Geoinformation for Disaster and Risk Management - ISPRS

(Grimm et al., 2008; Kerle and Alkema, in press).
Global warming, with associated sea level rise and
apparently more erratic and occasionally more
violent weather patterns, has added to a widespread
increase in flood risk. While weather forecasting
abilities have greatly increased, aided by
sophisticated space infrastructure and computer
models, floods continue to affect largely unprepared
communities, and often with little or no warning.
Some events, such as the floods in Taiwan caused by
Typhoon Morakot in August 2009, or in Manila
caused by Typhoon Ketsana a month later, are
results of extremely high rainfall, but the magnitude
of casualties and damages is also a result of poor
urban planning, clogged drainage systems, lack of
early warning and poor preparedness.
Floods are the most frequent disaster type globally
(CRED, 2008), and in some parts of the world also
the most costly. The generally straightforward
relationship between excessive upstream rainfall and
vulnerable areas exposed to potential flooding lends
itself well to a geoinformatics-based risk assessment
and management approach, and working examples
have been widely reported. They can involve detailed
maps of elements at risk and their associated flood
vulnerabilities, satellite-based precipitation
estimates, ground-based weather radar, river flow
gauges, and sophisticated preparedness and early
warning protocols. Many of the required data
acquisition and analysis steps have become standard
and automated, and hardware and data costs are
diminishing, resulting in the implementation of such
solutions also in economically less developed
countries (LDCs).
Weather services or related organisations in many
countries are monitoring the synoptic weather
situation and the levels of major rivers, and are able
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to warn of impending floods. However, this is
typically limited to major rivers or vulnerable urban
areas. The part of the population that thus benefits
less from such technical advances is the rural
population especially in LDCs. According to World
Bank estimates some 70% of the World's poor live in
these areas, and whatever small development steps
are made are readily compromised by frequent
disaster events. This, therefore, raises the question
to what extent geoinformatics-based flood
management solutions can be scaled down and
adapted to rural areas. A solution developed as part
of a German Technical Cooperation (GTZ) project in
Leyte in the Eastern Visayas, the Philippines, is
introduced in this best practice case.
Flood Prone Areas in Binahaan Watershed
Locator Maps
Legend
Municipal center
The flood situation in the Philippines
The Philippines is made up of more than 7000
islands, and annually affected by two monsoon
seasons and on average 9 typhoons that make
landfall. While those events can lead to exceptional
rainfall, such as the 450mm in 1 day during Typhoon
Ketsana, or the more than 2000mm in 2 days during
Morakot in Taiwan, local flooding is frequent during
monsoon times. The Philippines is a highly
mountainous country, and sizeable catchments
quickly drain large amounts of rainwater into
downstream areas.
Water level gauges
Rain gauges
Altitude (0-1400m)
Binahaan River
Figure 1: Location of the Binahaan watershed in
the Eastern Visayas of the Philippines, and
overview of the flood monitoring system
Flood Prone Area
(from Mines and
Geoscience Bureau,
2006, modified by GTZ)
10km