Das österreichische Internationale Institut für Angewandte Systemanalyse verbreitete am 10. November 2016 kräftig Klimaalarm:
Climate, human influence conspired in Lake Urmia’s decline
A combination of climate change and water usage are responsible for the staggering drying of Lake Urmia, what was once the second largest salt lake in the world.
The dramatic decline of Iran’s Lake Urmia—once the second-largest hypersaline lake in the world—has both direct human and climatic causes, according to a new study published in the Journal of Great Lakes Research. The study was the first to compare the relative impact of climate and water management on the water flowing into the lake. “Saving Lake Urmia will require both national action to improve water management, and international cooperation to address the issue of climate change,” says IIASA and Wageningen University researcher Somayeh Shadkam, who led the study.
Lake Urmia was once the world’s second-largest hypersaline lake, but has declined over 80% in recent decades. Previous work by Shadkam and colleagues had shown that climate change threatens the lake’s existence, using future scenarios of climate change to project water inflow into the lake. The new study aims to better understand the causes of the lake’s decline, teasing out the relative contribution of different factors such as human water usage as well as climate-related variables, using 50 years of data from 1960 to 2010.
The annual flow of water into Lake Urmia dropped by 48% over the study period. Using a model of water flow into the lake, the researchers found that 60% of this decline was caused by climate changes, such as change in precipitation and temperature, and that the remaining 40% of the decline could be attributed to water resources development, such as diverting water for irrigation that would otherwise flow into the lake.
Most previous studies have indicated the dominate role of water usage in changes in the lake surface area. The new study clear indicates that climate change and variability has contributed to the lake desiccation. That means that reduces water use without taking change in the climate into account might be insufficient in saving the lake. “Water resources and climate change are inextricably interlinked,” says IIASA Director General and CEO Professor Dr. Pavel Kabat, a coauthor on the study. “This is just one area where an integrated systems viewpoint is vital for providing sound advice to policymakers trying to solve such pressing issues.”
Reference: Shadkam S, Ludwig F, van Oel P, Kirmit Ç, and Kabat P (2016) Impacts of climate change and water resources development on the declining inflow into Iran’s Urmia Lake. Journal of Great Lakes Research, 42 (5). pp. 942-952.
Faktencheck: Warum ist der Urmia-See denn eigentlich geschrumpft? Der Kontext suggeriert, dass es wohl am menschengemachten Klimawandel liegen muss. Das englischsprachige Wikipedia gibt jedoch einen ersten Hinweis auf die wahren Gründe:
The lake seems to have had a complex hydrological history and its water levels have greatly fluctuated in the geological history.
In der geologischen Vergangenheit hat der Seespiegel stets signifikant geschwankt. Könnte die aktuelle Schwankung daher vielleicht auch andere Ursachen haben? Kelts & Sharabi (1986) dokumentierten eine bedeutende natürliche Variabilität:
Preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr B.P. with saline lake deposition in a cool arid climate. From 9000 to 7500 yr B.P., higher-energy facies prevailed in a shallow saline lake and, since then, present-day saline environments have persisted with evidence of numerous second-order water-level fluctuations.
Eimanifar & Mohebbi (2007) fanden zudem, dass neben Dürren vor allem die vermehrte Wasserentnahme zu landwirtschaftlichen Bewässerungszwecken den Wasserspiegel hat absinken lassen:
Due to drought and increased demands for agricultural water in the lake’s basin, the salinity of the lake has risen to more than 300 g/L during recent years, and large areas of the lake bed have been desiccated.
Ganz aktuell auch das im Januar 2015 im Fachjournal Remote Sensing of Environment erscheinende Paper von Tourian et al., in dem erneut der exzessive Wasserverbrauch bemängelt wird:
A spaceborne multisensor approach to monitor the desiccation of Lake Urmia in Iran
Lake Urmia, a hypersaline lake in northwestern Iran, is under threat of drying up. The high importance of the lake’s watershed for human life demands a comprehensive monitoring of the watershed’s behavior. Spaceborne sensors provide a number of novel ways to monitor the hydrological cycle and its interannual changes. The use of GRACE gravity data makes it possible to determine continental water storage changes and to assess the water budget on monthly to multi-annual time scales. We use satellite altimetry data from ENVISAT and CryoSat-2 to monitor the lake water level. Moreover, we employ optical satellite imagery to determine the surface water extent of the lake repeatedly and at an appropriate time interval. Our altimetry results indicate that, on average, the lake has lost 34 ± 1 cm of its water level every year from 2002 to 2014. The results from satellite imagery reveal a loss of water extent at an average rate of 220 ± 6 km2/yr, which indicates that the lake has lost about 70% of its surface area over the last 14 years. By combining water level from altimetry, surface water extent from satellite imagery and local bathymetry, we ascertain the changes in lake volume. Results indicate that the lake volume has been decreasing at an alarming rate of 1.03 ± 0.02 km3/yr. The water volume of the lake behaves differently from the water storage of the whole basin captured by GRACE. Our results show that the onset of a drought in 2007 over this region together with an increase in the rate of groundwater depletion caused a new equilibrium level for water storage of the whole basin. Comparing the results from GRACE and the obtained water volume in the lake with in situ groundwater level data reveals the anthropogenic influences on an accelerated lake desiccation. In fact, our monitoring approach raises critical issues regarding water use in the basin and highlights the important role of spaceborne sensors for any urgent or long-term treatment plan.
Auch die Washington Post berichtete am 2. Juli 2014 über den Urmia See. Die Stoßrichtung des Artikels geht jedoch erneut in Richtung überstrapazierte Nutzung der knappen Wasserressourcen:
Iran’s water crisis the product of decades of bad planning
[...] “Our water usage is twice the world standard, and considering the situation in our country, we have to reduce this level,” Massoumeh Ebtekar, a vice president and the head of Iran’s Department of Environment, said in a recent speech. [...] With Iran’s annual precipitation only a third of the global average, heavy overconsumption has ravaged its available water resources. [...] The Zayandeh River, which flowed through Iran’s heartland, is mostly a dry bed after being diverted and dammed to provide irrigation for farms. Disappearing lakes and dried-up rivers are the outward symptoms of Iran’s water shortage, but the root causes are less visible, stemming from the techniques and habits of a more traditional and less mechanized era. “In less than 50 years, we’ve used all but 30 percent of our groundwater supply, which took a million years to gather, and it’s getting worse and worse due to unsustainable development,” said Nasser Karami, an Iranian physical climatologist who is an associate professor at the University of Bergen in Norway.
Weiterlesen in der Washington Post.
Mit dieser fragwürdigen Studie hat sich das Internationale Institut für Angewandte Systemanalyse nicht gerade mit Ruhm bekleckert. Ob es den iranischen Ko-Autoren des Papers vielleicht vor allem um verbesserte Chancen auf Klimaschadensausgleichszahlungen ging?