Precipitation and the Water Cycle in the Philippines

Precipitation: Spatial Distribution

• Precipitation is water released from clouds as rain, sleet, snow, or hail.
• Precipitation begins when water vapor, condensed in the atmosphere, becomes too heavy to remain in atmospheric air currents and falls.
• One-fourth of total precipitation falling on continental areas is turned to the seas by direct runoff and underground.
• Rainfall patterns in the Philippines are influenced by major air streams, ITCZ movement, and cyclonic disturbances.
• The Philippines receives an average of 965 to 4,064 millimeters of rainfall annually.
• The country has an average of 175 rainy days per year.
• Eastern coastal regions generally receive more rainfall than the average, while western coastal regions generally receive less.

Hydrologic Cycle

• The hydrologic cycle is a water cycle involving the continuous circulation of water in the Earth-atmosphere system.

The Water Cycle

• Evaporation: Water (liquid) changes to water vapor (gas). An average of 47 inches (120 cm) evaporates from the ocean annually
• Transpiration: Evaporation of liquid water from plants/trees into the atmosphere. Nearly all water absorbed transpires.
• Sublimation: Ice or snow (solid) changes directly to water vapor (gas) without becoming a liquid.
• Condensation: Water vapor (gas) changes to water droplets (liquid), forming clouds.
• Transportation: Movement of solid, liquid, and gaseous water through the atmosphere.
• Precipitation: Water that falls to Earth (rain, snow, sleet, hail). An average of 39 inches (980 mm) falls annually globally.
• Deposition: Water vapor (gas) changes directly to ice (solid) without becoming a liquid (frost formation).
• Infiltration: Water moving into the ground from the surface.
• Percolation: Water moving past soil, deeper into groundwater.
• Surface Flow: River, lake, and stream transport of water to the oceans.
• Groundwater Flow: Flow of water underground in aquifers. This water may surface in springs or seep into oceans.
• Plant Uptake: Water from groundwater and soil moisture absorbed by plants. Only a small percentage is used by the plant; the rest is released into the atmosphere

Forms of Precipitation

• Drizzle/Mist: Tiny liquid water droplets (0.1-0.5 mm diameter).
• Rain: Liquid water drops (mostly larger than 0.5 mm).
• Snow: Ice crystals in complex, branched hexagonal forms, often agglomerated into snowflakes.
• Sleet: Transparent ice grains formed by freezing raindrops or refreezing of melted ice crystals falling through subfreezing air.
• Hail: Precipitation in the form of balls or pieces of ice formed in convective clouds.
• Rime: White, opaque deposit of ice granules. Formed by rapid freezing of supercooled water drops.
• Glaze: Ice coating formed by freezing of supercooled water. Usually happens on exposed surfaces during rain or drizzle.

Requirements for Precipitation to Occur

• Cooling of the air mass to or near saturation.
• Presence of condensation or freezing nuclei on which droplets or crystals can form.
• Growth of water droplets and ice crystals until their falling speeds exceed the ascent rate of the air.

Rainfall Characteristics

• Intensity: Rainfall depth per unit time (mm/hr). High intensity indicates heavy rain, while low intensity indicates light rain.
• Duration: Length of time a rainfall event lasts.
• Frequency: How often a rainfall event of a certain intensity (or greater) occurs (Return Period or Recurrence Interval).

Rainfall Measurement

• Rain gauges: Meteorological instruments for measuring precipitation.
• Types of rain gauges: Non-recording (standard 8" diameter), recording (tipping bucket, weighing).
• Estimation of Missing Precipitation Data: Arithmetic mean and Normal-ratio methods.
• Isohyetal Method: Determines mean rainfall over a region by creating contours of equal rainfall accumulation and multiplying the mean rainfall by the area between successive isohyets. This technique is more accurate that either the Arithmetic or Normal- Ratio methods.

Analysis and Interpretation of Precipitation Data

• Factors affecting data quality: Gauge location, gauge exposure, instrumentation, and observational procedures. Careful consideration of these factors are critical for accurate interpretations and avoid erroneous conclusions.

Explore the critical concepts of precipitation, its spatial distribution, and its role in the hydrologic cycle, particularly in the context of the Philippines. This quiz covers rainfall patterns, averages, and the importance of the water cycle in the Earth-atmosphere system.