UT researcher discovered: the number of lakes in the world is three times smaller than thought
In cooperation with foreign partners, a UT researcher Tiit Kutser counted all the lakes in the world one by one and found that the number of lakes is approximately three times smaller than so far thought based on statistical assessments. However, the total surface area of the lakes is larger than previously suggested by calculation methods.
"We found out that there are not 304 million lakes in the world but only 117 million," says Tiit Kutser, Lead Research Fellow of the Department of Remote Sensing and Marine Optics at the Estonian Marine Institute of the University of Tartu, outlining his most important discovery which was made in cooperation with researchers in Sweden, France and the US.
According to Kutser, the counting of lakes was not an easy task. "At first it may seem that there is nothing easier than to count the lakes from the satellite pictures — the lakes appear black when seen from the space and the land is much lighter," explained Kutser. "However, there are many objects on the land which are very similar to lakes when seen from space and at the same time some low or muddy lakes are very difficult to distinguish from land."
Therefore, the scientists combined the satellite pictures with the detailed height model of the Earth created by other satellite data and in addition to the picture processing methods they also used the GIS tools and different mathematical methods.
"We considered all water bodies which were larger than one and a half Olympic swimming pool to be lakes and we analysed how the lakes are divided on Earth, for instance according to the latitude and height," clarified Kutser. In order to identify all such lakes of at least 0,002 km2, the whole surface of the Earth had to be analysed by using the satellite pictures with 14-metre resolution images.
Counting of the lakes was one part of the research work conducted by Kutser and his colleagues, the aim of which is to solve the issues related to the global carbon cycle. "When the last report of the Intergovernmental Panel on Climate Change (IPCC) basically ignored the rivers and lakes, handling them just as the carriers of carbon from the mainland to the oceans, then in the recent report the lakes play an important role in the global carbon cycle," said Kutser.
After determining the actual number of lakes and their surface area and thanks to the new satellites, the researchers can now assess the amount of carbon in lake waters more accurately during the next few years. In this way it is possible to make a much more accurate assessment of the amount of water in the lakes of the world, to reassess the amounts of methane and carbon dioxide which are released to the atmosphere from the lakes and to obtain approximate assessments even about the amount of fish in the lakes of the world. These are the analyses that Tiit Kutser and his colleagues are about to conduct in the recent months.
In addition to global applications, the development of the remote monitoring of lakes also has regional applications. According to Kutser, the assessment of the amount of carbon in lakes is important for several reasons. "The carbon in the lakes has a direct impact on the health of the people living in those areas where lake water is used to produce drinking water. With remote monitoring methods it is possible to monitor the changes in the water and control the water treatment processes more accurately," provides Kutser an example of a practical implementation of the study.
Additional information: Tiit Kutser, Head of Remote Sensing and Marine Optics Department at Estonian Marine Institute of the University of Tartu, tel: +372 671 8947, e-post: tiit.kutser [ät] ut.ee