According to official figures, the month of December saw an increase in the volume stored in 11 watersheds and
a decrease in one, the SNIRH data shows.


The Sado river basin was the one with the lowest water availability, with 32.3 percent, closely followed by the Barlavento with 33.1 percent. The other basins below 50 percent of their respective total volumes were the Mira with 49.4 percent and the Oeste 50.5 percent.


According to the SNIRH, the basins with the highest levels of storage at the end of December were the Ave (93.9 percent), Tagus (88.5 percent), Douro (86.6 percent), Lima (86.1 percent), Cávado (83.1 percent), Mondego (75.2 percent), Guadiana (65.8 percent) and Arade (53.6 percent).


December storage by watershed was generally higher than the averages for the month from 1990/91 to 2018/19. However, in the case of the Sado, Oeste, Guadiana, Mira and Ribeiras do Algarve the levels were lower than the long-term average.
Some watersheds contain more than one reservoir.