Hydrometeorological Hazards
Table of Contents
Introduction
3
Essential Questions
4
Lesson 1: Typhoons
6
Starting Out
Learn about It
Check Your Understanding
Explore Your World
Case Study
Lesson 2: Thunderstorm
Starting Out
Learn about It
Check Your Understanding
Explore Your World
Case Study
Lesson 3: Flooding
Starting Out
Learn about It
Check Your Understanding
Explore Your World
Case Study
Lesson 4: Storm Surges
Starting Out
Learn about It
Check Your Understanding
6
6
12
13
14
15
15
16
20
21
22
23
23
24
28
29
29
30
30
31
35
1
Explore Your World
Case Study
37
37
Lesson 5: El Niño and La Niña
38
Starting Out
Learn about It
Check Your Understanding
Explore Your World
Case Study
38
38
45
46
46
Real World Challenge
47
Check and Reflect
49
Wrap Up
50
Bibliography
51
Glossary
54
Answers to Check Your Understanding
55
2
GRADE 11/12 |Disaster Readiness and Risk Reduction
Unit 7
Hydrometeorological Hazards
Interactions between the atmosphere and the hydrosphere are necessary for life on Earth. If
taken to extremes, natural phenomena such as precipitation and wind can be less than
helpful. Every year, the Philippines experiences an average of twenty tropical cyclones, a
fraction of which being more destructive than the others.
Fig. 1. Tacloban after Typhoon Yolanda
Image from Trocaire from Ireland, Tacloban Typhoon Haiyan 2013-11-14, CC BY 2.0
3
Essential Questions
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What is the difference between a typhoon and a thunderstorm?
How are storm surges different from tsunamis?
What can you do to help lessen the destruction caused by a typhoon?
Is it possible to predict hydrometeorological hazards?
How can you monitor incoming hydrometeorological hazards?
In this unit, you should be able to:
● distinguish and differentiate among and between different hydrometeorological
hazards;
● recognize signs of an impending hydrometeorological hazard;
● apply appropriate measures/interventions before, during, and after
hydrometeorological hazards;
● interpret hydrometeorological maps; and
● use available tools in monitoring hydrometeorological hazards.
● Wave shoaling is the process by which waves entering shallow waters increase in
height as an effect of increased velocity. It is involved in both tsunami and storm
surge formation.
● The continental shelf is the edge of a continent or landmass that is submerged in the
ocean. It begins from the coastline and continues downward until a point called shelf
break. From hereon is the continental slope which further down transitions into the
continental rise, the outermost portion of any continent or landmass.
4
Fig. 2. Cross section of the edge of the continent
The image above shows the elements that can be found in a continental margin. What
do you think are the effects of the different elements to developing waves from a
storm surge?
5
Have you ever wondered why there are no hurricanes reported in the Philippines? Or why a
higher storm warning signal is issued for your area even though there is hardly any
rain?
Think-Pair-Share
With your partner, share, what you recall, are the effects of typhoon in your daily lives.
Discuss how it affects the following aspects in your life:
1.
2.
3.
4.
physical surroundings including your house and the structures in your community
schooling
family
health
After discussing with your partner, make one general statement to answer the question:
How do typhoons affect our lives?
A tropical cyclone is an organized, rotating system of clouds and thunderstorms that
initially form over tropical ocean waters. The exact same phenomenon is called different
names depending on where it originated.
Typhoons are formed over the northwest Pacific. In the Atlantic and the east Pacific, the
term hurricane is used, while in the Indian Ocean and south Pacific, it is simply referred to
as tropical cyclone.
6
Fig. 1. Typhoon Haima at peak intensity on October 18, 2016
VIIRS DNB image captured by NOAA’s Suomi NPP satellite, converted by Wu Zhen and optimised by Meow, Haima 2016-10-18
1640Z, marked as public domain, more details on Wikimedia Commons
Parts of a Typhoon
A tropical cyclone has a center called the eye. The eye is the calmest portion of any storm
and the point at which the winds rotate. Winds converging toward the center are deflected
by the Coriolis force, which is a deflection caused by the rotation of the earth. This force is
zero at the equator and increases toward the poles. Air moving from high to low pressure in
the northern hemisphere is deflected to the right. The inverse applies for winds in the
southern hemisphere.
7
Fig. 2. Cross section of a cyclone.
The strongest winds of a tropical cyclone (maximum sustained winds) are located closest
to the eye of the storm, in an area called the eyewall or wall cloud. The magnitude of these
winds are determined through sampling and averaging, and are used as the basis for
classifying tropical cyclones.
Tropical Cyclone Intensity Scale
In its weakest form, a tropical cyclone is called a tropical depression. If the depression
intensifies and attains sustained winds of 62 kilometers per hour, it becomes a tropical
storm. A tropical cyclone is classified as a typhoon when its sustained winds reach 118
kilometers per hour.
8
Typhoons are from the northwest Pacific. Hurricanes are from the Atlantic and the east
Pacific. In the south Pacific and the Indian Ocean, they are called cyclones.
The Philippines uses a tropical cyclone intensity scale developed by the Philippine
Atmospheric Geophysical and Astronomical Services Administration (PAGASA), which
classifies tropical cyclones into five categories, namely: tropical depression, tropical storm,
severe tropical storm, typhoon, and super typhoon. Severe tropical storm and super
typhoon were only officially included as categories in PAGASA’s public storm warning list in
2015.
