Rainfall-Induced Landslides

• Rainfall-induced landslides involve the movement of rocks, mud, or debris down a slope due to rain saturation, developing over hours or days near steep slopes.

Cause of Rainfall-Induced Landslides

• These landslides are caused by a combination of rain duration, intensity, and ground saturation.
• Water accumulates in the ground when rainfall exceeds soil absorption.
• The added water weight increases soil mass and leads to landslides.

Warning Signs of Rainfall-Induced Landslides

• Cracks in the ground and tilting trees or poles.
• Sudden water flow from slopes, soil movement, and crumbling walls.
• Unusual sounds from slopes also indicate potential landslides.

Safety Measures for Rainfall-Induced Landslides

• Before: Stay informed on weather and landslide-prone areas, prepare emergency kits, and identify evacuation routes.
• During: Evacuate if warning signs are evident, avoid rivers and steep slopes, and follow authorities' instructions.
• After: Stay away from unstable ground, report damages, and seek medical help for injuries.

Sinkholes

• A sinkhole is a ground opening caused by the collapse of the surface layer, due to the breakdown of underground rock.
• This creates gaps that cannot support the soil above.

Causes of Sinkholes

• Sinkholes occur naturally when water dissolves soluble rocks like limestone, gypsum, or salt.
• Human activities such as groundwater extraction, construction, and poor drainage can contribute to sinkhole formation.

Warning Signs of Sinkholes

• Cracks on floors or roads indicate potential sinkholes.
• Depressions in the ground, leaning trees or poles, and unusual water pools also serve as early warning signs.

Safety Measures for Sinkholes

• Before: Look for warning signs like cracked floors or sinking ground, reduce groundwater use, stay updated on local geology, and prepare an emergency plan.
• During: Stay calm, move away from the affected area, and evacuate quickly if you see any ground movement. Keep a safe distance, warn others, and call emergency services.
• After: Avoid the area until officials inspect and confirm it is safe.

Hydrometeorological Hazards

• These hazards stem from atmospheric, hydrological, or oceanographic processes like cyclones, thunderstorms, floods, droughts, avalanches, and heatwaves.
• Hydrometeorological hazards can cause loss of life, property damage, and environmental harm.

Typhoon

• Typhoons develop over warm oceans (≥26°C) due to heat and condensation.
• Hurricanes, typhoons, or cyclones are regional names for the same phenomenon.
• The Philippines frequently experiences strong winds, floods, and destruction from typhoons.

Thunderstorm

• Thunderstorms always include lightning and arise from convection due to surface heating.
• 1,584 lightning-related deaths have occurred in the Philippines.
• Advisories are issued for affected areas within two hours.

Flash Flood/Flood

• Flash floods are caused by rainfall, land use, and soil conditions, accounting for 85% of flood cases and high mortality.
• The Philippines uses sensors and real-time systems for flood tracking.
• Health risks from floods include drowning, injuries, infections, and disease spread.

Storm Surge

• Storm surge is an abnormal seawater rise caused by storm winds pushing water onshore.
• Storm tides are highest during new and full moons because of sun and moon alignment.
• Typhoon Yolanda had a 7-meter storm surge in 2013, causing 6,300 deaths.

El Niño

• El Niño weakens trade winds, bringing warmer waters to the Pacific near the Philippines.
• It causes droughts, weak monsoons, and fewer typhoons.
• Fisheries are disrupted, reducing fish supply during El Niño.

La Niña

• La Niña strengthens trade winds, pushing warm water toward Asia.
• This causes heavier rains, stronger monsoons, and more typhoons in the Philippines.
• Colder seas disrupt fish migration, reducing catch for some species.

Potential Signs of Typhoon

• Increased ocean swell
• Changes in clouds
• Barometric pressure drop
• Abrupt changes in wind speed

Potential Signs of Thunderstorm

• Cumulonimbus clouds
• Darkening sky
• Lightning and thunder
• Gusty winds and changing wind direction

Potential Signs of Flash Flood or Flood

• Weather forecasts for typhoons or thunderstorms
• Puddles forming with rapidly rising water levels
• Muddy water
• Roaring sounds from upstream areas
• Floating debris.

Tools for Monitoring Hydrometeorological Hazards

Temperature Measurement

• Thermometer: Measures how hot or cold a substance is; mercury expands when heated and contracts when cooled.
• Maximum-Minimum Thermometer: Records highest and lowest temperatures; uses mercury to mark the peak and colored alcohol with a black index needle to mark the lowest temperature.
• Thermograph: Continuously records air temperature on graph paper using a revolving cylinder and a pen-point moved by a metallic coil.

Air Temperature Measurement

• Thermograph is housed in a ventilated thermometer shelter for accurate readings.

Air Pressure Measurement

• Mercurial Barometer: Measures atmospheric pressure using a mercury-filled glass tube, read with a Vernier scale and corrected for temperature, gravity, and latitude; results given in millibars, millimeters, or inches of mercury.
• Aneroid Barometer: Measures atmospheric pressure without liquid; a sealed, airless metallic box expands/contracts with pressure changes, moving a pointer on a scale; a spring prevents collapse and a corrugated surface ensures uniform movement.
• Barograph: Continuously records atmospheric pressure using a pen that traces changes on paper, controlled by levers connected to aneroid cells; multiple cells improve response to pressure variations.

Humidity Measurement

• Sling Psychrometer: Uses dry-bulb and wet-bulb thermometers, the latter wrapped in a moist cloth; whirling the instrument and noting the temperature difference determines dew point and relative humidity using a psychrometric table.
• Hygrometer: Measures humidity using oil-free human hair, which lengthens as humidity increases, moving a needle on a 0-100% scale; less precise than a psychrometer.
• Hygrothermograph: Uses a moisture-sensitive element (e.g., human hair) and a metallic coil to record humidity and temperature changes; a rotating drum ensures continuous recording on graph paper.

Rainfall Measurement

• 8-inch Raingauge: Directs rain into a smaller measuring tube, amplifying the rainfall depth by ten times; holds up to 2 inches (50.8mm) of rain, measured with a calibrated stick; excess rain is caught for later measurement.
• Tipping Bucket Raingauge: Directs rain into a pivoted tipping bucket that triggers an electrical signal each time it fills (0.5 mm of rain), marking rainfall data on a recorder.

Cloud Height Measurement

• Ceiling Light Projector: A narrow light beam is projected onto the cloud base, and a clinometer at a fixed distance measures the angle; height is found by multiplying distance by the tangent of the angle.
• Ceiling Balloon: A gas-filled balloon with a known ascent rate is released, and the time from release to disappearance into the cloud is recorded; cloud base height is ascent rate multiplied by time.