Precipitation
Precipitation is any form of water — liquid or solid — that falls from the atmosphere to the Earth's surface, including rain, snow, sleet, and hail. It forms when water vapor in clouds condenses or freezes around tiny particles called condensation nuclei, growing until droplets or crystals become heavy enough to fall. Precipitation is a critical component of the hydrological cycle, replenishing freshwater supplies in rivers, lakes, and groundwater systems.
Key Formula
P = V / A
LaTeX: P = \frac{V}{A}
| Symbol | Meaning | Unit |
|---|---|---|
| P | Precipitation depth | mm |
| V | Volume of water collected | mL or cm³ |
| A | Collection area of rain gauge | cm² |
Worked Example
Problem
A rain gauge with a circular opening of radius 5 cm collects 157 mL of water during a storm. What is the precipitation depth?
Solution
Step 1: Calculate collection area A = π × r² = π × 5² = 78.54 cm². Step 2: Convert volume: V = 157 mL = 157 cm³. Step 3: Apply formula: P = V / A = 157 / 78.54 = 2.0 cm = 20 mm.
Answer
Precipitation depth = 20 mm
Types of Precipitation and Their Formation Conditions
| Type | State | Temperature Condition | Drop/Particle Size |
|---|---|---|---|
| Rain | Liquid | > 0°C throughout | 0.5–5 mm diameter |
| Drizzle | Liquid | > 0°C throughout | < 0.5 mm diameter |
| Snow | Solid | < 0°C throughout | 1–10 mm snowflakes |
| Sleet | Solid (ice pellets) | Freezing layer aloft | < 5 mm pellets |
| Hail | Solid (ice balls) | Severe thunderstorms | 5–50 mm spheres |
| Freezing Rain | Supercooled liquid | Freezes on contact | 0.5–5 mm drops |
Interactive Tools
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Related Terms
Humidity
Humidity is the measure of water vapor present in the air, expressed either as absolute humidity (mass of water per unit volume of air) or relative humidity (percentage of water vapor relative to the maximum possible at that temperature). Warmer air can hold more water vapor, so the same amount of moisture feels "drier" on a hot day than a cool day, which is why relative humidity is the most commonly reported measure. High humidity reduces the body's ability to cool itself through sweating, making heat feel more intense and posing health risks during heatwaves.
Dew Point
The dew point is the temperature to which air must be cooled, at constant pressure and water vapor content, for saturation to occur and dew or fog to form. When air cools to its dew point, relative humidity reaches 100% and water vapor begins condensing onto surfaces as liquid water. The dew point is a direct measure of atmospheric moisture content: a higher dew point means more moisture in the air and is used to predict fog, frost, and thunderstorm intensity.
Climate
Climate refers to the long-term average patterns of temperature, precipitation, wind, and other atmospheric conditions in a region, typically measured over a 30-year period. Unlike weather, which describes short-term atmospheric conditions, climate represents the statistical summary of a region's typical weather over decades. Understanding climate is essential for agriculture, urban planning, disaster preparedness, and studying the effects of global climate change.
From Latin "praecipitatio," derived from "praecipitare" meaning "to throw headlong" or "to fall steeply," from "prae" (before) + "caput" (head). The meteorological sense developed in the 17th century.