Such changes have an insidious consequence: Even as they entice larger populations to live on deltas by providing jobs and the semblance of environmental stability, they also increase long-term vulnerability to storms and floods by exacerbating the land’s sinking. Meanwhile, global warming makes the whole dynamic worse because it introduces a huge arrow pointing in only one direction — sea level is going up, and up, and up.
“We characterized the rate of change of risk in delta systems due to combined land subsidence, sea level rise, geophysical setting, and socio-economic capacity to protect themselves,” explains lead study author Zachary Tessler of the City University, who conducted the research with scholars from three additional universities.
When it comes to human perturbations of the system, river deltas range from the pristine Yukon in Alaska, which is relatively lowly populated and has been little changed by humans in a way that would make it more vulnerable (much of it is a wildlife refuge), to the Ganges-Brahmaputra of Bangladesh and India — home to over 100 million people, where human activities and sea level rise are pushing the risks forward dramatically.
Indeed, Bangladesh has historically been the home to the deadliest tropical cyclone (or hurricane) disasters known to history, including the 1970 Bhola cyclone, which struck this very delta, the Ganges-Brahmaputra, and caused 300,000 to 500,000 deaths.
But there’s another key factor involved in determining a given delta’s risks — a society’s wealth, which translates into its ability to protect itself. Thus, while the Mississippi River is heavily managed and has been changed nearly beyond recognition by humans, the delta also has a high level of artificially imposed resilience — with vast levees along much of the river to prevent flooding, not to mention New Orleans’ huge new hurricane protections.
A similar story can be told about the Rhine, heavily altered by humans but also the home to arguably the world’s most impressive flood protections, constructed by the Dutch.