Urban Climate (Unit 1, Topic 4) Flashcards
Urban Heat Island/ Causes for Urban Heat Island/ Microclimate/ Urban Pollution Dome/ Climate Dome and it's Layers/ Rural-Urban Transect/ Albedo Effect/ Extremer Weather in Urban Regions/ Clean Air Act/ Channeling/ Venturi Effect.
What is a Urban Heat Island?
A city or metropolitan area that is significantly warmer than its surroundings rural areas due to human activities
What is the Urban Heat Island Effect Caused by Building Materials?
Concrete, bricks and tarmac act as bare rock surfaces, absorbing large quantities of heat during the day. They have a higher thermal capacity than natural surfaces. Much of the heat is stored and released slowly at night. Some urban surfaces, especially buildings with large windows, have a high reflective capacity. Multi-story buildings tend to concentrate the heating effect in the surrounding streets reflecting energy downward
What is a Microclimate?
The small scale variations in temperature, precipitation, humidity, wind speed and evaporation that occurs in an environment
What is the Urban Heat Island Effect Caused by Burning of Fuel?
From industries, buildings and vehicles which all burn fuels, air conditioning units release hot air into the atmosphere and people themselves release heat, so cities with larger populations will have heat generated in this natural manner
What is the Urban Heat Island Effect Caused by Urban Pollution Dome?
Air pollution from industries and vehicles ,increases cloud cover and creates a “pollution dome”. This allows short wave radiation in, but absorbs a large amount of the outgoing radiation, as well as reflecting it back to the surface. Particulate matter affects the amount of sunlight that reaches the city
What is the Urban Heat Island Effect Caused by Water Management?
In urban areas, water falling on the surface is removed quickly. This changes the urban moisture and heat-budget there will be less evaporation, so more energy is available to heat the atmosphere
What is a Climate Dome?
A city will create its own climate dome, this is where weather is different from the surrounding area. In large cities, the dome may extend upwards to 250-300m
What are the Two Layers of the Climate Dome?
Urban Canopy- this develops just under the roofs of buildings where processes will act between spaces in the buildings
Urban Boundary Layer- the dome extends downwind and at height as a plume, into surrounding rural areas
What is the Rural-Urban Transect?
Temperature is highest at the CBD and cools down as you move out towards rural areas. Temperatures are typically highest at mid-afternoon and there is the largest temperature range at night
What is the Albedo Effect?
The reflectivity of surface, the ratio between the amount of solar radiation absorbed and the amount of energy reflected back into the atmosphere by surfaces or the atmosphere. Lighter surfaces have a greater Albedo
Effect
Why is Precipitation typically Greater in Urban Areas?
On average precipitation is between 5-15% higher in urban areas compared to rural area, UHI generate convection currents with high rise buildings, air turbulence and encouragement of particular air motion, cities produce large quantities of water vapour from industrial sources and power stations
Why is Weather more Extreme/Common in Urban Areas?
Areas downwind of higher areas have seen potentially over 7% increase in the past few decades of rainfall, snow is less common and melts faster, there is a 25% greater chance of thunderstorms, up to 400% greater incidence of hailstorms due to stronger convection currents and the UHI effect
What is The Clean Air Act?
An act that aims to clean the air and prevent future smog and pollution Introduced in 1956 the act introduced smoke free zones with regulations imposed upon levels of airborne pollution. Air Quality Management areas. In the following years of this act the standards in London’s air quality has drastically improved, reduction of pollution, dust and industrial has contributed to this change
What is Channeling
Wind directed down long straight canyon-like streets where there is less friction. There are sometimes referred to as urban canyons
What is the Venturi Effect?
The squeezing of wind into an increasingly, narrow gap resulting in a pressure decrease and velocity increase
