Urban Microclimates and Drainage Flashcards
How is wind impacted by cities? State and expain the 2 effects. What happens with vortices too? How to counter?
-Venturi Effect. Fluids move quickly when channeled into smaller spaces/narrow streets.
-Urban canyon effect: Wind is funneled in streets where there a high-rise buildings e.g. the grids in America. Powerful.
-Buildings=friction=slower windspeeds than rural. Vortices can form behind large buldings.
Can’t spread our warm air
Counter by adding vegetation to increase friction (natural wind breaks) or aerodynamic building shapes
Explain the term urban microclimate
-Cities are in their own domes, separate to rural areas.
-They have their own temperature range (usually higher 1-3c)
-Greater precipitation and cloud cover. Condenstaion nuclei, urban heat island. 5-15% more and more intense.
-Less wind but can be more powerful.
Give 2+ and 2- of warmer urban areas
+Growth of vegetation. +Less need for heating.
-Health issues for elderly or sick e.g. heatstroke.
-Positive feedback AC loop
What is the urban heat island effect? Give 3 causes.
-Urban areas warmer than rural.
-Less albedo/reflectvity from dark surfaces e.g. concrete. Store heat and release most at night.Walkie talkie building in London 2013.
-More people, cars and industry=warmer and localised GH effect. Worse with congestion and harsh acceleration or deceleration
-Positive feedback loop with air conditioning (warmer=aircon=fuel=warmer)
-Less plants and thus less evapotranspiration, less shade, less CO2 stored
What is the difference between radiation fog and advection fog?
-Radiation: Particulates/dust from pollution = condensation nuclei
Radiation fog is a type of fog that forms close to the ground, typically overnight or early in the morning, under clear skies and calm conditions. It occurs when the ground cools rapidly by radiating heat back into space, causing the air close to the ground to cool as well. When this air temperature drops to the dew point (the temperature at which air becomes saturated and can no longer hold all its moisture), the water vapor condenses into tiny droplets, forming fog. Usually low-lying valleys or rural areas.
-Advection: Found at the coast where warm land air meets cool ocean air at a front.
Why are thunderstorms more common in urban areas?
-Urban heat island.
-Venturi/canyon effect for rapid updraughts of air.
-Condensation nuclei for cumulonimbus.
-Latent heat released to power storms.
-(Mention any characteristics of storm/how it forms) e.g. lightning from massive electrical charge build up that is suddenly released/thunder is rapid expansion of air due to heat from lightning.
What is particulate smog? What is photochemical smog?
–Particulate:
-Dust and pollutants from urban actvities. -Smoke+fog.
-Brown.
-Also, reaction of volatile compounds.
–Photochemical: Sunlight reacts with nitrogen oxides and or volatile compounds. Creates a noxious green mixture. Exacerbated by valleys where temperature inversions can occur (Mexico City) and anticyclonic conditions are present (low pressure).
What was the famous London 1952 smog called? Deaths? What law was made after this? What are these called (a__)
Pea souper. 4k deaths. 1956 clean air act to regulate industries pollution e.g. more chimneys. Airpocalypse
Give 2 ways gases in urban areas differ from rural areas
2x CO2.
200x more SO2. Acid rain/respiratory damage
State and explain 3 pollution reduction policies for urban areas
-London Congestion Charge: £15. Use new GPS. Can ringfence money. Dissuade use. Or ULEZ which says vehicles have to meet Env standards.
-New technology: Liverpool VOI scooters. Oslo incentivises electric cars with tax incentives and free parking.
-Urban greening: Bulding in Milan full of vegetation. Regulates air quality.
Define SuDS/sustainable urban drainage systems.
Use/replicate natural processes to reduce pluvial flood risk and reduce pollutants. Help create sponge cities for those prone to flooding
Why have urban drainage systems struggled?
-Built in Victorian times. Not supposed to deal with sewage and sheer amount from urbanisation.
-Easily clogged with debris.
Give 3 hard river engineering strategies
-Diversion spillways: Create new channel for river to flow through. Use sluice gates. Good for ammenity (wetlands) and emergency.
-Embankments: Dredged sediment or built-up levees. Prone to flood if breached.
-Channelisation/straightening: Laying concrete on river bed to reduce friction and encourage faster flow.
Give 2 examples of soft river engineering
-River restoration: Restoring natural fluvial processes. remeandering or maintaining a flood plain to store water. Links with Sheffiled Blue Loop. Restore natural processes.
-Afforestation/conservation of river banks. More biodiversity
What is site control? Give 3 examples.
Keep water close to where t fell.
-Swales.
-Detention basins.
-Permeable paving
