这里是全球“最危险首都”：下沉最快的城市

雅加达是印度尼西亚的首都，也是印度尼西亚最大的城市，有1000万人居住。这座城市坐落在湿地之上，有13条河流从这里流经，爪哇海的海浪拍打着它，这样的地理位置导致这里洪水频发，再加上近年来，由于全球气候变暖，海平面上升，洪涝灾害越来越严重，雅加达成了世界上下沉速度最快的城市。

据英国广播公司报道，研究人员称，如果再不采取措施，到2050年，这个城市的部分地区会被完全淹没。万隆技术学院的研究员赫里·安德烈亚斯（Heri Andreas）称，这并不是耸人听闻，研究模型显示，到2050年北雅加达地区95%的区域都会被淹没。

雅加达正以平均每年1到15厘米的速度在下沉，现在几乎有一半的区域位于海平面以下，在雅加达西部，地面平均每年下降15厘米，东部10厘米，中部2厘米，南部1厘米，在北部地区尤为严重，在这10年内，北雅加达地区已经下沉了2.5米，平均每年下沉25厘米，这样的下沉速度是其他全球沿海特大城市平均水平的两倍多。

北雅加达在历史上就是一个港口城市，直至今日仍是印度尼西亚最繁忙的海港之一，有180万人生活在这里。在麻拉巴鲁区（Muara Baru），有一座废弃的办公楼，这里曾经是一个渔业公司，由于周围的地势高，水无处可去，所以低楼层的地面上都是积水。另外，住在这里的居民里德万（Ridwan）称随着地下水位的下降，路面也是起伏不平的，地面也在下沉。

福尔图娜·索菲亚（Fortuna Sophia）住在海边的豪华别墅中，她说没有什么明显的房子下沉的感觉，但是每六个月，墙上和柱子上就会出现新的裂缝，维修人员称，裂缝是由地面移动导致的。她已经在这里住了4年了，好几次，海水会流进来，家里的游泳池会都被海水灌满，要把家具什么的搬上楼。有渔民说潮水每年都会涨5厘米左右，如今海边都建起了堤坝。

但对这里的居民来说这根本不是什么大事，雅加达的居民们每天都要应对各种各样的基础设施问题，这也是城市下降速度如此之快的原因之一。专家证实，政府只能满足40%的居民用水需求，所以在大部分地区，自来水的质量都不可靠，城市居民都选择使用地下水，而且这里的监管制度十分松懈，小到居民大到大型超市运营商都可以开采地下水，这导致地下水位迅速下降，地面就像坐在一个放空的气球上，沉降是不可避免的。

今年5月，雅加达政府抽查了雅加达中部商铺林立的坦尼路（Jalan Thamrin）。结果发现56栋楼有自己的地下水泵，33栋楼在非法取水。雅加达州长阿尼斯·巴斯维丹（Anies Baswedan）说，每个人都应该有一个许可证，这样政府才能够衡量地下水的抽取程度，那些没有许可证的会被吊销相关证书。

另外，为应对这一问题，印度尼西亚目前正在实施“大嘉鲁达”（Great Garuda）计划，这项大工程耗资高达400亿美元，要在雅加达湾外建一座32公里长的防浪墙，并修建17个人工岛屿，这项工程还得到了荷兰和韩国政府的支持。

这样的防浪墙就像修了一个人工湖，水位降低了，城市里的河水也可以排出，将有助于解决雨季河水泛滥的问题，但有三个荷兰非营利组织在2017发布了一份报告，对防浪墙和人工岛屿能否解决雅加达的地面沉降问题提出了质疑。他们认为这只是个临时措施，只能阻止20到30年的地面沉降问题，要避免重大沉降问题，必须停止抽取地下水，使用其他替代水源。