Table 1. PAGASA’s Tropical Cyclone Intensity Scale
Category
Super Typhoon
Typhoon
Severe Tropical Storm
Tropical Storm
Tropical Depression
Sustained Winds
(kilometers per hour)
> 220
118 - 220
89 - 117
62 - 88
< 61
source:https://www1.pagasa.dost.gov.ph/index.php/learning-tools/94-weather/479-tropical-cyclones#classification-of-tropical-cycl
ones
Typhoons cause damage and destruction through torrential rainfall which can induce flood
and landslides, violent gusts of wind, occasional thunderstorms, and strong waves from
storm surges.
Our country experiences an average of 20 tropical cyclones annually, and these may range
from a tropical depression to a super typhoon, or perhaps even beyond the maximum set by
the intensity scale. Some of the notable tropical cyclones that have struck the Philippines
include Tropical Storm Ondoy (international name: Ketsana), Typhoon Pablo (international
name: Bopha), and Super Typhoon Yolanda (international name: Haiyan).
Metro Manila was brought to a virtual standstill in 2009 when Tropical Storm Ondoy
9
delivered torrential rains which caused the flooding of streets and bridges in the area.
Nearby provinces such as Rizal, Laguna, Bulacan, and Batangas were also greatly affected.
Fig. 3. Unenhanced satellite photograph taken by the National Oceanic and Atmospheric Administration of the
U.S.A. as Typhoon Pablo (Bopha) makes a landfall in the Philippines.
NASA, NOAA, Typhoon Bopha Landfall Unenhanced - Dec 3 2012 2030 UTC, marked as public domain, more details on Wikimedia
Commons
In December 2012, the island of Mindanao was devastated by Typhoon Pablo. It was
considered as the ‘most powerful typhoon to hit Mindanao in decades.’ The death toll was
estimated to have been as many as 1900.
10
Fig. 4. Aftermath of Typhoon Pablo in Cateel, Davao Oriental
Sonny Day from Davao CIty, Philippines, Homes destroyed by Typhoon Bopha in Cateel, Davao Oriental, CC BY 2.0
Almost a year later, in November 2013, Super Typhoon Yolanda struck the country, with
sustained winds of 295 km/h and gusts as strong as 360 km/h. Central Philippines was the
worst hit, particularly the islands of Leyte and Samar.
Public Storm Warning Signal
PAGASA monitors tropical cyclones and low-pressure areas (LPA’s) as soon as these enter
the Philippine Area of Responsibility (PAR). After compiling data from concerned weather
stations and monitoring agencies, they release forecasts and weather bulletins.
A Public Storm Warning Signal (PSWS) is issued in the affected areas to inform the public
on the projected impacts of the storm and how soon these are expected to be felt.
Similar to the aforementioned new tropical cyclone categories, PSWS no. 5 was also recently
added. It is raised when a super typhoon is affecting the area.
11
Table 2. PAGASA’s Public Storm Warning Signals (PSWS)
PSWS
1
2
3
4
5
Lead Time from the First
issuance of the signal
36 hours
24 hours
18 hours
12 hours
12 hours
Sustained Winds
30-60 km/h
61-120 km/h
121-170 km/h
171-220 km/h
more than 220 km/h
Expected Damages due
to Winds
none to very little
light to moderate
moderate to heavy
heavy to very heavy
very heavy to widespread
source: https://www1.pagasa.dost.gov.ph/index.php/learning-tools/94-weather
Precautionary Measures for a Typhoon
In case of an incoming typhoon, you can do the following:
● Stay updated on the location and expected impacts of the typhoon through whatever
device is at your disposal;
● Stay indoors and ensure that windows and doors are locked;
● Bring in any belongings that may be blown/washed away by the typhoon;
● If in a coastal area, seek higher ground. This is especially important if a storm surge is
anticipated in your area; and
● Do not go out until doing so has been declared safe.
A. Complete the table below.
Tropical Cyclone Category
(1)
Super Typhoon
(3)
Tropical Storm
(5)
Sustained Winds
118-220 km/h
(2)
less than 60 km/h
(4)
89-117 km/h
12
B. Answer the following in complete sentences.
1. What is the difference between a hurricane and a typhoon?
2. What is the basis for classifying the intensity of tropical cyclones?
3. What information will you have if PAGASA announces a PSWS #2 in your area?
4. Cite at least three possible damages that can be caused by a typhoon.
C. Synthesis and evaluation.
Why do a Super Typhoon category and a PSWS #5 in the classification and warning
system added by PAGASA? Discuss the reasons to your answer.
In groups of 5, conduct a simple experiment to see how a typhoon affects objects as it
passes through them.
Simulate typhoon movement using the following materials:
small basin filled with water
paper clip tied to a string,
stick or any object you can use for stirring.
Do the following procedure:
13
1.
2.
3.
4.
5.
Stir the water to make it swirl for a few seconds.
Control the string to dip the paperclip in the center of the swirling water.
Note down your observations.
Repeat steps 1-3 two more times.
Repeat steps 1-4 but this time, dip the paperclip in a different position outside the
center of the swirl.
How did the paperclip move in different parts of the rotating (swirling) water?
How would you relate the movements of the paperclip to the impacts of the typhoon as it
passes through an area?
What other materials can you use to simulate typhoon movement and its impacts?
Share your answers in class.
If I Were a Storm
Imagine yourself as a tropical depression amassing strength somewhere on the eastern
portion of the Philippine Area of Responsibility. You can inflict damage in many
vulnerable areas. Metro Manila, the coastal city of Davao, and Baguio City are examples
of areas that have features that make them vulnerable to you. Metro Manila has the
largest population, a flat topography, and a drainage network highly susceptible to
blockage. You can generate storm surges and coastal floods in Davao City; and you can
produce many landslides in Baguio.
