Modelling Physical and Chemical Processes of the Hypersaline Lake Urmia: Water Level Decline and Restoration by Water Conveyance

Abstract

The decrease of the Lake Urmia water level from its peak around 1995 to present has had dramatic consequences for the lake ecosystem. To restore the lake, the salinity must be brought back to salinity values well below saturation levels. In this chapter, we adapt a 3D hydrodynamical ocean model to the physical and chemical setting in Lake Urmia. The model is forced by river runoff, surface wind stress, precipitation and sensible, latent, and radiative heat fluxes. Evaporation is derived from lake water conditions and atmospheric variables. We represent sodium (Na) and chloride (Cl) by tracers in the model. Saturation, precipitation of NaCl, and buildup of a bottom salt layer are included. We simulate the period from 1993 to 2016. Temperature, salinity, water level, and bottom salt layer distribution/thickness compares well with observations. Circulation strength decreases with decreasing water level, probably caused by bottom friction becoming more effective in a shallower water column. Next, we simulate near 20 years into the future and include conveyance from the Caspian Sea (32 m3/s). The model predicts that this will have minor impact on the lake. To maintain the lake at the level before the drought will require ∼300 m3/s of mean total water input. The conveyance from the Caspian Sea can only provide 10% of this.