Spain’s reservoirs enter September 2026 at a nationwide fill level of 64.0%. According to the Ministry for the Ecological Transition and the Demographic Challenge (MITECO), 35,875 cubic hectometres (hm³) of water were stored as of the reporting date, against a total capacity of 56,043 hm³. The volume fell by 495 hm³ compared with the previous week, equivalent to 0.9% of total capacity.
Trends vary across the major regions. The Atlantic basin side holds 28,154 hm³, down 271 hm³ over the week. The Mediterranean side holds 7,721 hm³, an increase of 226 hm³ over the week. MITECO attributes the opposing trends to regional rainfall and water withdrawals, which are traditionally high during the summer months.
There are marked differences between river basins. The highest proportional level is in the Guadalete-Barbate basin, at 77.9%, followed by Catalonia’s internal basins at 77.7% and the Basque Country’s internal basins at 76.2%. At the lower end are Segura at 53.2%, Júcar at 54.3%, and Ebro at 54.5%. These figures come from the latest Boletín Hidrológico, which reports weekly stocks and changes.
The year-on-year comparison is more favourable. In the same calendar week in 2025, nationwide reserves stood at 33,235 hm³; the current level is 2,640 hm³ higher. The latest weekly fall reflects the usual summer pattern: high temperatures, fewer rainfall events and increased demand from agriculture and water supply put pressure on reserves, although showers and thunderstorms can temporarily stabilise them in some regions.
The figures published by MITECO serve as a reference for water-resource management. National and regional authorities use them to manage drinking-water supplies, make irrigation decisions and, where necessary, take action during periods of water scarcity. Forecasts of future trends depend on short-term weather conditions, control of withdrawals and storage infrastructure; the Boletín Hidrológico updates the picture weekly.
The reported figures refer specifically to the situation on 1 September 2026. Differences between individual basins may result from ongoing releases for irrigation, power generation and ecological minimum flows. MITECO notes that the classification into Atlantic basin side and Mediterranean side provides a cross-regional overview as a matter of methodology, while local decisions are determined by the respective hydrological plans of the basin authorities.
Editor: Daniel Mayer (Article created with AI assistance).