scholarly journals Modelling Dynamic Hydrological Connectivity in the Zoigê Area (China) Based on Multi-Temporal Surface Water Observation

2021 ◽  
Vol 14 (1) ◽  
pp. 145
Author(s):  
Chao Gao ◽  
Chang Huang ◽  
Jianbang Wang ◽  
Zhi Li
Keyword(s):  
Surface Water ◽  
Population Increase ◽  
Hydrological Connectivity ◽  
Connectivity Indices ◽  
International Importance ◽  
Multi Temporal ◽  
Main Determinants ◽  
Temporal And Spatial Characteristics ◽  
Ruoergai Wetland ◽  
Global Surface

The sustainability of wetlands is threatened by the past and present land use practices. Hydrological connectivity is one of the most important aspects to consider for wetland rehabilitation planning purposes. Circuit theory and connectivity indices can be used to model and assess hydrological connectivity. The aim of this study was to assess spatiotemporal variation in the hydrological connectivity of the Zoigê area from 2000–2019 using both methods. The study area contains a Ramsar wetland of international importance, namely the Sichuan Ruoergai Wetland National Nature Reserve. We used a global surface water observation product as the major input for both methods, and then analyzed the temporal and spatial characteristics, in terms of important components and patches. We found that the overall connectivity has increased slightly in the last 20 years, while the probability of connection between patches of surface water has increased significantly. Important components and patches represent steppingstone habitat for the dispersal of organisms in the landscape. The main determinants of hydrological connectivity are mostly human oriented, predominantly a decrease in large livestock population size and population increase.

Observing Global Surface Water Flood Dynamics

2013 ◽  
pp. 839-852
Author(s):  
Paul D. Bates ◽  
Jefferey C. Neal ◽  
Douglas Alsdorf ◽  
Guy J.-P. Schumann
Keyword(s):  
Surface Water ◽  
Flood Dynamics ◽  
Global Surface

scholarly journals Construction of the Long-Term Global Surface Water Extent Dataset Based on Water-NDVI Spatio-Temporal Parameter Set

2020 ◽  
Vol 12 (17) ◽  
pp. 2675
Author(s):  
Qianqian Han ◽  
Zhenguo Niu
Keyword(s):  
Surface Water ◽  
Water Area ◽  
Temporal Parameter ◽  
Modis Ndvi ◽  
Water Index ◽  
Normalized Difference Water Index ◽  
Spatio Temporal ◽  
Global Surface ◽  
Global Water

Inland surface water is highly dynamic, seasonally and inter-annually, limiting the representativity of the water coverage information that is usually obtained at any single date. The long-term dynamic water extent products with high spatial and temporal resolution are particularly important to analyze the surface water change but unavailable up to now. In this paper, we construct a global water Normalized Difference Vegetation Index (NDVI) spatio-temporal parameter set based on the Moderate-resolution Imaging Spectroradiometer (MODIS) NDVI. Employing the Google Earth Engine, we construct a new Global Surface Water Extent Dataset (GSWED) with coverage from 2000 to 2018, having an eight-day temporal resolution and a spatial resolution of 250 m. The results show that: (1) the MODIS NDVI-based surface water mapping has better performance compared to other water extraction methods, such as the normalized difference water index, the modified normalized difference water index, and the OTSU (maximal between-cluster variance method). In addition, the water-NDVI spatio-temporal parameter set can be used to update surface water extent datasets after 2018 as soon as the MODIS data are updated. (2) We validated the GSWED using random water samples from the Global Surface Water (GSW) dataset and achieved an overall accuracy of 96% with a kappa coefficient of 0.9. The producer’s accuracy and user’s accuracy were 97% and 90%, respectively. The validated comparisons in four regions (Qinghai Lake, Selin Co Lake, Utah Lake, and Dead Sea) show a good consistency with a correlation value of above 0.9. (3) The maximum global water area reached 2.41 million km2 between 2000 and 2018, and the global water showed a decreasing trend with a significance of P = 0.0898. (4) Analysis of different types of water area change regions (Selin Co Lake, Urmia Lake, Aral Sea, Chiquita Lake, and Dongting Lake) showed that the GSWED can not only identify the seasonal changes of the surface water area and abrupt changes of hydrological events but also reflect the long-term trend of the water changes. In addition, GSWED has better performance in wetland areas and shallow areas. The GSWED can be used for regional studies and global studies of hydrology, biogeochemistry, and climate models.

scholarly journals Changes in Net Global Surface Water Area Since 1985

Proceedings ◽  
2020 ◽  
Vol 30 (1) ◽  
pp. 69
Author(s):  
Zahra Kalantari ◽  
Sonia Borja ◽  
Georgia Destouni
Keyword(s):  
Surface Water ◽  
Ecosystem Functioning ◽  
Water Allocation ◽  
Land Use Changes ◽  
Water Area ◽  
Aral Sea ◽  
Surface Water Resources ◽  
Global Surface ◽  
Spatial And Temporal Characteristics

