Environmental Issues

            URBAN HEAT ISLANDS

                                                  by:Gilgan Guirjen

                  37 degree's celcious is the average heat of our body.It is important to maintain the temperature of our body or else your body get an under and over temperature.that can also happened in our world.If you will not maintain the average heat of our world.Our wold have also a temperature but if an island is an over temperature it is called URBAN HEAT ISLANDS (UHI).

                    An urban heat island (UHI) is a metropolitan area which is indicative warmer than its surrounding rural areas.The phenomenon was first considered and defined by Luke Howard in the 1819s,although he was not the one to specify to phenomenon.The temperature departure usually is larger at at night than during the day,and is most discernible when winds are weak seasonally,UHI can be seen during both summer and winter.The main reason of the urban heat island is qualification of the land surface by urban development which uses materials which effectively retain heat.Waste heat generated by energy usage is a collateral contributor.As the population center grows,it aims to expand its area, and increase in the average temperature. The lesser-used term heat island refers to the area, populated or not, which is consistently hotter than the surrounding area.

                      Monthly rainfall is bigger downwind of cities, partially due to the UHI. Increases of heat within urban centers increases the length of growing seasons, and decreases to the occurrence of weak tornadoes. The UHI decreases the air quality by increasing the production of pollutants such as ozone, and decreases the amount of water quality as warmer waters flow into area streams, which stresses their ecosystems.

Causes

There are several reason of an urban heat island (UHI). The principal causes for the nighttime warming is that buildings block surface heat from radiating into the relatively coll night sky. The other reasons are changes in the thermal properties of the surface materials and lack of evapotranspiration  in urban areas. Materials are commonly used in urban areas for pavement and roofs, like the concrete and asphalt, have indicative different thermal bulk properties  and surface radiative properties  than the surrounding rural areas. This are causes a change in the energy balance of the urban area, often leading to the higher temperatures than surrounding rural areas.

Other impacts on weather and climate

Aside from the effect on temperature, UHIs can produce a secondary effects on local meteorology, including the altering of the local wind patterns, the development of the clouds and fog, thehumidity, and the rates of precipitation. The extra heat provided by the UHI conduct to greater upward motion, which can actuate additional shower and thunderstorm activity. In addition, the UHI creates during the day a local low pressure area where relatively moist air from its rural surroundings converges and possibly leading to more favorable conditions for cloud formation.


                                                    URBAN HEAT ISLANDS(UHI)