OBSERVER: Monitoring freshwater quality with Copernicus
Freshwater, one of the world’s most scarce and precious resources, is essential for all life on Earth. Freshwater shortage can be devastating for the environment and humans. However, it is not just about freshwater availability, but also about the quality of the available freshwater. Healthy lakes and rivers are important for the environment and humans alike. Freshwater management and sustainability policies, such as in the EU’s Water Framework Directive, take into account the importance of both availability and quality of freshwater, requesting information about the ecological status of freshwater bodies.
The Copernicus programme, through its services and data, can help monitor the status and quality of freshwater bodies around the world, supporting policymakers and enabling local authorities and the general public to make informed decisions.
Beyond borders with observations from space
The sustainable management of freshwater is characterised by its inter-regional and sometimes even international nature. In many countries, a significant amount of freshwater originates from neighbouring countries, with lakes and rivers extending over geopolitical boundaries. Their monitoring thus must be equally broad, international and borderless. By putting water quality at the centre of their policies, researchers and decision-makers need data about the current state of water quality of the world’s water bodies.
Water quality can be measured either by collecting in-situ samples from water bodies, or through satellite monitoring. The former can be time-consuming and costly, whereas the latter provides the possibility to cover large areas, across borders, on a regular basis, reducing the need for in-person monitoring infrastructure and efforts.
Satellites are thus key for monitoring water quality around the world. But how do they monitor it? The water’s optical properties are measured through optical multispectral sensors onboard satellites such as Copernicus Sentinel-2.
Complete maps of important water quality characteristics, such as chlorophyll concentrations and suspended matter, can be derived by combining the amount of light leaving the water body’s surface at certain wavelengths compared to natural sunlight.
Observations of water quality from space - Lake Lubāns (Latvia) in Sentinel-2 satellite image from 23-08-2018 (left) and estimated chlorophyll-a concentration from Sentinel-2 MSI spectral data (right). Image: Institute for Environmental Solutions, Source: SentiLake: Sentinel-2 service for regular water quality monitoring in lakes
Water quality indicators through the Copernicus Land Monitoring and Climate Change Services
The global component of the Copernicus Land Monitoring Service provides up-to-date, reliable and accurate data on medium and large freshwater lakes around the world.
The Lake Water Quality product provides semi-continuous observations of over 4200 medium and large-sized lakes around the world for three water quality parameters: turbidity, trophic state index and lake surface reflectances.
Turbidity describes water clarity, i.e. whether sunlight can penetrate deeper parts of the lake. It can vary seasonally according to river discharge and phytoplankton growth. The trophic state index indicates the lake’s productivity in terms of phytoplankton and indirectly, over a long-time scale, reflects the eutrophication status of a water body. Lastly, lake surface reflectances describes the apparent colour of the water body, which can be used by scientists for further development of algorithms.
Turbidity in Lake Huron (10 days average between 11th and 20th of August 2008) (left) and time series of turbidity (MERIS - blues crosses) and in-situ data from US Data bases STORET and WQP (green dots). The red arrows on the map indicate the locations where the time series are plotted i.e. the Saginaw Bay (top) and central lake (bottom). Note the different scales of the y-axes. Source: Copernicus Global Land Service
The Lake Surface Water Temperature product of Copernicus Land Monitoring Service provides information on the temperature of the lake surface, which is an important indicator of lake hydrology and biogeochemistry. This information can be complemented by the Lake Surface Temperature dataset from Copernicus Climate Change Service (C3S), which provides a consistent record starting in 1996. The long-term temperature trends and anomalies derived from the C3S dataset can be an indicator of how climate change is affecting lakes, whereas the CLMS data capture the current state of water. Lake Surface Water Temperature is internationally recognised as an Essential Climate Variable and complements the water quality information.
Lake surface water temperature anomalies (coloured dots) in Europe in July 2020 (left) and in August 2020 (right) relative to the 1996–2016 reference period. Data source: GloboLakes/C3S lake surface water temperature data record. Credit: C3S/ECMWF/University of Reading. Source: Copernicus C3S Climate Bulletin: European State of the Climate 2020
Monitoring the impact of climate change on European waters
Climate change is affecting the environment as a whole, and freshwater is no exception. It is likely to increase the occurrence of extreme weather events and modify the normal balance of water bodies, thus degrading freshwater quality. Indeed, freshwater quality can be affected by changes in the water cycle, rising water temperature (water acidity, build-up of pathogens, the toxicity of certain compounds, etc), as well as changes in mineral and nutrient concentrations (higher eutrophication). It is thus important to monitor and understand how climate change is affecting and will affect freshwater bodies, in order to adapt policy responses to preserve this precious resource.
The Copernicus Climate Change Service provides several datasets relevant for monitoring the impact of climate change on water quality. For example, the Hydrology related climate impact indicators and Temperature and precipitation climate impact indicators for Europe from 1971 to 2100 datasets, which are now accessible through the Climate Data Store.