但巴斯维丹提出了一种开挖生态洞（biopori）的合法的取水方法，直径100厘米深10厘米的洞，这样地面上的水能流到地下。有批评人士说，这个方案只会在浅层水上有作用，而在雅加达，水通常都是从地下几百米处抽出来的，所以根本于事无补。50年前，东京也曾面临过严重的地面沉降问题，当时政府采取了一种人工补给深层水的方法，但造价非常昂贵，此外，当时政府还限制地下水开采，规定企业只能使用再生水，才遏止了地面沉降问题。但在印度尼西亚，寻找替代水源是件很困难的事，各项设施不够完善，可能需要近10年的时间去清理河流、堤坝和湖泊，才能够投入使用。

Image caption 北雅加达正在以大约每年25厘米的速度下沉。

Image captionHeri Andreas points at a dyke built to prevent sea water from flooding houses when it rains

It's already happening - North Jakarta has sunk 2.5m in 10 years and is continuing to sink by as much as 25cm a year in some parts, which is more than double the global average for coastal megacities.

Jakarta is sinking by an average of 1-15cm a year and almost half the city now sits below sea level.

The impact is immediately apparent in North Jakarta.

In the district of Muara Baru, an entire office building lies abandoned. It once housed a fishing company but the first-floor veranda is the only functional part left.

这座废弃建筑的一层已有部分沉于地面以下。

The submerged ground floor is full of stagnant floodwater. The land around it is higher so the water has nowhere to go. Buildings that are so deeply sunk are rarely abandoned like this, because most of the time the owners will try to fix, rebuild and find short-term remedies for the issue. But what they can't do is stop the soil sucking this part of the city down.

建筑的一层地上遍是积水。

An open air fish market is just a five-minute drive away.

"The walkways are like waves, curving up and down, people can trip and fall," says Ridwan, a Muara Baru resident who often visits the fish market. As the water levels underground are being depleted, the very ground market-goers walk on is sinking and shifting, creating an uneven and unstable surface.

"Year after year, the ground has just kept sinking," he said, just one of many inhabitants of this quarter alarmed at what is happening to the neighbourhood.

鱼市地基的巨大裂缝见证了这个地区的严重地面下沉。

North Jakarta has historically been a port city and even today it houses one of Indonesia's busiest sea ports, Tanjung Priok. Its strategic location where the Ciliwung river flows into the Java Sea was one of the reasons why Dutch colonists chose to make it their bustling hub in the 17th Century.

Today 1.8 million people live in the municipality, a curious mixture of fading port businesses, poor coastal communities and a substantial population of wealthy Chinese Indonesians.

Fortuna Sophia lives in a luxurious villa with a sea view. The sinking of her home is not immediately visible but she says cracks appear in the walls and pillars every six months.

索菲亚说，每次下雨，她家的泳池都会被淹没。

"We just have to keep fixing it," she says, standing beside her swimming pool with her private dock just a few metres away. "The maintenance men say the cracks are caused by the shifting of the ground."

She's lived here for four years but it has already flooded several times: "The seawater flows in and covers the swimming pool entirely. We have to move all our furniture up to the first floor."

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But the impact on the small homes right by the sea is magnified. Residents who once had a sea view now see only a dull grey dyke, built and rebuilt in a valiant attempt to keep seawater out.

"Every year the tide gets about 5cm higher," Mahardi, a fisherman, said.

None of this has deterred the property developers. More and more luxury apartments dot the North Jakarta skyline regardless of the risks. The head of the advisory council for Indonesia's Association of Housing Development, Eddy Ganefo, says he has urged the government to halt further development here. But, he says, "so long as we can sell apartments, development will continue".

The rest of Jakarta is also sinking, albeit at a slower rate. In West Jakarta, the ground is sinking by as much as 15cm annually, by 10cm annually in the east, 2cm in Central Jakarta and just 1cm in South Jakarta.

Coastal cities across the world are affected because of rising sea levels caused by climate change. Increased sea levels occur because of thermal expansion - the water expanding because of extra heat - and the melting of polar ice. The speed at which Jakarta is sinking is alarming experts.

It may seem surprising but there are few complaints from Jakartans because for residents here the subsidence is just one among a myriad of infrastructure challenges they have to deal with daily.

And that is part of the story of why this is happening.

