عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Urmia Lake is the largest inland water body in Iran and the second hyper-saline lake in the world. It has been designated as a “conserved region of biosphere” by UNESCO due to its environmental importance and unique aquatic ecosystem. The lake has faced a variety of natural and anthropogenic hazards in recent years and has encountered dramatic changes in its natural hydrodynamic condition. There are a number of reasons for these changes, where primary causes are increased water consumption, especially in the agricultural sector, development of water storage structures in the lake basin, construction of the causeway, climate change, global warming, and droughts. Due to changes in the lake's natural condition, the study of its hydrodynamic pattern is inevitable. In this regard, the current study aims to simulate changes in the water temperature of Lake Urmia in order to study its hydrodynamic.
MIKE hydrodynamic models are developed by DHI Water and Environment for simulation of flows in estuaries, bays, coastal areas, lakes, and oceans. To perform the simulations in this study, MIKE3 model was used. In the modeling process, the flow simulation is carried out simultaneously with the heat transfer model, covering all the hydrodynamic conditions of the lake. In order to simulate water temperature and its effects on the lake hydrodynamics in the MIKE model, density is considered as a function of temperature, then the heat transfer equations are solved at each time step. The forces governing the hydrodynamic equations include wind, air pressure, tide, wave, and Coriolis forces. However, the forces governing heat transfer/diffusion equations are of a different nature. Air temperature, relative humidity, and clearness coefficient are important inputs for the simulation of changes in the water temperature in the lake. Due to the high accuracy of the obtained values, ECMWF model data were used in the model. The validity of the numerical model was also assessed by comparing the simulated results against satellite data. The information is provided by the Group for High Resolution Sea Surface Temperature (GHRSST). In this group, global sea surface temperature data are generated using a multi-scale two-dimensional variational (MS-2DVAR) blending algorithm. These sea surface temperature data are obtained from various satellites with multiple sensors (such as AVHRR, AATSR, SEVIRI, AMSRE, TMI, MODIS, GOES, MTSAT-1R, etc.). In this study, changes in the water temperature of Lake Urmia were simulated in order to study its hydrodynamic condition. Initially, the data used to simulate water temperature changes are presented. These data included air temperature, relative humidity, and clearness coefficient. Due to the high accuracy and generalizability of the ECMWF model output to the entire computational domain, the output of this model were used to obtain the above data.
MIKE3 hydrodynamic model was used to perform the simulations. In order to investigate the effects of precipitation, evaporation, and rivers discharge on water temperature changes, two models, one with and the other without considering these factors were implemented. The water temperatures were compared in these two models. The results showed that water temperature values were approximately the same for the two cases. Also, a comparison between the water temperature output results at different depths revealed that due to the low depth of the lake, the temperature difference between the surface layer and the near-bed layer was low and reached a maximum of 0.2 °C. In addition, GHRSST satellite data was used to validate the model results. Evaluations indicated that the model results were in good agreement with the measured data, and seasonal variations in lake surface temperature were also well simulated. Moreover, the effect of causeway on the spatiotemporal distribution of lake water temperature has been investigated. For this purpose, simulation of temperature changes was considered over a one year period. The results demonstrated that the water temperature of the lake did not change significantly in both with and without causeway, and the temperature exchange between northern and southern parts of the lake occurred in both conditions. Hence, this model can be used as an efficient tool to assess the effect of causeway on the flow pattern, salinity distribution and sedimentation process in both parts of the lake