they can encourage settlement in vulnerable low-elevation areas (NRC, 2012b). In other cases, so called “green” infrastructure solutions are used, where floodplains are reconnected hydrologically with rivers to allow flood waters to spread out over the entire floodplain. This reduces the flooding risk to downstream communities by reducing the height of peak flows in a river.
Flood management also includes early warning systems, which can reduce deaths and injuries, and disaster response capacity, which is highly variable in the region. Improvements in each of these areas would be adaptive to both glacial melt and hydrological change.
There is a growing sentiment within parts of the climate science community that the social effects of climate change are already more extensive than previously thought or recognized, and are mounting more quickly and more extensively than predicted. This suggests that in discussions of climate change impacts over 50-year-plus time horizons may have to be replaced with ten-year-plus time horizons, and more comprehensive approaches to hydroclimatic forecasting, natural hazards mitigation, and water management.