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The dramatic rate at which Jakarta is sinking is partly down to the excessive extraction of groundwater for use as drinking water, for bathing and other everyday purposes by city dwellers. Piped water isn't reliable or available in most areas so people have no choice but to resort to pumping water from the aquifers deep underground.

But when groundwater is pumped out, the land above it sinks as if it is sitting on a deflating balloon - and this leads to land subsidence.

Media captionWhy Indonesia's capital Jakarta is sinking

The situation is exacerbated by lax regulation allowing just about anyone, from individual homeowners to massive shopping mall operators, to carry out their own groundwater extractions.

"Everyone has a right, from residents to industries, to use groundwater so long as this is regulated," says Heri Andreas. The problem is that they take more than what is allowed.

People say they have no choice when the authorities are unable to meet their water needs and experts confirm that water management authorities can only meet 40% of Jakarta's demand for water.

雅加达绝大部分居民的生活依赖地下水。

A landlord in central Jakarta, known only as Hendri, runs a dormitory-like block called a kos-kosan and has been pumping his own groundwater for 10 years to supply tenants. He is one of many on his street who do this.

"It's better to use our own groundwater rather than relying on the authorities. A kos-kosan like this needs a lot of water."

The local government has only recently admitted it has a problem with illegal groundwater extraction.

In May, the Jakarta city authority inspected 80 buildings in Central Jakarta's Jalan Thamrin, a road lined with skyscrapers, shopping malls and hotels. It found that 56 buildings had their own groundwater pump and 33 were extracting water illegally.

Jakarta's Governor Anies Baswedan says everyone should have a licence, which will enable the authorities to measure how much groundwater is being extracted. Those without a licence will have their building-worthiness certificate revoked, as would other businesses in the same building.

当局在谭林路一次检查中发现，雅加达市中心许多机构在未经允许的情况下开采地下水。

Authorities are also hoping that the Great Garuda, a 32km outer sea wall being built across Jakarta Bay along with 17 artificial islands, will help rescue the sinking city - at a cost of about $40bn.

It's being supported by the Dutch and South Korean governments and creates an artificial lagoon in which water levels can be lowered to allow the city's rivers to drain. It will help with the flooding which is an issue when the rains come.

当局希望通过海堤缓解洪水灾害。

But three Dutch non-profit groups released a report in 2017 which cast doubt on whether the sea wall and artificial islands could solve Jakarta's subsidence problem.

Jan Jaap Brinkman, a hydrologist with the Dutch water research institute Deltares, argues it can only ever be an interim measure. He says it will only buy Jakarta an extra 20-30 years to stop the long-term subsidence.

"There is only one solution and everybody knows the solution," he says.

Image copyrightGETTY IMAGESImage captionThe construction of the sea wall is underway

That would be to halt all groundwater extraction and solely rely on other sources of water, such as rain or river water or piped water from man-made reservoirs. He says Jakarta must do this by 2050 to avoid major subsidence.

Image copyrightAFPImage captionAlternative water sources like the Citarum river are extremely polluted

It is not a message that is being taken to heart yet and Jakarta's Governor Anies Baswedan thinks a less drastic measure will do.

He says people should be able to extract groundwater legally as long as they replace it using something called the biopori method.

This involves digging a hole, 10cm in diameter and 100cm deep, into the ground to allow water to be reabsorbed into the soil.

Critics say this scheme would only replace water at a superficial level, whereas in Jakarta water is often pumped out from several hundred metres below ground level.

Image captionHouses once overlooking the ocean now face a dyke

There is technology to replace groundwater deep at its source but it's extremely expensive. Tokyo used this method, known as artificial recharge, when it faced severe land subsidence 50 years ago. The government also restricted groundwater extraction and businesses were required to use reclaimed water. Land subsidence subsequently halted.

But Jakarta needs alternative water sources for that to work. Heri Andreas, from Bandung Institute of Technology, says it could take up to 10 years to clean up the rivers, dams and lakes to allow water to be piped anywhere or used as a replacement for the aquifers deep underground.

印尼总统佐科·维多多曾表示，清理雅加达河流需要多年时间。