Factoring what you know about the characteristics of these places, how do you think will
each area be affected if you develop into a typhoon?
What can the community do to lessen the negative impact of a strong typhoon?
14
Is it true that lightning doesn’t strike the same place twice? Is it possible to hear thunder
before seeing lightning?
Form a group with five members. On a piece of paper, write a word that you can associate
with thunderstorm then pass the paper to the next group member to add another word to
the list. Circulate the list until everybody in the group has written a word. Make sure there
are no repeated words in the list. You may again circulate the list until the group runs out of
words or five minutes have passed.
Use the next five minutes to study the
list as a group and create a mind map
to describe what the group knows
about thunderstorms.
On another piece of plain white paper,
write the word thunderstorm in the
middle. Use lines to connect the words
on your group list to see how the
different words you have are linked to
thunderstorm and with the other
words or concepts. Present your mind
map in class.
What are the hazards associated with a thunderstorm?
15
A thunderstorm is a weather condition characterized by heavy rain and wind accompanied
by lightning, thunder; sometimes with hail and tornadoes. It can last for 30 minutes to
several hours.
Fig. 1. A thunderstorm Port la Nouvelle, France
Maxime Raynal from France, Port and lighthouse overnight storm with lightning in Port-la-Nouvelle, CC BY 2.0
Thunderstorms require moisture and rapidly rising warm air, which is why they are common
in humid areas. They are frequently observed near the equator and rarely in the polar
regions.
Thunderstorm Formation
Convection is the key mechanism in thunderstorm formation. Warm air near the ground
rises and cooler air sinks. Warm surface air will continue to rise since it is less dense than the
surrounding air. The rising air is called updraft, while the downward moving air is called
downdraft. Thunderstorms form when there is a balance of updrafts and downdrafts.
16
As air continues to rise, it cools and condenses to form clouds. As condensation progresses,
the clouds increase in size and spread upward into an anvil-like shape, forming
cumulonimbus clouds. Clouds can contain millions of suspended water droplets and ice
particles which continuously collide due to turbulent air currents. These collisions knock out
electrons. These knocked out particles travel to the lower portion of the cloud, creating a
negative charge, while rising moisture that just lost an electron moves positive charges
toward the top of the cloud.
Fig. 2. thunderstorm cloud formation. The main charging area in a thunderstorm occurs
in the central part of the storm where air is moving upward rapidly (updraft) and
temperatures range from −15 to −25 Celsius.
The below-freezing temperatures at the top of the cloud causes droplets to freeze and
17
become negatively charged. The frozen droplets will likely fall to the lower portion of the
cloud, which will enhance the negative charge. Or they may continue downward to the
ground. This negative charge will continue building up to the point that it repels the existing
negative charge on the Earth’s surface, effectively giving the objects on the ground a positive
charge.
When sufficiently ionized, air can become electrically conductive (plasma). Air is
ionized when the separation between protons and electrons is greater than before, meaning
more movement for these charged particles. This ability to move is what makes conduction
possible. The electrons now seek the path of least resistance. While mathematics and
physics teach us that the shortest distance between two points is a straight line, this is not
necessarily true for lightning. An electric field can be represented as flux lines, which are
similar to the lines on a basketball or the lines between slices of orange.
While ionization occurs and plasma is being formed above, the objects on the ground reach
out to the clouds by growing finger-like electrical discharges called streamers. Even our
bodies can produce streamers which is why it is not advised to be outdoors during a
thunderstorm.
Lightning and Thunder
Plasma travels downward to create a path for the current to flow. The electrons surge down
to meet the streamers, creating lightning. The core of a lightning bolt is hotter than the
surface of the sun. It is because of this heat that we observe a white or blue flash. As
lightning strikes, the air around it is heated and expands rapidly to the point that it explodes.
Thunder is a shockwave caused by this explosion, which manifests as a loud booming
sound.
Lightning strikes can occur in succession, and can certainly hit the same place repeatedly.
Such is the case with the 444-meter tall Empire State Building, which gets struck 25 to 100
times a year.
Types of Thunderstorms
Thunderstorms can be classified by severity or structure. According to the National Weather
Service of U.S., a thunderstorm is severe if it contains wind gusts of at least 94 km/h, hail at
least an inch in diameter, or a tornado. A thunderstorm can be single cell, multi-cell, or
supercell, or a squall line.
A single cell thunderstorm is a short-lived storm consisting of a single updraft-downdraft
18
couplet. It is capable of producing heavy rainfall and lightning.
A multi-cell thunderstorm is a system of individual cells. Each cell usually lasts for 30
minutes to an hour, while the entire system can last for hours. Multi-cells may produce hail,
flood, and brief tornadoes.
A supercell thunderstorm is a highly organized thunderstorm with a large rotating updraft
that can be 20 km in diameter and 15 km in height. It can last for several hours and
produces violent tornadoes.
A squall line is a group of storms arranged in a straight line. It is shorter-lived than multicells and supercells, and are less likely to produce tornadoes. Squall lines are typically 15 to
20 km long, but can reach up to hundreds of kilometers.
Thunderstorms in the Philippines
Most of the thunderstorms that have
occurred in the Philippines are associated
with typhoons. In 2013, a thunderstorm
caused by tropical depression Wilma
created a water spout, or a tornado that
originated from a water body. This
tornado hit north Bohol and Cebu, with
winds up to 80 km/h. One week later, a
tornado with winds of 200 km/h also hit
Leyte. Tornadoes are not uncommon in
the Philippines, but are not as frequent or
severe as in countries such as the U.S.
