| 30 Jan 2026
Climate change and irrigation expansion reshape the water pressure and upstream–downstream interactions in the Lancang–Mekong River Basin
Abstract. In transboundary river basins, water resource pressure results from the combined effects of internal water use growth, external transboundary withdrawal, and climate change, yet the relative contributions of these drivers to both water pressure and upstream–downstream interactions remain poorly quantified. To address this issue, this study adopts the Pressure–State–Response analytical framework to explicitly disentangle and characterize the spatiotemporal patterns and evolution of irrigation water withdrawal pressure in the Lancang–Mekong River Basin under the climate change. Results indicate that the proportion of irrigation water withdrawal relative to available water exhibits a persistent increasing trend. Under the SSP5-8.5 scenario, this proportion is projected to rise to 19 % annually and 59 % during the dry season by 2040. The impact of irrigation water withdrawal on downstream water availability is significantly greater than that on upstream regions, particularly during the dry season. In the historical period, internal irrigation water withdrawal pressure dominates in Subregions 1 (China), 8 (primarily in Thailand), and 13 (primarily in Vietnam), exceeding external pressure from upstream irrigation water withdrawal, whereas external irrigation-induced water appropriation is the primary driver in the remaining subregions. Under future climate scenarios (2021–2040), both internal and external irrigation pressures intensify across the basin, exhibiting pronounced nonlinear dynamics and spatial heterogeneity. Notably, Subregion 8 undergoes a structural shift in dominant pressure, transitioning from internally driven irrigation pressure in the historical period to externally driven irrigation appropriation in the future. Meanwhile, the growth rates of irrigation water withdrawal pressure are redistributed spatially: compared to the historical period, the growth of external irrigation pressure slows in downstream subregions (9–13), while it continues to increase in midstream and upstream subregions (2–8). The analysis aims to identify vulnerable components of the basin system, clarify transboundary responsibility allocation, and support differentiated water governance strategies.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences.
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This manuscript presents a timely and well-structured investigation into irrigation-induced water pressure and upstream–downstream interactions in the Lancang–Mekong River Basin under climate change. The study’s integration of the Pressure–State–Response (PSR) framework with hydrological modelling (THREW), bias-corrected CMIP6 projections, and spatially explicit irrigation withdrawal estimates represents a strong methodological contribution. The work addresses a critical gap in attributing basin-scale water stress drivers and demonstrates high relevance to hydrological science, water resources management, and climate impact assessment. Overall, the manuscript is scientifically sound, novel, and highly suitable for publication in HESS.
1) The manuscript would benefit from a clearer explanation of how the PSR components interact dynamically. While the framework is well introduced, explicitly linking “Pressure → State → Response” with examples from the results (e.g., Subregion 8 regime shift) would improve readability.
2) The study reserves 30% of simulated runoff as environmental flow. Please provide a brief justification or citation supporting this threshold, and discuss how sensitive the results might be to this assumption.
3) Although climate projections and bias correction are described rigorously, the uncertainty associated with irrigation withdrawal estimation (e.g., irrigation efficiency coefficients, canal detection) could be discussed more explicitly.
4) The manuscript is generally well written and easy to follow. Nevertheless, minor language polishing would improve clarity and fluency. In particular, the authors may wish to review article usage and phrasing consistency. For example, expressions such as “under the climate change” could be smoothed to “under climate change,” and “30% simulated runoff was reserved as environmental flow” could be phrased as “30% of the simulated runoff was reserved as environmental flow.” Additionally, several sentences would benefit from small stylistic refinements to enhance readability. A careful proofreading is recommended.
5) A relevant recent contribution appears to be missing from the references. The authors are do strongly encouraged to cite ‘Assimilation of Sentinel-based leaf area index for modeling surface–groundwater interactions in irrigation districts,’ which closely aligns with the manuscript’s themes of irrigation modelling and land-surface dynamics.