Understanding Tropical Cyclones and Other Hydrometeorological Hazards
1. Tropical cyclones
are hydrometeorological hazards characterized by strong
winds and heavy rain. Every year, an average of 19 tropical
cyclones enter the Philippine Area of Responsibility and
approximately 9-10 make landfall in the Philippines. This is
because the Philippines is located on the western rim of
the Pacific Ocean, where most tropical cyclones pass.
Tropical cyclones can have a forecast lead time of 5 days.
2.
3. Thunderstorms
are generally local storms produced by
cumulonimbus clouds and are always
accompanied by lightning and thunder, usually
with strong wind gusts, heavy rain and sometimes
with hail and/or tornado. Thunderstorms are
typical in warm environments like the tropics and
may persist for 1 to 2 hours.
4.
5. Flood
is the overflowing of the normal confines of a
stream or bodies of water, or the
accumulation of water over areas that are not
normally submerged. While flooding may last
days or even weeks, Flash Floods are also
caused by heavy precipitation in a short
period of time, usually less than 6 hours.
6.
7. Storm surge
is the rise and onshore surge of seawater as the result primarily
of the winds of a tropical cyclone, and secondarily of the surface
pressure drop near the center of the tropical cyclone. The
height of storm surge is dependent on the size, intensity and
movement of the tropical cyclone, shape of the coastline as well
as nearshore underwater topography and astronomical tides.
Below is a list of things that you can to do before, during and
after a storm surge event.
8.
9. El Niño
is a significant increase in ocean temperature over the
eastern and central Pacific ocean. It occurs at irregular
intervals ranging from 2-7 years usually developing in
the early months of the year and decay the following
year. In the Philippines, El Niño conditions are often
characterized by dry and warm-hot events.
12. Return period
also referred to as recurrence interval, is the
probability of an event such as heavy rain,
intense typhoon of floods to happen. It is a
statistical measurement mainly based on
historical data that gives the estimated time
interval between similar extreme events.
13. For example:
the return period of a heavy rainfall event is 100 years, this
can be expressed as an event with a probability of
happening equivalent to 1/100 or 1%. This does not mean
that the next similar extreme event will happen 100 years
after, instead, it means that in a given year, there is a 1%
chance what the event will happen. Consequently, 100-year
floods can happen in 2 consecutive years. In analysis of
extreme hydrometeorological events, “return periods” are
usually used to infer the severity of an event.
14. Rainfall in the Philippines
Rainfall is the most important climatic element in the Philippines. Rainfall
distribution throughout the country varies from one region to another,
depending upon the direction of the moisture-bearing winds and the
location of the mountain systems.
The mean annual rainfall of the Philippines varies from 965 to 4,064
millimeters annually. Baguio City, eastern Samar, and eastern Surigao
receive the greatest amount of rainfall while the southern portion of
Cotabato receives the least amount of rain. At General Santos City in
Cotabato, the average annual rainfall is only 978 millimeters for the
whole year. What is the usual rainfall in you area?
15.
16. While we are usually concerned with heavy rainfall
events, lack of rain is also a significant condition that we
also experience. Weather in different parts of the
Philippines can vary significantly for certain years as a
response to changing global climate. One of the main
climate drivers that affect the Philippines is the El Niño
Southern Oscillation (ENSO) or simply El Niño.
17.
18.
19. PAGASA
The Philippine Atmospheric, Geophysical and Astronomical
Services Administration (which means "hope" as in
the Tagalog word pag-asa) is the National Meteorological and
Hydrological Services (NMHS) agency of the Republic of the
Philippines mandated to provide protection against natural calamities
and to insure the safety, well-being and economic security of all the
people, and for the promotion of national progress by undertaking
scientific and technological
servicesin meteorology, hydrology, climatology, astronomyand other
geophysical sciences
23. The Nationwide Operational
Assessment of Hazards
or NOAH is a program under the Department of Science
and Technology (DOST) with the mission to undertake
disaster science research and development, advance the
use of cutting edge technology and recommend
innovative information services in government’s disaster
prevention and mitigation efforts. DOST-NOAH can be
accessed online at http://noah.dost.gov.ph.
27. Nababaha.com
Another local website, http://www.nababaha.com, a non-
profit project by the members of the Volcano-Techtonics
Laboratory of the National Institute of Geological
Sciences of University of the Philippines, publishes a list
of flood hazard maps of different regions
(http://www.nababaha.com/list.htm), with the same
dataset as DOST-NOAH.
30. National Mapping and Resource
Information Authority
is an agency of the Philippine government under the
Department of Environment and Natural Resources (DENR)
responsible for providing the public with mapmaking services
and acting as the central mapping agency, depository, and
distribution facility of natural resources data in the form of
maps, charts, texts, and statistics. On its website’s download
page,
http://www.namria.gov.ph/download.php,hazard/susceptibility
maps for storm surge, rain-induced landslide and flood are
freely available.
33. The Mines and Geosciences Bureau
a government agency also under the Department of
Environment and Natural Resources (DENR), is
responsible for the conservation, management,
development and proper use of the country’s mineral
resources including those in reservations and lands of
public domains. MGB maintains a geohazard visualization
portal accessible at this URL
http://gdis.denr.gov.ph/mgbgoogle/.
