Evaluation of the changes in water areas of the Tigris and Euphrates basin based on time series analysis of various environmental factors

Extended abstract:

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Title:

Evaluation of the changes in water areas of the Tigris and Euphrates basin based on time series analysis of various environmental factors.

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Introduction:

Surface water is the most important source of water from planetary water resources, which covers 71% of the earth's surface and is vital for the survival of human and ecological systems. However, during recent decades, due to the combined effects of climate change and human activities, the water balance of lakes has changed. In this regard, surface water changes as one of the most important resources of the earth are very important in local, regional and global planning. Accordingly, one of the prime regions within the Middle East is the Tigris and Euphrates Basin (TEB) which has undergone tremendous changes in the past decades due to matters of global warming and climate change, drought, desertification, and population growth or human-related activities. Nevertheless, much attention has not been paid to the pattern of changes in water areas and understanding the potential effects of various environmental factors. Therefore, in the present research, the time series of surface water changes in this basin has been evaluated in relation to the impact of various environmental factors.

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Materials and methods:

The conventional methods of monitoring water bodies are very expensive and time-consuming due to their special characteristics. Hence, remote sensing (RS) techniques have facilitated water bodies change analysis, where the required maps can be retrieved at any time and spatial scales at unprecedented speed and extent. In this regard, the time series of environmental parameters have been extracted using various GEE products. The time period studied in the research is a long-term period from 2001 to 2021 and the analyses have been done in two phases and in total using 252 months of data in the form of a composite time series. Our data are extracted from products such as FLDAS, TerraClimate, MOD13Q1.061, MYD17A3HGF.061, WorldPop and JRC 1.4. The main goal of this framework was to analyze the trend of TEB surface water changes and determine its correlation with the temporal changes of various environmental factors.

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Results and discussion:

The results showed that lakes and wetlands have witnessed various changes during the period of 2001-2021. In this regard, the area of Hamrin and Razzazah lakes has gradually decreased. In other words, the area of Lake Hamrin in northeastern Iraq has decreased from 157.98 square kilometers in 2001 to 107.63 square kilometers in 2011 and 37.05 square kilometers in 2021. In addition, the area of Razzazah lake in Karbala province has decreased from 1260 square kilometers in 2001 to 440.04 square kilometers in 2021. Furthermore, Qadisiyah, Tarthar, Habbaniyah lakes and Horul-Azim wetlands have had different trends in different years. The results show that the average surface water area of the region in the period of 2001-2021 was about 9287.58 square kilometers and in 9 years of this period, the values were higher than the average and in the other 13 years, the values were lower than the long-term average. According to the analysis, the surface water area of the region was at its lowest level (8199.52 square kilometers) in 2010 and at its highest level (11424.76 square kilometers) in 2021. In addition, the time-varying trend of water changes in the region has been observed. In general, the linear trend model has indicated a general increasing trend in this time period. Our findings show that due to the ever-increasing expansion of urbanization and the growth of urban areas, the population has an exponential trend that has always increased from the beginning to the end of the period. The evaluation of temperature values has indicated that the air temperature suddenly became abnormal after a relatively stable trend. The beginning of this trend was in 2010, when the maximum temperature reached 28.55 degrees Celsius and the minimum temperature reached 14.11 degrees Celsius, and the average temperature increased to 21.4 degrees Celsius. In the meantime, according to the trend governing the topography of the basin, precipitation did not have a significant effect on the mentioned changes, and instead, evapotranspiration played an important role. In other words, water areas and evapotranspiration have a negative correlation, and the increase in evapotranspiration is associated with the decrease in water area. Moreover, the results have shown that other environmental parameters such as vegetation, soil texture and wind speed did not have a significant effect on the water level changes in the region and did not have a significant relationship in this regard. Therefore, it should be said that climate changes considered as the most important factors in the process of increasing or decreasing the water level in the TEB.

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Conclusion:

Based on the research methodology and the results obtained, it can be said that the Google Earth Engine (GEE) platform can provide researchers and decision makers with valuable tools in the field of water level monitoring. In the case of time series, the volume of data is very large, which increases the data processing time and its computational load and from this point of view, continuous monitoring of water bodies in the TEB in the context of this platform is very important, taking into account the annual changes and environmental conditions. On the other hand, the efficiency of the various products of GEE has made the desired processes to be performed with maximum accuracy and speed without the need for special hardware and software prerequisites. In general, the GEE platform enables the proposed research framework to be used to monitor and analyze surface water changes at different spatial and temporal scales. Nevertheless, due to the large scale of the study in the current research, it is suggested that in the next research, a case study of each of the water bodies in the TEB will be conducted and monthly and seasonal time series data should be used to analyze the trends of changes and factors involved in this field.

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Keywords:

Surface water, change assessment, Tigris and Euphrates, time-series data, GEE.

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