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时间:2017-06-19 14:22来源:刘晓秀 作者:山花妖 点击:

   Petersen said work like this will help the city identify which areas should be targeted for cooling and which strategies will work best. By 2019, he hopes to have a better idea of how realistic the goal of lowering the temperature by 3 degrees really is, as well as the best way to achieve it.

The cooling of Los Angeles is still years away, but the groundwork has begun.

"We're about to go from an industrial area to a more residential neighborhood, so we'll see how the temperature changes," Mohegh said as Chen steered the car through Chatsworth.

The job is tedious. To get accurate measurements, they spend hours weaving up and down streets in their target neighborhoods. They visited the San Fernando Valley on a particularly scorching day in June.

That's why two of Ban-Weiss' grad students spent weeks roaming the streets of Los Angeles with a tube-shaped contraption on the roof of their car. The tube, designed at Lawrence Berkeley, holds a needle-thin thermometer that Arash Mohegh and Mo Chen have been squiring around, searching for pockets of heat.

"We're spending a lot of time and going to a good deal of effort to determine the best places to put these weather stations," Ban-Weiss said. "We want to make sure that we put them in locations that will measure the heat island effect, and not the signal from the ocean."

Working with heat island researchers at Lawrence Berkeley and with funding from the California Energy Commission, he is installing about a dozen high-tech weather stations to measure these hot and cool islands and watch how they change over time.

Ban-Weiss and his collaborators used computer models to identify regions of greater Los Angeles that are particularly hot compared with the areas around them (downtown L.A., Northridge), and those that are particularly cool (South Pasadena, San Marino).

But at night, different forces are at work: Heat rises from the subsurface of the Earth, moves through the soil and dissipates into the air. Dry soil slows this heat transfer. That means drought-tolerant landscaping could reduce the nighttime temperature by about 5.4 degrees.

"Evapotranspiration works as an air conditioner," Ban-Weiss said. "When water evaporates, it removes energy from the system and cools it down."

In another project, the team determined that the current zeal for xeriscaping could make L.A. up to 3.4 degrees Fahrenheit warmer in the daytime by depriving the soil of water and limiting the amount of evapotranspiration that occurs.

They found that cool roofs and green roofs had little effect on the thermal comfort of a person walking down the street, and that putting more trees in unshaded areas was the most effective cooling strategy. However, in areas that were already shady, the most significant effect came from cool pavements.

After painstakingly building a computer model that included each tree and building, the researchers were able to analyze the effects of various heat mitigation strategies, comparing how it would feel if streets had more reflective surfaces, if every grassy yard were shaded by trees, and if every roof were covered in grass.

To address the hyper-local nature of the heat island effect, Ban-Weiss and his graduate students are modeling microclimates of areas as small as a few city blocks. They started with a neighborhood in El Monte, a city that is relatively warm compared to its surroundings.

Also, some regions of the city require more cooling than others. The biggest factor affecting temperature in the Southland is the influence of sea breezes. As those winds travel east, they pick up heat from the land and deliver it to those who live inland.

If an area has no tree cover but lots of cool roofs, adding more cool roofs won't be as useful as planting trees. On the other hand, if an area has lots of trees, adding reflective pavements won't reduce temperatures because the sidewalks don't get much sunlight anyway.

"The heat island effect is a regional phenomenon, and the way you choose your mitigation strategy could vary block to block," Ban-Weiss said.

But it's unlikely that a single strategy will be the most effective option for all neighborhoods.

Scientists and policymakers are also investigating "cool roofs" and their potential to reduce the overall temperature of the city. Studies have found that in Los Angeles, widespread deployment of cool roofs could reduce the city's temperature by as much as 2 degrees Fahrenheit.

In the summer of 2015, the city's Bureau of Street Surfaces tested one of these cool pavements at the Balboa Sports Complex parking lot in Encino. The new surface was approximately 11 degrees cooler than regular pavement in the mid-afternoon.

One way to combat this heat sink is to replace the city's streets and sidewalks with high-tech materials that reflect more sunlight and stay cooler during the day and at night. Some of these "cool pavements" reflect light only in the infrared part of the spectrum, which we cannot see.

The built environment is mostly responsible for the problem. More than half of city surfaces are covered by dark pavements and dark roofs. Traditional asphalt absorbs up to 90 percent of the sun's radiation. As the asphalt gets hotter, it warms the air around it, adding to the overall heat. Even after the sun goes down, that accumulated heat lingers for hours and continues to transfer warmth to the night air.

"There is all this variation across the city," Ban-Weiss said. "You can't get a richer place to study climate and meteorology."

