Adaptation and mitigation are the two crucial actions needed to navigate the climate crisis.
Both are urgent priorities for investment.
But what if an investment in one undermines the other – if an investment in mitigation reduced the effectiveness of adaptation or, conversely, an investment in adaptation increased emissions?
Right now, policymakers along the Mekong River face a choice that illustrates this either-or tradeoff. In the past two decades, nearly 170 large hydropower dams have been built on the river and its tributaries. Dozens more are under construction or proposed. The region needs to expand electricity generation and, to meet climate targets, must also do so through low-carbon generation technologies.
Hydropower remains the world’s largest source of low-carbon and renewable energy (despite massive recent growth globally in wind and solar). But achieving climate mitigation objectives through hydropower carries distinct risks for climate adaptation in the Mekong basin – particularly for the Mekong Delta, one of the most climate-vulnerable regions in the world.
And while there are other competitive substitutes for climate mitigation besides Mekong hydropower expansion, there are no such substitutes in the basin for the natural resources needed for climate adaptation—resources that hydropower expansion would degrade.
In Deltas, Sand Underpins Climate Resilience
A key to understanding this mitigation/adaptation tradeoff—and how to navigate it—is understanding the role that the flow of sediment, such as sand, plays in a river delta’s health…and how dams can choke off that flow.
MORE FROM FORBES ADVISORWith densely populated cities and vital agriculture located just a few vertical feet above the ocean, the Mekong Delta is highly threatened by coastal erosion, land subsidence, and the climate change-driven rise in sea level. And there is much to be threatened: the Delta is home to nearly 20 million people and supports a quarter of Vietnam’s gross domestic product (GDP). The Delta also holds phenomenally productive agriculture land, producing more than half of Vietnam’s staple crops and 90% of its rice exports — significant for global food security given the country is the third largest exporter of rice in the world and exports from the delta represent up to 10% of rice traded globally.
But this densely populated, highly productive landscape is also a landscape under siege. Saltwater is intruding deeper into the Delta, stressing crops, and, on average, land the size of a football field erodes into the ocean every day.
Investments in adaptation are pouring into the Delta aimed at reducing this loss of land. But these projects—levees and seawalls—are focused on temporary relief from symptoms, while the underlying illness goes untreated and advances each year. That underlying illness is the loss of sediment from the Mekong River.
The Mekong, and other rivers, are not just channels of water. They are also conveyor belts carrying sediment, such as sand, from the mountains to the sea (that sediment is the reason most big rivers look brown). When rivers reach the sea, they deposit much of their sediment there, creating a delta. While rivers create deltas, other forces—erosion, compaction and, now, sea-level rise—are continually working to tear them down. A delta that continues to receive sand and other sediment can stay in balance with these forces. Without continued replenishment, deltas begin to shrink and sink.
A big challenge is that deltas aren’t the only place a river can drop its sediment. When a river flows into a reservoir behind a dam, its sediment deposits there, preventing it from moving further downstream.
Prior to large-scale changes in how people managed the river, the Mekong delivered to its delta between 140 and 160 million metric tons of sediment each year. Approximately 70% of that volume is now trapped in the reservoirs behind dams (the mining of sand from rivers and the delta exacerbates this deficit).
Scientists forecast that with current trajectories, more than 90% of the delta could be underwater by 2100, a chilling projection given the delta’s outsized contribution to regional economies and global food security.
Last year, I reviewed a blueprint for saving the Mekong delta from drowning. Implementing that blueprint’s strategies could mean that rather than 90% loss of the delta by 2100, only 10% would become submerged (some loss is inevitable due to sea level rise).
So, the Mekong delta does indeed have hope for adapting to climate change—but only if it continues to receive sediment. Without sufficient sediment, adding seawalls and rip-rip to the delta is like adding more armor to a sinking battleship.
Collapse of a house in the Mekong Delta due to erosion (near Can Tho, Vietnam). The loss of sand and . [+] other sediment in the Mekong River is driving this erosion in Vietnam's "rice bowl."(Photo by NHAC NGUYEN/AFP via Getty Images)
AFP via Getty Images
Why Let Dams Accelerate the Loss of the Mekong Delta When Wind & Solar Are This Cheap?
Meanwhile, hydropower dams are still being constructed on the mainstream Mekong (at Luang Prabang, Laos) and on one of its few undammed tributaries that still provide sediment, the Sekong River in Laos. Each of these, along with other proposed dams, moves the Delta closer to an irreversible and watery tipping point.
There is no substitute for Mekong sediment as an adaptation resource. But is there a substitute for the low-carbon electricity that will be produced by the dams that will foreclose adaptation for the delta?
Yes, and they are abundant and affordable. Wind and solar have declined dramatically in cost and are now the cheapest sources of electricity generation on the planet. Combined with improvements in other options for managing and interconnecting grids, analyses now show that the region can meet its needs for low-carbon electricity without building the dams that would trap this sediment. A report released last month, funded by the United States Agency for International Development (and developed by an energy consulting firm, IES, and WWF, my employer), confirmed that countries in the region can fully meet their projected energy needs with low-cost and low-carbon power from interconnected grids dominated by wind and solar—without building the dams that would undermine adaptation for the delta.
Southeast Asia can achieve its climate mitigation goals in ways consistent with a resilient delta or in ways that lead to its disappearance. The window for choosing the first option is rapidly closing.
In the next blog post, I’ll review a second resource jeopardized by Mekong hydropower dams: the most productive freshwater fishery in the world, an incredible food source that, if lost, would require substitute sources of protein. Those substitutions would require dramatic expansions in regional land dedicated to crops and livestock and a corresponding increase in emissions that would undermine even the dams’ mitigation benefits.