Portugal ratifies protocol establishing minimum flows for the Guadiana in Pomarão

Portugal has ratified the Second Revision Protocol of the Convention on Cooperation for the Protection and Sustainable Use of the Waters of Luso-Spanish River Basins, which establishes the flow regime of the Guadiana river in the Pomarão section and allows for the abstraction of up to 30 hm³ annually to reinforce the water supply to the Algarve. The ratification is contained in Presidential Decree No. 145/2026, signed on September 11, and Assembly of the Republic Resolution No. 249/2026, approved on July 17, both published in the Diário da República on September 22, 2026.

The protocol was signed in Madrid on February 24, 2026, between the Portuguese Republic and the Kingdom of Spain, and revises the flow regime provided for in the Albufeira Convention, concluded on November 30, 1998. The revision became possible under Article 8 of the 2008 Revision Protocol, which allowed for the definition of the Guadiana regime in the Pomarão section when appropriate studies were available, based on the proposal presented by the Commission for the Application and Development of the Convention.

Presidential Decree No. 145/2026 was countersigned on September 17 by the Prime Minister, Luís Montenegro, and promulgated by the President of the Republic, António José Martins Seguro. The text was signed in Madrid by Ambassador José Augusto Duarte and the Third Vice-President and Minister for Ecological Transition and the Demographic Challenge of Spain, Sara Aagesen Muñoz.

Minimum flows and monitoring stations

The protocol identifies the monitoring stations for the flow regime in the Guadiana basin:

• Badajoz Weir, upstream of the confluence of the Caia river;
• Pomarão hydrometric station, upstream of the confluence of the Chança river.

Until a flow curve is defined, or in the event of a failure in Pomarão, the Pulo do Lobo hydrometric station in Portugal may be used, with the respective correspondence between the two sections.

In the Pomarão section, the monthly integral flow varies according to the hydrological classification of the month: 239 hm³ per year in a dry month, 504 hm³ in an average month, and 708 hm³ in a wet month. The average daily flow is 2.7 m³/s and, in non-dry years, the continuous discharge of flows equal to or greater than 300 m³/s for two days in February, corresponding to 45.8 hm³, should be promoted.

Abstractions for the Algarve and Huelva

The Pomarão flow regime includes the ecological regime established by Portugal in 2005, plus the volume for socio-economic uses, which can reach a maximum of 90 hm³ in hydrologically more favorable years. The equitable distribution recognizes two abstractions:

• Pomarão Intake, to reinforce the water supply to the Algarve, with a maximum annual volume of 30 hm³, expandable up to 60 hm³;
• Bocachança Pumping, to reinforce the water supply to Huelva, with a maximum annual volume of 60 hm³.

The intakes may only operate between October and April of each year, and the concessionaires are required to install automatic flow measurement systems that transmit the captured volumes to both Parties in real time. The Parties will also develop a technological platform (geovisualizer) to receive this data.

Exceptions and environmental guarantees

The protocol provides for exceptional situations: when the total volume of the Alqueva reservoir is equal to or less than 2500 hm³, only reduced monthly flows are guaranteed, which drop to 194 hm³ annually in dry months. If the accumulated precipitation is less than or equal to the reference precipitation for the 5th percentile, only a daily flow of 2.7 m³/s is guaranteed, and in dry months, only 50% of the volume for socioeconomic uses is ensured.

The hydrological classification of each month is based on precipitation records from three reference stations, with the weightings of Vila Viçosa (32%), Herdade da Valada (42%), and Castro Verde (26%). The intakes may not, under any circumstances, compromise the environmental flows of the transitional waters of the Guadiana estuary, and the Parties agree to prepare a joint study and a monitoring program for the quality of the estuary’s water bodies.

The protocol enters into force under the terms of Article 31 of the Albufeira Convention and will be submitted for registration with the United Nations Secretariat. The agreed text also provides that the Parties shall prioritize the study of the sustainable use of the international section of the Erges river, in the Tagus basin.

The ratification closes a negotiation process of nearly two decades and becomes legally binding regarding the minimum flows that Spain must allow to reach Pomarão, with a direct impact on agriculture in the Alentejo, urban supply in the Algarve, and the conservation of the Guadiana estuary.

Source: Diário da República, no. 184, of September 22, 2026, 1st series, p. 1 (official reference: Decree of the President of the Republic no. 145/2026 and Resolution of the Assembly of the Republic no. 249/2026).