The Panama Canal Beyond Seasonable Drought Changing Rainfall Patterns Threaten an Artery of Global Trade

巴拿马运河非季节性干旱：降雨模式的改变威胁全球贸易的一条动脉

 

Take in the view from atop Gatun dam and fathom what is missing. Container ships float idly on Lake Gatun, near the midpoint of the Panama Canal, awaiting passage to the Caribbean sea, their gateway to the Atlantic Ocean. What look like islands are hilltops poking up from a valley that American engineers flooded a century ago, creating what was then the world’s largest artificial lake. All seems well. But a security guard from the Panama Canal Authority (ACP) points down to a problem: the water lapping against the dam is 1.8 metres (six feet) lower than it should be.

 

从加通大坝的顶部俯瞰，看看到底哪里不对劲。集装箱船在靠近巴拿马运河中点的加通湖上静静地漂着，等待进入通向大西洋门户加勒比海的通道。在坝顶能看到许多小岛，其实是一个世纪前被美国工程师淹没的一个山谷中露出的小山山顶，当年这项工程创造出了当时世界上最大的人工湖。一切似乎都很正常。但是，来自巴拿马运河管理局（Panama Canal Authority，以下简称ACP）的一名保安指出了一个问题：拍打着堤坝的湖水比正常水位低了1.8米。

 

That water is Panama’s lifeblood. Lake Gatun stores rain during the wet season, which usually runs from mid-April through to mid-December, for use in the dry one. It supplies drinking water to Panama city, the capital, as does man-made Lake Alajuela nearby. It is also two-fifths of the canal, a shortcut between oceans for 3% of the world’s maritime trade, as well as for cruise ships and an occasional nuclear submarine. The ACP provides an eighth of the national government’s revenue. “Water is money here,” says Oscar McKay, an engineer at the dam site.

 

这些湖水是巴拿马的命脉。加通湖在雨季（通常从4月中旬持续至12月中旬）储存雨水，用于在旱季保持水位。它与附近的人工湖阿拉胡埃拉湖（Alajuela）一同向首都巴拿马城提供饮用水。它还占了巴拿马运河五分之二的长度。这条运河是大西洋和太平洋之间的捷径，货物运输量占全球海上贸易的3%，同时也供邮轮和偶尔经过的核潜艇通行。巴拿马政府年收入的八分之一来自ACP。“在这里，水就是金钱。”大坝工程师奥斯卡·麦凯（Oscar McKay）说。

 

A normal rainy season fills Lake Gatun to 26.5 metres above sea level. By the end of the dry season that usually falls to 25.9 metres. Prolonged dry seasons have big consequences. If the water level falls below 24.4 metres, the ACP must limit the weight of big “NEOPANAMAX” container ships lest their hulls scrape on the lake bed. Below 24 metres smaller “PANAMAX” ships would risk bumping on the bottom of the locks reserved for them as they enter and leave the lake. This June, after Panama’s most intense drought since independence in 1903, Lake Gatun fell nearly to that level. In 2016, during a longer (but less severe) dry spell, it fell below that for the first time.

 

正常的雨季会让加通湖的水位涨至海拔26.5米。到旱季结束时，水位通常会下降至25.9米。旱季延长会带来严重后果。如果水位下降到24.4米以下，ACP就必须限制大型“新巴拿马型”（NEOPANAMAX）集装箱船的载重量，以免船体剐蹭湖床。水位降至24米以下，更小一点的“巴拿马型”（PANAMAX）船进出加通湖时就有可能碰到专为它们保留的船闸的底部。今年6月，巴拿马经历了自1903年独立以来最严重的旱灾，加通湖的水位降至接近24米。2016年的旱灾时间更长（但没那么严重），其间水位第一次低于24米。

 

Panama city’s rising population and the canal’s growing traffic make such low water levels more likely. Each time a ship passes through the canal’s locks, Lake Gatun releases 200m litres (52m American gallons) of water. In a dry month, outflows through the canal can reduce the lake’s level by 80cm.

