Remote Sensing Monitoring of Natural Disasters and Human Impacts in Asian Rivers

Dear Colleagues,

Asia contains several of the world’s largest rivers, such as the Pearl, Mekong, Yangtze, Indus, Ganges, Amu Darya, Salween, Red, Chao Phraya and Rajang Rivers, and smaller river basins that are among the most productive in water and sediment yield of the whole planet. For example, the South China Sea is the largest sink of sediments among the marginal seas worldwide and is estimated to trap more than 700 million tons of fluvial sediments each year. The hydro-sedimentologic regimes of the fluvial basins in Asia are largely vulnerable to tropical cyclones, recurrent floods and frequent landslides and to episodic geological events such as earthquakes and volcanic eruptions. For that reason, Asian rivers are considered the riskiest and most vulnerable area to natural hazards and disasters in the world. This area currently concentrates many of the fastest growing and important economic activities in countries (e.g., India, China and Association of Southeast Asian Nations) and also contains some of the most important geopolitical hotspots of international territorial conflicts. Because of the explosive growth in demography, development, and economy experienced by such Asian countries, the impacts on the fluvial systems have been suffering from the population explosion and the resultant extreme human impacts, which are the highest ever recorded in recent history. As a consequence, human-induced changes in the hydro-geomorphologic regimes, sediment inputs, and floodplain storage capacity have triggered substantial impacts on deltas, and coastal and marine environments that depend on the organic and inorganic fluxes contributed by fluvial systems.

Since most of the deltas around the Indo-West Pacific are “river-dominated deltas,” their complexity, mass balance, and land areas depend on the balance between river supply, coastal removal of sediment, and crustal subsidence. For example, reductions of sediment supply reduce the area of the deltas. This is considered one of the most significant geological changes in the world affecting habitability. It has been recently reported that Asian deltas are facing the most severe challenges on the planet in terms of vulnerability to population pressures, combined with relative sea-level rise and poor delta governance.

For example, in southern China, explosive urbanization and land-use change have dramatically affected the sediment fluxes to the South China Sea. The sediment fluxes from 10 major Chinese rivers to the Pacific Ocean had decreased from about 2100 Mt per year to only 575 Mt per year during the period 1955-2007. The Pearl River Delta, the most densely urbanized place in the world, is currently no longer experiencing aggradation, mainly due to the impoundment of sediment in reservoirs and to river bed sediment dredging from rivers and coasts, which reduced sediment fluxes to the South China Sea by 67% across the 20^th century. Massive sand extraction from the Pearl River and in the coastal zones to build skyscrapers and to construct thousands of kilometers of river dikes, hydroelectric dams, and artificial islands in the South China Sea not only modified river hydraulics but are also depleting sediment storages in the basin. Indus, Mekong, Chao Phraya and Red Rivers in Vietnam also experienced a dramatic decrease in sediment fluxes recently due to reservoir trapping. Although reservoir trapping, farming, and rapid urbanization have significantly elevated sediment yields in Taiwan. Despite the significant impact of the rivers in Malaysian Borneo on the annual sediment budget of the South China Sea, the human impacts on their fluvial systems have yet been studied.

Remote sensing can be considered one of the most efficient and relevant means to regularly assess the spatiotemporal dynamics of various riverine environments, including channels, floodplains, lakes, reservoirs, and wetlands over a large scale, due to environmental impacts. Remote sensing technology has widely shown that it can aid in addressing some of the critical drivers and consequences of the fluvial environmental changes at multiple spatiotemporal scales. This Special Issue on “Natural disasters and human impacts in Asian rivers” is dedicated to contributing to the fast-growing current trend of remote sensing applications to assess environmental impacts in Asian rivers. We invite studies on recent advances in the study of rivers in Asia solidly based on any types (active or passive) and platforms of remote sensing from multidisciplinary points of view, including water resources issues, fluxes, or the management of large rivers, as well as review articles synthesizing the history and development of remote sensing with a focus on any aspects of environmental impacts concerned with rivers in Asia. We particularly encourage the submission of remote sensing studies analyzing the vulnerability and responses of fluvial systems suffering from unprecedentedly high human impacts in Asia, the highest ever recorded in recent Earth history, such as dam construction, deforestation, or sand mining activities.

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• Asian rivers
• Human impacts
• Natural disasters
• Hydrological regimes
• Environmental impacts