In 2016, two individuals were killed in a
house fire ignited by lightning during a
thunderstorm brought by
typhoon
Marce. This typhoon caused heavy rains
and thunderstorms in Davao. It was
suspected that lightning struck the main
electricity line, igniting the house.
19
Signs of Approaching Thunderstorm
An approaching thunderstorm has apparent warning signs, such as gentle warm air
suddenly replaced by strong, chilly bursts of wind, lightning strikes accompanied by
deafening thunder, and abrupt, intense rain. Apart from these observable indicators, there
are forecasts and weather bulletins to let you know of any impending thunderstorms.
PAGASA begins a thunderstorm watch when thunderstorm formation is likely within the
next twelve hours. Updates will be disseminated thru media networks and the PAGASA
website. When there is indication that a thunderstorm is threatening a specific area within
the next two hours, PAGASA issues a thunderstorm advisory.
Precautionary Measures Before and During a Thunderstorm
When a thunderstorm is imminent, you can do the following:
● Stay indoors and make sure windows, doors, or other openings are locked;
● Seek shelter. A car is ideal for this purpose because it lets the current bounce around
its walls, not because the rubber tires keep the charges away;
● Unplug electrical appliances and avoid using corded phones or any gadget physically
connected to the wires outside. It is safe to use cellular phones and remote controls;
● Avoid any contact with water. This includes bathing and washing your hands;
● If on water, get to land immediately; and
● If in an open field, keep distance from trees/high points because they have a higher
possibility of being struck by lightning.
Squall lines and multicells consist of more than one cell or individual thunderstorm.
A. Answer the following questions.
1. What is an updraft?
2. What is thunder?
3. What are the four kinds of thunderstorms?
20
B. Answer the following in complete sentences.
1. Why are thunderstorms not as common in the polar regions as they are in the
equator?
2. What is the difference between a thunderstorm and a typhoon?
3. Why should you stay away from water and metals during a thunderstorm?
4. What is the difference between a thunderstorm watch and a thunderstorm
advisory?
C. Synthesis and Evaluation
A lightning rod is metal structure that are placed on high points in structures like
buildings. It is installed as a safety precaution against lightning hazards. It is
connected to a long wire that has its other end buried underground. Based on what
you have learned about lightning, how do you think lightning rods help keep
structures safe from lightning?
The speed of sound varies with temperature and humidity. In dry air at 0 degrees Celsius, it
is 331.3 meters per second, and increases to 346 m/s at 28 degrees Celsius.
Using this information, determine how far the lightning strike is if you hear the thunder 5
seconds after you see the flash. Knowing this, what should be your plan of action?
21
Flying in Storms
It is incredibly dangerous to fly into a hurricane so airlines cancel their flights when
there is a hurricane, but flights usually go on through regular thunderstorms.
Thunderstorms bring a lot of hazards to aircrafts. Dangers of windshear, microbursts,
severe turbulence, icing and torrential rain can all take place at the same time when the
airplane comes across a thunderstorm. Airplanes that wander into a thunderstorm are
at risk of structural failure or even the physical breaking of planes.
Windshear is a sudden change in wind direction and velocity and this results to severe
turbulence. Microbursts are severe updrafts, downdrafts, and horizontal windshear
that can really test the performance capabilities of the pilot and the plane. Modern
airplanes are equipped to withstand lightning strikes but pilots still try to avoid lightning
because occasionally, there can still be damages incurred from lightning strikes.
Lightning strikes cannot always be avoided because even if the plane is far from the
thunderstorm, the lightning can still reach the plane.
Pilots regularly encounter areas with thunderstorms and they need to rely on the
plane’s onboard weather radar and windshear detection systems, ground-based
observation, and experience, to make the safest decisions possible. Sometimes it can
be hard to make decisions because there are other factors to consider such as the
route and the schedule that they have to follow.
Let us investigate!
What are the risks of flying into areas with thunderstorms?
Why do you think that unlike hurricanes, flights are not always cancelled even
when there is thunderstorm?
How do planes and pilots minimize the risks of thunderstorm hazards?
22
Are floods limited to low-lying, urbanized areas? Can flooding occur in areas of higher
altitude?
Recall the most recent flooding event that made the national news. From what you know or
experienced, fill in the diagram below to identify the possible causes and the actual impacts
of that flooding event.
What possible ways can we minimize or totally prevent flooding events?
23
Fig. 1.Aerial view of the area around the Manggahan floodway in the aftermath of typhoon Ondoy flooding.
Chajedidiah, ManggahanFloodwayOndoy, CC BY 3.0
Flooding is when areas usually not covered by water are engulfed or submerged. It is
usually caused by a temporary rise in or overflowing of streams, rivers, or confined bodies of
water. It may also be caused by heavy and prolonged rainfall, tsunamis, and storm surges.
Failure of manmade structures such as dams and clogging of drainage systems are also
common causes of flooding. Floods typically develop in a span of hours to a few days. In
cases wherein there is rapid inundation (less than six hours), it is considered a flash flood.
24
Factors that Influence Flooding
Several factors influence the occurrence of flood. These include rainfall intensity and
duration, topography, soil conditions, and ground cover. Most flash flooding is the result of
prolonged, heavy rainfall from typhoons or slow-moving thunderstorms.
Flooding is more common in low-lying areas such as plains and deltas which stream
networks naturally drain water to. Surface runoff, or the water that does not enter the soil
and moves downslope, is more dominant in impermeable materials such as clay, or in cases
where the soil is too saturated to allow infiltration.