 

巴拿马城的人口和运河通航量不断增加，增加了出现这种低水位的可能性。每当船只经过运河船闸，加通湖就会释放2亿升的水。在干旱的月份，向运河放水会让湖泊水位降低80厘米。

 

This year many ships had to transit the canal with less than their maximum load of cargo. That cost the ACP a few million dollars in revenue. The canal came “this close” to losing much more, says an executive, holding his thumb and forefinger together. It narrowly avoided having to impose draught restrictions on PANAMAX ships.

 

今年，许多船只通过运河时的实际载重量都必须低于最大载重量。这让ACP损失了几百万美元的收入。一位高管把拇指和食指捏在一起说，“就差这么一点”运河就会损失得更多。它差点就必须对巴拿马型船也实施载重限制。

 

Rain since July has raised the water level to 24.7 metres but has not lowered apprehensions. Several severe droughts since 2014 may indicate that dry seasons are becoming longer. That would threaten not only Panama’s water supply and government revenues but the canal’s role as a hub of trade. “The whole global supply chain depends on consistency,” says Onésimo Sánchez, a former manager at the ACP. If the canal falters, shipping firms will turn to competing routes, even if they cost more.

 

七月以来的降雨让水位回升至24.7米，但并未减轻人们的忧虑。从2014年以来发生的几次严重干旱来看，旱季可能会越来越长。这不仅会威胁巴拿马运河的水供应和政府收入，还会威胁运河的贸易枢纽地位。ACP的前管理人员欧内斯莫·桑切斯（Onésimo Sánchez）说：“整个全球供应链依赖稳定性。”如果运河的状况不确定，船运公司就会转向竞争性路线，即便费用更高。

 

Precipitation, Meet Precipice

暴雨频发，雨量不足

 

There is little doubt that climate change threatens Panama. Rising seas will submerge the low-lying Caribbean islands of San Blas, a tourist attraction and home to several thousand Guna, an indigenous group. Warmer temperatures will speed evaporation, and thus reduce water levels in Lake Gatun. But pinning blame for recent droughts on climate change is harder.

 

毫无疑问，气候变化威胁着巴拿马。海平面不断上升，加勒比海上低海拔的圣布拉斯群岛（San Blas）将被淹没，这里既是旅游胜地，也是数千名土著古纳人（Guna）的家园。气温升高将加速蒸发，进而降低加通湖的水位。但越来越难将近年的干旱归咎于气候变化。

 

Panama’s worst droughts have happened during extreme occurrences of El Niño, a natural phenomenon in which warm water moves eastwards across the equatorial Pacific Ocean. Longer cycles like the Pacific Decadal Oscillation, which alternates every 20-30 years between warm phases that make El Niños stronger and more frequent and cooler ones, make the role of climate change harder to discern.

 

巴拿马最严重的干旱都发生在极端厄尔尼诺现象期间，这是一种温暖海水流向赤道东太平洋的自然现象。周期更长的自然现象让气候变化的影响更难辨别。比如太平洋十年涛动，其暖相位和冷相位的变换周期为20至30年，涛动处于暖相位时厄尔尼诺现象会更强、更频繁。

 

Residents of the capital do not doubt that changes are afoot. The rainy season once brought daily showers of three to four hours. Now the same amount of rain falls in an hour. Eight of the ten biggest storms in the city, measured by rainfall within 24 hours, have occurred since 2000. Despite those downpours, the canal area has had six straight years of below-average rainfall. The dry season is lengthening. This year it began a month earlier than usual and ended a month late. The current drought is the first severe one to occur in a mild El Niño year.

