Delta 2011

23 March 2011 | Article

This meeting, the third in a series, was sponsored by IWMI, FAO, WorldFish Center, IRRI, SEI, and MONRE’s Institute of Meteorology, Hydrology, and Environment (IMHEN). Jim Syvitski of the University of Colorado gave the keynote speech. He was the lead author of the sinking deltas paper that was published in Nature and has attracted a lot of attention. Deltas sink naturally unless they are replenished with sediment, which they are under normal conditions. The formula describing this relationship is: R = A ± E - Cn - Ca - M
 

where R is relative sea level rise, A is aggradation from sediment delivered and retained on the delta, E is eustatic (global) sea level change, Cn is natural compaction, Ca is human induced accelerated compaction, and M is sinking as a result of the weight of sediment.

Under natural conditions, deltas rise at an average rate of 5.5 cm/year: +5.5 = 10 - 0.5 - 2 - 0 - 2. But under contemporary conditions, some deltas are sinking on the order of 15 cm/year: -15 = 5 - 3 - 2 - 13 - 2. The main causes of this sinking are reduced aggradation as a result of dams that trap sediment and dykes that raise the level of the river bed but stop the lateral flow of sediment; and accelerated compaction because of groundwater and natural gas pumping.

What’s striking about these numbers is that the impacts of A and Cn are much greater than E. In other words, global warming (which Vietnam has no control over) makes a small contribution to relative sea level rise compared to reduced aggradation and groundwater pumping (which Vietnam does exert some control over). According to the Nature paper, the Mekong Delta is one of the “Deltas in peril: reduction in aggradation plus accelerated compaction overwhelming rates of global sea-level rise.” (This is why the paper upset so many climate change scientists.)

Jim expects that the rapid sinking of densely populated, economically critical deltas will result in catastrophe sooner rather than later with the Pearl River Delta in southern China being in the most precarious position. When asked about the possibility of building defenses against sea level rise, he observed that you can’t build perfect systems and that we need to reconsider the blind pursuit of certainties; consider what happened to New Orleans where the U.S. Army Corps of Engineers spent billions of dollars on coastal defenses.

Jim pointed out that a constraint on Vietnam’s ability to adapt smartly is the lack of a data sharing policy or culture (the same is true for China). (The Nature paper was based almost entirely on publicly available data from the USGS and other sources.) For example, one of the presenters talked about the dramatic drop in the level of Red River in Hanoi since 2000 and the impact this has had on rice production in the 30 polders that make up the Red River Delta. But when asked about what factors (e.g., reservoir impoundment, irrigation withdrawal) might have contributed to this decline he couldn’t say because he didn’t have access to upstream discharge data.

There were a series of presentations on new rice varieties to withstand greater temperatures and longer periods of inundation. It is primarily the intensification of rice that lies behind the huge increase in rice production in the Mekong Delta: from 16M tons in 1985, to 35M tons in 2003, to 40M tons in 2008, to a projected 42M tons in 2020. Rice yields in the delta average 5 tons/hectare/year. I asked if it makes sense to devote even more effort to producing even more rice from a system that is already struggling to cope with the negative social and environmental impacts. I was reminded of the saying that if you’re a hammer (or rice researcher) everything looks like a nail (or improved rice strain).

After the presentations, the participants split up into two groups. I attended the group discussing coastal climate change adaptation. Given the breadth of the subject, we decided to focus on strategic issues (with particular reference to the Mekong Delta). We came up with the following principles:

1. Focus on people not places: invest in education, health, etc. to give people the best life opportunities (increase resilience).

2. De-engineer/re-wild the hydrology: break the dykes, reconnect the river and the floodplains, etc. to improve water quality and reduce probability of catastrophic floods (reduce exposure).

3. Take into account upstream-downstream linkages: manage the river basin as a hydrological system, address the impact of dams (reduce exposure).

4. Understand the political economy: there’s a lot of money in dykes and strong incentives to maintain the status quo; we need to build alliances to advocate for change (reduce exposure).

5. Establish conflict resolution systems: climate change will result in winners and losers; some land will be submerged and win-win solutions may not be possible (reduce exposure).

6. Strengthen data and information systems: climate change is not a tsunami; there is no need to rush into expensive (and risky) solutions, but smart adaptation needs access to good data.