5.2.2 Change in weather extremes As the country is one of the regions of the world most prone to EWEs, how much these events have already changed in terms of their occurrence rate and/or strength and how they will change in the future is of great interest. EWEs changes in the past The major burden for the archipelago in particular under future SLR is that of Tropical cyclones (TC) (World Bank, 2013a; Nicholls et al., 2008). They influence and will further influence every sector of human livelihood - i.e. infrastructures, agriculture, and ecosystems - due to heavy precipitation, storms and landslides (Peduzzi et al., 2012). There are various publications dealing with extreme precipitation, monsoon, TCs, the ENSO effect and so forth – but not necessarily in connection to a changing climate (e.g. Cayanan et al., 2011). Also Yumul et al. (2010) gives an example of the possible impacts of an EWE without a deeper discussion about the relationship to a changing climate. However, they describe in detail the impacts of a series of extreme weather events in the years 2005 to 2007. Starting with a La Niña event with very wet conditions, disastrous flooding and landslides, the country’s resilience was tested by several typhoons before the series passed over into El Niño mode. That was accompanied by the strong drought of 2007, which affected almost all sectors, mostly in Luzon. It is critical to distinguish between changes in frequency and changes in the intensity of TCs. Some use the term ‘increase in threat’ or ‘increasing impact’ of TCs, but do not necessarily mean frequency and intensity, but rather the impact in terms of monetary or health impact. This could be independent from changes in the patterns of TCs, as these increases can mostly be traced back to the enormous growth in coastal populations, installed infrastructures, and economic values that could be affected in the region (Cruz et al., 2007; Knutson et al., 2010; Mendelsohn et al., 2012; Peduzzi et al., 2012). The whole issue of past trends in TCs is controversial. Various sources discuss a change in the cyclone activity in the 20th century (IPCC, 2007; Geng and Sugi, 2001; we do not refer to extra-tropical cyclones). Peduzzi et al. (2012) was seeking clear signs of a change in occurrence rate of TCs in a data set of 1970 to 2004 – but could not prove any trends – either on a global or individual basis. The only exception was made by Knutson et al. (2010), who showed an increasing trend for the North Atlantic, although they could not determine how far this was based on multi-decadal variability or greenhouse-forced warming. Only a positive correlation of Atlantic TC frequency to SST could be shown. On the other side, looking at the trends of strong cyclones (category 4 and 5) in different regions of the world, Webster et al. (2008) found significant signals for an increase. However, there was no significant trend in the total number of cyclones. Elsner et al. (2008) and Knutson et al. (2010) stated an increase for the upper limit of the distribution of TC intensities in the past – this means stronger storms become even stronger. Elsner et al. (2008) analyzed the period 1981 to 2006 and found significant upward trends for intensity on a global basis, but also for the western North Pacific. Further studies on TCs for the region of SEA and the Philippines follow. 11