 

巴拿马城的居民毫不怀疑即将发生的变化。过去，雨季每天有三到四个小时的降雨。现在，一小时内就有同等降雨量。巴拿马城24小时内降雨量最大的十次暴雨中有八次发生在2000年以后。尽管暴雨频发，但运河地区的降雨量已经连续六年低于平均水平。旱季正在变长。今年的旱季提前了一个月到来，又晚了一个月结束。当前的干旱是首次在厄尔尼诺现象温和的年份里发生的严重干旱。

 

This unprecedented concurrence suggests that climate change is directly responsible, the ACP believes. “To be completely sure you’d have to wait a hundred years,” notes Carlos Vargas, the ACP’s vice-president for water and environment. And even if climate change is not the culprit now, it may strengthen future El Niños, which would lengthen droughts and increase their intensity. Some scientists think that if, as expected, the equatorial eastern Pacific warms faster than other regions, extreme El Niños will double in frequency to once a decade by 2100.

 

ACP认为，这种前所未有的并存现象表明气候变化是直接原因。ACP水与环境事务副总裁卡洛斯·瓦尔加斯（Carlos Vargas）指出：“要百分百确定这一点还得等一百年。”而即使现在气候变化还不是罪魁祸首，它也可能在未来加剧厄尔尼诺现象，让干旱延长并加重。一些科学家认为，如果如预期的那样，赤道东太平洋的升温速度快于其他地区，那么到2100年，极端厄尔尼诺现象出现的频率将翻倍，达到十年一次。

 

Water shortages imperil the canal’s expansion plans. In 2016 a new set of locks allowed the passage of NEOPANAMAX ships. The canal needs another upgrade to accommodate new “ultra-large” vessels. But work cannot start while water levels are so uncertain, ACP officials say.

 

水资源短缺危及运河的扩建计划。2016年，一组新船闸建成，“新巴拿马型”船只得以通行。为了能让新的“超大型”船只通行，运河还需要再次升级。但ACP的官员表示，水位如此不确定，无法开启升级工作。

 

If droughts become frequent, shipping firms may favour more reliable routes between the Atlantic and Pacific oceans, such as rail lines across the United States. Someday, climate change could open up for navigation the ice-clogged Northwest Passage through the Arctic. That would cut by about 4,000km (2,500 miles) the length of a journey from Shanghai to New York, which is 19,500km via Panama.

 

如果干旱频发，船运公司可能会选择大西洋和太平洋之间更可靠的路线，例如穿越美国的铁路。未来，经过北极冰封海域的西北航道可能会因气候变化变得适于通航。届时，从上海到纽约的航程将减少约4000公里，而经巴拿马运河需航行1.95万公里。

 

To secure the canal’s future, the ACP has to plan now. “We cannot go back to what we had in the past,” says Mr Vargas. Already the ACP has stopped producing hydroelectricity from the Gatun dam. It is studying ways to raise water levels, including by digging a third artificial lake to supply Panama city and piping water from the Indio river to Lake Gatun. “They’re going to have to do all of them,” says Merei Heras, a former environment minister, sipping a drink in a café as rain pelts down. Deepening Lake Gatun is not an option because the mountains nearby would collapse.

 

为了确保运河的未来，ACP必须立即制订计划。瓦尔加斯说：“我们没法再回到从前。”ACP已经停止了加通大坝的水力发电，现在正在研究提高水位的方法，包括挖掘第三个人工湖为巴拿马城供水，以及从印第奥河（Indio）向加通湖送水。“这些项目都得上。”前环境部长梅雷·赫拉斯（Merei Heras）在咖啡馆里啜着一杯饮料说，外面大雨如注。加深加通湖是行不通的，因为附近的山体会崩塌。

 

Drought-proofing the canal will be disruptive, forcing people to move and hurting habitats down-river from water-diversion projects. Panama’s only answer to the global havoc caused by climate change, it seems, is to do local damage.

 

给运河做防旱工程将产生破坏性后果，迫使人们搬迁，损害引水工程下游的自然环境。看来，巴拿马运河应对气候变化造成的全球性破坏的唯一办法就是在当地搞破坏。

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