1. Introduction

Water security—the reliable availability of an acceptable quantity and quality of water for health, livelihoods, ecosystems, and production—has emerged as one of the defining challenges of the twenty-first century (UNESCO, 2021). Unlike other resources, water is indispensable and non-substitutable. Yet, its spatial distribution is highly uneven, and its availability is increasingly undermined by climate change. The melting of glaciers, changes in rainfall patterns, and more frequent droughts and floods are altering hydrological regimes globally (IPCC, 2022).

One critical dimension of water security is the governance of transboundary waters. Over 310 rivers and lakes and more than 500 aquifers cross national boundaries, sustaining 52% of the world’s population (Swain, 2025). These watercourses underpin agriculture, energy, industry, and ecosystems across borders. Yet, they are simultaneously flashpoints of tension, as shifting hydrological flows collide with rising demand, population pressures, and geopolitical rivalries.

This article explores how climate change interacts with transboundary waters to reshape the risks of conflict and cooperation. Building on the insights from my newly published book, Climate Security (2025), it examines the dynamics of water disputes, the prospects of cooperation, and the institutional and policy frameworks required to ensure sustainable management. It concludes with policy recommendations to prevent water from becoming a driver of instability and instead position it as a platform for peace and resilience.

2. Climate change as a stress multiplier

Climate change acts as a threat multiplier in the water domain. It amplifies pre-existing scarcity and magnifies vulnerabilities in regions already under stress. The effects are multiple and mutually reinforcing. Rising global temperatures increase atmospheric moisture by about 7% per degree Celsius, intensifying rainfall in some regions while reducing it in others (IPCC, 2022). This makes flows in transboundary rivers more erratic, creating problems for water-sharing arrangements that are based on predictable patterns of distribution.

In the Himalayas and Andes, accelerated glacier melt has increased summer flows temporarily but threatens long-term dry-season shortages, intensifying disputes between upstream and downstream states (Wester et al., 2019). The Indus River basin illustrates the challenge vividly: Pakistan depends on glacier-fed waters for more than 90% of its agriculture. Climate models predict reduced flows later this century, which could devastate food security in one of the most densely populated regions of the world (Swain, 2025).

Groundwater, which supplies drinking water to two billion people, is also under increasing pressure. Aquifers are being depleted faster than they recharge, particularly in South Asia, the Middle East, and North Africa. Yet governance remains weak: only six binding international agreements exist for shared aquifers (UNESCO, 2021). The invisibility of groundwater makes it politically less salient, even as it is becoming central to survival (Swain, 2025).

Extreme events compound these pressures. Floods, droughts, and storms are increasing in frequency, testing the resilience of existing water-sharing treaties that were never designed for such variability (WMO, 2021). For instance, the 2025 flooding of the Indus devastated millions in Pakistan, creating tensions with India over upstream releases, despite both states having a treaty in place (at least legally). In the Zambezi basin, recurring droughts have pushed Zimbabwe, Zambia, and Mozambique into repeated disputes over hydropower releases.

The combination of higher demand and lower predictability erodes trust between riparian states. Long-standing agreements such as the Indus Waters Treaty (India-Pakistan, 1960) or the Ganges Treaty (India-Bangladesh, 1996) are under severe strain from shifting flows, raising doubts about their durability in a climate-changed future (Swain, 2025).

3. Conflict potential in transboundary waters

Although no full-scale war has been fought exclusively over water, transboundary rivers have frequently fueled political tensions and localized conflicts. Climate change raises three major risks that could escalate disputes.

Quantity disputes occur when reduced flows threaten irrigation and drinking supplies, leading downstream states to accuse upstream neighbors of withholding water. Egypt’s fierce opposition to Ethiopia’s Grand Renaissance Dam (GERD) exemplifies this dynamic. For Cairo, which relies on the Nile for 97% of its freshwater, Ethiopia’s plans represent an existential threat (Swain 2012; Swain & Jägerskog, 2016). Similarly, India and Pakistan have clashed repeatedly over hydropower projects on the Indus, with New Delhi claiming treaty compliance while Islamabad insists its lifeline is being undermined.

Quality disputes are also intensifying. Reduced volumes exacerbate pollution, since contaminants are less diluted. Industrial discharge into shared rivers like the Mekong or Tigris–Euphrates escalates into cross-border grievances (Weinthal & Sowers, 2023). In Central Asia, declining flows in the Syr Darya and Amu Darya have worsened salinity and pesticide concentration, reducing arable land and fueling tensions among successor states of the Soviet Union.

Control disputes arise when hydropower dams and diversions allow upstream states to regulate flows, creating asymmetrical power relations. China’s cascade of dams on the Mekong has heightened anxieties in Cambodia and Vietnam, whose economies depend on stable downstream flows. On the Brahmaputra, Chinese projects raise fears in India and Bangladesh of future manipulation.

Moreover, political asymmetry magnifies tensions. Powerful upstream states often dictate terms, while weaker downstream states perceive existential threats. Climate change does not by itself cause wars, but it heightens uncertainty and raises the risk of escalation in already fragile regions such as South Asia, the Middle East, and Sub-Saharan Africa (Swain, 2025). Climate-induced migration and displacement add another dimension: when water becomes scarce, populations may move across borders, fueling nationalist backlashes.

