AbstractExtreme heat poses significant risks to the world’s growing urban population, and the heat stress to human health is likely to escalate with the anthropogenically increased temperatures projected by climate models. Thus, the additional heat from the urban heat island (UHI) effect needs to be quantified, including the spatial pattern. This study focuses on the city of Valencia (Spain), investigating the intensity and spatial pattern of UHI during three consecutive hot summer days accompanying a heat record. For the analysis, long-term in situ measurements and remote sensing data were combined. The UHI effect was evaluated using two approaches: (a) based on air temperature (AT) time-series from two meteorological stations and (b) using land surface temperature (LST) images from MODIS products by NASA with 1 km resolution. The strongest nighttime UHI estimated from AT was 2.3 °C, while the most intense surface UHI calculated as the difference between the LST of urban and rural regions (defined by NDVI) was 2.6 °C—both measured during the night after the record hot day. To assess the human thermal comfort in the city the Discomfort Index was applied. With the increasing number of tropical nights, the mitigation of nighttime UHI is a pressing issue that should be taken into consideration in climate-resilient urban planning. View Full-Text
Keywords: urban heat island; heat stress; MODIS; urban planning; Valenciaurban heat island; heat stress; MODIS; urban planning; Valencia►▼ Figures
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15th July 2015
During the summer, especially during a heat wave like we had a couple of weeks ago, the temperatures in cities like London are considerably higher than those in surrounding rural areas. This is known as the Urban Heat Island Effect. Why does this happen? Is there anything that can prevent this issue?
What is the Urban Heat Island Effect?
The effect is due to darker surfaces in cities such as buildings and tarmac absorbing, retaining and releasing heat from the sun slowly back into the atmosphere. The Urban Heat Island Effect is greatest in areas of densest building and tails off in the suburbs out to the countryside. The heat island effect can also change the weather in an urban area; leading to showers, thunderstorms and hail, especially during the summer.
Fighting the Effect
Ken Livingstone has created a plan to help reduce the Urban Heat Island Effect in London. The document is called Living Walls and Roofs: Technical Report: Supporting London Plan Policy. It was released in February 2008 and investigates how green roofs could be of use to the city. It provides policy support to the London Plan and attempts to break down barriers that are currently in place that work against the installation of green roofs in and around London. One of the ways it does this is by suggesting that larger developments are now expected to incorporate living roofs and walls where possible. This is a very positive step for the green roofing industry in London and the UK, and is a great move to help reduce the effects of climate change in London.
Not Just in London
However, the Urban Heat Island Effect is not just a problem in London. Rapid urbanisation and industrialisation across the globe means this effect is becoming more and more of an issue. With current changes to our climate in London and other large, dense urban areas, we are experiencing warmer and wetter winters with hotter and drier summers. This is set to change in the future. Green roofs are certainly part of the solution to this, along with their many benefits. Through excellent architecture and design, green roofs, walls and roof gardens can provide extra recreational space and a support system for the city. The support system would work by limiting the impact of climate change by keeping the city cooler, whilst reducing energy use and carbon dioxide emissions.