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Long-Term Analysis of Water Balance Components and Water Level Changes of Lake Urmia using a Combination of Field aAnd Remote Sensing Data

Rahemi Ghale Joghi, Nazanin | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57201 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Safaie, Ammar
  7. Abstract:
  8. In recent years, global salt lakes have faced severe environmental challenges. Lake Urmia, the world’s second-largest hyper saline lake, is located in the northwest of Iran, has experienced a significant shrinkage in last years. Lake Urmia is a terminal lake where water enters through precipitation and rivers inflow and loses through evaporation. Analysis of long-term trends (1990-2018) using the Mann-Kendall test indicates no significant trend in precipitation, an increasing trend in evaporation, and a decreasing trend in river discharge. However, precipitation during 1990-1999 (beginning of accelerated lake drying) showed a decreasing trend. An investigation of the correlation between water balance components shows highest correlation between lake water level and daily river discharge (correlation coefficient of 0.2). This suggests that river discharge has the most significant impact on the lake, which is highly dependent on human factors and management dimensions in the basin. This study aims to investigate the interaction of water balance components and compare them with observed water level at the Golmankhaneh station. First, the input data to the water balance are validated, and the behavior of water inflow to the lake after evaporation is examined to determine whether all of it contributes to the increase in water level. To obtain the water level for 1999-2018, the lake surface area was calculated using the NDWI index from Landsat 7 and 8 images, using two approaches. In the first approach, the threshold for water body detection was set so that only the fully water-covered area was considered as the effective area, and the surrounding salt flats and mudflats formed due to lake drying were neglected. In the second approach, by lowering the NDWI threshold, a larger area was considered, and in addition to the fully water-covered area, areas that were previously water and are not yet completely dry according to satellite images were also included in the lake area calculation. Calculating the water level using the water balance equation shows that in the second approach, the water level matches the observed data with R2=0.98 and RMSE=0.29 meters. This indicates that not all water entering the lake after evaporation contributes to the increase in the lake's water level. In other words, the lake does not act as a rigid container that responds strictly to the water input, but rather like a sponge that absorbs part of the water. On average, from 1999 to 2018, 9% of the lake's water was absorbed by the surrounding wet area and did not contribute to the increase in the lake's water level
  9. Keywords:
  10. Urumieh Lake ; Water Balance ; Remote Sensing ; Long-term Effects ; Urmia Lake Level ; Correlation Coefficient

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