Was watching newspaper reviews on BBC after 10pm news. Australian bushfires were the top item, as usual. They also covered – with much handwringing about balanced reporting – the New Year floods in Jakarta which have killed 30 people, more than the Australian fires. One of the reviewers (a self-confessed nerd) was the comments editor from The Times. She had the temerity to suggest that we don’t spend enough time comparing the severity of events before deciding if they are out of the ordinary. The BBC anchor quickly pointed out that they had been covering this and that she had read that Jakarta would be under water in 30 years, implying that it was the fault of climate change.
She mustn’t be very acquainted with their own reporting. The Indonesian president himself “blamed delays in flood control infrastructure projects for the severity of the damage”. Jakarta floods every year at this time. And the reason – as mentioned on here before – is that Jakarta is sinking due to groundwater extraction. Since 1970 the land level has sunk by four times the IPCC’s most pessimistic predictions for sea level rise by 2100. That’s why they’re planning to move Indonesia’s capital city.
I remember asking someone once why the sea and the land are so close in level where they meet. They looked at me as if I had two heads. But I think it’s a reasonable question. The continents rise out of the ocean floor quite sharply. And there are places in the world where the sea meets 600 ft. cliffs. But it’s usually places where discontinuities allow harder rock to be left behind by weathering. It’s more common that, over geologic time, sea and wind erosion cause the land to slump into scree slopes and talus piles. The alluvium builds up in nearshore sand bars and banks. Meanwhile, the reduced hydraulic gradient causes rivers to meander and create deltas which then silt up into large flatlands.
The end result is that there are many flat coastlines, with features that make them particularly attractive for human settlement. But they are fragile places that can easily be damaged by human activity, most particularly groundwater extraction, damming, culverting and dredging. And in the longer term natural sea-level changes inevitably alter the land-sea boundary. Subsidence is common to most of the world’s biggest and most populous deltas – the Nile, Ganges-Brahmaputra, Yellow River, and Mississippi, along with two thirds of the worlds 30 biggest mega deltas.