of the Verde Island Passage, Philippines - weADAPT

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climate change vulnerability assessment of the verde island passage, philippines passed through the Philippines indicate a southward shift in the typhoon trajectories in the past decade (Anglo 2005) and an increased relative frequency of typhoons generated in the South China Sea (Ho et al. 2004) (Figure 10). Several investigators however, have indicated the high natural variability of tropical storms and typhoons, which makes it difficult to detect long term changes that can be attributed to climate change. The Verde Island Passage lies within the track of most of the typhoons in the western Pacific and it is during these events that sea conditions can become rough. Historical typhoon track data (Figure 11a) show that 160 typhoons passed to within 200 km of the VIP from 1952-2008 (Japan Meteorology Agency 2009) amounting to about 11% of the total tropical cyclones in the Western Pacific since the 1950s. The typhoon track data within 200 km from VIP are shown in (Figure 11b). The color of the data points represent year with blue as the oldest (1952) and dark red as the most recent (2008), and the size is scaled according to the storm category. It can be seen that there were no strong typhoons (Category 4-5) in the period before 1975 and for the most recent years (dark red points), roughly more than half belong to the strong typhoon categories. a) b) latitude latitude 16ºN 15ºN 14ºN 16ºN 15ºN 14ºN 13ºN 12ºN 11ºN 119ºE 120ºE 121ºE 122ºE 123ºE 124ºE longitude 2005 2000 1995 1990 1985 1980 From the JWTC dataset which starts after WWII, an average of two to three storms passed near the Verde Island Passage corridor annually. However, there were some years when at least six typhoons crossed the area. The highest occurrence was in 1993 with eight storms (Figure 12). 13ºN 12ºN 11ºN 1975 1970 1065 1960 1955 119ºE 120ºE 121ºE 122ºE 123ºE 124ºE longitude latitude 40ºN 20ºN 0ºN 100ºE 120ºE 140ºE 160ºE longitude Figure 10. Number of tropical cyclones are increasing in the Pacific and significantly passing through the middle of the Philippines (Anglo 2005). 1.0 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 Figure 11 a) Plot of typhoon tracks from 1950- 2009; and b) Storm track data from 1952-2008 within 200 km from Verde Island. Size of points scaled to storm category (2-5) while color is scaled to year. (Data source: Japan Meteorology Agency 2009). frequency 8 6 4 2 0 1940 1950 1960 1970 1980 1990 2000 2010 year Figure 12. Storm frequency within a 200 km radius from Calapan, Mindoro. Data is from JWTC. 10
chapter 1 • vulnerability assessment of marine ecosystems and fisheries to climate change: introduction Changes in rainfall PAGASA precipitation records from Calapan, Mindoro and Ambulong, Batangas for the period 1961 to 2004 show that annual rainfall fluctuates from 1000 to 3500 mm (Figure 13). The two records display similar seasonal fluctuations but opposing long-term precipitation trends over the 43-year period. Annual rainfall has increased in Calapan, but Ambulong shows an overall decrease. This highlights the spatial heterogeneity of rainfall and the need for more monitoring stations. More specifically, there is a need for meteorological stations distributed along representative coastal areas of the VIP. Sea level rise The Global Sea Level Observing System has two sites in the Philippines (i.e., Manila and Legaspi). Both of these coastal data show a relative sea-level increase of between 20cm and 40cm since the 1960s (Figure 14). This observed rise is most likely a compounded 3500 3000 consequence of excessive land reclamation, possible subsidence due to groundwater extraction and residual rise in sea-level due to warmer oceans. Altimetry data from the satellites TOPEX–Poseidon (1992-2005) and JASON–1 (2001-present) gives a time series of offshore sea level on either side of Verde passage (Figure 15). Both sides have undergone changes fluctuating around mean sea level with the eastern side of the passage being more variable. Since 2005, there seems to be a more steady positive increase of about 1.0 mm/yr on the east and 0.5 mm/yr on the west. These offshore altimetry observations however are not enough to determine site-specific relative sea level rise. Unfortunately, there are no long-term tide gauge data along the VIP. This poses a problem for local decision development planning. a) 10 8 6 west 4 annual rainfall (mm) 2500 2000 1500 1000 mean sea level (mm) 2 0 -2 -4 -6 -8 Figure 13. Annual rainfall from 1961 to 2004 for Calapan, Mindoro and Ambulong, Batangas. Data is from PAGASA. relative sea level (cm) 500 0 740 720 700 680 Calapan, Mindoro Ambulong, Batangas 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 year b) mean sea level (mm) -10 10 east 8 6 4 2 0 -2 -4 -6 -8 -10 Figure 15. SSH time series from satellite altimetry. 660 1900 1920 1940 1960 1980 2000 year Figure 14. Relative annual-mean sea-level for Manila, South Harbour, (blue; 1901-1997; 14.58°N, 120.93°E) and Legaspi (red; 1947-1997; 13.15°N, 123.75°E) in the Philippines. (http://www.cru.uea.ac.uk/~mikeh/research/ philippines.pdf) 11
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Conservation International (CI) Mis
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