What's happening to our city weather?
It's the hottest, coldest, driest, wettest, calmest, windiest, foggiest, clearest, cloudiest,
smoggiest year anyone can remember.
Is it really?
Has the weather changed?
Is it changing?
One
fact is known, there are now more people living in cities to talk about the weather.
Every day, 10,000 people are added to the cities of the world.
Every year we are increasing our urban areas by an amount equal to cities the size of Los
Angeles, Philadelphia, or Detroit.
To build we scrape, scratch, and dig.
We change the surface of the earth.
Thousands of acres per day are being transformed from rural land to city concrete.
The surface changes are permanent.
The amount of change is increasing every day.
Does our changing of the surface of the earth affect the atmosphere above the earth?
Does it affect our weather?
Most cities were in existence long before scientists became concerned with the changing
environment.
However, between Washington, D.C. and Baltimore, there is an area of rural countryside which
in 1967 began to be transformed into the city of Columbia, a new type of city.
This city is still being built.
The transformation of 17 square miles of rural land into 17 square miles of planned city
has given scientists an opportunity to gather data and measure changes in the environment.
Meteorologists at nearby University of Maryland have gathered data that already shows changes
in the atmospheric environment resulting from the development of this city.
Measurements of temperature, humidity, wind force and direction, precipitation, and radiative
characteristics of the surface have enabled meteorologists to construct a physical model
of the area and predict the changes that will occur as the area continues to be developed.
Trees, brush, and grass are being replaced with asphalt and concrete.
What does this surface change due to the atmosphere above the surface?
What might it do to the weather?
These models represent urban and rural areas.
With them, we can demonstrate some of the changes that may occur.
These materials have been stored in this darkened room long enough for the thermometers to indicate
that the internal temperatures, surface temperatures, and above-surface air temperatures are all
approximately 18 degrees Centigrade.
Two heat lamps overhead represent the sun.
Let's start our demonstration at sunrise and turn the sun on at 6 a.m.
It's 8 o'clock.
For two hours, our suns have been radiating the same amount of heat energy on both surfaces.
Let's compare the internal temperatures.
The rural thermometer indicates 19 degrees Centigrade.
The urban thermometer indicates 23 degrees Centigrade.
Why is the rural temperature four degrees lower than the urban temperature?
Which surface materials absorb, conduct, and store the most heat energy?
It's four hours later and the sun is still shining.
Let's have a cloud darken the sky for a short spring rain.
Both surfaces are being exposed to the same amount of rainfall.
Most of the water that falls upon the brick and concrete runs off into storm drains.
The rest quickly evaporates, leaving a dry surface.
Most of the water that falls upon the vegetation soaks into the ground.
Some of it evaporates.
Two hours later, the water is still evaporating.
What effect does evaporation have upon our surface temperatures?
The rural temperature is now 25 degrees Centigrade.
The urban temperature now reads 30 degrees.
The ability of the rural surface to store water, which can then evaporate over a long
period of time, has caused the rural surface to be five degrees Centigrade cooler than
the urban surface.
Let's turn our sun off and see what happens at night.
The urban surface temperature is 25 degrees.
The rural surface temperature is 22 degrees.
The rural air temperature is now 21 degrees.
The urban air temperature is now 27 degrees.
The air over our model city is six degrees warmer than the air over the country.
We have used thermometers to observe temperatures in our demonstration environment.
Meteorologists have another method of observing temperature variations over large areas of
the Earth's surface.
Warm objects emit heat energy as infrared radiation.
The infrared film in this camera is sensitive to this radiation.
If we photograph our two models with infrared film, our picture should indicate hot and
cold surfaces of our model.
The cool grass photographs as red and pink.
The hot bricks as light blue-green.
In the infrared print of the Columbia area, the wooded areas photograph as dark red, indicating
cool surface temperatures.
The open fields and grass areas are lighter red, warmer than the forest.
The shopping center and asphalt parking areas are almost white, indicating relatively hot surfaces.
The infrared photo indicates that the brick and asphalt surfaces of the city have absorbed
a great deal of the sun's heat energy and are now radiating this energy back to the
atmosphere as infrared radiation.
This stored heat creates an island of warmth surrounded by relatively cooler rural areas.
A blanket of snow covers hundreds of square miles around Grand Island, Nebraska.
Yet the stored heat of the city has melted much of the snow, creating a heat island.
