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Modelling Evaporation & Salinity Variation in Saline Lakes Using Spatial System Dynamics: The Case of Urmia Lake

Sima, Somayeh | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45226 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Tajrishy, Masoud
  7. Abstract:
  8. Evaporation is the most important water loss from terminal lakes which can influence the chemistry of lakes. In large lakes, the spatial distributions of meteorological and water quality variables affect the evaporation rates. Therefore, it is crucial to consider such variations in estimating evaporation rates from large lakes. This study aims at developing an evaporation estimation model for saline lakes considering salinity and spatial distribution of variables in/over the lakes and investigating the interaction between meteorological, hydrological and water quality variables in natural saline systems. To accomplish these objectives, first a distributed model was developed for estimating daily evaporation rate from the lakes based on the energy balance model and remote sensing data. The required data layers for evaporation estimation including air and water surface temperatures, air and water vapor pressure, albedo and emissivity were obtained from remote sensing data (MODIS satellite images) and GIS techniques and were validated against in situ data. The model was used to estimate daily evaporation rates from Urmia Lake between 2009 and 2010. Then, an integrated water, energy and salt balance (WESB) model was developed based on the spatial system dynamic approach (SSD) to understand the interactions between evaporation, water quality and geochemical state of saline lakes. In the WESB model, the energy balance, water and salt balance and the thermodynamic equations of mineral precipitation/dissolution are coordinately solved at each time step to simulate the lake status. The WESB model was used to simulate Urmia Lake during a 14 month period (from August 2009 to September 2010). Comparison of the simulation results with the field data indicated an acceptable performance of WESB in simulating volume, density and ionic composition of Urmia Lake. The daily evaporation maps of Urmia Lake showed an increasing pattern from the shallower coastal regions toward the interior parts of the Lake. Although the estimated evaporation rates from the interior north and south parts of the lake are close to each other, the volume of evaporation loss from the south part is about 1.5 times of the north during the 2009-2010 water year. The extent of the spatial variation of evaporation rate over the lake ranged from 3 to 7 mm/day, during various months. It was investigated that the evaporative fraction is not stable during the day over Urmia Lake. Thus, it is not proper to upscale daily evaporation rates from instantaneous rates using the evaporative fraction. In such cases daily evaporation models such as SDDE are superior compared to the instantaneous algorithms. Comparison of the results of SDDE with previous estimation of Urmia Lake evaporation using a single station data indicated that excluding the spatial variations of both meteorological and water quality variables can lead to up to 55% underestimation in monthly rates of evaporation. Moreover, comparison of the estimated evaporation rates from the distributed RS_based model and the WESB model revealed that considering the salinity controlling effect in a static way, rather than a dynamic, lead to 25% and 2.5% underestimations in monthly and yearly evaporation rates, respectively. Comparing the relative reduction in the lake evaporation rate due to its increased salinity and reduced surface area showed that the effect of salinity of the lake is more dominant than its surface area. Based on a linear relationship between the density and the activity of Urmia Lake water, its density at the evaporation ceasing state was calculated to be 1385 kg/m3, which is much higher than the current density of the lake. Thus, the evaporation from the lake is still continuing. The annual volume of evaporation losses from Urmia Lake was 23% more than its environmental water requirements. This means that the desiccation of Urmia Lake in the mid- time will continue, even if its water requirements can be totally supplied. Results of this study showed the successful application of the distributed RS_based evaporation (SDDE) model and the WESB model as tools to assess the effect of water resources management policies on the hydrology, water quality and geochemistry of saline lakes
  9. Keywords:
  10. Evaporation ; Remote Sensing ; Flamingo ; Dissolution ; Urumieh Lake ; Mineral Precipitation ; Spatial Distribution ; System Dynamic

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