Tagus
The Tagus river basin has an area of 80600 km2, 30% of which correspond to the downstream catchment, in the Portuguese territory.
The BINGO RS Tagus focused on the lower part of the Tagus river basin, aiming to:
- Assess how the potential changes in surface water flow regimes will jeopardize the current and future planned water uses;
- Determine how potential reduction in aquifers recharge and, in coastal lowland areas, possible saltwater intrusion, may reduce the availability of groundwater to agricultural uses and water supply;
- Assess climate change impacts in the Tagus estuary bordering lands where expected sea level rise, possibly associated with more frequent storm surges, and salt water intrusion are the driving forces;
- Propose a Framework for Managing the Risk (FMR), aiming at helping to sustain key economic sectors and the environment and protect people and property in Tagus Research Site.
Which sectors did it involve?
The Portuguese research site addresses climate change adaptation of key sectors, one concerning an important public service, water supply, and the other concerning agriculture, one of the most relevant economic activities in the region. The Tagus CoP also engaged several actors from national, regional and local organisations and water users’ associations.
Being water the central topic in BINGO, the climate change adaptation concerns, essentially, how changes in water resources availability and quality compromises both sectors and how they should prepare themselves to deal with these changes.
Reduction in water availability and quality degradation, associated with more frequent and intense droughts, were the main concerns of both sectors but, in some specific cases, inundations are also of concern, essentially if they are due to storm surges in the estuary, or other events that increase the salt water intrusion in the water abstraction points or cause farming lands inundations with high salinity content and population safety.
What was done?
Risk management (assessment and treatment) for water dependent sectors was carried out in Tagus RS both for water scarcity and inundations. First the impacts were assessed and then risk was managed through a Risk Management Process approach.
In order to study the impacts of climate change on surface water resources and detect vulnerabilities in the current water uses due to water scarcity induced by new rainfall regimes, two main case-studies were selected: i) The Zêzere River basin (a northern Tagus tributary), where the main water use is in Castelo de Bode Reservoir for power generation, which is not consumptive, and ii) The Sorraia River basin (a northern Tagus tributary), with two main reservoirs in the headwaters, for irrigation purposes in the downstream valley.
For groundwater, the objectives were to study the impact of eventual climate changes (and droughts) in the recharge of four selected Lower Tagus aquifer systems and, for three of them, to study and analyse the corresponding impact in the groundwater piezometric levels.
Also modelling Tagus estuary for water availability and inundation was carried out.
Local stakeholders have been actively engaged in six CoP workshops and an open event was promoted in a local public space with the population to share and discuss BINGO co-productions and issues.
Which were the main results?
Better understanding of the river flows, water availability, inundation and salinity dynamics in the Lower and Tagus estuary was achieved. The main conclusions were:
- the gross majority of the rainfall-replicas’ input projected for the decade 2015-2024 generates groundwater recharges and river flows that are not very different from the historical records also storminess is not expected to increase in the near future, but the hazard will increase marginally due to sea level rise;
- extreme storms lead to the overflowing of existing dikes and the inundation of extensive agricultural land;
- low river flows prevent the water uptake for irrigation due to the increase of the salinity upstream and the problem is aggravated for longer drought period;
- drought can lead to mild groundwater drawdowns in multi-year droughts.
What is BINGO’s legacy in Tagus?
Lower Tagus region has always been prone to climatic variability. Climate change adaptation is in fact not a novelty as the region suffered already several extreme periods but a process that requires optimization of already existing practices.
BINGO provided new and useful information for the stakeholders dealing with agricultural activities and water supply in the Lower Tagus and estuary. A better understanding of the water availability, inundation and salinity dynamics was achieved, which provides the stakeholders with information that may support decision-making during the development of their activities. All the mathematical models built in BINGO scope will be used in future related studies.
The river flow in the Tagus River is mainly controlled by decisions on the operation of dams. Therefore, from the undertaken studies it was highlighted the importance of external vulnerabilities in all case studies of Portuguese research site, identifying integrated water resources management and (IWRM) / Water resources governance as a key issue for both public water supply, agriculture and population uses. In fact, for this RS, adaptation is centered on integrated water resources management.