Overview visualisation of annual mean river discharge and relative change of annual mean precipitation in Europe derived from European climate projections by Copernicus Climate Change Service. Source: Climate Data Store (left: Hydrology related climate impact indicators from 1970 to 2100 derived from bias adjusted European climate projections; right: Temperature and precipitation climate impact indicators from 1970 to 2100 derived from European climate projections)
In this context, the C3S SIS Operational Service for the water sector supports decision makers, water managers and engineers better understand and adapt to the impact of climate change on water quality. Developed by the Swedish Meteorological and Hydrological Institute and the Wageningen University & Research Centre for C3S, the service aims to strengthen the capacity and knowledge of water managers, engineers and policy makers working in the water sector to help them adapt their strategies in order to mitigate the effects of climate change. Once the application is fully developed, it will provide 20–40 different climate impact indicators (CIIs) with high relevance for water management. The information will be accessible via an interactive web page, where stakeholders will find maps, graphs and download options for climate-impact indicators and seasonal forecasts.
Map visualization in C3S Operational Water Service. Changes in total mean nitrogen concentration for 2071-2100 relative to 1971 – 2000 in % in RCP8.5 scenario derived from an ensemble of climate and hydrological models. Source: https://climate.copernicus.eu/operational-service-water-sector
Copernicus data enabling applications and supporting EU policies
Copernicus data can enable solutions and applications that monitor water quality to support informed decisions by the general public and water management authorities.
For example, Mark Matthews, the 2014 Copernicus Masters Ideas Challenge winner, developed a satellite-data based online service providing early warnings of the health risks caused by toxic cyanobacteria blooms: the CyanoLakes RealTime service.
Cyanobacteria blooms, which are becoming more common due to eutrophication, pose a serious health threat to humans and animals due to their toxicity. They can devastate natural ecosystems and substantially increase the cost of water treatment. Monitoring cyanobacteria blooms and distinguishing them from algae blooms is important for local authorities to be able to quickly respond to these hazardous conditions.
Using Copernicus Sentinel-3, the service is able to carry out near real time monitoring: “Sentinel-3 is the backbone of the CyanoLakes RealTime service, given its unique instrument characteristics. Without it, we could not provide our service to the market,” Matthews explains. The Ocean and Land Colour Instrument (OLCI) on Sentinel-3A is able to support near real-time detection of cyanobacteria, thus powering applications such as CyanoLakes RealTime which allows the public, water utilities and governments to make informed decisions.
The CyanoLakes RealTime detailed viewer showing water hyacinth (magenta) at Hartbeespoort Dam, South Africa, on 11 October 2017. Contains modified Copernicus Sentinel data (2017), processed by CyanoLakes Pty Ltd. Source: Sentinel-3 helps water-quality monitoring, Sentinel Online
Copernicus data can also support the implementation of EU water policies. Indeed, after the EU’s Water Framework Directive was adopted in 2000, it created a need for efficient mapping and monitoring of the water quality of inland and coastal water bodies. The EOMORES project, developed under the EU Horizon 2020 programme, addressed exactly this need. Researchers developed fully automated products for water monitoring by combining satellite data from the Copernicus Sentinels, on-site measurements and ecological modelling.
The EOMORES project uses variables which can be monitored by satellites, such as Chlorophyll-a concentration, turbidity, water surface temperature and others, combining them with in-situ measurements such as station sampling and underway sampling from ships. This provides significant added value, especially in areas where in-situ sampling stations are sparse or a large area needs to be covered. Finland can serve as an example of such an area, with 4,617 lakes and 276 coastal water bodies under the Water Framework Directive. For such a large amount of water bodies, the traditional measuring techniques cannot support the current monitoring requirements and the combination with satellite data is a necessity. EOMORES does that and provides products such as Phytoplankton bloom timing or Scum forecasting to enable better design of mitigation measures. It also offers an “Early warning” service, alerting the user of a high risk of scum appearance or identification of high biomass and thus supporting rapid mitigation action.
EOMORES in action: Identifying locations sensitive to phytoplankton dynamics in order to optimise chlorophyll-a (chl-a) sampling in Lake Trasimeno (Italy). From left to right, the first three maps reflect the mean, maximum and coefficient variation (i.e. standard deviation divided by mean) of chl-a. Combining these maps results in a synthetic representation (in purple), which shows the areas most sensitive to phytoplankton dynamics. Source: EOMORES Product Portfolio
Freshwater is vital for the very survival of life on the Earth, but it is constantly threatened by pollution, a warming climate and subsequent ecosystem changes. The Copernicus programme and its services provide data and products that help monitor freshwater quality and enable sustainable use and protection of this natural resource. These data help decision makers, water utility companies and the general public make informed decision and set up water management plans. The reliable and near real time information provided by the Copernicus programme can also support the implementation of EU water-related policies such as the EU’s Water Framework Directive.
Whether monitoring water surface temperature, nutrient and mineral concentrations, or detecting toxic blooms, the Copernicus programme and its Services keep an eye on the world’s lakes and rivers, helping secure a safer future for our planet’s freshwater sources and its inhabitants.