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EXPLORING CLIMATE CHANGE EFFECTS ON WATERSHED SEDIMENT YIELD
AND LAND COVER-BASED MITIGATION MEASURES USING SWAT MODEL, RS
AND GIS: CASE OF CAGAYAN RIVER BASIN, PHILIPPINES
Jeark A. Principe
Graduate student, Department of Geodetic Engineering, University of the Philippines Diliman,
Melchor Hall, College of Engineering, U.P. Diliman, Quezon City, Philippines;
Tel: +63-02-9818500 loc. 3124; E-mail: jeark principe@yahoo.com
KEY WORDS: Climate Change, Land Cover Change, SWAT model, RS, GIS
ABSTRACT:
The impact of climate change in the Philippines was examined in the country's largest basin—the Cagayan River Basin—by
predicting its sediment yield for a long period of time. This was done by integrating the Soil and Water Assessment Tool (SWAT)
model, Remote Sensing (RS) and Geographic Information System (GIS). A set of Landsat imageries were processed to include an
atmospheric correction and a filling procedure for cloud and cloud-shadow infested pixels was used to maximize each downloaded
scene for a subsequent land cover classification using Maximum Likelihood classifier. The Shuttle Radar Topography Mission
(SRTM)-DEM was used for the digital elevation model (DEM) requirement of the model while ArcGISTM provided the platform for
the ArcSWAT extension, for storing data and displaying spatial data. The impact of climate change was assessed by varying air
surface temperature and amount of precipitation as predicted in the Intergovernmental Panel on Climate Change (IPCC) scenarios.
A Nash-Sutcliff efficiency (NSE) > 0.4 and coefficient of determination (R2) > 0.5 for both the calibration and validation of the
model showed that SWAT model can realistically simulate the hydrological processes in the study area. The model was then utilized
for land cover change and climate change analyses and their influence on sediment yield. Results showed a significant relationship
exists among the changes in the climate regime, land cover distributions and sediment yield. Finally, the study suggested land cover
distribution that can potentially mitigate the serious negative effects of climate change to a regional watershed's sediment yield.
1. INTRODUCTION
The Philippines cannot escape the negative impacts of climate
change. The country was tagged as a climate hotspot and
vulnerable to some of the worst manifestations of climate
change (Jabines & Inventor, 2007). As with other developing
countries in Asia, the Philippines is highly subject to natural
hazards as exemplified by the 2006 landslide and the havoc
wreaked by typhoons Frank, Ondoy and Pedring in 2008, 2009
and 2011 respectively. The country is also prone to various
hydro-meteorological and geological hazards because of its
geographic and geologic setting, threatening the country by the
passage of tropical cyclones and occurrences of extreme or
prolonged rainfall, strong earthquakes, volcanic eruptions and
tsunamis and these hazards will be aggravated and the impact
of geological events can be worsened by global warming
(Solidum, 2011). Furthermore, climate change threatens the
country by increasing the intensity and frequency of storms and
droughts. CAD-PAGASA (2004) reported that the country is
likely to be adversely affected by climate change since its
economy is heavily dependent on agriculture and natural
resources. Given these scenarios, it is timely that research
pertaining to the impact of climate change to the country be
quantitatively assessed.
The study particularly explored the influence of land cover on
sediment yield and suggested land cover conversions that can
potentially mitigate the serious negative effects of climate
change to the sediment yield of a large basin. The study is
significant for a proposed watershed management in the
country that will incorporate the possible impacts of climate
change on sediment yield.
2. STUDY AREA
2.1. Geographical and Political boundaries
The Cagayan River Basin (CRB) is the largest river basin in the
Philippines. It is located in the northeastern portion of the
island of Luzon and between 15°52’N-18%23°N latitudes and
120°51°E-122°19’E longitudes (Figure 1). CRB has a drainage
area of approximately 27,700 km’ covering the provinces of
Regions 2, Cordillera Autonomous Region (CAR) and small
parts of Region 3 (RBCO, 2007).
2.2. Climate, Topography and Physiography
CRB falls under Type III climate zone which is characterized
by no pronounced maximum rain period and a short dry period
(BRS-DPWH, 2002). According to PAGASA (2009), the
northern part of the basin has an average annual rainfall of
1,000 mm and 3,000 mm in the southern mountains. The mean
annual temperature and average relative humidity are 23.6-
26.0°C and 75-85%, respectively (DPWH & JICA, 2001).
The area is relatively flat plain but is broken by low rising
ridges and hummocks in some places (BRS-DPWH, 2002).
Approximately 50% of the area is relatively flat with slope that
varies from 0-17%. About 33% of the area has slopes between
17-42% while the rest are with slopes greater than 42% based
on a slope map derived from the SRTM-DEM. It is also
surrounded by three mountain ranges: Sierra Madre, Cordillera
Central and Caraballo-Maparang in the east, west and south.
respectively (DPWH & JICA, 2001).