T.A. Cinco et al. / Atmospheric Research 145–146 (2014) 12–26
high as 4.8 °C before century end (relative to 1986–2005)
under the most extreme IPCC representative concentration
pathway (RCP 8.5) and seem likely to reach 1.8 °C (RCP 4.5)
without a significant and continuous reduction in GHGs
(IPCC, 2013a; May, 2011). Indeed, one of the longest running
continuous time series monitoring stations, Mauna Loa in the
mid-Pacific (Quirk, 2012) has recorded CO2 concentrations in
excess of 400 ppm for the first time in 2013 (NOAA, 2013)
and the IPCC's latest estimate is that concentrations for 2011
were 391 ppm. Perhaps of most concern is that this is a stock,
not simply a flow problem in that these concentrations of
GHGs will remain in the atmosphere for a significant period,
seemingly committing us to further future warming. This
will create significant challenges for those nations most at
risk from the effects of extreme climate change. Developing
nations least able to cope with climate change related impacts including rising sea levels due to thermal expansion
and the melting of polar ice caps, changes in the frequency
and intensity of flood and drought will be disproportionately
affected (ADB, 2009; Cruz et al., 2007; IPCC, 2012).
IPCC projections and regional level studies suggest that a
changing climate is likely to impact agricultural production,
adversely affect human health through climate induced heat
stresses and diseases as well as altering the hydrological cycle in
East and Southeast Asia (Cruz et al., 2007; IPCC, 2012; Su et al.,
2005; Webster et al., 2005; Yue and Hashino, 2003). In the
Philippines in particular, observed data already points to a
decreasing trend in mean annual rainfall (Cruz et al., 2013).
Regional level studies have noted an increase in frequency and
intensity of El Niño–Southern Oscillation (ENSO) events and
tropical cyclones originating in the Pacific (Trenberth et al.,
2007; Lyon and Camargo, 2008) and that these events are
causing more damage than before (ADB, 2009; Yumul et al.,
2013). Furthermore, there is evidence of an increase in rain
induced land slides and flooding in the Philippines with
significant loss of life, disruption to livelihoods and economic
activity (Evans et al., 2007; PAGASA, 2011; Yumul et al., 2012,
2013). Conversely, during El Niño episodes widespread drought
and water shortages have been observed. During the strong El
Niño event recorded in 1997–1998 late onset of the southwest
monsoon (wet season) led to water shortages, crop failures and
forest fires in some areas of the Philippines (Cruz et al., 2007,
2013; Moya and Malayang, 2004). More recently however,
there appears to have been an alteration in the sub-national
effects of ENSO events making such episodes more unpredictable, in turn demonstrating the complexity of the regional
climate system (Lyon et al., 2006; Yumul et al., 2013).
Such a compelling body of evidence highlights the need for
generating and gathering reliable, country level climate data to
provide a scientific basis for an appropriate response to these
multiple challenges. In order to increase levels of certainty for
modelled and predicted changes in temperature, precipitation
and extreme events including the frequency and intensity of
tropical cyclones, empirical data based on direct observations is
of vital importance. Consistent, high quality, daily time-series
data for precipitation and temperature allows for the identification and quantification of longer term climatic trends.
Furthermore, accurate data on climatic variables can be used
to develop, test and validate algorithms for satellite derived
data and for modelling predictions of future climate (Cruz et al.,
2013; Jamandre and Narisma, 2013).
13
However, long term climatic data for the Southeast Asia and
Asia-Pacific region is limited, particularly at the country level.
Two authoritative early studies offer regional level trend
analysis for temperature, precipitation and climatic extremes
covering the period 1961–1998 (Manton et al., 2001) and
1961–2003 (Griffiths et al., 2005). They demonstrate largely
coherent inter-country data which reveal an overall warming
trend within the region, including an increase in the occurrence
of hot days and warm nights and a decrease in cool days and
cold nights.
These studies used observed data gathered from synoptic
stations from across Asia-Pacific countries. In the case of the
Philippines, Manton et al. (2001) selected 5 weather stations
and Griffiths et al. (2005) just 3 stations which met their
selection criteria in terms of data quality. Such collaborative
efforts produced for the first time a robust data set for the
region, contributing to global efforts to record, detect and
monitor climate trends. Such studies have also encouraged
relevant authorities in participating nations to improve the
quality of their data, continue national level studies to identify
climate trends and share this data more widely. This paper
is the result of such efforts and has the following specific
objectives: (1) to analyse and quantify near surface temperature trends; (2) to identify trends in extreme temperature and
rainfall events (climate extremes); and (3) to discuss the
results and their significance in a national, regional and global
context.
2. The Philippines: location and climate in context
The Philippines is located in the western north Pacific
between 4°40′N to 21°10′N, 116°40′E to 126°34′E, and consists
of more than 7,000 islands totalling some 30 M hectares. The
climate is influenced by both mesoscale and synoptic systems
including monsoon and tropical cyclones as well as ENSO
events (Chang et al., 2005; Jamandre and Narisma, 2013;
Villafuerte et al., 2014). Whilst there are four climate types
based on mean annual rainfall using the Modified Coronas
Classification which is influenced by land–sea interactions as
well as orography, the two major monsoons seasons, the
northeast monsoon (NEM) from November to April and the
southwest monsoon (SWM) from May to October, have the
greatest influence on recorded precipitation at the national
level.
The Philippines receives roughly 2000 mm of rainfall
annually on average although there is significant sub-national
and inter-island variation depending on the location of the
weather station, with the north and Pacific (east) coasts
receiving almost double the national mean in some years
(Jamandre and Narisma, 2013). Spatial variation of rainfall
relating to orographic effects are generally confined to the
mountainous areas of north-western and far south of the
Philippines which influence the inter-seasonal effects of
the SWM bringing a later wet season to the north eastern
Philippines (Chang et al., 2005). The predictability of rainfall
quantity and timing is extremely important for a country
in which agriculture plays a significant role in the economy
and livelihoods of millions of people (ADB, 2009). However
the timing of the onset of monsoon rains has become less
predictable in recent years and the effects of extreme climatic
events such as flood, drought and tropical cyclones have all