Runoff (and consequently, the likelihood of flooding) is high in urban areas since much of
the ground is covered by concrete and such places are often situated in flat, low-lying
topographies. Vegetation lessens runoff, as it absorbs water and improves the ability of
the ground to take in more moisture.
Fig. 2. Residents making use of makeshift boats to travel across Ondoy floodwater in Pasig City.
Department of Foreign Affairs and Trade, Flooding from Typhoon Ondoy (Ketsana), Philippines 2009. Photo- AusAID
(10695893643), CC BY 2.0
Typhoon “Ondoy” (Ketsana) brought record-breaking rainfall to the northern Philippines,
25
with the highest recorded amount having been 455 mm of rain in 24 hours in Metro Manila.
This is equivalent to a month’s worth of rainfall in the area! Rainfall-induced floods affected
over 400,000 people in Manila and surrounding areas, submerging entire streets and
stranding pedestrians and vehicles. Marikina City, in particular, experienced floodwaters
from the waist level to about two storeys high, which can be attributed to the 10.99 m rise in
the water level of Marikina River.
Flooding can also occur in coastal areas due to tsunamis and storm surges, which will be
discussed in the next lesson.
Flood Hazard Mapping
Flood hazard maps are used to anticipate the degree of flooding in an area and the extent
of damage that the event can cause. In the Philippines, these are sourced from PAGASA and
Nationwide Operational Assessment of Hazards (NOAH).
PAGASA makes use of aerial photographs and satellite images to produce a preliminary
flood hazard map. This method involves the analysis of the geology and morphological
characteristics (geomorphology) of the area. Verification of this map is done through
geomorphological field mapping and interviews. All data are then integrated using
Geographic Information System (GIS) software. GIS is a system that allows integration
and analysis of geographic or spatial data and organizes them into visualizations such as
maps. Google Earth is an example of a GIS software.
The Nationwide Operational Assessment of Hazards (NOAH) is a program for disaster
research development which makes use of advanced technologies and provides information
services for improved disaster risk reduction and mitigation. Some of NOAH’s projects
include: weather monitoring equipment such as rain gauges and water-level sensors; highresolution landslide, flood, and storm surge maps; hazards information dissemination
through media and communication platforms; and providing open access to real-time data
and information which is especially helpful for communities affected by these hazards.
NOAH makes use of GIS software, simulations and models, and crowd sourcing of flood
events to create flood hazard maps.
26
Fig. 3. Flood hazard map of the province of Bulacan
image ( https://www.bulacan.gov.ph/pdcc/images/l_Flood_10K.JPG ) from Provincial Risk Reduction and Management Council of
Bulacan (https://www.bulacan.gov.ph/pdcc/hazardmaps.php)
27
Flooding occurrence is influenced by rainfall intensity and duration, topography,
soil conditions, and ground cover.
A. Answer the following questions.
1. What is flooding?
2. What is surface runoff?
3. What institutions can be relied on for flood hazard information?
4. What kind of software is used to integrate all the data needed to create a flood
hazard map?
B. Answer in brief and concise sentences as needed.
1. How is flooding classified as a flash flood?
2. What is the effect of vegetation on flood occurrence?
3. How do man-made structures contribute to flooding.
4. What is the relationship between surface runoff and flooding?
C. Synthesis and evaluation.
Many areas in Metro Manila are highly susceptible to flooding. What do you think are
the factors that contribute to being flood-prone of those areas?
28
Research on previous occurrences how fast and how high flood water rises in your
community or a nearby urban center. Take a screenshot of that area on Google Earth or
Google Map. Based on the flood data you gathered, create a flood hazard map by shading
on the image of your area. Use red for high flooding susceptibility and yellow for low
flooding susceptibility.
To check the accuracy of your map, go to nababaha.com or noah.up.edu.ph to find the
flood map corresponding to your mapped area.
Heightened
Low-lying areas are more susceptible to flood, but this does not necessarily mean that
areas in high altitudes are completely safe. Baguio City, with an elevation ranging from
900 to 1700 meters above sea level, experienced flooding on more than one occasion.
Among the reported flooded areas are City Camp Lagoon, Burnham Park, and major
streets such as Leonard Wood.
Let us investigate!
What do you think are the reasons for the flooding incidents in Baguio?
What are the impacts of flooding in Baguio to the surrounding provinces?
You may research more about a specific flooding event that occured in the areas
mentioned above.
In your opinion, what measures could be undertaken to avoid flooding in urban
areas such as Baguio City?
29
Tsunamis are waves generated by seismic activity. Apart from offshore earthquakes, are
there other means of creating such destructive, powerful waves?
Study the picture of a storm surge below.
Find a partner and discuss your observations from the picture. Be guided by the questions
below.
1. How would you describe a storm surge?
2. Is it easy to tell if it is a storm surge or a tsunami based on your observations?
What can you infer about the impacts of a storm surge?
30
Fig. 1. Wind and pressure components of a storm surge and their contributions to storm surge formation.
A storm surge is an abnormal rise in seawater level during a storm. Similar to tsunami
formation, the water undergoes wave shoaling. The natural flow of water from sea to shore
is delayed by the friction between the water and the seabed, causing it to pile up. However,
unlike the earthquake-induced tsunami, storm surges are driven by the force of storm
winds.
As more water moves landward, excess water accumulates on the shore line and may flow
farther inland. The water can then cause flooding and contaminate freshwater lakes,
streams, and aquifers. In some cases, especially in low-lying islands or coastal areas, a storm
surge can sweep across the area, erode land, and destroy buildings and roads.
