The great basin and the drought's trial by fire
The total storage capacity of the Alqueva reservoir stands at 4,150 cubic hectometres, according to data released by EDIA in 2024. This colossal volume serves as an anchor for a vast region in the south of the country, contrasting with much more dramatic scenarios recorded in other national river basins, such as the Sado basin, which showed storage levels below 30% in the same period in 2023, as reported by APA in its reservoir bulletin.
In 2022, considered a year of extreme drought, the volume stored in Alqueva reached a minimum of about 65% of total capacity, according to records from APA's SNIRH that same year. This mark demonstrates that, even under severe and prolonged weather conditions, the reservoir retains a considerable water cushion, serving as a central buffer for the basic and economic needs of about 200,000 people distributed across 20 municipalities in Alentejo, according to 2023 EDIA data.
For those living in one of these municipalities, the body of water represents apparent security in the face of the Mediterranean climate's vagaries. However, the apparent stability hides growing pressure on the resource, fueled by the continuous expansion of irrigation infrastructure and the need to guarantee public supply without failures, shaping daily life and the local economy in dozens of Alentejo municipalities.
The relentless expansion of irrigated fields
The irrigated area of the Alqueva Multipurpose Development reached 138,000 hectares in operation in 2023, according to official EDIA reports. This physical growth of the irrigated agricultural patch is directly reflected in the volumes of water consumed annually, transforming the traditional agrarian landscape into extensive areas of intensive and super-intensive production that demand water constantly and regularly.
Between 2018 and 2022, water consumption for irrigation in the EFMA increased from 250 million cubic metres to about 450 million cubic metres, according to data released by the Público newspaper in 2023. This expressive leap in consumption illustrates the intensity with which the water resource has begun to be mobilized to sustain the new agricultural rows installed in the region over just four years.
In parallel, the structure of crops has undergone a profound mutation that accentuates this dependence. The area of almond groves in Alentejo increased by 400% between 2010 and 2021, according to INE data, making it a crop highly dependent on drip irrigation. Added to this growth is the expansion of hedge olive groves, which grew from 15,000 hectares in 2010 to more than 70,000 hectares in 2020, consolidating a water-thirsty agricultural model.
Invisible loss and structural limits
The management of Alqueva is not only debated over the volumes withdrawn for cultivated fields, also facing inevitable natural losses due to the region's climatic conditions. A study published by the University of Évora in 2021 points out that annual evaporation in the Alqueva reservoir can reach 200 million cubic metres, an expressive value that consumes a substantial slice of the stored water before it even reaches any irrigation canal or public tap.
Faced with these depletion factors, researchers from the Instituto Superior Técnico warned in 2023 that the continuous expansion of intensive irrigation could seriously compromise the global resilience of the system under climate change scenarios projected up to 2050. The scientists stress that the combined pressure of evaporation and agricultural intensification narrows the reservoir's margin of maneuver in the face of prolonged sequences of dry years.
This structural vulnerability was also noted by the Court of Auditors in an audit report published in 2021, which questioned the long-term economic and environmental sustainability of irrigation expansion in the face of structural water scarcity. The document points to discrepancies between the impetus to expand irrigation infrastructure and the real availability of water in adverse climatic horizons.
The self-sufficiency argument and the arithmetic of risk
The obvious reading frequently pointed out is that Alqueva functions as an inexhaustible and perfectly shielded reserve, capable of protecting Alentejo against any future climatic severity. EDIA stated in 2022 that the reservoir has the technical capacity to guarantee irrigation for three consecutive years of extreme drought, even in the total absence of any new water inflow into the basin, supporting the idea of a highly robust safety cushion.
If this proportion remained unchanged and if we looked only at the maximum capacity of 4,150 cubic hectometres declared by EDIA in 2024, we could conclude that the current agricultural model would be safeguarded for many years. However, if this consumption trend continues to grow at the rate observed between 2018 and 2022 — a period in which irrigation rose from 250 to 450 million cubic metres —, the announced three-year margin would shrink drastically over a two-decade horizon.
Furthermore, the National Irrigation Plan, approved by the Ministry of Agriculture in 2022, foresees the expansion of another 50,000 hectares of irrigated land in Alentejo by 2030. Should this new plan advance in full and the cost of water, currently subsidized through variable tariffs regulated by EDIA in 2024, continue to encourage the establishment of these crops, the volume of annual extraction would quickly annul the reservoir's supposed immunity in prolonged drought cycles.
The arithmetic horizon in the municipalities of Alentejo
If this trend of agricultural consumption growth were to proceed linearly over the next twenty years, and if climate change were to reduce the frequency of rainy years as warned by the Instituto Superior Técnico in 2023, the minimum volume of 65% recorded by SNIRH in the extreme drought of 2022 would drop to critical levels. In a purely arithmetic projection based on the pace verified until 2022, the reservoir would see its useful capacity exhausted long before reaching the time limits foreseen by EDIA.
This conditional scenario would be completely broken if a profound legal change occurred in the allocation of water subsidies or if an insurmountable physical limit arose in the flows of the tributary rivers feeding the system. If public irrigation policies were readjusted by 2030, the rate of depletion would decelerate, changing the rupture horizon to levels much less aggressive for local populations.
For the inhabitants of the 20 municipalities supplied by the EDIA system in 2023, the arithmetic of Alqueva translates into a thin line between the economic development promoted by cash crops and the water security essential to human life. If nothing changed in use restrictions and the National Irrigation Plan fulfilled the expansion of 50,000 hectares by 2030, the balance between agricultural thirst and civic survival would depend strictly on the unpredictability of future winters.