The Arctic region is home to several millions of lakes. Their surface changes constantly in size and appearance, due both to natural causes and climate change. In fact, their changes can be good indicators of climate change. As ground temperatures increase because of climate change, they impact land surface hydrology. Changes in Arctic lakes can alter the land-atmosphere exchange process, with potential impacts on global climate. Large parts of the Arctic are important areas for the oil and gas industries. As a large portion of the gas delivered to Central Europe comes from the lake-rich Russian Arctic, the warming temperatures put not only the Arctic ecosystem at risk.
The mapping of the long-term spatial and temporal patterns of Arctic lakes is of high interest due to their relationship to the surrounding permafrost. Permafrost degradation can result in terrain change altering water flow and storage. Water logging and drying up condition the fate of carbon stored in the soils, which is released as either methane or carbon dioxide.
Due to the vastness and harsh conditions of the Arctic tundra, the monitoring of its lakes and their condition relies almost entirely on satellite data. In order to capture the status and changes of Arctic lakes, satellite imagery needs to be of high quality and detail. Optical data such as the Copernicus Sentinel-2 mission reveal information on degradation along the lakes’ shores as suspended sediments in the water impact the reflectance of the sunlight. Satellite imagery also allows the monitoring of the extent of former lake shores and the fragmentation of lakes over time.
If the water is clear, it is possible to observe the shallowness of these water bodies along their rims. This can be even more clearly distinguished through the use of radar satellite data. In winter, an ice cover thicker than one meter develops over most of the lakes, freezing them partially to the ground. The radar signal penetrates through the ice and gives a distinctive response when it encounters frozen ground. Such processes allow the mapping of lake shallowness across the entire Arctic. This has been recently realized through the joint work of an Austrian-Russian team of researchers: https://www.frontiersin.org/articles/10.3389/feart.2017.00012/full.
Changes of Arctic lakes are studied as part of several ongoing initiatives of the European Space Agency (ESA), which focus on the use of satellite information for monitoring permafrost and keeping track of climate change. The GlobPermafrost project, for example, specifically investigates lake change through optical and radar data. The CCI+ Permafrost project, which is part of the Climate Change Initiative of the ESA, identifies trends linked to changes in ground temperatures. International teams from across Europe and Canada jointly work on deciphering these complex interactions of climate and landscape across the Arctic. CCI+ delivers time series of ground temperatures which allow to observe changes in land surface hydrology as climate change indicators. The CCI+ project builds on the GlobPermafrost project, whose first analyses was made with data from the new Sentinel-2 satellites. ESA expects CCI+ Permafrost to eventually be able to use changes in lake surfaces as powerful climate change indicators.
European Sentinels and acquisitions from other national missions, including Japanese, Canadian, French, German and US allows ESA to identify relevant phenomena and processes that can affect the Arctic ecosystem, including in areas close to the Arctic coast. This is, for example, the focus of the ongoing HORIZON2020 project Nunataryuk, which investigates the impacts of thawing coastal permafrost on global climate, and develops adaptation and mitigation strategies for the Arctic coastal population.
Lake ice spatial patterns relate not only to the thickness of the ice, but also to movements of the water bodies below. As radar imagery does not depend on sunlight, cracks, openings and ice jams become visible even during the long polar night. In some cases, circular features are observed whose origin is still unknown. Theories about these features include uprising large methane bubbles as well as specific circulation patterns of the water which lead to temperature differences. They can be identified with optical as well as radar images from space (Pointner et al, 2018).