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Factors that Affect Occurrence and Severity of a Storm Surge
The severity of a storm surge is dependent on factors such as strength and speed of the
storm, shape and characteristics of the coast, angle of approach of the storm to the coast,
and width and slope of the continental shelf. Naturally, stronger storms cause more
destructive storm surges. Fast moving storms generate more storm surges on straight
coastlines while slow moving ones have a greater effect on bays and estuaries.
Bays and coasts that bow inward are more likely to experience larger storm surges than
coasts that bow outward. Bays or other similar coastline geometries concentrate the
accumulated water in a smaller area.
Fig. 2. Manila Bay is an example of a coast bowing inward.
Eugene Alvin Villar (https://commons.wikimedia.org/wiki/User:Seav), Ph locator ncr manila, shape of bay labeled, CC BY-SA 3.0
A gently sloping continental shelf is more prone to storm surges and coastal inundation than
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areas where the seafloor is deep. A shallower seafloor allows the water to travel inland with
less difficulty.
Fig. 3. Flooding induced by storm surges is more likely in a gently sloping continental shelf (left)
than one with a steep slope.
A typhoon directly approaching the coastline is more likely to create a large storm surge
than one moving obliquely.
Fig. 4. Typhoon approaching the coast head on vs typhoon approaching at an oblique angle
A well-known example of a series of storm surges occurred with the Super Typhoon Yolanda
(Haiyan) in 2013. It is the deadliest typhoon to hit the Philippines in recent history, leaving
6300 dead, 1061 missing, and 28,689 injured. The storm surge that was brought about by
the typhoon had gone as far as 2 kilometers inland and reached heights of 4-5 meters.
Storm Surge Preparedness
Storm surges can be predicted. The Storm Surge Hazard Mapping Team of Project NOAH ran
simulations to predict storm surge heights and inundated areas during Yolanda. Initial
simulations estimated 98 km and 93 km in Leyte and Samar, respectively, to have been
flooded by storm surges.
PAGASA makes use of a color-coded storm surge warning system which is based on wave
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heights, with an increasing danger level from green to red.
Fig. 5. Storm surge warning system by PAGASA
Image from http://www.officialgazette.gov.ph/laginghanda/storm-surges/
Disaster Risk Reduction efforts in communities that are exposed to storm surge hazard can
include the construction of seawalls and storm surge breakers to protect buildings and
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weaken wave impact.
In the event of an impending typhoon and/or storm surge, you can do the following:
● keep track of any storm signal/storm surge warnings and related announcements;
● stay away from low-lying areas/steep coastal areas prone to landslide; and
● prepare evacuation plans and procedures.
Storm surges are large waves that are powered by strong typhoon winds and the water
can reach far inwards and cause severe flooding and damage to exposed area.
A. Answer in brief and concise sentences.
1. What is a storm surge?
2. What is the shape of the coast that will most likely experience a relatively larger
storm surge?
3. What kind of continental shelf slope will most likely experience a relatively larger
storm surge?
4. How would you describe the typhoon winds that generate more storm surges on
straight coastlines than on bays?
B. Answer in brief and concise sentences.
1. What is the difference between storm surges and tsunamis?
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2. What difference does angle of approach of a typhoon make on storm surges?
3. How does the shape of coasts affect the impact of storm surges?
4. How can storm surge predictions help in preparing for a storm surge hazard?
C. Synthesis and evaluation.
Do you think that it was possible to have prevented the disaster from the storm
surges brought about by Super Typhoon Yolanda? Explain your answers.
In pairs, explore the website http://noah.up.edu.ph/#/ and use its features to find the data
on the Super Typhoon Yolanda storm surge hazard map of Visayas region. You would find
the color-coded storm surge hazard map that is interactive. Use the application features to
answer the following:
1. How were the hazard areas marked and differentiated as high, medium, or low in the
hazard map?
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2. Zoom in and out to study the general shape of the area affected by Yolanda, as well as
the other features such as the topography of the areas affected. Based on the
observed factors, what features of the area made them vulnerable to the storm
surges of Super Typhoon Yolanda?
3. Do you think storm surges can be avoided in general? What suggestions can you
recommend to better prepare the communities for a storm surge hazard?
High and Dry
Yolanda storm surges demolished everything in their path without any regard for what
kind of buildings or structures these are, as is the case with any hazard. In those storm
surges, most of the existing evacuation centers in Tacloban City have been hit by this
hydrometeorological hazard.
Let us investigate!
Using this information from the previous storm surge disaster and other storm
surge maps you can find, what improvements can you suggest regarding
evacuation plans and the location of evacuation centers?
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Have you ever felt like the weather is too hot and dry, even for months when it is supposed
to be warm? Have you experienced a time when it seems like it is raining more than usual?
Why do unusually long dry and wet spells occur?
Think-Pair-Share
Discuss the following questions with your partner:
1. How are the following affected by too little rain?
a. food supply
b. health
c. freshwater supply
2. How are the following affected by too much rain?
a. food supply
b. health
c. freshwater supply
In what ways do hydrometeorological hazards affect our water supply?
El Niño-Southern Oscillation (ENSO) cycle
El Niño and La Niña are the warm and cold phases of the El Niño-Southern Oscillation
(ENSO) cycle. The ENSO cycle refers to the changes in oceanic and atmospheric
temperatures in the Equatorial Pacific. It significantly affects not only ocean processes, but
also rainfall, wind, and tropical cyclone patterns.
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This is not to be confused with monsoon which is the seasonal reversal of the direction of
prevailing winds due to the asymmetrical heating of a landmass and an adjacent ocean.
