Monitoring of the wetland hydrology using remote sensing and historical data series: The case of Palos lagoon (Southwestern Spain)

The wetlands are essential for ecology and environmental regulation but also for the economy and social service functions. However, the natural hydrology of this kind of system is often modified by the agricultural drainage of the upstream areas. Remote sensing and GIS methods are currently emerging as an alternative to traditional methods like field survey (usually laborious, time consuming and expensive) to analyse the effects of the anthropogenic activities in the water bodies.

In this paper, the Palos lagoon (Southwest Spain), a Ramsar site whose surrounding lands have been intensively modified by petrochemical industry and greenhouse strawberry crops, was taken as a research object. The Global Surface Water (GSWE) online machine, combined with bathymetric and historical meteorological data, were used to spatially quantify water surface during the period 1984-2020. This allowed us, through a water balance approach on a monthly basis, the estimation of water inputs and outputs to analyse the hydrological changes in terms of seasonality and persistence.

The results show greater fluctuations with seasonal changes marked by the climatic regime during the first two decades of the study period. From 2000, linked to a large increase of the greenhouse strawberry crops, the surface water remained stable around 80% of the maximum lagoon extension, which allowed the use of the last twenty years to describe the current state in terms of water balance. On one hand, water inputs exceed outputs from October to March, raising the lagoon water level and increasing the water surface from 80 to 92% of the maximum extension (drying period). On the other hand, water outputs exceed inputs from April to June, when water surface changes from 85 to 76% (wetting period), a percentage which remains from July to September (balance period). This approach was verified with field measurements in the main control points.

This highlights that remote sensing products, combined with local information, can be used to successfully evaluate hydrological behaviour in those places where historical hydrological data series are not available. These kinds of methods and tools can provide the knowledge to support better informed water-management decision-making.