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According to climate model for the 21st century, summer warming trends might increase the incidence, intensity and duration of heat waves, particularly in western and central Europe, the Mediterranean regions, and the western and southern regions of the United States, (Meehl and Tebaldi, 2004; Shar et al., 2004).
Heat waves are especially deadly in cities due to the alteration of their surfaces, a decrease of surface moisture available for evapotranspiration, changes in radiative fluxes and near surface flow, and production of anthropogenic heat and pollutants.
At night, while temperature may drop in rural areas, cities release the heat stored in the buildings, inducing a lack of relief and increasing the risk of heat stress and mortality for the more vulnerable population (the elderly, infants and people with chronic diseases).
In summer 2003, the western Europe experienced a heat wave of exceptional strength and duration, with a death toll exceeding 70 000 (Robine et al., 2008).The heat wave led to health crises in several countries and combined with drought to create a crop shortfall in Southern Europe. In August, the Paris metropolitan area encountered nine consecutive days with temperature reaching 38°C in daytime and increasing from 20°C to 25°C in nighttime at the peak of the heat wave, resulting in a 4,867 excess mortality.
Mean diurnal cycles of land surface temperature, at an industrial site, in downtown Paris, and in an urban park, constructed from 50 NOAAAVHRR images (August 4 13,2003
Estimates of urban heat stress and vulnerability requires observations at high spatial resolution, which are best obtained from satellites thermal infrared imagery.
Figure 6 shows three maps of temperature thresholds and areas vulnerable to heat stress, delineated from the NOAA-AVHRR time series images. Using the land cover classification from the SPOT4 image and the Paris geographic database, those maps impart the displacement of heat stress and level of risk according to the occurrence and intensity of heat islands and thermal anomalies, surfaces properties (especially the albedo), water and vegetation, and building and population density.
The combined analysis of satellites thermal images and public health data of the Paris region, during the summer of 2003, confirms the importance of high minimum temperatures in the heat wave process and the subsequent heat stress and mortality. A summertime satellite surveillance system is being developed to monitor heat waves over the Paris Metropolitan area, and to inform the local public and authorities on extreme surface temperatures and potential heat stress. The use of satellite thermal remote sensing over cities is yet a trade-off between accuracy and efficiency. However, it should improve the current health alert systems, contribute to adaptation strategies and reduce the societal impacts of climate change.
(* Article By Sara Goudarzi*)
History shows that heat waves are deadlier than hurricanes or tornadoes. And studies have indicated that extreme weather events will become more common with global warming.
The warming is underway. With temperatures up to 30 percent higher than the seasonal average over the past few decades in most of Europe, the summer of 2003 was one of the hottest in centuries. Scientists expect 2005 to set a modern record for the warmest average global temperature. Leading computer models show continued warming for at least several decades, even if greenhouse gas emissions are curbed, with only wild schemes proposed to put the brakes on.
Urban areas are particularly vulnerable, because dark asphalt and rooftops absorb more solar radiation than natural landscapes, raising nighttime temperatures by as much as five degrees, according to NASA studies.
In order to see the effects of extreme heat events on the United States, the researchers developed models to simulate scenarios analogous to that of Europe's for heat-sensitive urban areas.
"We tried to take the Paris heat wave in 2003 and transpose it onto the climate of five different cities," Kalkstein said. The cities: Detroit, New York, Philadelphia, St. Louis, and Washington, D.C.
The results were not cool.
In the nation's capital, there were 11 days with temperatures at or above 105 degrees in the virtual scenario. St. Louis reached an all-time maximum of 116. New York and Philadelphia each broke all-time highs for four days. In Detroit the mercury set all-time records twice.
The total simulated excess deaths were more than five times the historical summer average, with New York and St. Louis showing the highest numbers. This the researchers attribute to size and city structures.
"New York is much bigger and clearly will have more deaths than cities like Washington and Detroit," Kalkstein said. "The second thing is that [a place such as] New York is a very sensitive city with a lot of high-rises and buildings that are sensitive to extreme heat."
Plan for it
Better planning and simple innovations in architecture could effectively reduce mortality rates should things heat up.
There are many things that can be done immediately, Kalkstein told LiveScience.
Cities could provide air-conditioned shelters and cut down on the use of black asphalt in favor of lighter-colored materials. More heat-absorbing trees and gardens could dot urban areas. Cities could work to provide better public transportation, decrease traffic congestion and minimize commutes. Property owners could be encouraged to paint roofs white and build roof gardens.
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