Bhambra_Kanika_A3
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School
University of Waterloo *
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238
Subject
Geography
Date
Dec 6, 2023
Type
Pages
4
Uploaded by DeaconBarracuda1640
Assignment #3: Precipitation Concepts and Calculations
Question 1:
a)
Define ‘adiabatic cooling’ and briefly state its significance with respect to
precipitation.
Adiabatic cooling refers to the cooling of air caused by volume expansion without the
environment exchanging heat with its surroundings. Due to a decrease in atmospheric pressure,
air expands as it rises in the atmosphere. With respect to precipitation, adiabatic cooling
initiates cloud formation as moist air rises and reaches a dew point causing condensation of
water vapour and forming clouds. This causes clouds to expand and grow eventually leading to
precipitation.
b)
Define ‘relative humidity’ and briefly state its significance with respect to
precipitation.
Relative humidity refers to the amount of moisture present in the air compared to the
maximum amount of moisture the air can hold at a certain temperature. It is usually expressed
as a percentage. With respect to precipitation, relative humidity indicates the amount of
moisture of the air and when the air reaches 100% relative humidity, the air cannot hold any
more moisture which causes condensation to occur, and eventually precipitation. High relative
humidity increases chances of precipitation.
c)
Draw a labelled diagram to briefly explain how: i) frontal, ii) convective, and iii)
orographic lifting mechanisms form clouds and precipitation.
d)
Using Figure 1 below, answer the following questions:
i. Does cooling air increase or decrease in relative humidity? Why?
Cooling air increases relative humidity because cooler air has a lower capacity to hold moisture.
As the air cool, its ability to hold moisture and water vapour decreases meaning the amount of
moisture un the air increases.
ii. Is a parcel of air at 10°C and a vapour pressure of 2kPa saturated?
A parcel of air at 10°C and a vapour pressure of 2kPa is not saturated because it is past the
saturation point for that specific temperature. For 10°C, the saturation vapour pressure is 1.0
kPa therefore it is condensed rather than saturated.
iii. At what temperature will a parcel of air with a vapour pressure of 0.5 kPa become
saturated?
At 0°C a parcel of air with a vapour pressure of 0.5 kPa will become saturated.
iv. What is the relative humidity of air with a vapour pressure of 0.5 kPa at 10°C?
The relative humidity of air with a vapour pressure of 0.5 kPa is 50% at 10°C.
e)
Describe two differences between rain and snow from a hydrological point of view
(
other than the fact that one is frozen and the other is not
).
From a hydrological point of view, two differences between rain and snow are:
1.
Formation: Although the processes by which snow and rain are generated are similar,
they are quite different. Ice nuclei are essentially the building blocks of ice crystals and
develop through condensation, a process that produces ice crystals more quickly than
water droplets. Snowflakes are created when water vapour is immediately transformed
into ice crystals. The process of rain begins when water vapour rises to the atmosphere
and cools down to form droplets of water (caused by condensation) which essentially
form into clouds. As they become larger and too heavy to remain in the air, the droplets
are released from the clouds as rain.
2.
Conditions/timing: The two require distinct climates for rain and snow to occur, which is
another difference between the two. Rain can rain at any time of the year, although it
tends to occur more frequently in hotter climates and/or during the warmer months. On
the other hand, because of the cooler temperatures and lower freezing levels, snowfall
occurs much more frequently during the winter months.
Question 2:
a)
Estimate the precipitation from Station 2 by interpolation from the data (Table 1) from
the remaining stations.
P
2
=
𝑁2
6
[
𝑃1
𝑁1
+
𝑃3
𝑁3
+
𝑃4
𝑁4
+
𝑃5
𝑁5
+
𝑃6
𝑁6
+
𝑃7
𝑁7
]
P
2
=
96
6
[
140
118
+
120
93
+
115
91
+
110
87
+
90
65
+
70
50
]
P
2
= 124.63 cm
125 cm
b)
Using Table 1 & Figure 2, calculate the volume of precipitation over the watershed
during 2013, using the Arithmetic Average method.
P =
𝑃1+𝑃2+𝑃3+𝑃4+𝑃5+𝑃6+𝑃7
𝑁
P =
140+125+120+115+110+90+70
7
P = 110 cm
Area = 7200 km
2
Volume = 110 cm x 7200 km
2
= 7.92 km
3
c)
Using Table 1 & Figure 2, calculate the volume of precipitation over the watershed using
the Isohyetal Method (Please use 10 cm contours and draw the isohyetal lines directly
on Figure 2) using the stations in Table 1 as a guide to draw your contours. NOTE: You
can assume that the top and bottom points of the watershed are +/- 10cm from the
closest isohyetal contour.
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d)
The GRCA senior hydrologist has estimated that the error in precipitation
measurements is ~5%. With that in mind,
comment
on the
accuracy
of the two
calculations of precipitation volume over the year above, noting which method you
think is
best
and if there is a significant
difference
in the methods.
The method that is the best and most accurate would be the isohyetal method because the
gauges are plotted, and more specific values are used. The isohyetal method also utilizes more
geographical aspects which is what makes it more precise than other methods. In comparison
to the Arithmetic Average method, the interpolation method is also accurate since it calculates
an estimate of unknown precipitation using data from the current and past years.