Combining hydrological and water-use models for watershed management: informing stakeholders on resource projections and strategic allocation

Sustainable water resource management increasingly relies on integrated modelling approaches that jointly address the evolution of hydrological processes, and the quantification of anthropogenic water uses. This contribution aims to illustrate the maturity of such an approach by combining hydrological modelling results with spatially explicit estimates of water withdrawals and consumption. The objective is to support territorial stakeholders by providing a coherent view of future water resource trajectories and associated allocation challenges.

The study is conducted over the Vienne River basin (~22,000 km²) through a partnership between three French actors with complementary expertise and an interest in the future of water resources:

• CEREMA, the French public agency leading expertises for adapting territories, has developed STRATEAU [1], which reconstructs monthly water-use volumes by sector (agriculture, industry, energy production and tertiary activities), and aims at contributing to the quantification of water withdrawals and consumption.
• EDF (leading electricity producer in Europe) contributes with the hydrological modelling at the basin scale, using its experience gained through its involvement in the French EXPLORE2 project [1] which addresses the impacts of climate change on hydrological regimes.
• Vienne EPTB (Vienne River Basin Public Authority) provides in-depth knowledge of the territory, supported by previous hydroclimatic studies conducted to inform regulatory approaches related to allocable water volumes.

The set-up of STRATEAU (definition and calibration of the underlying assumptions) relies on shared expert judgement among the partners, with a central role played by the EPTB in ensuring the consistency of scenarios with local hydrological and territorial realities. STRATEAU is then used to translate climate and societal evolution scenarios — consistent with national reference studies [2] — into projections of water withdrawals and consumption. These results are combined with hydrological projections derived from the EXPLORE2 framework, enabling an integrated analysis of the joint evolution of water availability and water uses.

The results highlight the benefits of the dialogue between scientific, industrial, and institutional stakeholders and the added value of combining heterogeneous modelling tools. Preliminary spatial analyses illustrated below (for the year 2020), show the distribution of available water volumes across the basin and the estimated total withdrawals for all sectors, while temporal analyses allow the exploration of the seasonal dynamics of ratio between resource availability and water use.

This work identifies several perspectives: the need for a more explicit representation of the sensitivity of hydrological simulations to water abstractions, depending on their origin (surface versus groundwater), and the desirable integration of water management measures, that influence availability of water at annual and basin scales.

Total estimated withdrawals (left) and average discharge (right) for 2020 summer period (jja) over the Vienne River watershed.

[1] Lecomte J., et al. STRATEAU – une approche novatrice et un outil innovant de gestion prospective des tensions sur l’eau, 2023, DOI : 10.54563/asgn.2359

[2] Tristan Jaouen et al. Will rivers become more intermittent in France? Learning from an extended set of hydrological projections. Hydrology and Earth System Sciences, 2025