Urban Heat Islands

It has been established that the two adjacent cities tend to be warmer compared to the rest of the surrounding regions. It is imperative to point out that the temperature within the Rotterdam urban area in most instances is higher compared to that in the Rhoon rural area. This situation can be considered as a presence of hot island that is well established in a relatively cool region, and this is called urban heat island (UHI) effect (Rizwan, Dennis & Chunho, (2008). Therefore studies on UHI are essential to the understanding of Rotterdam urban heat equilibrium in addition to city protection, city building design, effective resource utilization and even ecological city construction. The urban heat island has further shown the potential of influencing air pollution concentration (Collier, 2006).

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The figure below shows the urban heat island. The temperature differences in most instances are large during the night compared to the day especially in winter than in summer. As the nations population center expands, they change a great part of the land regions that in the process experiences elevated temperatures (Yuan & Bauer, 2007).

From the figure, the changes on the land cover tend to impact the surface air temperatures

Fig: 1 Urban Heat Island Effect (Yuan & Bauer, 2007).

Studies have pointed out that the industrialization and urbanization processes transform the climate and weather in various ways, including, most of the urban surfaces are made of glasses, concrete, stones and even metal hence increasing the level of reflection resulting from high days and night temperatures compared to the rural regions. Further, most of the urban surface is believed to be highly paved hence making it difficult for the penetration of precipitation to the soil hence leading to high water runoff (Jensen, 2000). This, therefore, provides less water available for evaporation and expends less net radiation. According to Collier (2006), there is also a high level of fossil fuel consumption in cities in vehicles leads to more heat being released into the atmosphere than that released.

In most instances, heat islands are often formed when the vegetation is replaced with building structures and even asphalt and concrete used for development of roads. These surfaces, therefore, tend to absorb heat energy from the sun rather than reflecting them hence resulting in a rising surface and ambient temperatures. Studies have pointed out that trees and vegetation reduction tend to reduce the overall natural cooling effect of evaporation of water from various tree leaves and the soil. According to Garcia-Cueto et al., (2007), the tall building has been argued to result into crowded roads and streets, hot air is trapped in between the narrow and congested streets resulting to reduced normal air flow. Most of the waste that is released from motors, air conditioners and even from manufacturing companies also tend to add some significant warmth to the air near the earths surface hence exacerbating the heat island effect.

According to Quattrochi et al., (2000), heat islands have the potential of occurring throughout the year and during both the day and night. It is clear that urban-rural temperatures tend to differ greatly where it is large especially on calm days and clear evenings. This has been argued to be the case since most of the rural areas tend to cool faster during the night compared to the cities which in this case retains most of the heat that are stored in various parts including building structures and roads. An urban heat island (UHI) is thus an area in a city that is warmer compared to the adjacent surroundings in rural areas as a result of mans activities. Luke Howard was the first to study urban heat islands in 1810s. He reported that this was is a phenomenon that is highly noticeable during the night than during the day.

The monthly rainfall has been proven to be high on the downwind of the Rotterdam city mainly because of UHI. The amount of heat in the urban centers therefore significantly increases the overall growing season lengths and further tend to reduce potential occurrence of weak tornadoes. Urban heat island, therefore, decreases the amount of air quality and this is often due to increased pollutants production including Ozone (Rizwan, Dennis & Chunho, (2008). Further, it reduces the amount of water quality in the event where warm water runs into the regions streams and as a result of this, they stress marine life and overall ecosystem.

Additionally, as cities develop in sizes, they come together forming massive heat domes hence resulting in the huge impact on the global climate patterns. According to Weng, Lu & Schubring, (2004), the combination of these factors has been argued to be behind urban heat Island, which in this case is believed to be a human induced climatic modification of the earths surface. The following table will provide a comparison between cities and the rural regions in addition to their respective climatic elements:

Rhoon Rural - Rotterdam Urban Climatic Difference

Temperature

Annual mean0.9-5.4 F0 More

Winter low (average)1.8-3.6 F0 More

Summer high1.8-3.0 F0 More

Heating degree days10% less Precipitation

Amount5-15 % more

Days with less 0.2 in. 10% more

Snowfall, inner city 5-10% less

Snowfall downwards of the city 10% more

Thunderstorms10-15% more

Radiation

Total on horizon surface 0-20% less

Ultraviolet, winter 30% less

Ultraviolet, summer 5% less

Sunshine duration 5-15% less Relative humidity

Annual mean6%

Winter2%

summer8%

Contaminants

Condensation nuclei 10 times more

Particulates10 times more

Gaseous mixtures5-25 times more Cloudiness

Clouds5-10% more

Fog, Winter100% more

Fog, summer30% more

Wind speed

Annual average20-30% less

Extreme gusts10-20% less

Calm5-20% more

In Rotterdam city, very little vegetation exists and further very small part of the soil is exposed to the sun energy, therefore, as a result of this, most of the solar energy is retained by various structures in the city centers and the asphalt (Gill et al., 2007). During the warm daylight hours, there is very minimal evaporative cooling that occurs in these urban centers and as a result, the surface temperatures tend to rise significantly compared to the rural areas. In addition to these, research has shown that city heat is also emitted by various types of motor vehicles and various established manufacturing companies in addition to domestic heating.

