hydrology

1. WMSU
WESTERN MINDANAO STATE UNIVERSITY
WMSU
Hydrometeorology
Temperature, humidity and wind relevant
to weather

2. TEMPERATURE
Temperature is the measure of thermal
or internal energy of the molecules
within an object or gas. We can
measure temperature of an object
using either direct contact or remote
sensing. Temperature of air is closely
related to other atmospheric properties,
such as pressure, volume and density.

3. Temperature controls planting dates
and the growth of plants as well as
insect pests and crop diseases. As
an integral part of weather,
temperature also determines the
type of precipitation (rain/snow/sleet)
that might occur if you are in a
location that is experiencing near
freezing conditions.

4. If there are two objects with different
temperatures, energy always flows
from the warmer object to the colder
object.
In the atmosphere, temperature is
related to volume, pressure, and
density. Temperature is inversely
related to density but directly related
to pressure and volume.

5. TEMPERATURE SCALES
There are three different scales frequently
used to measure
temperature. Fahrenheit, the most
commonly used scale in America, was
developed in the early 1700s and is the
oldest of the three scales we still use. The
lowest temperature G. Daniel Fahrenheit
was able to reach using a combination of
salt, ice, and water was set as zero
degrees F in his scale.

6. The second oldest scale is the Kelvin
scale, developed by Lord Kelvin in
the mid 1800s. This scale begins at
absolute zero and has no negative
numbers. Absolute zero is when all
molecular motion stops, which is not
known to exist anywhere in the
universe. Even space has a
background temperature of 3 K.

7. The Celsius scale was developed
after the Kelvin scale in the
1800s. One degree C is the same
size as one degree K except that
zero is at a different value. In the
Celsius scale a change of one
degree is equivalent to one Kelvin
and 1.8 degrees Fahrenheit

8. MEASUREMENT OF TEMPERATURE
The temperature of an object or gas
can be measured either using direct
contact or with remote sensing.
The thermometer is calibrated so that it
can accurately measure the
temperature of the substance. More
modern thermometers use electronic
sensors to measure temperatures
using the thermal properties of the
sensor to determine how hot an object
or gas is.

9. Figure 10 shows a temperature sensor
that is contained within this unit and
shaded from the sun. Vents on the
outside allow for the wind to flow over
the temperature sensor inside. The
particular sensor shown is a Vaisala
WXT520 sensor that measures many
different weather variables, including
temperature and wind speed, and is
used at NC ECONet stations.

10. HOW DOES THIS RELATE TO PUBLIC HEALTH?
Rising average temperatures and more
frequent and more intense heat waves
due to climate change are affecting
human health in several ways. Most
directly, warmer average temperatures
and more extreme temperatures put
more people at risk for heat-related
death and disease, such as heat stroke
and dehydration.

11. Warmer temperatures also diminish
air quality by increasing exposure
levels of ground-level ozone. Ozone
is a dangerous air pollutant that is
damaging to lung tissue and lung
function, and can exacerbate
respiratory diseases such as asthma
or chronic obstructive pulmonary
disease (COPD).

12. Cyanobacteria, or bluegreen algae, are commonly
found types of harmful algal blooms in North Carolina.
This algal bloom occurred on the Chowan River in
Edenton, NC.

13. Exposure to these pathogens can
result in waterborne diseases. For
example, consumption of food such
as shellfish that is contaminated
with Vibrio vulnificus, a naturally
occurring estuarine bacterium,
generally causes vomiting, diarrhea,
abdominal pain, and death.

14. Warmer average temperatures have led to milder winters
and hotter summers, which in turn is likely to impact the risk
for vector borne or zoonotic diseases. As temperatures rise,
the geographical spread and seasonality of diseases like
Lyme disease or West Nile virus may change.1,5 The
Southeast, a region that already has favorable conditions
for mosquitoes, has the greatest projected increase in the
West Nile virus due to climate change.

15. HUMIDITY
Humidity is a measure of the amount
of moisture in the air. It tells you how
comfortable it is to be outside, and if
there is enough moisture to create
clouds and rain.

16. Humidity has a large impact on
human and animal health and the
health of crops. It affects the ability
of both plants and animals to cool
themselves through evaporation. It is
also important to precipitation
formation.

17. RELATIVE HUMIDITY
Relative humidity is given as a
percentage and tells you how close the
air is to being saturated. If the relative
humidity is 100%, the air is saturated. If
the relative humidity is 50%, the air
contains half the water vapor required
for it to be saturated. If the amount of
water vapor in the air increases, the
relative humidity increases, and vice
versa.

18. DEW POINT
Dew point is a better indicator of
humidity than relative humidity
because it is not a percentage
dependent on temperature. The dew
point is the temperature to which the
air would have to be cooled to
become saturated. Below the dew
point, water will condense out of the
air onto surfaces.

19. When humidity is high, the dew point
temperature is only a few degrees
below, or equal to, air temperature.
In dry places, like deserts of the
southwest, air temperature can be
50 or 60 degrees above the dew
point.

