Global water flows form a highly complex system and are for that reason difficult to track. But Dr. Mohammad J. Tourian of the University of Stuttgart’s Institute of Geodesy has found a way to make them more transparent by linking three satellite- supported observation techniques.
One cubic kilometer of water is so much that it is hard to imagine it - as if a cube 1,000 meters on a side were to be filled. Another way of putting it: five billion bathtubs would be required to hold the same amount. This is the volume that Dr. Mohammad J. Tourian of the University of Stuttgart’s Institute of Geodesy arrived at when researching Urmia Lake in Northwestern Iran. It was once about 10 times as large as the Lake of Constance, but now its surface has been shrinking annually by an average of about 220 square kilometers, so that the lake has lost the above-mentioned cubic kilometer of water. The water level has sunk annually by an average of 34 centimeters a year with far-reaching consequences for the environment. 33-year-old Tourian, who studied in Teheran and then applied for a doctoral candidate position at the University of Stuttgart, is not the type of researcher who measures water samples in a glass. Quite the contrary: he gathers his data from satellites. In the case of Urmia Lake, however, he found that the analysis of satellite images was not enough for him to arrive at a comprehensive understanding of the causes and impact of water losses.
'We now link three observation techniques in order to get an overall picture,’ says the Iranian who has now been carrying out his research in Stuttgart since 2008. Among other things, he uses satellite altimetry, in which radio impulses are sent vertically to the earth, to determine the level of the water surface. And he uses satellite gravimetry to measure changes in the earth’s gravity field, which fluctuates when, for example, large areas of ice in the arctic melt or Lake Aral shrinks. Finally, he appraises satellite photos to gain insights into the causes of change. In Tourian’s view, climate has less to do with the changes in Urmia Lake than the human beings who drain off massive amounts of groundwater for agriculture and dam up some of the lake’s tributaries, thus cutting off more and more of the lake’s water replenishment. The Iranian government has now adopted a plan of action which aims to prevent illegal water removal.
Satellites would have to carry out more precise measurements
These and other results provide new incentive to Tourian and his colleagues. ‘We’re working to break down the data better in order to study specific regions in greater detail.’ For example, the satellites would have to carry out more precise measurements in order for research to be carried out on changes in the cyclical circulation of water in permafrost regions. Gravimetry in particular has problems in registering infinitesimal changes in the gravity field. Tourian is nevertheless confident that the study of global water circulation flows can help mitigate the consequences of climatic change. ‘Above all, political decisions are required on a worldwide scale,’ says scientist Tourian. ‘But even today, much can be done in individual regions if causes and effects can be precisely identified - as at Urmia Lake.’ Jens Eber