CLIMATE AND DISASTER RISK INFORMATION

Flood Hazard Areas

About 4% of the total land area are in very high to high flood susceptibility and 11% in moderate to low flood susceptibility. In 2015, there are 894 households in areas with very high to high flood susceptibility. There are 23 hectares of existing built-up areas in very high and high flood susceptible zones, of which 16.41 hectares are residential uses and 3.47 hectares are for institutional use. A total of 307 hectares of agricultural lands are in very high and high flood susceptible zones and 231 hectares of that are rice areas.

Figure 1. Flood Susceptibility Map

Landslide Prone Areas

Twenty-two out of the 28 barangays of Irosin have zones with landslide hazard and a total of 102 landslides were mapped. One-fourth of the total land area are in very high to high and 37% are in moderate to low landslide susceptibility. There are 15 households in very high landslide susceptible areas, 609 in high, 421 in moderate and 2,149 in low.  Areas in very high to high landslide susceptibility includes 32 hectares of built-up areas of which 18.85 hectares are utilized as residential areas, 2,223.3 hectares of agricultural lands mostly planted to coconuts, and 1,166.7 hectares of lands with forest cover.

Figure 2. Landslide Susceptibility Map

Volcanic Hazard Zones

The active crater of Bulusan Volcano is located 7.5 kilometers north from the urban center.  The hazards associated with Bulusan Volcano are pyroclastic flows, lava flows, lahars and ash fall. A four-kilometer radius around the volcano is declared a permanent danger zone. The pyroclastic flow hazard zone is about 2,224 hectares which encompasses the BVNP forest areas and reaches up to the built-up area of Cogon and Mapaso. On the other hand, the lava flow hazard zone overlaps the pyroclastic flow hazard zone and extends further up to five kilometers radius and includes the built-up area of Cogon, Mapaso and portions of the national highway. The lava flow hazard zone covers 2,973 hectares of mostly forest and agricultural use lands. Lahar flows from 2006-2007 ash explosions are mainly confined to gullies at the slopes of the volcano which flows down to the dry creeks of Cogon, Gulang-gulang, Monbon, Mapaso and Patag. Lands with high risk to lahar covers 3,057 hectares. Recent activities of Bulusan Volcano are phreatic or steam driven which results to explosion of ash, rock and volcanic materials. The area affected by ash fall is largely determined by the volume of material ejected and the prevailing wind direction.

Observed Conditions (Problems /Issues) on Disaster Risk Reduction and Management

  • Absence of CDRA
  • Many public infrastructure are not disaster resilient
  • 67% of farmers covered with crop insurance
  • Some barangays lack warning system communication equipment
  • Absence of Automatic Weather Station (AWS)
  • School sites in landslide hazard zone (Salvacion, Bulawan and Omagom ES) and flood hazard zone (Tulay ES)
  • About 358 households and 23 hectares of urban use area are in very high and high flood hazard susceptibility zone along the Cadacan River
  • About 621 households and 32 hectares of urban use areas are in very and high landslide susceptibility zones mostly in Salvacion, Bolos and Gulang-gulang
  • About 231 hectares of palay production areas are in very high and high flood hazard susceptibility zone along the Cadacan River
  • Cogon barangay site with 248 households is near volcanic hazard zone
  • 72 households in Mapaso are within the 4 km permanent danger zone of Bulusan Volcano
  • Insufficient services on agricultural climate information and climate-sensitive technologies
  • Some member of community lack awareness, capacity and skills on DRRM
  • Inadequate rescue equipment and supplies
  • Late conduct of DANA
  • Lack of adequate evacuation center
  • Lack of local funds to reconstruct/restore damage properties

Extreme Climate and Weather Events

Historical and current extreme weather/climate event that have affected the municipality include El Nino-related droughts and La Nina- related floods. Irosin is exposed to tropical cyclones and associated maximal values of 24-hour rains and winds, particularly during the northeast monsoon season from October to February. From the period 1948 to 2006, there were 84 tropical cyclones which crossed the Sorsogon province and within 50 kilometers from its boundaries or an average of three every two years. For that 58-year period, the frequency of tropical cyclones is six during January to March, 16 in April to June, 21 in July to September and 41 during October to December.

Figure 3. Lava and Pyroclastic Flow Hazard Map

Local Climate Change Scenarios for 2050

By 2050, the amount of annual rainfall in Irosin is projected to increase. The months of December, January and February will have dramatic increase in precipitation with 54%, 87% and 55% percent change in rainfall respectively. Increase in monthly rainfall is also projected in the months of April at 29% percent change, June at 23%, July at 34%, October at 19% and November at 23%. Less rainfall is projected during the months of March at -15% percent change, May at -10%, August at 4% and September at -22%. Increase in temperature is also projected by 2050, with an increase in minimum temperature highest by 1.9 °C in May and lowest by 1.4 °C in December. Maximum temperature increase is highest in September with 2.1 °C increase and lowest in January with 0.8 °C increase. Based on the climate model, the future local climate will experience changes in annual and seasonal averages with wetter wet season during the northeast monsoon and will be warmer and drier during the months of May, August and September. Changes in extremes are also forecasted with more very hot days in the months of April, May, August, September and October and more intense downpour in the months of December, January and February.

 

The identified climate change drivers in the municipality are increased precipitation, decreased precipitation, higher temperature and increased intensity of typhoons. With these drivers are increased exposure to the hazards of flooding, landslides, dry spells and strong winds. The projected impacts of climate change for the agriculture sector are decrease in crop yield, increase in post-harvest losses, increase in crop pests and disease incidence and decrease in livestock production. Impacts on water resource and infrastructure are increased siltation of water bodies, increased damage to potable water system, declining water quality, increased damage to irrigation system, reduction of available water supply and increased demand for water. The health sector will have increased incidence of water-borne diseases and increased number of casualties from hazards. Impacts to social and economic support infrastructure would include increased damage to schools and administrative centers, inundation of roads, bridges and spillways, increased damage to roads and bridges, inundation of drainage systems and increased damage to utilities. Forest ecosystem and biodiversity impacts are increased forest loss due landslides, increased soil erosion, increased forest loss due to bush/forest fire and loss of biodiversity in fragile environment. Human settlements are expected to have increased property damages, increased number of settlements at risk to flooding and increased number of climate induced evacuees.

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