Exploring the Spatial and Temporal Dynamics of Optical Water Types (OWTs) in Portugal's Largest Water Reservoir Over Two Decades Using NASA and ESA Satellites

A qualitative analysis using different optical water types (OWTs) can be easily and efficiently applied by entities outside scientific research in water quality monitoring programs, as well as in the creation of alert systems for rapid deterioration of water quality. In this study, we present the monitoring of different OWTs using the MERIS, OLCI, and MODIS instruments, onboard satellites, during the period 2003-2022 over the entire Alqueva reservoir and also for five distinct areas of the same reservoir. It was found that the northern area of the reservoir consistently presents the worst water quality, not only in terms of microalgae bloom intensity but also in turbidity of the water due to the characteristics of the reservoir in this area. The increasingly warm autumns in Portugal are leading to a more intense microalgae blooms occurring in the fall.