In the previous post I mentioned the sensitivity of salt lakes to the fluctuations of water level. It is worth to repeat that the water level in salt lakes depends on the balance of precipitation and evaporation which lead to its fluctuations within relatively short time. The fluctuation of water level affects the salt lake not only by changing the area or structure of habitats but also by changing the salinity of the water. The perfectly calculated proof of this statement entitled “An examination of the sensitivity of the Great Salt Lake to changes in inputs” was published by Ibrahim Mohammed and David Tarboton recently in Water Resources Research.
The story with Great Salt Lake is exactly classical. It has no outflow. The lake level is controlled by precipitation, streamflow inflows and evaporation. The rate of evaporation depends on the lake area and salinity. The task to calculate the water level seems to be very simple … for those who are not familiar with this type of calculations.

The Great Salt Lake. Photo from http://freshwatertuttle.wikispaces.com/NatalieDeadSea

All processes that influence the water level are functions of several factors. Some of them are interdependent. For example evaporation depends on salinity which depends on water volume of the lake which of course depends on evaporation. These are, so called by scientists, feedbacks that make life of those who make mathmodels rather complex.

Nevertheless, the task to calculate the water level was done. The model nicely predicted the historical records of water level. Authors demonstrated that the volume of streamflow is the most important factor for the lake level. The most interesting result is the sensitivity of the lake level to changes in streamflow and air temperature inputs. Results are easy to see in the picture below. As expected the temperature increase would decrease the lake level while increase/decrease in streamflow would increase/decrease the level.

What is nice and important with models (and in general with good science) the results are quantitative. Water managers get perfect decision-support system which can be used to make scientifically based evaluations of water use practices. The lake, due to feedbacks that are not easy to calculate in mind, can behave unexpectedly but science provides tools to understand this behavior.

Fig. 13 and 14 from WATER RESOURCES RESEARCH, VOL. 48, W11511, doi:10.1029/2012WR011908, 2012

PS. In our current research we need to reconstruct and predict the water level in Lake Shira. The lake is quite similar. There is no outflow. The inflow water comes with small river, rain and snow, antropogenic load and groundwater. I think the Great Salt Lake calculations are good example of how to approach the problem.

Mohammed, I., & Tarboton, D. (2012). An examination of the sensitivity of the Great Salt Lake to changes in inputs Water Resources Research, 48 (11) DOI: 10.1029/2012WR011908