Global lake responses to climate change

Climate change is one of the most severe threats to global lake ecosystems. Lake surface conditions, such as ice cover, surface temperature, evaporation and water level, respond dramatically to this threat, as observed in recent decades. In this Review, we discuss physical lake variables and their responses to climate change. Decreases in winter ice cover and increases in lake surface temperature modify lake mixing regimes and accelerate lake evaporation. Where not balanced by increased mean precipitation or inflow, higher evaporation rates will favour a decrease in lake level and surface water extent. Together with increases in extreme-precipitation events, these lake responses will impact lake ecosystems, changing water quantity and quality, food provisioning, recreational opportunities and transportation. Future research opportunities, including enhanced observation of lake variables from space (particularly for small water bodies), improved in situ lake monitoring and the development of advanced modelling techniques to predict lake processes, will improve our global understanding of lake responses to a changing climate

Morphological changes in the Aral Sea. Satellite imagery and water balance model.

The Aral Sea, once the worlds fourth largest lake, has suffered a dramatic loss of both area and volume, as a result of greatly reduced river inflow brought about by increasing irrigation (mainly of cotton and rice) along the two rivers, Amu Darja and Syr Darja, that flow into it. The ecological consequences are severe and have been discussed in a variety of scientific publications (Micklin, 1991 and 2000, Giese, 1998, Letolle, & Mainguet, 1996). Satellite images have helped to monitor and document the desiccation process and to describe the associated morphological changes. This includes changes of the water body itself as well as the related changes of the surrounding environment and plant communities, such as the newly formed desert areas like the so-called Aral Kum. Low spatial resolution data such as NOAA-AVHRR has proven to be valuable to monitor the desiccation on a frequent basis. The use of high resolution satellite data has been limited for morphological change studies due to higher costs (Resurs-MSU-SK/E, Landsat-TM) and only partial coverage of the lake surface. New satellite systems such as Terra-MODIS are useful because of full coverage of the lake, easy access on a daily basis and provision to researchers at no cost. Besides remote sensing data, GIS modelling techniques have proven to be a useful tool for forecasting the desiccation process of the Aral Sea under specific circumstances. Several probable water inflow scenarios have been assumed to forecast the future desiccation of the lake. Further investigations will include automatic change detection and automated monitoring of the desiccation process