4. Cooperation pathways

Despite the conflict potential, history shows that water is more often a catalyst for cooperation. Over 3,600 water treaties have been signed since 805 AD, including 600 in the last 200 years (Eckstein, 2017). Several prominent examples illustrate both resilience and fragility.

The Indus Waters Treaty of 1960 has survived three wars between India and Pakistan, demonstrating remarkable resilience despite extreme hostility. While disputes persist and India claims to have kept it in abeyance since May 2025, the treaty provides a legal and institutional framework that prevents collapse into outright conflict. The Rhine Commission helped European states address pollution and navigation, transforming the river from a source of industrial contention into a model of cross-border cooperation and eventually contributing to European integration. The Mekong River Commission, though limited by the absence of China as a member, provides a platform for dialogue and joint projects among Southeast Asian states, demonstrating the importance of even partial cooperation.

The dominant view in water conflict literature suggests that scarcity often drives states to negotiate rather than fight, since conflict would endanger a vital and irreplaceable resource (Wolf, 1998; Bernauer & Böhmelt, 2020). Yet cooperation is not automatic. As we have argued in our book (Swain and Jägerskog, 2016), it requires political will, trust, and effective institutions. External mediators such as the World Bank, which brokered the Indus Treaty, can play crucial roles in bridging divides. The role of civil society and basin communities is also increasingly recognized, particularly in building confidence and ensuring that agreements reflect local needs.

5. Institutional challenges

Existing governance structures for transboundary waters are inadequate to meet the challenge of climate change. Only 38 countries are party to the 1997 UN Watercourses Convention, leaving most rivers without a global legal framework (Swain, 2025). The 1992 UNECE Water Convention has had greater traction in Europe, but its global expansion has been slow.

River Basin Organizations are essential but uneven in effectiveness. Some, like the International Commission for the Protection of the Rhine, succeeded in reducing pollution and fostering cooperation. Others, such as the Aral Sea arrangements, collapsed under weak enforcement, nationalist politics, and lack of financial autonomy (Mitchell & Zawahri, 2015).

Groundwater remains neglected. Despite aquifers being the main source of freshwater, they are absent from most political agendas (Wada et al., 2016; Swain, 2025). The Guarani Aquifer Agreement in South America is one of the few exceptions, yet even it has weak enforcement mechanisms.

Nationalism and populism exacerbate the problem. Leaders often politicize water to rally domestic constituencies, framing disputes in zero-sum terms. In South Asia, for instance, water agreements are frequently invoked in electoral politics as symbols of sovereignty. This short-term use of water for political gain undermines cooperative mechanisms and stokes mistrust (Swain, 2025).

These weaknesses highlight the urgent need for adaptive, flexible, and depoliticized governance that incorporates scientific knowledge, considers local contexts, and engages both state and non-state actors.

6. Policy implications

Water-sharing agreements must be revised and climate-proofed. They must incorporate mechanisms for variability, not just fixed quotas. For example, future revisions of the Ganges Treaty, due to expire in 2026, must factor in climate-induced unpredictability and include provisions for drought and flood contingencies (Swain, 2025).

Multilateral institutions must be strengthened. Expanding ratification of the UN Watercourses Convention and encouraging regional frameworks are essential. River Basin Organizations should be given greater enforcement power and financial autonomy to act effectively. This requires financial backing from international institutions such as the World Bank, UNDP, and regional development banks.

International law and basin agreements must explicitly address aquifers. Given their invisibility yet critical importance, cooperative monitoring and sustainable extraction frameworks are essential. Shared groundwater must be recognized as strategically significant, particularly in regions like the Sahel and the Middle East, where it underpins survival.

Political leaders must resist the temptation to instrumentalize water in nationalist politics. Technical experts should be empowered, with decision-making insulated from populist pressures. The success of the Rhine regime and even the Indus Treaty stems partly from their technocratic management structures, which insulated technical issues from high politics.

Rivers should be treated as integrated systems rather than dividing them into national sections. Policies should incorporate ecological sustainability, cultural contexts, and community participation (Swain, 2013). Local communities, who are often the first affected by scarcity or floods, must be included in monitoring and decision-making.

Transparency through data sharing is key. Joint hydrological monitoring and open data platforms can build confidence and reduce suspicion. Remote sensing technologies and satellite monitoring can help overcome mistrust by providing independent verification of flows.

Finally, water must be elevated to a national security priority. Recognizing water security as a national security concern would give leaders the mandate to negotiate seriously and prioritize long-term cooperation over short-term populism (Swain, 2025). Yet it is equally important to avoid a militarized approach that sidelines human security. A balanced framing that combines national security imperatives with human development needs offers the most promising path forward.

7. Conclusion

Water security is one of the most urgent and complex challenges of our time. Climate change exacerbates scarcity, undermines predictability, and increases the stakes of transboundary disputes. Yet water also holds the potential to foster cooperation, as history demonstrates.

To harness this potential, states must urgently revise outdated treaties, strengthen institutions, and integrate neglected resources such as groundwater into governance frameworks. Political leaders must depoliticize water, empower technical expertise, and treat transboundary water management as a central component of climate adaptation and national security.

The path ahead demands not just incremental improvements but transformative governance. With over half the world’s population dependent on transboundary waters, the choice is stark: adapt institutions to foster cooperation, or risk escalating conflicts in a warming and water-insecure world.

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