Remote Sensing (RS)
Heshmat Karami; Hadi Abdolazimi
Abstract
Extended AbstractIntroductionWetlands are considered valuable resources of the environment. Despite the importance of wetlands, they are currently threatened by intensive water harvesting for irrigation, industrial development, deforestation, construction of dam reservoirs, and changing rainfall patterns. ...
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Extended AbstractIntroductionWetlands are considered valuable resources of the environment. Despite the importance of wetlands, they are currently threatened by intensive water harvesting for irrigation, industrial development, deforestation, construction of dam reservoirs, and changing rainfall patterns. Monitoring can determine the changes in the location, extent, and quality of the wetland and therefore plays an important role in the maintenance and protection of the wetland. Ecosystem monitoring with remote sensing methods offers the advantage of difference, frequent and uniform coverage of large areas. The study of effective parameters or up-to-date maps that show spatial and temporal changes in the sub-basin of Horul Azim Wetland is not available. Therefore, considering that currently, this wetland is struggling with various problems to continue its survival, the purpose of this research is to use Google Earth Engine and satellite data to study the process of wetland changes.Materials & MethodsThis study was done on the platform of Google Earth Engine open source system. In this study, the data of water area, vegetation cover, precipitation, evaporation, and surface temperature were coded in the Google Earth Engine system in a standard way and their time series was obtained. Also, the NASA GRACE data analysis tool (DAT) was used for time series of groundwater levels. In this research, the Mann-Kendall test and Spearman's correlation were used in order to evaluate the changes in different parameters. In this research, the period from 2000 to 2022 was considered to investigate the trend of the data according to the available time range of the data. Finally, to check the fact that the changes in the zones were affected by floods, the data of the Global Surface Water of Water Occurrence (GSWE) probe was used.Results, discussion, and conclusion The results of the analysis graph of the water area data trend showed that from 2007 to 2019 the water area trend is increasing, with 2007 being the minimum year and 2019 being the maximum year, and the reason for this was the 90% water withdrawal of the Hor al-Azim wetland in the Iranian part. Also, the reason for the increase in the water area in 2017 is heavy rains that lead to floods and overflowing of the Karkheh dam in the sub-basin of the Hor al-Azim wetland. In 2017 and 2020, 2021, the water area shows a significant increase, which is due to the change in climatic behavior and the occurrence of floods in these years. Finally, the trend of the blue zone will be downward until July 2022. The results of a careful analysis of the data trend by the Mann-Kendall test showed that the trend of the available time period was observed. Kendall's tau value also confirms the increasing trend. It seems that the increasing trend of the water area in the years 2019 to 2021 in this study using the Google Earth Engine system is the result of the floods of the last few years, that Considering only this parameter and these data leads to errors in the study and investigation of the condition of Hor-al Azim wetland. No significant trend was observed in the time series of vegetation cover, but according to the positive Mann-Kendall vegetation cover statistic, one of the causes of the non-significant decrease in the groundwater level could be the increase of pastures and agricultural lands. Kendall's tau value for the surface temperature also showed a negative value (-0.24). According to this result and the sensitivity of the evaporation parameter to temperature, we can point to the role of this parameter in reducing evaporation in the sub-basin of the Hor al-Azim wetland. The northwest and southeast regions have the highest temperature up to a part of the central region of the sub-basin. The western part, which includes the border of the Hor al-Azim wetland, has the lowest temperature, and most of the central part has the lowest temperature, one of the causes of which can be the presence of vegetation and the development of agricultural lands. The time series graph of precipitation showed that the parameter of precipitation in the years 2017 to 2020 had an upward trend, which led to recent floods in the studied area. The results of the Mann-Kendall test for the general trend of evaporation and transpiration parameters, ground surface temperature, and precipitation in the sub-basin of the Hor al-Azim wetland did not show a significant trend. Using the Global Surface Water Explorer (GSWE) data, the occurrence of water, the intensity of water changes, and the seasonal change of water on the wetland were studied for the period of 1984-2021. The study of this dataset confirmed the human interference (creating the Karkheh Dam and draining its lake) and the occurrence and effects of the flood on the sub-basin of the Hor-al Azim wetland. The results of Spearman's correlation test also showed that climate changes such as changes in precipitation patterns and human activities can become factors that affect the surface of the water body of Hor al-Azim Wetland. The results of this research can be used in the management of Hor al-Azim wetland and wetlands with similar conditions.
Geographic Data
Shahin Jafari; Saeid Hamzeh; Hadi Abdolazimi; Sara Attarchi
Abstract
Extended AbstractIntroductionHuman activities as well as environmental and climate changes affect the trends of wetlands. Detecting and monitoring aquifers are considered to be very important for evaluation of past, present, and future influential factors, and the findings of such studies are essential ...
