Historical and current extreme weather/climate event that have affected the municipality include El Nino-related droughts and La Nina- related floods. Irosin is also is exposed to tropical cyclones and associated maximal values of 24-hour rains and winds, particular during the northeast monsoon season from October to February. From the period 1948 to 2006, there were 33 tropical cyclones that crossed the Province of Sorsogon or an average of one tropical cyclone every two years. For the same period, the number of tropical cyclone which crossed the province and 100 kilometers from boundaries was 140 tropical cyclones or an average of five every two years. One of the most intense tropical cyclone that directly crossed the municipality was Typhoon Dinang (Lee) on December 25, 1981 with a peak intensity of 150 kilometer per hour winds.
In 2020, projected temperature increase are 0.8 ⁰C during the month of December to February, 1.0 ⁰C in the quarter from March to May, 0.8 ⁰C during the 3-month period from June to August and 0.8 ⁰C again from September to November. 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 1.8 ⁰C, 2.2 ⁰C, 1.9 ⁰C and 1.7 ⁰C in December to February, March to May, June to August, and September to November respectively. Again, the highest projected increase is during the warmest months (MAM) as can be seen in Figure 5.
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 increase in rainfall 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. A 19% increase in rainfall volume in December to February would most likely result to an increase of 200 mm rainfall volume in 2020.
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 night decreasing. Total rainfall shows an increasing trend, with also an increase in the number or frequency and intensity of extreme rain events. These indicate increasing maximum and minimum temperatures coupled with increasing rainfall and thus increasing flooding risk.