How are reservoirs being discharged in the face of drought?

Droughts in Spain are an increasingly recurrent phenomenon that is amplified by the effects of climate change. 2022 was the third driest year of the 21st century and the fourth since 1961, according to AEMET. Many provinces are already suffering from a lack of water in reservoirs.

Due to the low rainfall and the dryness of the land as a result of the high temperatures, in 2022 the volume of water reserves was 21% lower compared to 2021. After an autumn, winter and spring among the driest in the historical series, several river basins are in an emergency situation or suffering from prolonged drought.

In this scenario, many questions are being asked including: Who is responsible for managing water reserves? What role do hydroelectric power plants play during a drought? These seven key factors will help you understand.

1. What are the uses given to water from a reservoir?

First things first. Before talking about its uses and understanding why reservoirs are so necessary, we must remember that the preservation of the biodiversity of these sites is a legal requirement, even in drought situations.

The priority uses of these hydraulic infrastructures are the supply of drinking water to populations, and the supply for irrigation and industrial uses. But there are also uses that do not require proper consumption of water, such as electricity production and the organisation and performance of recreational, cultural and sports activities.

2. Who manages these water reserves?

Although we may think otherwise, the power companies do not freely decide when to use the water of a reservoir to generate electricity. The state authorities manage the water reserves, through various regional organisations (basin agencies/"Organismos de Cuenca") and, within these agencies, through the reservoir discharging commissions ("Comisiones de Desembalse"). The aim of these commissions is to coordinate the diverse needs of all water beneficiaries to ensure compliance with its priority uses.

3. What is the "Iberian exception" and what does it have to do with all this?

The "Iberian exception" consists of an intervention mechanism in the electricity market that tries to mitigate the impact of the rising price of gas on the wholesale market price. Unfortunately, although higher hydroelectric production would help mitigate the impact of gas prices, this year hydroelectric contribution is very limited due to water scarcity.

Endesa's hydroelectric power plants have helped to minimise the severity of this situation. We have tried to reduce the need to use gas by meeting demand outside the hours when other renewable technologies are not available. Currently, hydropower is the main manageable renewable source .

4. Why is reservoir water sometimes only discharged at night?

This happens for three main reasons:

• So that the discharging schedule coincides with the schedule of water demands for irrigation. It is more efficient to use water for irrigation at night, especially when the target area is close to the reservoir.
• Due to the complementarity of hydroelectric production with other renewable energies. As regards the night use of water, the ability to set the hours of highest and lowest hydroelectric production helps to reduce gas consumption when photovoltaic generation is not available.
• The schedule of water movements in reservoirs is also set by the time elapsed between the exit from the reservoir and the place where water is demanded for other uses.

5. Is it necessary to generate electricity from water in times of drought?

Electricity production is fully compatible with priority uses. In fact, it offers added value to the intrinsic value of water since, although it uses it, it does not alter or limit it. Reservoirs whose main water use is not hydroelectric or in any basin in a state of drought, the water is discharged strictly as necessary to guarantee the ecological flow and other basic uses of water.

Considering solely the contribution of hydroelectric production to meet the electricity demand from the population as a whole, water provides power to the electricity system that complements the rest of the energy produced from other sources, and helps reduce gas consumption.

Electricity production is not a consumptive use, that is, the water used to produce electricity is not consumed nor are its properties altered in any way. Therefore, unlike what happens with water for consumptive uses, such as supply to populations, irrigation or industrial uses, the water is reintegrated into the central channel so that it can be reused.

6. Under what conditions should a hydroelectric power plant cease its activity?

Hydroelectric power plants harness the energy of the water flow released from the reservoirs, water that feeds the river's ecological flow or ensures other water uses such as the supply to populations, livestock farms, etc.

Two situations can occur that can make it impossible to harness the flows released from a reservoir for the production of hydroelectric energy:

• When the maximum flow rate to be released is so extraordinarily low that the turbines are not able to harness it.
• When the discharged flow means that the reservoir's level is so extraordinarily low that the water intake to feed the turbines is at such low a level that capturing the necessary flow becomes impossible.

The criteria for defining the maximum flows to be discharged are as per the prioritisation of the uses legally established by current legislation. In addition, in the case of Endesa, these criteria are always based on our commitment to sustainability and the creation of value in the territories.

Most of Endesa's hydroelectric plants are currently not at risk of long-term shutdown due to a lack of water in their reservoirs. Even so, in this extreme scenario, with river basins in an emergency situation or suffering from prolonged drought, in some cases it will be necessary to minimise water outflows to ensure the following priority uses: Supply for people, ecological flows and irrigation, with the final decision always left to the "Comisiones de Desembalse" (Reservoir Committees), dependent on the corresponding River Basin Organisations.

7. What is Endesa doing in the face of the current shortage of water in the reservoirs?

In constant coordination with the basin agency, Endesa is minimising the reservoir outputs to essential minimum volumes. Once the irrigation campaign is over, in many plants, the turbinated flow will be adjusted to the minimum with the aim of storing as much water as possible for the irrigation campaign in the next hydrological year.

At Endesa, we always try to integrate sustainability into our activities through the application of the CSV process (Creating Shared Value). Endesa and local agents engage in diverse activities in areas with hydroelectric power plants. These initiatives include tasks like coordinating plant operation to ensure flows for recreational, cultural and sports activities; guided group tours of our facilities coordinated by the municipal corporations to raise the profile of local tourist attractions; the assignment of use to facilitate access to high mountain areas; and visits to the facilities by schools and universities.

At the moment, we have implemented this model in 100% of the generation facilities concerning the construction of new renewable plants, thermal and renewable installations in operation and decarbonisation projects.