Who Needs Whose Water? A First-Principles View of Transboundary Conflict

I read Jiang et al., 2025, a recent Nature Communications paper with curiousity. This paper examines transboundary conflict from surface-water scarcity under climate change and estimates that, without adaptation, roughly 35–41% of the world's transboundary river basins could face conditions conducive to water-scarcity-related conflict by mid-century. With sufficiently effective cooperation and other adaptations, that fraction could fall dramatically.

What stands out is that the authors do not treat conflict risk primarily as a correlation problem. Instead, they build the analysis around the physical water balance and ask how the situation changes when control over upstream water changes.

For each downstream region, they pose a pair of counterfactual questions.

What happens if upstream withdrawals disappear, so that the downstream region has access to the natural upstream runoff? If this removes downstream scarcity, there is an incentive for the downstream side to seek a larger share of upstream water. The authors call this a Type I conflict mechanism.

Conversely, what happens if upstream inflow is removed and the downstream region must rely on its own runoff? If scarcity becomes worse, the upstream region has the ability to create additional pressure by storing, diverting or retaining water. This becomes their Type II mechanism.

I like this counterfactual construction. It has something of a first-principles character: begin with the resource balance, change who effectively controls a contested component, and examine the consequence. It also has a game-theoretic flavor, although it is not a formal game-theory model. The framework identifies the physical incentives facing the two sides rather than trying to infer them entirely from historical correlations.

One result I found somewhat surprising is that the first mechanism is more prevalent. The familiar narrative of transboundary water conflict often emphasizes an upstream country withholding water from a vulnerable downstream neighbor. Here, however, much of the pressure arises because growing downstream demand makes the downstream region increasingly dependent on water generated upstream. Their further analysis similarly suggests that increasing local demand is often a stronger driver of downstream scarcity than increasing upstream withdrawals.

The same construction also makes the treatment of cooperation interesting. Once scarcity has been diagnosed as a spatial or seasonal mismatch within a basin, one can ask the reverse counterfactual: what if the basin could coordinate allocation across countries and across time? The authors use this to estimate how much scarcity—and therefore the hydrological pressure underlying potential conflict—could in principle be removed by intra-basin cooperation.

This is not an empirical estimate of the causal effect of treaties or diplomacy. It is closer to an estimate of the hydrological opportunity available to effective cooperation. That distinction matters, but it is also part of what makes the framework useful.

Of course, an analysis of this kind places unusually heavy demands on the underlying hydrology.

The study divides transboundary basins into country–basin units and reconstructs monthly local runoff, upstream inflow and water withdrawals. Historical water availability comes primarily from runoff simulated with the VIC hydrological model, while future runoff is obtained using VIC with climate forcing from five ISIMIP3b global climate models. Monthly agricultural, industrial and domestic withdrawals come from a separate global water-use dataset. These ingredients are then combined to estimate how much water is locally generated, how much arrives from upstream, and how upstream use changes the water reaching each downstream country.

The authors conduct extensive uncertainty experiments and find that perturbations of runoff and withdrawal estimates do not substantially alter their aggregate conclusions. Still, there is a broader challenge here that extends well beyond this particular study. Basin-scale runoff production remains imperfectly described in many parts of the world; reservoir operations, groundwater use, environmental-flow requirements and actual withdrawals introduce additional uncertainty. Monthly errors matter especially when a classification can depend on whether scarcity persists for one additional month.

That makes the paper interesting for another reason. If water accounting is increasingly used not simply for hydrological assessment but to inform questions of transboundary rights, dependency and responsibility, then credible national- and basin-level estimates of where water originates, where it goes, and who uses it become increasingly consequential.

There may not always be a uniquely "correct" estimate of available water. Different models, observations and assumptions can legitimately produce different numbers. But in contested basins, improving the accuracy, transparency and verifiability of those estimates may itself become an important part of cooperation. Shared hydrological understanding is not only an input to analyzing water conflict; in some cases, it may be part of what is needed to settle it.

Jiang, R., Lu, H., Chen, D. et al. Transboundary conflict from surface water scarcity under climate change. Nat Commun 16, 8166 (2025). https://doi.org/10.1038/s41467-025-63568-y