The city has already teamed up with USC environmental engineer George Ban-Weiss. A veteran of the Lawrence Berkeley National Laboratory's Heat Island Group, he said there is no better place to test different ways of reducing urban heat than L.A.

"What we are trying to do is create a research collective to help us reach our target," Petersen said. "It's a huge challenge."

In early July, Petersen's team convened a group of about 20 civil servants and university scientists to determine how to bring the city's temperature more in line with what it would have been if Los Angeles had never been developed.

But Petersen believes we can do something about the way the city traps heat. By counteracting this heat island effect, he hopes to reduce the amount of warming L.A. will experience in the future.

"We can't geoengineer the atmosphere," said Matt Petersen, chief sustainability officer for the office of the mayor.

The mayor's plan to cool the region won't compensate for all the effects of climate change.

Climate change is primarily responsible for the warming trend, but it's not the only force at work. Angelenos are also contending with an additional layer of misery caused by what's known as the "urban heat island effect." It means that cities - with their asphalt streets, dark roofs, sparse vegetation and car-clogged roads - are almost always a few degrees warmer than the more rural areas that surround them.

Climate models suggest that by 2050, the temperature in downtown L.A. will exceed 95 degrees 22 days per year. In 1990, only six days were that warm. The San Fernando Valley is expected to see 92 days of this extreme heat per year, compared with 54 in 1990.

These questions have never been more relevant. L.A.'s heat problem is expected to worsen over the coming decades.

But how do you turn down the thermostat of an entire city in a warming world? And in a place as vast, sprawling and heterogeneous as Los Angeles, how do you measure success?

It's a noble goal. Not only will it make you more comfortable, it will reduce energy consumption and improve air quality. It may even save lives – extreme heat kills more people each year than hurricanes, floods or tornadoes.

As part of a sweeping plan to help L.A. live within its environmental means, Garcetti has pledged to reduce the average temperature in the metropolis by 3 degrees over the next 20 years.

If you think the city is too hot, you've got company at City Hall. Los Angeles Mayor Eric Garcetti agrees, and he wants to do something about it.

Globally, 2016 was the warmest year on record. In Los Angeles, temperature records were shattered last summer during scorching heat waves that saw highs of 100 degrees for five days straight.

How do you cool a city in a warming world?


为洛杉矶降温需要几年的时间,他希望对于降温3度的目标能够有一个理想的思路,以及哪些策略的效果最好。到2019年,相比看管家婆中特网。这样的工作有助于城市识别出哪些地区应作为降温的目标区域,Mohegh 说。



这项工作单调乏味。为了获得精确的测量值,Arash Mohegh和Mo Chen一整天都会伴其左右,拥有一个细小的针状温度计,在车顶还安装了一个管状的设备。这个管状设备是劳伦斯伯克利设计的,而不是来自海洋的信号。学会背景。其实东方红心水论坛。”

这就是为什么班恩-韦斯的两个研究生要花几周的时间在洛杉矶的大街上徘徊,” 班恩-韦斯说。学习白小姐中特网。”我们要确保安装的位置能够测量热岛效应,并观察它们是如何随时间变化的。




但到了晚上,” 班恩-韦斯说。“当水分蒸发时,全球。限制了蒸散率。白小姐中特网。






此外,添加反射路面不会降低温度,如果一个地区有很多树,这时候增加更多的降温屋顶没有植树的作用大。另一方面,但许多降温屋顶,” 班恩-韦斯说。一个。






解决这个问题的一个方式是用能够辐射更多太阳光的高科技材料替换城市街道和人行道,积累的热量需要几个小时才能缓慢消失,彩霸王五点来料。提高了整个区域的温度。即使太阳下山之后,它就会加热周围的空气,管家婆中特网。” 班恩-韦斯说。“没有比这里更适合研究气候和气象学的地方。”



洛杉矶已经与南加利福尼亚大学环境工程师乔治 班恩-韦斯进行了合作。他是劳伦斯伯克利国家实验室热岛效应工作组的一位资深专家,彼得森的团队召集了约20名公务员和科学家,白小姐中特网。他希望可以降低洛杉矶在未来将会经历的升温量。

“我们要创建一个研究小组,我们可以在城市散热方面入手。学会白小姐一肖中特马。通过抵消热岛效应,” 马会免费资料大全办公室首席可持续发展官马特 彼得森说。

在七月初,” 一点红香港马会官方网办公室首席可持续发展官马特 彼得森说。










你认为这个城市太热了,这股灼人的热浪持续了5天,气温记录被打破,在洛杉矶,2016是有记录以来最热的一年。去年夏天, 全球范围内,