Spatiotemporal Assessment of Water Inundation Changes in the Mighan Wetland Based on Satellite Image Time Series in the Google Earth Engine Platform

Document Type : Research Paper

Author

Assistant Professor, Desert Research Division, Research Institute of Forests and Rangelands, Agricultural Research, Education and Extension Organization (AREEO), Terhran, Iran.

Abstract

Mighan Wetland has experienced severe hydrological fluctuations and declining water stability in recent decades. In this study, the wetland was monitored over the period 1995–2024 using Landsat 5, 7, and 8 imagery within the Google Earth Engine (GEE) platform. The aim was to analyze the spatiotemporal changes of the water body and assess hydrological instability using the Normalized Difference Water Index (NDWI) and the Transition and Seasonality algorithms from the JRC Global Surface Water dataset. The results showed that the average water body area decreased from 10.7 km² (1995–2004) to 3.9 km² (2005–2014), representing a 63% decline, then increased to 19.8 km² (2015–2024). More than 80% of annual inundation occurs in winter and spring, corresponding to snowmelt and higher precipitation periods. The Seasonality algorithm revealed that 25% of the wetland is permanently dry, approximately 70% holds water for only 1 to 5 months per year, and only 4.5% has persistent water cover. The Transition results indicated the conversion of some seasonal areas to permanent zones and the emergence of new seasonal water bodies. Overall, the hydrological regime of the wetland has become highly unstable over three decades, transforming into a seasonal system dependent on short-term climatic events, posing a serious threat to its ecological functions, including habitat loss for migratory birds and increased dust emission from dry playa surfaces. The novelty of this research lies in integrating long-term monthly analyses with the NDWI index and the Transition and Seasonality algorithms within the GEE platform, enabling continuous monitoring, improved water resource management, and effective wetland restoration planning.
Introduction
Wetlands in arid and semi-arid regions are among the most vulnerable natural ecosystems due to their high dependence on limited precipitation and intermittent runoff. These ecosystems provide critical ecological services, including groundwater recharge, flood regulation, biodiversity conservation, and climate moderation. However, they are increasingly threatened by anthropogenic pressures such as excessive groundwater extraction, land-use changes, upstream water diversion, and climate change. Mighan Wetland, located in the central plateau of Iran near Arak City, is one of the most important salt wetlands in the region, which has experienced severe hydrological fluctuations and declining inundation stability in recent decades. The desiccation of this wetland can lead to widespread environmental consequences, including the activation of dust sources, increased wind erosion, degradation of surrounding agricultural lands, loss of habitat for migratory birds, and weakening of ecological functions. Despite its ecological and economic significance, long-term monitoring of its hydrological dynamics has been limited. The main purpose of this study is to monitor and analyze the spatiotemporal changes in the water body area of Mighan Wetland over a 30-year period (1995–2024) and assess its hydrological instability trend using remote sensing data within the Google Earth Engine platform.
Materials and Methods
In this study, Landsat 5, 7, and 8 satellite images (time series from 1995 to 2024) were used to extract and analyze water body changes. The Google Earth Engine platform was employed for all processing due to its powerful cloud-computing capabilities, access to extensive satellite archives, and efficient handling of large-scale time-series data. The Normalized Difference Water Index (NDWI), a widely used spectral index for water body extraction, was applied with a threshold of 0.2 to delineate water surfaces. The NDWI leverages the reflectance differences between visible green and near-infrared bands to effectively distinguish water bodies from other land cover types. To analyze the stability and structural changes of water bodies, the Transition and Seasonality algorithms from the JRC Global Surface Water dataset were used. These algorithms provide detailed classification of water presence over time, identifying patterns such as permanent, seasonal, ephemeral, and transitional water bodies. Water surface areas were calculated at monthly, seasonal, annual, and decadal scales, and their trends were analyzed to understand both short-term fluctuations and long-term patterns. Additionally, inundation classification maps were prepared based on 11 Transition classes and 12 Seasonality classes, enabling a comprehensive assessment of hydrological stability and change dynamics across the wetland.
Results and Discussion
The results showed that the average water body area of Mighan Wetland decreased from 10.7 km² in the first decade (1995–2004) to 3.9 km² in the second decade (2005–2014), representing a 63% decline. This significant reduction reflects the combined effects of prolonged drought, upstream water diversion, and increased groundwater extraction. However, the wetland area then increased to 19.8 km² in the third decade (2015–2024), largely due to wetter climatic conditions and increased rainfall events. The maximum inundation area was recorded in 2019 with 29.5 km², while the minimum was recorded in 1999 with only 0.1 km², indicating extreme interannual variability. Seasonal analysis indicated that the largest water area occurs in winter (15 km²) and spring (14.6 km²), corresponding to snowmelt and higher precipitation periods, while the smallest occurs in summer (1.5 km²) and autumn (4.4 km²), reflecting high evaporation rates and reduced runoff. Seasonality algorithm results revealed that 25% of the wetland area remains permanently dry, approximately 70% is inundated for only 1–5 months annually, and stable inundation areas (more than 6 months) comprise merely 4.5% of the total area. Transition algorithm results showed that the "No Change" class (21.9 km²), "Permanent" class (24.5 km²), "New Seasonal" class (2 km²), "New Permanent" class (2 km²), and "Seasonal to Permanent" class (6.4 km²) are among the most important change classes, highlighting the dynamic nature of wetland hydrology.
Conclusion
The findings of this study indicate that the hydrological regime of Mighan Wetland has become extremely unstable over the past three decades, and the wetland has transformed into a seasonal system dependent on short-term climatic events rather than a stable, permanent water body. Although the increase in water area in the third decade is significant, it is mainly due to the expansion of seasonal zones and the wetland's response to short-term wet periods, not the return of structural stability to the permanent cores of the wetland. The novelty of this research lies in the integration of long-term monthly analyses with NDWI and Transition and Seasonality algorithms within the Google Earth Engine environment, enabling continuous monitoring, improved water resource management, and restoration planning for Mighan Wetland. Based on the results, determining and providing sustainable environmental water rights, integrated watershed management, controlling excessive groundwater extraction, and improving water use efficiency in the agricultural sector are among the most essential actions needed to preserve the stability of this valuable ecosystem. Without timely intervention, the wetland faces the risk of permanent desiccation, with severe environmental and socio-economic consequences for the region.

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References

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Geography and Environmental Sustainability
Volume 16, Issue 3 - Serial Number 60
September 2026
Pages 111-130

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