Spatial and temporal characteristics of surface water resources (e.g., extension, connectivity, seasonality) are key elements in water allocation, climate and hydrological regulation, ecosystem functioning, and the food-energy-water nexus. Changes in surface water area due to losses/gains to land could strongly affect these processes on different scales. Previous findings on changes in the Earth’s surface water area are contradictory. Based on water–land year classification datasets, we estimated global surface water area changes between 1985–2000 and 2001–2015. We found a net global gain in surface water of 100,454 km2, attributable to a large net gain in seasonal water (83,329 km2) and a small net gain in permanent water (17,125 km2). In general, net changes were highly heterogeneous in space, with local exceptions of clear drying and wetting trends, e.g., the Aral Sea and Quill Lakes, respectively. These findings raise multiple questions as to why seasonal water gains dominate and how different intertwined drivers (e.g., hydroclimate and human-induced water–land use changes) shape the distribution of the Earth’s surface water. Understanding these long-term changes is essential to predicting water-related pressures and prioritizing management decisions.

scholarly journals Identifikasi Genangan Banjir di Wilayah DKI Jakarta Menggunakan Citra Satelit Sentinel-1

2021 ◽  
Vol 4 (2) ◽  
pp. 95
Author(s):  
Ana Mardhiyana Alawiyah ◽  
Harintaka Harintaka
Keyword(s):  
Surface Water ◽  
Change Detection ◽  
Ratio Image ◽  
Global Surface ◽  
Optimum Threshold

Provinsi DKI Jakarta merupakan wilayah dengan karakteristik topografi yang berada pada kemiringan lereng relatif landai dan terletak pada dataran rendah. Hal ini menyebabkan wilayah Jakarta menjadi semakin rentan tergenang air dan banjir pada musim hujan. Pada awal tahun 2020, Jakarta mengalami banjir yang diakibatkan oleh hujan lebat yang turun sejak 31 Desember 2019 hingga 1 Januari 2020. Untuk keperluan antisipasi dan mitigasi bencana terkait banjir tersebut diperlukan ketersediaan data tentang luas genangan banjir dan letaknya secara cepat. Salah satu teknologi yang potensial untuk diterapkan adalah menggunakan citra satelit Sentinel-1. Berdasarkan kondisi tersebut, telah dilakukan kajian untuk mendeteksi daerah terdampak genangan banjir dari citra satelit Sentinel-1. Adapun teknik yang digunakan adalah metode change detection dan thresholding. Pada kajian ini digunakan citra Sentinel-1 perekaman tahun 2019 dan 2020, DEMNAS, Global Surface Water dan batas administrasi wilayah DKI Jakarta. Adapun tahapan pelaksanaan kajian mencakup proses change detection dengan ratio image dari dua citra Sentinel-1 GRD sebelum dan saat banjir, perhitungan nilai optimum threshold untuk menentukan banjir dan tidak banjir, masking banjir, dan perhitungan luas genangan. Berdasarkan hasil kajian diperoleh luas total daerah yang terkena banjir sekitar 1.156,84 hektar, sedangkan luas area banjir dari data Pemprov DKI sekitar 12.896,35 hektar. Hasil validasi menggunakan data Pemprov DKI dengan membandingan antara citra Sentinel-1 tahun 2019 dan 2020, diperoleh hasil 61 lokasi atau sekitar 28,96% termasuk ke dalam hasil interpretasi kelas banjir dan terdapat 157 lokasi atau sekitar 71,04% termasuk ke dalam hasil interpretasi kelas tidak banjir.

scholarly journals The Hydrological Viability of Te Harakiki Wetland, Waikanae

2021 ◽  
Author(s):  
◽  
Rebecca Anne Law
Keyword(s):  
Surface Water ◽  
Water Balance ◽  
Urban Area ◽  
Hydrological Regime ◽  
Population Increase ◽  
Pest Species ◽  
Groundwater Abstraction ◽  
Wetland Extent ◽  
Wetland System ◽  
Surface And Groundwater

<p>Wetlands are unique natural resources that play an important role in the hydrological cycle. There is a dynamic link between wetland hydrology and inputs from both surface and groundwater resources. Shallow groundwater abstraction near the Te Harakiki wetland at Waikanae has the potential to impact on the wetland' hydrosystem. To assess the likelihood of this occurring, a detailed analysis of recent changes, the hydrological regime, and the water balance of the Te Harakiki Wetland system was undertaken. The hydrological regime of the wetland system was assessed by various monitoring sites established around Te Harakiki to measure rainfall, soil moisture, surface and groundwater levels. Analysis of (decadal) historical aerial photographs allowed changes in spatial extent of the open water habitat (lagoon) and the urban area of Waikanae Beach. Comparisons were made between wetland extent, population increase and urban area expansion. These data, together with a simple water balance, and historical climatic records, were used to explain the drastic decrease in wetland extent. Climatic factors and goundwater are the major driving forces behind the wetland's hydrologic regime. The surface water outflow from the system is greater than the surface water inflow, but this may be affected by the tides. The surface and groundwater systems in the area are closely linked. They have similar responses to rainfall events. Groundwater abstraction in the area appears to have minimal impact on the water level within the wetland. The exact nature and extent of abstraction around the wetland is unknown. The reduction in flood pulsing as a result of channel modification, and the fragmentation of the area for the construction of the oxidation ponds are the likely explanation. The current restoration efforts in regard to controlling pest species and excluding stock from the wetland have halted the decline in wetland area. The future of the Te Harakiki wetland system is now more positive.</p>

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