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Irosin, Sorsogon


The municipality of Irosin, Sorsogon is defined by a Type 2 climate (based on the modified Corona’sclimate classification). This means that the municipality, on the average, does not have a dry season but with a very pronounced maximum rain period from November to January/February (the northeast monsoon season). The minimum rain period is in April and May. Mean monthly rainfall values in the nearest representative station indicate a high of approximately 550mm during the wettest month of December and a low of 180mm during the relatively driest month of April (See Fig.1).


Figure 1



Mean values of monthly maximum and minimum temperature range from 28.7 degrees centigrade in January to 32.3 degrees centigrade in May, and from 22.7 degrees centigrade still in January to24.7 degrees centigrade again in May respectively.


Figure 2



The municipality is largely affected by tropical cyclones, especially during October, November and December.


Figure 3



Indicated in the results of extreme daily temperature-and rainfall- trends analysis are that the number of hot days and warm nights are increasing, with the number of cool days and cold nights decreasing. Total rainfall show an increasing trend,with also an increase in the number (frequency) and severity (intensity) of extreme rain events. These indicate increasing maximum and minimum temperatures coupled with increasing rainfall and thus; increasing flood risks.

Historical and current extreme weather/climate events that have affected the municipality include El Nino-related droughts, La Nina-related floods. It also is exposed to tropical cyclones and associated maximal values of 24-hour rains and winds, particularly during the northeast monsoon season (October to February). Farmers confirmed that the most recent continuous rains (end of 2008 to start of 2009) had caused rice fields to be largely submerged and consequently, crop failures in most cases. There is every indication that unusual rain patterns during the supposedly drier times of the year could cause crop failures because these were not expected. In not very recent years, the worst El Nino event at the end of the 20th century had caused high incidence of pests and diseases; thus decreased yields.


2020 Climate Projections and Future Risks

Projections for climate scenarios in 2020 and 2050 could spell decreases in rice yields, particularly if the right agricultural planning is not in place. In 2020, projected temperature increases are 0.8C during the months of December to February (DJF), 1.0C in the quarter from March to May
(MAM), 0.8C during the 3-month period from June to August (JJA) and 0.8C again from September to November (SON). The highest increase in
mean temperature is definitely during its warmest summer months.

The projections for mean temperature increase in 2050 are quite higher with 1.8C, 2.2C, 1.9C and 1.7C in December to February (DJF), March to May (MAM), June to August (JJA), and September to November (SON), respectively. Again, the highest projected increase is during the warmest
months (MAM) as can be seen in Fig. 3. On the other hand, the projected increase in rainfall volume at 2020 climate change scenarios ranges from 2 % in March to May to 23 % in June to August. The middle values were projected at 13 % in September to November and 19 % in the quarter of December to February. Projected increases in rainfall in Irosin in 2050
are higher with 11 % in December to February, 20 % in September to November, and 31% in June to August. The warm months of March to May will have a 12 % decrease.


Figure 4



A 19% increase in December to Februarywould most likely result to an increase of 200 mm rainfall volume in 2020. This could lead to further decrease in yields unless it coincides with the appropriate farming activities and with the correct choice of crops and cultivars.


Future Risks and Implications for Agriculture

An increase in temperature of 1.0C in the warmest months of March, April and May could cause substantial damage to crops if not addressed with the appropriate corrective adaptation practices. The rise in temperature could be beneficial during these warm months if the right cropping systems are in place, and crops that are resistant to drought and flood as well as resilient to pests and diseases are used. Support services and infrastructure should be available, and sustainable farming systems such as organic farming, and diversified cropping such as aquaculture are practiced.





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