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Extended AbstractIntroductionHuman activities as well as environmental and climate changes affect the trends of wetlands. Detecting and monitoring aquifers are considered to be very important for evaluation of past, present, and future influential factors, and the findings of such studies are essential for taking measures and making decisions based on the goals of sustainable water and soil resources management. Over the past decade, many researchers around the world have been attracted to remote sensing and especially satellite remote sensing and used this technology to detect such changes over time. The present study has used Landsat (monitoring the area of water body), TRMM (monitoring rainfall), MODIS (monitoring vegetation and evapotranspiration), Grace (monitoring groundwater) satellite images available in Google Earth Engine to study last two decades changes (from 2000 to 2019) in Maharloo wetland, Goshnegan catchment and their surroundings. Materials & MethodsMaharloo wetland is located in Fars province and Goshnegan catchment (426 square kilometers). The present study has used Landsat 7 and 8 images to extract the area of water body, TRMM images to obtain precipitation values, MODIS products to calculate NDVI and evapotranspiration, and data received from Grace to extract changes in groundwater level. These satellite images were available in Google Earth Engine. Mann-Kendall test was also used to assess the overall trend of the aforementioned factors. Results & DiscussionThe automated water extraction index was used in the present study to identify and estimate the area covered by water bodies in the study area. The largest area belonged to 2006 (216.76 square kilometers) and the smallest belonged to 2018 (66 square kilometers). In 2000 (the beginning of the reference period), an area of 216.52 square kilometers was covered by this wetland which is close to what was observed in 2006. In 2018, this has reduced to 66 square kilometers. Thus, there is about 150.72 square kilometers (69.54 percent) difference between these two years. In 2009, the total area has reduced to 66.67 square kilometers. A numerical comparison between 2000 and 2019 also indicates a reduction of 91.17 square kilometers (42% decrease) in the total area covered by this wetland. Also, a 53.72 square kilometers (29.60%) difference was observed between the average area covered by the water body in the first and second ten years. Since calculated p-value value (< 0.00001) is less than the alpha level (0.05), so a significant trend was observed in the average annual data of the area covered by this wetland. Kendall's tau also indicated declining trend of the collected data. Groundwater level was calculated using data received from Grace Satellite to investigate the role of groundwater level in reducing the area covered by the water body. Results indicated that since 2008, groundwater level have always showed a negative value (a decreasing trend). For an instance, a groundwater level of -10.86 cm in 2019 indicates a decrease in the water level in the study area. As the calculated p-value (< 0.0001) is less than the alpha level (0.05), so a significant decreasing trend was observed in the groundwater level. Results of Mann-Kendall test (-0.6) also indicated that changes in water bodies, vegetation, rainfall and groundwater level had a decreasing, increasing, increasing and decreasing trend, respectively. No significant trend was observed in evapotranspiration. It seems that the expansion of agricultural lands and subsequent water extraction from aquifers have intensified the decreasing trend of water bodies in this wetland. ConclusionWetlands provide many ecological services including water treatment, natural hazard prevention, soil and water protection, and coastline management (Amani et al., 2019). Therefore, understanding the importance of wetlands and their management need to be seriously considered by relevant organizations in different countries of the world, and Iran is no exception. Satellite data and remote sensing methods and techniques are considered to be one of the most important and cost-effective methods of monitoring wetlands. The present study used satellite data collected by Landsat, MODIS, Grace, and TRMM to monitor water bodies, vegetation, groundwater level, and rainfall in Goshnegan catchment in which Maharloo wetland is located. The results of Mann-Kendall test showed a decreasing annual trend for changes in the average area of this wetland. This decreasing trend is considered to be a serious threat to human settlements around the wetland which can intensify over time. It will also affect the thermal islands of Shiraz and Sarvestan in near future. Obviously, management of agricultural and forest land uses with the aim of stopping their increasing trend can improve water balance in catchment areas. A 132.2 ha (approximately 36.16%) difference was observed between the average vegetation cover in this catchment area over the first and second ten years (233.4 vs. 365.6 ha). It seems that the expansion of agricultural lands and subsequent water extraction from aquifers have intensified the decreasing trend of water bodies in this wetland. Due to the proximity of this wetland to the city of Shiraz and its importance as an ecological and tourist attraction, it is suggested that related authorities (Department of Environment and Water Organization) demarcate lake bed and riparian zone with the help of remote sensing researchers to improve the management of this wetland and prevent it from drying up. Also, it is suggested that the Organization of Agriculture Jihad review and improve water consumption methods and cultivation patterns in the areas surrounding this wetland.
