科学美国人60秒 SSS 树木击败草坪成洛杉矶旱灾救星（在线收听）

Trees Beat Lawns for Water Hungry L.A. 树木击败草坪成洛杉矶旱灾救星

When California was strangled by drought, the city of Los Angeles was offering home owners cash to replace their lawns with landscaping that was less thirsty. Because water just evaporates from overwatered lawns. But how much?

当加州遭遇干旱困扰时，洛杉矶通过向业主们提供现金，让他们用需水量较小的园林绿化来代替草坪。因为水只会从灌溉过的草坪上蒸发掉。但到底会蒸发掉多少呢?

"So that turned out to be a lot of water." Diane Pataki, an ecologist at the University of Utah. "It turned out to be 70 billion gallons of water a year."

“那其实是非常多的水。”犹他大学的生态学家黛安·帕塔基说道，“结果是每年要消耗700亿加仑的水。”

Pataki and her team got that number using a combination of real-world sensor data and modeling. And they found that, of water wasted specifically in urban landscaping, lawns were to blame for three quarters, with L.A.'s six million trees accounting for the rest.

帕塔基和她的团队通过将真实的传感器数据和建模相结合获得了这一数字。他们发现，城市绿化中用掉的水，有四分之三都用到了草坪上，而余下的水量则用到了洛杉矶的600万棵树上。

The study also uncovered something these ecologists were not expecting to study: economic disparity. "The amount of vegetation is really closely related to affluence. So in L.A. that means wealthy neighborhoods actually have twice the evapotranspiration of poorer neighborhoods." Meaning low income neighborhoods not only miss out on that greenery: but also the natural, built-in cooling effect of evapotranspiration. The findings are in the journal Water Resources Research.

该研究还为这些生态学家揭开了一些她们未曾料到的课题：经济差异。“植被的数量与富裕程度密切相关。这意味着在洛杉矶，富裕社区的水分蒸散量竟达贫困社区的两倍。“即低收入社区不仅错失了植被的绿茵，还错失了植被天然的、自带制冷效果的蒸发蒸腾作用。”这项研究发表在《水资源研究》杂志上。

Finally: if you think native trees are the solution to water waste? Think again, Pataki says. "Some of the highest water users in L.A. are those species, including the native California sycamore, which is a very, very popular tree." The reason being that southern California doesn't have a lot of native trees, except alongside rivers—meaning they're water guzzlers by nature.

研究最后表示：如果你认为原生树种是水资源浪费的解决方案，那还请你三思，帕塔基说道。“在洛杉矶，水量消耗最高的就是那些物种，其中包括加州本土梧桐——一种极为受欢迎的树。”形成这种现象的原因是，除了傍水而生的树木，加州南部并没有很多原生树木，而这就意味着它们天生嗜水。

Better, she says, to plant other species that thrive in Mediterranean climates, like water-thrifty pines and palms. Because even if the drought comes back, she says, L.A.'s secret to staying green may be its trees. "It doesn't take a lot of water in terms of absolute gallons to keep them alive. So moving forward L.A. could be very water efficient and maintain a very extensive tree canopy, which I think is good news."

她表示，最好种植那些喜爱在地中海气候条件下生长的植物，像节水的松树和棕榈树。因为即使干旱再次来袭，洛杉矶保持绿化的秘诀可能就是它种植的树木。“它们无需很多绝对量的水来存活。因而长此以往，洛杉矶将可能发展成水资源利用率很高，树木覆盖面极广的地区。我认为这是一个好消息。”