METEOROLOGIST JEFF HABY
The next series of 5 Haby Hints will look at the urban environment and important weather influences. The majority of the Earth’s population now
lives in urban areas, thus being aware of urban meteorology is important. An urban area is within the city limits and generally contains
business centers, housing, commerce, dense networks of roads and parking. Urbanizing of the planet is one of the primary ways that humans
are terraforming the Earth. Terraforming is modifying the surface which is turn changes the temperatures, atmosphere and surface characteristics. This
involves removing a large amount of vegetation, altering the land to allow for transportation and commerce and building large numbers of structures,
roads and parking lots.
The Earth’s population is currently a little over half urban but as the decades go by it is expected that this fraction will increase. In
a few decades up to 75% of the world’s population could be living in urban centers. At the same time the world population continues to
grow. This will cause most urban centers to continue to expand into the neighboring countryside. The population of most urban centers
will grow and the city limits of urbanization will continue to expand. As urban centers expand over the globe, they will have a more
pronounced influence on weather and climate.
1. URBAN WX SERIES: TEMPERATURE
This writing is particularly interested in the influence on temperature. Urban centers tend to have an influence of increasing the
temperature. This is due to less moisture and less vegetation. Vegetation is
an important factor to regulating temperature. Vegetation absorbs some of the sun’s energy to produce photosynthesis. Vegetation contains
moisture and moisture is more abundant where there is more vegetation. Water has a high heat capacity and is thus able to absorb
an abundance of solar energy. Wet soils and plants do not warm as quickly as materials such as concrete and metal when absorbing
solar radiation due to the high heat capacity of water. When rain falls into an urban environment, it quickly runs off into the
drainage system instead of soaking into the ground. The expansion of urban centers will contribute to less water and plants, and
this has a net heating impact. A term used for this is the urban heat island. Urban construction tends to warm quickly when exposed
to sunlight. As urban locations become a greater percentage of the surface land cover on Earth it can be expected that temperatures
will continue to warm.
2. URBAN WX SERIES: AIR QUALITY
This next writing focuses on air quality within the urban environment. While efforts and results will occur on making transportation
and industry more energy efficient, it will be partially offset by the continuing increase of the urban population. People migrating
to urban areas and the overall world population increasing will ensure urban areas continue to grow. This means more cars on the roads
and more industry. The demand for fossil fuels will increase in order to sustain the growing urban areas. Known reserves of coal, natural
gas and oil will continue to be mined and retrieved. New reserves will be found and developed. Eventually the world supply of these
resources will be depleted but it could be centuries before the current resources and newly discovered reserves are totally depleted. During
this time other sources of energy will be increasingly more important. However, for the next century and beyond, poor air quality will
continue to be a problem in urban areas due to fossil fuel emissions.
The results of poor air quality include allergies, asthma, lowered visibility, and general health issues. The particulates in the air
can make it more difficult to breath. The body’s reaction to certain particulates in the air can cause or intensify allergies. The
particulates in the air can produce a white or brown haze in the air. If the humidity is high it can lead to denser fog.
There are several things that can be done for humans to adapt to these conditions and lessen the severity. One way is to stay in close
contact with a primary doctor and specialists on how to reduce the negative health influences from poor air quality. Another way is to
reduce emissions by focusing on energy efficient transportation and home appliances. Maintaining clean air in the home environment is
important also. Inside air can sometimes be less clean than outside air. Make sure the home environment air is safe and clean. Also,
making the issue of air quality an important political issue helps since many of the changes to safeguard the air will come
from elected officials.
3. URBAN WX SERIES: MESOSCALE INFLUENCES
Mesoscale meteorology is weather influences that occur on smaller size and time scales as compared to the synoptic scale. Mesoscale processes
occur in time scales from minutes to hours and space scales of kilometers to many 10s of kilometers. The size of a major metro area can take
an hour or more to drive from one side to the other and the distances can be 10s of kilometers. Thus, mesoscale influences can occur over
the urban area and due to influences from the urban area.
One mesoscale influence occurs due to the heat generated by the urban area. A higher temperature leads to more instability and a greater
potential for rising air. When the environment is already unstable, an urban area can make it more unstable. An urban area can be the
burst point for convection. In many cases convection will begin over the urban area and then drift downwind with the mean wind direction. Areas
downwind from an urban area often tend to get more precipitation when the precipitation is generated from convective air mass type storms.
