Residential area expansion and microclimate

[old man emu]

A question that has been on my mind recently concerns the effect of the rapid expansion of residential areas in the Sydney Basin, and its effect on the micro-climate of the Basin.

 

The Sydney Basin is named for the city of Sydney which is centred within it and stretches from Newcastle in the north to Batemans Bay in the south, and west to the Great Dividing Range. The basin is also home to the major centres of Newcastle and Wollongong.

 

 

In the past five years, the south-west corner of the basin, as shown by the blue line in the diagram below, has experienced massive, rapid conversion from pastureland to medium density residential housing.

 

 

Not only has this resulted in the majority of the area being covered with impervious materials (roofs, roads etc) but the roofs are generally of a dark grey colour. This area of the basin experiences very high air temperatures during summer, which create a daily air movement cycle.

 

From sunrise to midday, the air is heated and rises. From mid-afternoon a north-easterly sea breeze begins to blow, reaching Camden about 4:00pm AEST. This breeze can be strong at times.

 

I'm wondering if this residential development is adding to the heating of the air, creating a more intense Low Pressure gradient and consequently causing stronger north-easterly winds.

 

I'd appreciate comments on this phenomenon from anyone who flies gliders out of Camden, or has noted any change in conditions whilst flying southwest of Bankstown.

 

OME

 

 

[nomadpete]

I haven't been around Camden for many years so I can't offer any observations on it. However I am very interested in any anecdotal contributions. Like you, I suspect that the human plague must be affecting local weather. Loss of trees combined with hard surfaces has already been shown in other places to aggravate flooding due to instant runoff of rain.

 

 

[Nobody]

I don't think that the residential expansion and changes in land use will lead to higher wind speed on sea breeze days for a few reasons.

 

Firstly the sea breeze relies on convection of the inland air creating a void for the sea air to move into. Soon after the sea breeze arrives the convection diminishes. This is not really because the cool air stops the heating but that the air becomes stable as there is now cooler air under the warmer air and the air has become stable. see the earlier discussion about stability here Weather Conditions Analysis. What this will mean is that the sea bree affect is itself in equilibrium. The sea bress destroys the conditions that create it.

 

When you look at sea breezes around the world they all have about the same peak velocities (approx 20 knots) despite wide variation in the terrain that causes them.

 

A good discussion of sea breezes is in the book by Frank Bethwaite "High Performance sailing" https://www.amazon.com/High-Performance-Sailing-Faster-Techniques/dp/1408124912

 

 

[facthunter]

I would be fairly sure the widespread use of heat pumps. (air conditioners) motor vehicles, power stations etc raises the temps in densely settled areas. Bushfires create their own thunderstorms in the right conditions and rivers affect Cb formation as well, if the run of the river is the same as the prevailing wind direction particularly. Nev

 

 

[Yenn]

Cities must affect the micro climate. I remember as a kid that London never felt as cold as the country areas around it.

 

i came to Sydney in 1962 and at that time a lot of the area you refer to was just trees. I remember the first time I drove out of Sydney on the Hume, I stopped on top of a hill near bankstown and gazed in awe at the miles and miles of trees I could see. All gone now.

 

 

[Nobody]

Just to clarify, I do think that urbanisation will lead to increased temperatures compared with open farmland. Its my view that this increased temperatures won't lead to an increase in the wind speed on seabreeze days.

 

 

[facthunter]

The sea breeze effect is mainly from convection over the hotter land mass. The temperature difference is what powers it. the hot air rises and the sea bereeze rushes into replace it If clouds form over the land there is more heat energy available depending on the water content of the airmass. A reverse effect occurs over the sea in the tropics at night. Warmer over water temps cause moderate cloud formations that usually dissipate after sunrise. Nev