The nature of the city and the activities of its inhabitants add to this temperature
rise.
Such fuel is used to cook, to keep homes warm, to move cars, to run industries.
Most of the heat produced ultimately gets into the air.
In warm weather, inside heat is pumped out into the atmosphere by air conditioners.
When the city is warmer than the surrounding countryside, changes occur.
Some are welcome.
Snow will melt faster in the city than it will in the country.
This will start growing earlier in the spring and bloom later into the fall.
Some changes probably go unnoticed by most people, but the meteorologist measures the
changes and is concerned.
Studies show that more clouds form over the city than over the countryside.
Why?
We have observed how concrete and brick store and release heat energy.
We have also found the temperature of the air above the concrete and brick surface to
be higher than the rural surface.
What happens to this hot air?
We can place a source of smoke above the heated surface and observe that the smoke rapidly
rises.
Any water present on the surface evaporates and is carried upward.
This rising column of warm air cools and the water vapor in it condenses, forming clouds.
The city and its people add thousands of tons of water vapor and carbon particles to the
atmosphere.
Result?
There are more foggy days in the city than in the country.
Water vapor production, particle production, heat production, rising currents of air all
add up to a five to ten percent increase in precipitation.
More rain and more snow fall in the city.
The records of the meteorologist give cause for concern.
Measurements over a 22-year period indicate that precipitation is increasing over the
years in the ever-expanding urban centers of the world.
As this trend of increased precipitation in urban areas continues, will it affect crop
production?
Will there be less snow for skiing?
Lower water levels in mountain lakes?
Meteorologists don't know the answers to these questions.
They do know there is reason to be concerned.
The nature of the city and its concentration of energy needs also magnify the problem of
contamination of the atmosphere with tons of visible particles.
One ton of these may settle per square mile per day in cities.
But invisible particles can be of greater concern.
They stay in suspension and can travel far.
Some can penetrate deeply into our lungs and provoke disease.
They act in many ways in the atmosphere.
Cars using leaded gasoline emit lead particles to the atmosphere.
Near the sea, where there's always iodine in the air, they form lead iodide.
This is a substance similar to the chemicals used in cloud seeding operations.
It can produce rain in certain clouds and, in an uncontrolled use, change the natural
water balance.
The buildings of the city disturb the wind.
When it blows hard, they often channel it and speed it up.
But when the wind is light, they ruffle and slow it down to almost nothing in the canyons
of the city.
When the sun sets and the air is still, the stored heat of the city creates a unique rising
air movement.
It would be nice to hope that this created updraft would carry away the stagnant, polluted
air of the day.
But on calm nights, this is not the case.
A column of warm air rises from the center of the heat island and sometimes reaches a
layer of air warmer than itself and can rise no higher.
This rising column of air spreads a layer of polluted air over the surrounding countryside.
The difference in temperature between the cooler countryside air and the warm city air
creates a circulation that moves the polluted air back to the city to replace the air being
forced aloft by the stored heat.
Instead of the pollutants of the city being dispersed, they recirculate to the city and
raise the overall concentration.
Can this flow of pollutants account for the medical fact that asthma attacks often strike
sensitive people early in the morning hours before the winds of the day can disperse the
concentrated pollutants?
The change of a rural area to an isolated urban area may only create an isolated set
of problems.
But isolation between cities is ending.
In changing the surface of the earth, man is changing the atmosphere above the earth.
He is changing his local climate.
What are the long-range effects of this change?
We have already observed and recorded patterns of change here before unknown on this planet.
In some regions, the spaces between isolated cities have been filled in.
We now see urban belts sprawled over hundreds of square miles between San Francisco and
San Jose, between Santa Monica and San Diego, between New York and Washington.
There are reasons why most people will continue to live in cities, and cities will continue
to get larger.
But planning can minimize the adverse effects on the atmosphere caused by many people living
in a small space.
Rows of tall buildings and narrow streets can interfere with air circulation.
This knowledge can be used in planning cities.
Developing areas help to restore the altered heat balance caused by asphalt and concrete.
These corrective effects can be calculated and designed into developing areas.
Power plants and incinerators are part of any metropolitan complex.
The problems they present can be minimized by proper placement based on meteorological
data.
It is difficult for one individual to bring about great changes in a large city, but a
city contains millions of individuals who together can determine the environment they
will live in.
War