Water and sanitation are at the very core of sustainable development – critical to the survival of people and the planet – and touch on many other areas, including food and agriculture, climate, health, education and poverty reduction. This means that SDG6 “not only addresses the issues relating to drinking water, sanitation and hygiene, but also the quality and sustainability of water resources worldwide.” Satellites provide repeatable and objective observations of the water cycle with consistency across regions and globally, supporting the implementation and scalability of monitoring systems.
Observations for integrated water resource management
Satellite observations of the water cycle cover a broad range of parameters and at present hydro-meteorological and space agencies around the world are operating or planning instruments to monitor all phases of the cycle.
Satellite capabilities are subject to a range of accuracies, and include the monitoring of clouds, precipitation (rain and snow), soil moisture, groundwater storage, inland water bodies, river and lake surface levels, the cryosphere (e.g., snow, ice, glaciers) and a number of ocean parameters. These observations support holistic management approaches, including hydrological modeling and the implementation of Integrated Water Resources Management (IWRM), identified as a key aspect of sustainable water management in the 2002 Johannesburg Plan of Implementation. The development of IWRM is a focus of water-related overseas development aid disbursements, with water management projects representing 5% of the total ($8.6 billion) in 2015.
One example of Earth observation support of the development of IWRM is the Water Observation and Information System (WOIS), developed as a part of ESA’s TIGER initiative in response to the 2002 Plan of Implementation. WOIS helps address problems faced in the collection, analysis and use of water-related geo-information, and the software is available free of charge.
Global surface water monitoring
The presence of inland and coastal surface water affects human and ecosystem well-being globally. While national and regional inventories, statistical extrapolation and satellite imagery are used to produce surface water snapshots, systematically monitoring long-term changes at high resolution has remained a challenge. Several efforts have been undertaken using the long time series of Landsat imagery (since 1984) to try and address this challenge, including the European Commission’s Joint Research Centre’s (JRC) Global Surface Water Explorer (GSWE).
Leveraging massive parallel computing capabilities provided by Google Earth Engine, the GSWE maps the location and temporal distribution of water surfaces using 3 million Landsat images, quantifying the extent and change in global surface water monthly over the past 32 years at 30m resolution. The maps show that between 1984 and 2015, permanent surface water has disappeared from an area of almost 90,000 square kilometres, equivalent to slightly more than the area of all the surface water in Europe, though new permanent bodies of surface water covering 184,000 square kilometres have formed elsewhere. Over 70% of the global net permanent water loss occurred in the Middle East and Central Asia, linked to drought and human actions, including river diversion or damming and unregulated withdrawal.
The GSWE provides a freely available dataset to the public, scientists, and policymakers to help countries improve the modelling of surface water, provide evidence of changes in water-related ecosystems ecosystems, and inform water management decision-making including in support of SDG Indicator 6.1.1.
