Why Deltas?
Understanding the complex human-environment tradeoffs taking place within the densely populated and dynamic spaces of river deltas embodies one of the greatest challenges to sustainability science.
The fertile soils, vibrant ecosystems and abundant waterways of river deltas have attracted humans and supported social, cultural and economic development for millennia. Occupying just 5% of global land area, deltas house over 7% of the world’s population, including rapidly developing, densely populated Asian megacities. Consequently, deltas are more than coastal landforms providing rich environmental resources to support their large populations. They also contain intricate socio-ecological systems facing the challenge of balancing resource demands with conservation, political stability, food and freshwater security, social equality, and sustainable development.
From a biophysical point of view, 20th century societies changed the nature of how deltas function. Dams and reservoirs constructed to provide communities in river basins with water for irrigation and energy have reduced net downstream sediment discharge to the coastal ocean by 15%. With less sediment carried to shorelines, they retreat and become more vulnerable to wave erosion and coastal flooding. Upstream water diversion projects have also reduced the regular supply of freshwater to downstream reaches of deltas, causing river distributaries feeding coastal areas to become dry except during flood events. On the downstream end, embankments designed to reduce the risk of devastating river floods alter the sediment balance on deltaic surfaces by restricting the natural migration of channels that replenish carbon-rich soil needed to naturally sustain crop productivity. In the absence of regularly replenished surface sediment, deltas are subsiding; the extraction of sub-surface fluids for energy and consumption further enhances subsidence. Because of their low-lying elevations and large number of inhabitants and infrastructure, deltas are also ground zero for climate change impacts, particularly from sea-level rise and storm surges.
Deltas are therefore true sentinels of global change: sensitive to climate and anthropogenic modifications in their river basins, and shaped by river, coastal and human processes on their surfaces.
Feedbacks between human activity and physical processes resonate at all scales. Within the boundaries of deltas, rural farmers are facing particularly tough choices at both the individual and population scales: adapt their farming practices to cope with increasing coastal salinity or loss of land at the risk of costly upfront investment, cultural upheaval, and unintended ecological consequences, or abandoning their farms and migrating to urban centers or across geopolitical boundaries. As cities in deltas grow and demands for space and resources intensify, these decisions have implications for both urban and rural socio-ecological stability.
Understanding the complex human-environment tradeoffs taking place within the densely populated and dynamic spaces of river deltas embodies one of the greatest challenges to sustainability science.
The fertile soils, vibrant ecosystems and abundant waterways of river deltas have attracted humans and supported social, cultural and economic development for millennia. Occupying just 5% of global land area, deltas house over 7% of the world’s population, including rapidly developing, densely populated Asian megacities. Consequently, deltas are more than coastal landforms providing rich environmental resources to support their large populations. They also contain intricate socio-ecological systems facing the challenge of balancing resource demands with conservation, political stability, food and freshwater security, social equality, and sustainable development.
From a biophysical point of view, 20th century societies changed the nature of how deltas function. Dams and reservoirs constructed to provide communities in river basins with water for irrigation and energy have reduced net downstream sediment discharge to the coastal ocean by 15%. With less sediment carried to shorelines, they retreat and become more vulnerable to wave erosion and coastal flooding. Upstream water diversion projects have also reduced the regular supply of freshwater to downstream reaches of deltas, causing river distributaries feeding coastal areas to become dry except during flood events. On the downstream end, embankments designed to reduce the risk of devastating river floods alter the sediment balance on deltaic surfaces by restricting the natural migration of channels that replenish carbon-rich soil needed to naturally sustain crop productivity. In the absence of regularly replenished surface sediment, deltas are subsiding; the extraction of sub-surface fluids for energy and consumption further enhances subsidence. Because of their low-lying elevations and large number of inhabitants and infrastructure, deltas are also ground zero for climate change impacts, particularly from sea-level rise and storm surges.
Deltas are therefore true sentinels of global change: sensitive to climate and anthropogenic modifications in their river basins, and shaped by river, coastal and human processes on their surfaces.
Feedbacks between human activity and physical processes resonate at all scales. Within the boundaries of deltas, rural farmers are facing particularly tough choices at both the individual and population scales: adapt their farming practices to cope with increasing coastal salinity or loss of land at the risk of costly upfront investment, cultural upheaval, and unintended ecological consequences, or abandoning their farms and migrating to urban centers or across geopolitical boundaries. As cities in deltas grow and demands for space and resources intensify, these decisions have implications for both urban and rural socio-ecological stability.