20. HOW DOES THIS RELATE TO AGRICULTURE?
If you're a person that likes to spend
time outdoors, then you know that
humidity can have a great effect
upon human health. As growers work
outside during the hottest part of the
day, they need to take extra care to
stay hydrated when temperature and
humidity are high.

21. HUMIDITY EFFECTS ON PLANTS
When humidity is low, and dew
points are in the 50s and low 60s,
moisture evaporates from plants very
quickly. When this happens, plants
can wilt rapidly if too much water is
pulled out of plant cells through
transpiration.

22. Humidity also influences plant
diseases, especially fungi and molds
that grow and spread rapidly when
humidity is high. Humidity can also
affect the fruit set of some plant
species

23. Humidity is also an important
consideration for post-harvest storage
of crops. Cold temperature and low
humidity are important for the long-term
storage of grains (corn, wheat etc).
Conversely, fleshy vegetables and
fruits (apples, cucumbers) need to be
stored in cold temperatures and high
humidity in order to prevent water loss
from the fruit that results in shrivelling.

24. WHAT IS WIND? HOW DOES WIND FORM?
Wind is the horizontal motion of the
air past a given point. Winds begin
with differences in air pressures.
When air pressure is higher at one
place than another, it sets up a force.
This force pushes from the high
pressure towards the lower pressure.
The greater the difference in
pressures, the stronger the force.

25. WHAT DETERMINES WIND SPEED?
Wind speed is determined by air
pressure. Besides force, the distance
between the area of high pressure
and the area of low pressure also
determines how fast the moving air
accelerates. Meteorologists refer to
the force that starts the wind flowing
as the “pressure gradient force.”

26. OTHER WIND FACTORS
Wind is used to describe the
prevailing direction from which the
wind is blowing with the speed given
usually in miles per hour or knots.
Also, friction along the ground and
the Coriolis effect plays a significant
part in the speed and direction of
wind.

27. WHAT ARE WIND GUSTS?
The National Weather Service (NWS)
defines wind gusts as sudden, brief
increases in wind speed. According to the
U.S. weather observing practice, gusts occur
when the peak wind speed reaches at least
16 knots. To be a wind gust, the variation in
wind speed between the peaks and lulls must
also be at least 9 knots. The duration of a
gust is usually less than 20 seconds.

28. TYPES OF WIND & WIND CLASSIFICATIONS
A katabatic wind is the technical
name for a drainage wind. A drainage
wind is a type of wind that carries
high-density air from higher
elevations down a slope under the
force of gravity. Also called fall winds,
katabatic winds can rush down
slopes at hurricane speeds, but most
are no faster than 10 knots.

29. Anabatic winds are a type of wind
that move upslope. Warmer surface
temperatures on the mountain slope
compared to the surrounding air drive
these winds upward.

30. WHAT ARE CLASSIFICATIONS OF WINDS?
There are two popular wind
classification scales, including the
Beaufort Wind Force scale and the
Saffir-Simpson Hurricane Wind scale.

31. Since 1805, mariners have
used Beaufort Wind Force
scale. Named after the Irish
hydrographer who invented it,
this 0-12 scale takes into
account the strength of the wind
and tries to match it up with sea
conditions in open water. On
this scale, 0 refers to calm
winds while 12 refer to
hurricane force winds.

32. The Saffir-Simpson Hurricane Wind scale is another way
of classifying winds for tropical systems. This is a much
more popular wind scale, as mostly everyone has heard
hurricane classified by categories.

33. WIND ADVISORY
A Wind Advisory is issued for either of
the following two reasons:
• When there are sustained winds of
31 to 39 mph for an hour or more
• When there are wind gusts of 46 to
57 mph for any duration

34. HIGH WIND WATCH
The next type of wind warning is
a High Wind Watch. A High Wind
Watch is issued when the following
conditions are possible:
1. When there are sustained winds
over 40 mph for an hour or more.
2. When there are wind gusts of 58
mph or higher for any duration.

35. HIGH WIND WARNING
A High Wind Warning is for the same conditions as a
High Wind Watch. The only difference is that a warning is
for when these conditions are expected rather than
possible. As a reminder, we included the conditions again
below:
• When there are sustained winds over 40 mph for an
hour or more
• When there are wind gusts of 58 mph or higher for any
duration.

36. HURRICANE FORCE WIND WARNING
These wind warnings are for when one or both of
the following conditions are expected to begin in
the next 36 hours but are not directly associated
with a tropical cyclone:
• When there are sustained winds over 64 knots
or greater
• When there are frequent gusts (duration of
two hours or more) of 64 knots or greater

37. HOW DO YOU FORECAST WIND?
• First, meteorologists must forecast the likely barometric
pressure. They do this based on existing high- and low-
pressure fronts as well-known causes of increasing and
decreasing pressure. Michael Barnard does a great job of
explaining the rest of the factors that go into forecasting
wind further on Quora. They include:
– The rotation of the Earth
– Cyclonic storm patterns
– Storm lines

38. Wind shear
Wind shear is the change of wind
speed and/or wind direction over a
certain height. Agricultural pilots deal
with wind shear on a regular basis
when flying planes such as crop
dusters. When spraying crops, these
planes tend to fly low so that the
sprayed material goes in the direction
and location the pilots want.