There are two types of monsoons: the southwest or summer monsoon, and the northeast or
winter monsoon. The southwest/summer monsoon, locally known as Habagat, is a warm,
moist air originating from the southwest Indian Ocean. It is associated with heavy rainfall
and humid climate. Its cold counterpart, the northeast/winter monsoon locally known as
Amihan come from Mongolia and northwestern China. Amihan is characterized by moderate
temperatures, and little to no rainfall.
Fig. 1. Direction of seasonal winds that affect the Philippines annually.
El Niño
El Niño is a Spanish term that translates to “The Little Boy” or “Christ Child.” It was originally
observed in Southern America as unusually warm seawater. It was named such because the
phenomenon typically occurs around Christmas.
El Niño in the Philippines usually starts between December and February. It is indicated by a
delayed onset or early termination of the rainy season, and weak monsoon and tropical
cyclone activity. While this phenomenon brings fewer and less intense storms, it is also
associated with severe dry spells or droughts which can be just as damaging. Drought
assessment maps and advisories are released in the event of an El Niño.
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Fig. 2. Global sea surface temperature (SST) anomalies for January 1, 2016 in the 2015-2016 El Niño event.
NOAA, Sstdailyanom20160101, marked as public domain, more details on Wikimedia Commons
A primary concern during El Niño season is water supply. It is important to regulate your
usage as much as possible and minimize the adverse effects of this shortage. Here are a few
ways to do that:
● Stay hydrated.
● Prepare a specific amount of running water used for brushing or bathing.
● Collect rainwater whenever possible but make sure your containers are properly
covered to keep mosquitoes from breeding there.
● Reuse water from laundry/cooking to clean bathrooms, wash your car, or water the
plants.
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Fig. 3. Drought/dry spell assessment by PAGASA (as of May 2015)
https://www.google.com/url?q=https://www1.pagasa.dost.gov.ph/images/climate_and_agromet_files/dryspell-drought/drought_dryspell_assessmen
t_May31_editedsize.jpg&sa=D&ust=1524316630063000&usg=AFQjCNFs1EGo2R0wiWcZqUJYFhMZvcwCAw
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La Niña
La Niña, meaning “The Little Girl,” is characterized by sea surface temperatures lower than
average. It is also referred to as El Viejo (The Old Man) or anti-El Niño, since its local effects
on weather are generally the opposite of those of El Niño. La Niña is caused by the upward
movement of cold water by unusually strong trade winds and ocean currents in a process
called upwelling. Upwelling brings cooler, more nutrient-rich waters from lower depths to
the surface, which is profitable to the fishing industry.
Fig. 4. Regional effects of La Niña throughout the world
NOAA, La_Nina_regional_impacts.gif , CC BY-SA 3.0
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During La Niña, the air pressure is higher than normal in the central and eastern Pacific.
These high-pressure zones cause decreased cloud production and rainfall, and
consequently, drier climate. This is usually observed in South America and the Gulf Coast of
U.S.
The air pressure conditions in the western Pacific are opposite of those in the central and
east. Increased rainfall is observed in Southeast Asia as a result of lower-than-normal air
pressure. Northwest India and Bangladesh, in particular, benefit from the greater rainfall
associated with the summer monsoon, as this leads to a greater agricultural production. In
Australia, however, strong La Niña events were seen to have caused some of the country’s
most devastating floods.
La Niña in the Philippines causes an increase in rice output. However, it is also correlated
with destructive typhoons, heavy rainfall, and associated landslides and floods.
ENSO Monitoring
El Niño and La Niña are monitored, assessed, and predicted through the Ocean Niño Index
(ONI). The NOAA defines ONI as the average deviations in sea surface temperatures (SST’s)
in the Niño region over a period of three months. El Niño is indicated by a positive ONI
greater than or equal to +0.5ºC, while La Niña is indicated by a negative ONI less than or
equal to -0.5ºC. ONI values falling between +0.5ºC and -0.5ºC are considered ENSO-neutral.
The Climate Prediction Center (CPC) and the International Research Institute (IRI) predicted a
transition from La Niña to ENSO neutral in the northern hemisphere from March to May
2018. ENSO-neutral conditions are likely to occur during the second half of the year.
La Niña was declared in the Philippines by PAGASA in November 2017 and was predicted to
last until February 2018.
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Fig. 5. Ocean Niño Index (ONI) from 1950 to 2018. Portions of the graph that fall above
the red line indicate El Niño; those below the blue line indicate La Niña. The area between
the two lines is considered ENSO-neutral.
Image
from:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
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● ENSO significantly affects not only ocean processes, but also rainfall, wind, and
tropical cyclone patterns.
● El Niño in the Philippines brings fewer and less intense storms, but is also
associated with severe dry spells or droughts which can be just as damaging.
● La Niña in the Philippines is correlated with destructive typhoons, heavy rainfall,
and associated landslides and floods.
A. Complete the table below. Fill in the boxes with higher or lower.
La Niña Conditions and Effects to the different parts of the Pacific Ocean
Area
Sea surface
Air pressure
Rainfall
temperature
E Pacific
1.
2.
3.
W Pacific
4.
5.
6.
B. Answer in complete sentences.
1. Why is rainfall greater in the Philippines during La Niña?
2. Describe what happens in upwelling?
3. How does ENSO affect monsoons?
4. What can you do to mitigate the effects of drought? Give an example.
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C. Synthesis and evaluation.
Which do you think will have more adverse effect on the agricultural production in
the Philippines, El Niño or La Niño? Explain your reasons.
