## 4 Discussion  
This paper has demonstrated that there is a broad and growing scientific interest in investigating the effects of natural and man-induced disaster risks in coastal and river delta regions. Worldwide coastal regions and river deltas are vulnerable environments experiencing many pressures and are subject to numerous natural and human-made threats, some of which are triggered by global climate changes. EO technologies have proven valuable tools for local authorities and national governments to design, maintain, and manage effective disaster plans and obtain consistent and frequently updated information about environmental conditions and their temporal variations. Additionally, we remark that the growing availability of EO datasets has led in recent years to a significant shift in the perceptivity of RS technologies and the role of GIS [489; 490; 491] for the planning and organization of suitable disaster management cycles. EO instruments can contribute significantly to management of major technological and natural disasters and help during humanitarian crises. The increased scientific interest in the design and maintenance of effective disaster management plans in coastal communities is also demonstrated by the increased number of publications addressing this research theme in the literature. The paper has addressed the different conditions of risk in coastal and river delta environments.  
Coastal flood risk and adaptation are a worldwide concern. Significant inundation is increasingly common in many delta regions of Asia and Europe, including China, the Netherlands, Vietnam, and Egypt, subject to relatively high flood exposure. Global climate change can significantly increase the population's exposure to coastal flooding risk. Satellite RS is a valuable tool for detecting and monitoring flood phenomena, allowing for the rapid differentiation between inundated and non-inundated areas. Extreme rainfall can also cause flooding, enormous economic losses, and civilian casualties. Another generator of flooding in coastal regions is storm surges associated with tropical cyclones. The combined effects of high winds and water levels are responsible for considerable damage to property and casualties in densely populated river delta regions worldwide.  
Coastal flood risk is due to total sea levels, not just mean sea level, and the effects of tidal evolution can make the influences of MSL rise much more severe. The tidal anomaly correlation method (TACs) described above demonstrate that changes in tidal evolution that may accompany sea level rise can amplify the magnitude of total water levels, which can, in turn, strengthen all the detrimental risks to coastal regions and deltas described in this review. The TACs and \(\delta\)-HATs observed from worldwide surveys show that nearly half of all locations are significant. However, large-magnitude tidal responses (which can either be positive or negative) are predominantly found in coastal regions, mainly in delta and estuarine regions.  
Local ground subsidence can significantly increase the exposure to coastal flooding risk. Ground subsidence has become a significant global problem for world coasts. River delta regions are considerably more susceptible to subsidence than other coastal areas, partially due to the increased urbanization rates. The causes of ground subsidence in different deltas are numerous. Most major river deltas are sinking much faster than historical sea level rise rates. However, the mechanisms behind the subsidence are still not well understood, and reliable subsidence data for entire regions are scarce. Long-term and large-scale subsidence measurements for the most important delta regions are still lacking.  
Accelerated coastal erosion is also a common issue nowadays on the world's coasts. Over half of the world's delta regions are in overall erosion due to reduced river sediment loads. Intensive human activities have dramatically reduced coastal wetland areas. Accelerated sea level rise may also exacerbate saltwater intrusion.