# Assessing COVID-19 lockdown effects on coastal water quality in a strongly impacted tourist destination using Sentinel-2 multispectral data

## TL;DR

This study used satellite data to assess how the 2020 lockdown affected coastal water quality in a Mexican tourist area, comparing it to pre- and post-pandemic years.

## Contribution

The study provides novel insights into the environmental impact of the pandemic on coastal water quality using high-resolution satellite data.

## Key findings

- Water quality indices showed clear differences between pre-pandemic, pandemic, and post-pandemic periods.
- Sewage and harbor areas had lower chlorophyll-a and higher suspended matter during the lockdown.
- Mangrove forests showed reduced CDOM in post-pandemic years, indicating possible recovery or changes in water quality.

## Abstract

Remote sensing data from satellite platforms were the only available source of information for environmental studies during the COVID-19 lockdown in many regions of the world. We analyzed the spatial variability of representative water indices derived from the Sentinel-2 sensor across six coastal land cover classes along a tourist destination on the North Pacific coast of Mexico. A comparative assessment was conducted between the 2020 lockdown period and the same holiday season in 2019, 2020, and 2022, evaluating the spatial distribution of water indices per coastal class. Principal coordinate analysis of organic content matter (CDOM), Chlorophyll-a (CHLA), and total suspended matter (TSMC2 and TSM_Clear) indices demonstrated clear distinctions in water quality among pre-pandemic (2019), pandemic (2020), and post-pandemic (2021−2022) periods. Canonical analysis of principal coordinates during the lockdown year revealed two key patterns: (1) sewage and harbor areas displayed a significant decrease in CHLA levels alongside elevated TSMC2, while (2) mangrove forest exhibited markedly reduced CDOM in post-pandemic years. Distance-based redundancy analysis further showed interannual variability across coastal zones, while the pandemic year (2020) was particularly distinguished by diminished CDOM in tourist and industrial areas. The high-resolution (10 m/pixel) and revisit time (5 days) of Sentinel-2 data was invaluable for monitoring water quality dynamics during the COVID-19 lockdown.