熱浪點樣形成?

熱浪是指一段不同尋常的讓人熱得難受、通常情況下濕度過高的暑熱天氣。這個術語通常與地區相聯繫，所以一個對較熱氣候地區來說是正常的溫度對一個通常較冷的地區來說可能是熱浪。

熱浪可分為日射型和熱射型兩種類型。

日射型多發生於幹熱天氣，由於太陽輻射中的紅外線可穿透顱骨，導致腦組織溫度驟然升高，致使腦神經功能受損。

熱射型是因為皮膚在高濕熱浪的侵襲刺激下，溫度驟然升高，使得皮膚散熱功能下降，體內熱量不但不能散發，還會影響全身各器官組織的功能，出現局部肌肉痙攣、發熱、口幹、咳嗽、哮喘、呼吸困難、血壓升高和呼吸衰竭等症。

熱浪對健康的影響在城區比郊區和農村要大得多。

由於城市“熱島效應”，市區溫度不僅高且持續時間長，炎熱強度及持續時間比暫態最高溫度對死亡率有更大影響。空氣污染也是城區較高，而熱浪又往往與高的污染水平相聯繫。

如1995年美國和威爾士熱浪期間，估計死亡人數有一半以上是由當時空氣污染加重引起的。

熱浪對人體健康的影響還與城市生活狀況、社會經濟因素和預防干預措施等有關。城市生活狀況是一個重要的危險因數，住在頂樓、鬧市區、沒有空調環境的居民區具有較高的發病率和死亡率。

為什麼近年來熱浪會如此頻繁地發生呢？

根據科學家們對近100多年來全球氣溫資料的分析，全球平均地面溫度已升高了0.3℃～0.6℃，全球氣候變化伴隨著熱浪頻率和強度的增加，夏季變得更熱。濕度增加也加劇了夏季極端高溫對人類健康的影響。另一方面，由於城市化進程，城市人口密度增加，城市熱島效應愈加明顯。

2007-02-19 10:24:28 補充：
A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity.

A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave; the term is relative to the usual weather in the area. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area. The term is applied both to routine weather variations and to extraordinary spells of heat which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning.

A heat wave is a prolonged period of excessively hot weather, which may be accompanied by high humidity. There is no universal definition of a heat wave; the term is relative to the usual weather in the area. Temperatures that people from a hotter climate consider normal can be termed a heat wave in a cooler area if they are outside the normal climate pattern for that area. The term is applied both to routine weather variations and to extraordinary spells of heat which may occur only once a century. Severe heat waves have caused catastrophic crop failures, thousands of deaths from hyperthermia, and widespread power outages due to increased use of air conditioning.
Definition of Heat Wave
In the Netherlands, a heat-wave is defined as period of at least 5 consecutive days in which the maximum temperature in De Bilt exceeds 25 °C (77 °F), provided that on at least 3 days in this period the maximum temperature in De Bilt exceeds 30 °C (86 °F).
This definition of a heatwave is also used in Belgium, Denmark and Luxembourg
Impact

Effects on health
Severe heat waves can lead to deaths from hyperthermia, also known as heat stroke. Older adults, very young children, and those who are sick or overweight are at a higher risk for heat-related illness. [4] Heat waves are the most lethal type of weather phenomenon, overall. Between 1992 and 2001, deaths from excessive heat in the United States numbered 2,190, compared with 880 deaths from floods and 150 from hurricanes. [5] One public health measure taken during heat waves is the setting-up of air-conditioned public cooling centers.

Mortality and the "harvesting" effect
Part of the mortality observed during a heat wave, however, can be attributed to a so-called "harvesting effect", a term for a short-term forward mortality displacement. It has been observed that for some heat waves, there is a compensatory decrease in overall mortality during the subsequent weeks after a heat wave. Such compensatory reduction in mortality suggests that heat affects especially those so ill that they "would have died in the short term anyway".[3]

Power outage
Heat waves often lead to electricity spikes due to increased air conditioning use, which can create power outages, exacerbating the problem. During the 2006 North American heat wave, thousands of homes and businesses went without power, especially in California and the St. Louis, Missouri area. In Los Angeles, electrical transformers failed, leaving thousands without power for as long as five days. [6]

Wildfires
If a heat wave occurs during a drought, which dries out vegetation, it can contribute to wildfires. During the disastrous heat wave that struck Europe in 2003, fires raged through Portugal, destroying over 3010 km² (740,000 acres) of forest and 440 km² (108,000 acres) of agricultural land and causing an estimated €1 billion worth of damage. [7] High end farmlands have irrigation systems to back up crops with.