Jakarta, Houston, Shanghai, Manila, California, Bangkok, New Orleans and many other cities/regions all face a common problem – they are sinking.
But we won’t get Atlantis 2.0, eigh?
First of all it is crucial to know simply that land is not sinking without a major reason. Before we dive deeper into the topic, I just want to pinpoint, that humanity is connected to the natural environment. Period. Therefore we always have to keep in mind that every action we are taking, small or big, the environment is effected, too. I find this fact essential for this topic of sinking cities, because it shows what happens if we forget exactly about that connection.
Getting specific data about how much land is sinking, is not that easy. I found that the central area in Bangkok sinks 2-3 cm per year. Manila sinks estimated 8 centimeters per year. Jakarta is more or less famous as worst sinking city. There the ground is already like a Swiss cheese, and people are still digging deeper, even if the area sunk 4 meters during the last three decades.
One might comment, well those couple of centimeters won’t make such a difference, will they? The answer is: Every centimeter matters, because many of those sinking cities sink under sea level. Combined with sea level rise due to climate change, the risk of severe flooding increases towards a much higher level. For example 40% of Jakarta is under sea level … and counting.
Here is a tool where you can see and measure the risk of flooding ( I tried several cities and it might work in USA only.) But it is impressive to see. Try New York, New Orleans or Manhattan Beach, LA or Houston (Texas).
So here comes the ultimate questions: Why? Why do cities sink? The main reason is groundwater extraction. 80% of all land subsidence goes back to excessive local groundwater withdrawal. Imagine the water underneath a city gets extracted to a state where it cannot obtain the normal level and therefore sinks much lower. As the British Geological Survey points out:
“When recharge is less than natural discharge plus abstraction, groundwater levels fall.“
As a consequence of groundwater depletion, soil above might compact and collapse ergo the land sinks. Have you heard of sinkholes? Those holes are a likely consequence of groundwater depletion and land subsidence. California is a current example where, because of a severe drought, water pumping increases together with land subsidence. A recent NASA article stated that in only four months of 2014 some Californian areas sank about 20 centimeters. Wow!
However, many of those affected regions are coastal Mega cities, which means agglomerations of at least 10 Million inhabitants. Mega Cities where construction sites and big building are the course of things, increase the land subsidence through their weight of infrastructure and buildings.
So, what do we got?
- excessive groundwater depletion
- increasing land subsidence
- rising sea levels due to climate change
- many coastal Mega Cities with Millions of people
Wait, is there a solution?
We have to tackle excessive water pumping and include the reality of groundwater-related subsidence into planning processes all over the world. Ignorance is no option. I think that local institutions have to gather in order to share information, experience and solutions. Finding measures that work effectively towards water saving, ground stability and data collection, is key. Building great barriers as flood protection is one thing, but working together towards a save operating space within the capabilities of natural environment is another.