Another mesoscale influence is the urban heat island. Concrete and metal absorb solar radiation and cause the temperature to warm more as
compared to solar radiation striking vegetation. On sunny days, the urban area can end up being several degrees warmer than the
surrounding countryside. Over many years this can cause the average temperature for a city to increase. Climate data is sometimes
calculated for the last 30 years so that data before 30 years ago (that was a little less reliable and when the city was a much
different size) does not influence the record. 30 years is used to have a sample size large enough so that a climatic average is
meaningful. However, record temperatures will often be used for the entire history of temperature measurements at a location. It is
common to have record high temperatures as the urban region expands.
Other mesoscale influences include less moisture to evaporate into the air, gustier winds and funneling of wind due to obstructions
to wind flow, the potential for severe damage to occur when severe weather strikes, more particulates in the air to develop clouds/fog when the
relative humidity is high, and warmer nighttime temperatures due to the building
materials releasing heat that was absorbed during the day.
4. URBAN WX SERIES: STORM DAMAGE
Tornadoes and hurricanes are not attracted or unattracted to urban areas but it can be expected that storm damage in urban areas will
increase in the future. This is due to urban areas progressively occupying a larger area. As urban area increases, the chance that a
severe storm will move over the urban area instead of over vegetated fields or forests will increase. Also, much of the world’s population
lives near the coast. The population and construction in coastal areas will continue to increase in the future thus increasing the
damage risk in hurricane prone areas.
Storms can produce damage through flash floods, hail, strong straight-line winds, tornado winds, hurricane winds, and lightning. Urban
areas do not allow water to soak in the ground where concrete covers the ground thus a very good drainage system is needed to reduce
the threat of flooding from flash floods. Sometimes the rain is too heavy to be removed fast enough and it can lead to flood damage. River
floods also can flood urban areas near the river or stream system. It can cost a significant amount of resources to block river waters from
flooding buildings. Hail can do significant damage to exposed vehicles, roofs and other structures. Hail storms lead to a significant
amount of the insurance claims that take place. Strong straight-line winds are convective wind gusts from thunderstorms. These can do
damage to fencing and any other structure exposed to the wind. The snapping of tree branches can produce damage when the branches fall
on housing, business structures or vehicles. Tornado winds only impact a very small area of land but where they do strike the damage
can be very severe. Lightning is a threat to temporarily cutting out power, starting fires and damaging the structures it strikes. Severe weather will
continue to be a dominate reason for having high quality weather analysis and forecasting. Knowing the threat can save
lives and reduce damage costs.
5. URBAN WX SERIES: WEATHER PREP & MAINTENANCE
There are several weather preparations and maintenance needs that are very important in urban areas. These preparations, although costly,
help transportation and commerce run closer to normal and decrease threats created by the weather. The costs for these preparations are
more than made up for by quickly returning the city to normal business operations. One of these preparations includes keeping the roads
clear. This is done through plowing and adding agents to be roads that promote melting. A winter storm can cause activity in an urban
area to slow to a crawl. Quick snow/ice removal and road treatments help the city get back to normal more quickly.
Another weather maintenance is road repairs. Ice can be especially damaging to roads. The damage can occur when water gets into cracks,
freezes, then expands. The expansion breaks the road even more and vehicles driving over the icy cracks damages them even more. Once
the ice melts, cracks and pot holes are left behind. Road crews then need to come in and fill and seal the cracks. Untreated cracks
and pot holes can damage tires and vehicles. Urban resources dedicated to road repairs are important to maintaining and safe and
quick flow of traffic.
Other necessary urban weather maintenance needs include:
1) restoring power from storm damage and lightning strikes
2) keeping the public advised of threatening weather
3) maintaining plants, flowers, trees and vegetation within city public areas
4) having effective first responders in cases of weather emergencies, having contingency plans for particular weather emergencies
5) maintaining weather warning systems such as sirens
6) having clean and effective storm drainage systems
7) effective air quality policies
8) help for people and pets that are exposed to extreme heat or extreme cold
9) repairing damage caused by storms
10) adequate insurance and staff to deal with severe weather situations