According to Garcia-Cueto et al., (2007), during the night, most of the solar energy that has been stored as energy in various city building and roads are significantly released gradually into the city environment. Studies have further shown that the dissipation of heat in the Rotterdam city is stopped by various buildings hence obstructing the infrared radiation from escaping as it should be (Yuan & Bauer, 2007). Therefore, as a result of this slow heat release, the city temperatures rise significantly. During night hours especially when the nights are still, and the heat island pronounced then there is a higher possibility for the formation of thermal low-presser regions within the city regions. A country breeze will then blow coming from the Rhoon rural areas to the Rotterdam city. Further the concentration level of pollutant is concentrated at the city center (Quattrochi et al., 2000).

During the night hours, extra city warmth will then significantly produce a shallow layer which is often formed near the surface of the earth and is highly unstable. At this layer, pollutants emitted tend to concentrate here and as a result, it makes the air within these regions unhealthy hence unsuitable for breathing. Studies have further shown that the constant outpouring of various forms of pollutants especially from the factories and homes into the air will gradually impact the city climate (Arnfield, 2003). Most of the pollutants have been identified to have the capacity of reflecting a majority of the solar energy and as a result of this, the amount of sunlight that will reach to the earths surface will be reduced significantly. Further, most of the particles in the air serve as nuclei and provide elements where water and ice will be formed hence forming haze which has been associated with reduced visibility and city fog (Voogt & Oke, 2003). The pollutants also tend to impact negatively on the weather downwind.

It has been established that most species believed to be good colonies such as ants tend to have an increased level of heat tolerance. This is where they can utilize the provided condition by the urban heat island hence, they tend to do well in various regions that are outside their usual range. Additionally, beside the impact on temperature UHI has shown to have the potential of generating secondary effects especially in the local meteorology, such as alteration of the patterns of the local wind, humidity, and even fog. According to Voogt & Oke, (2003), the concentration of heat then results into an increased upward motion from the earths surface to the air.

The control and management of urban heat island can be successfully achieved by use of green roofs in addition to the application of light colored surfaces especially in most prone urban regions that tend to reflect more of the suns energy rather than absorbing all of the heat. Research has proven that the impact of urban heat island is far reaching, including a huge contribution to climate warming by approximately 30% (Voogt & Oke, 2003).

In conclusion, the urban heat island often is developed where the industrial and the urban regions are developed and as a result, the heat tends to rise significantly. The study has identified major contributing factors of heat island and these entails, Size and shape of cities, Urban deserts, Urban canyons, Humidity effects, Urban haze and even Anthropogenic heat. Studies have further shown that in most rural areas such as Rhoon, a greater part of the heat from the sun is utilized in evaporating water particularly from the soil and vegetation. Industrialization and urbanization have for long been major factors that transformed the earths surface hence determining the absorption of solar energy. Studying urban heat island has proven essential to most construction and development policy makers since it helps in city planning and development to prevent potential future changes in temperatures at night hence resulting into urban heat island.

References

Arnfield, A. J. (2003). Two decades of urban climate research: a review of turbulence, exchanges of energy and water, and the urban heat island. International journal of climatology, 23(1), 1-26.

Collier, C. G. (2006). The impact of urban areas on the weather. Quarterly Journal of the Royal Meteorological Society, 132(614), 1-25.

Garcia-Cueto, O. R., Jauregui-Ostos, E., Toudert, D., & TEJEDA-MARTINEZ, A. D. A. L. B. E. R. T. O. (2007). Detection of the urban heat island in Mexicali, BC, Mexico and its relationship with land use. Atmosfera, 20(2), 111-131.

Gill, S. E., Handley, J. F., Ennos, A. R., & Pauleit, S. (2007). Adapting cities for climate change: the role of the green infrastructure. Built Environment (1978-), 115-133.

Jensen, J. R. (2000). Remote Sensing of Environment: An Earth Resource. Saddle River.

Quattrochi, D. A., Luvall, J. C., Rickman, D. L., Estes, M. G., Laymon, C. A., & Howell, B. F. (2000). A decision support information system for urban landscape management usingthermal infrared data: Decision support systems. Photogrammetric Engineering and Remote Sensing, 66(10), 1195-1207.

Rizwan, A. M., Dennis, L. Y., & Chunho, L. I. U. (2008). A review on the generation, determination, and mitigation of Urban Heat Island. Journal of Envir...