Make a survey of the water needs of your immediate community (school/residential or both)
by listing down its most common uses (e.g. hygiene, production, cooking, etc.). Based on the
water consumption and needs of your community, make a poster to give tips on how to
conserve water that is applicable to your context.
Make your poster large and with graphics/illustrations to make it easily understandable.
Include how water conservation can help prepare for hydrometeorological hazards such as
El Niño.
It’s Raining When?
Envision yourself in the near future where technology has advanced to the extent that
we can manipulate rainfall. The ENSO, monsoons, and phenomena related to trade
winds are still in effect. Your job is to set the distribution of water resources and decide
where to focus the precipitation. Based on the drought/dry spell assessment map in
Figure 3, which areas are in need of most water?
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Your goal is to prepare your whole family for hydrometeorological hazards. As a responsible
member of your family, you will take the lead in specific disaster preparedness measures.
Create a floor plan of your house. Identify areas by using lines for partitions and doors and
shapes to represent furniture, appliances and other fixtures such as the main switches, LPG
tanks or electric outlets. You may include type of materials such as wood, cement, metal, etc.
Add space in-between the neighborhood and describe partitions/gates you have in between.
1. Identify any zones of weakness or any possible entryways for rain or flood. These can
be broken windows, cracked floorboards, or leaky ceilings. Mark them with an X on
your floor plan.
2. Make a plan on how you can discuss your investigation with your family and
collaborate on how you can make your home more effective against
hydrometeorological hazards.
As a family, create an exit/evacuation plan. Determine routes for exiting the house safely.
Identify areas in this path that require repairs or reconstruction. Create a table to
summarize the what, where, when, how, and who are involved in these
repairs/improvements. Rehearse your exit/evacuation plan for different hazards (e.g. flood,
thunderstorm).
You will document the procedures and outputs of your disaster preparedness tasks. The
documentation will include the following:
1. house hazard map;
2. family meeting proceedings;
3. timeline of events from your planning to execution of tasks;
4. results of repair/improvement plan; and
5. evacuation plan and route for different hydrometeorological hazards.
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You will be rated based on the following rubrics:
Criteria
Beginning
(0-12 points)
Developing
(13-16 points)
Accomplished (17-20
points)
Content
none to few concepts
learned were applied
in the map and family
preparedness plan
some concepts
learned were applied
in the map and family
preparedness plan
concepts learned were
correctly applied in the
map and family
preparedness plan
Organization
documentation is none
to incomplete (lacks
essential parts)
documentation is
complete, but
organization can still
be improved
documentation is
complete, organized in
a logical manner, and
exceeds expectations
(additional pertinent
data included)
Presentation
none to poorly
presented
documentation
neat but aesthetic
aspect can still be
improved
neat and aesthetically
pleasing presentation
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Check
I can…
...distinguish and differentiate among and between different
hydrometeorological hazards.
...recognize the signs of an impending hydrometeorological hazard.
...apply appropriate measures/interventions before, during, and after a
hydrometeorological hazard.
..interpret hydrometeorological maps.
..use available tools in monitoring hydrometeorological hazards.
Reflect
I find
I got
checks because
I need to improve on
I need to practice
I plan to
the most interesting because
because
because
.
.
.
.
.
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● Hydrometeorological hazards affect and sometimes induce each other.
● Typhoons/hurricanes/tropical cyclones are organized systems of rotating winds
that can bring about floods, thunderstorms, and storm surges.
● El Niño and La Niña have significant effects on rainfall, winds, and consequently,
other hydrometeorological hazards.
● Hydrometeorological hazards can be predicted, monitored, and mitigated.
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Agence-France Presse.”Deadliest typhoons in the Philippines.” ABS-CBN News, November 8,
2013. Accessed March 21, 2018.
http://news.abs-cbn.com/focus/11/08/13/deadliest-typhoons-philippines.
Caballero, Angelo. “Two killed as lightning strike ignites house fire.” ABS-CBN News,
November 26, 2016. Accessed March 22, 2018.
http://news.abs-cbn.com/news/11/26/16/2-killed-as-lightning-strike-ignites-house-fire.
Cebu Daily News. “Tornado developed in Bohol, Pagasa says.” Philippine Daily Inquirer,
November 6, 2013. Accessed March 21, 2018.
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https://edition.cnn.com/2012/12/04/world/asia/philippines-typhoon/index.html National
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https://www.nasa.gov/mission_pages/hurricanes/archives/2009/h2009_Ketsana.html
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Metro Manila.” Accessed March 19, 2018.
http://center.noah.up.edu.ph/ondoy-flood-metro-manila/
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Glossary
Condensation -process by which water vapor in the air is changed into liquid water
Conduction - movement of heat or electricity through a medium
Continental slope - the slope from the outer edge of the continental shelf to the deep
ocean floor
Convection - heat transfer due to movement of molecules in fluids
Coriolis force - inertial force that causes apparent deflection of the path of an object that
moves within a rotating frame of reference
Downdraft - downward moving air in a thunderstorm
Drought - insufficiency of rain for an extended period that causes depletion of groundwater
and soil moisture.
Electrically conductive - has the capacity to carry/transport electrical charges
Geomorphology - the study of landforms, their processes, form and sediments at the
surface of a planet
Infiltration - the process by which water on the ground surface enters the soil
Inundation - flooding
Ionized - charged atoms or molecules
Monsoon - major wind system that seasonally reverses its direction
Surface runoff - water from precipitation that flows over land
Updraft - upward moving air in a thunderstorm
Wave shoaling - deformation that results to an increase in wave height as waves reach
shallow water.
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