Abstract
Net subsidence of most major deltas in the world and related vulnerability are thought to be increasing, and this is often linked causally to human activities. This paper examines this causality against a range of co-varying factors. We do so with a principal component analysis of co-variability of a range of geophysical and socio-economical indicators of 33 deltas mainly derived from the DIVA tool. Land potentially lost and people at risk of flooding are our indicators of vulnerability. The former correlated positively with maximum surge height and negatively with net sea level rise. The latter correlated positively with delta area, average river discharge, and maximum surge and negatively with net uplift (or subsidence). Thus, variation in societal vulnerability across deltas depends on short-term, instantaneous risks linked to lowland area, river discharge and storm surges rather than on longer-term, slow, net sea level rise. Delta management should focus on precautionary spatial planning, and on maintenance or restoration of historical sediment delivery and accretion rates. Especially larger deltas with high population densities combine a high risk with the potential to accommodate flood water and mitigate flooding risks. The deltas of the Yangtze-Kiang and Ganges-Brahmaputra share these characteristics. Here space should allow engineering of flood retention, sedimentation and diversion channels as well as refuges and safe economic hotspots. At the other end, in deltas with a high population density and limited space, like the Chao Praya, means for adaptation must be sought outside the delta proper. In deltas with low population densities, such as the Lena, Yukon or Fly, natural delta dynamics can prevail.
Highlights
Most modern deltas will not keep up with current and projected sea level rise, as Ericson et al (2006) and Syvitski et al (2009) have demonstrated
We extracted from DIVA those coastal segments that have a delta
A scenario run in DIVA generates stepwise annual worldwide climate, demographic and economic output for a user-defined period up to 2100, disaggregated to coastline segments from regional and national estimates (Hinkel and Klein 2009)
Summary
Most modern deltas will not keep up with current and projected sea level rise, as Ericson et al (2006) and Syvitski et al (2009) have demonstrated. Delta area, subsidence and the maximum storm surge height co-varied distinctly with the first principal component, and in a direction orthogonal to net sea level rise, Table 1 Variables extracted from the DIVA tool for 33 deltas* that have been used in the PCA. GDPpc dike height maximum surge height land below 1/1000 surge height in 2000, for A2 and B1 people potentially flooded people at risk in 2100, for A2 and B1 relative sea level rise, for A2 and B1
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