Understanding rainfall measurement: meaning, methods, and applications
Rainfall Measurement:
Rainfall is the total amount of liquid or melted solid that falls on the ground. This happens over a specific time, usually 12 or 24 hours. There is a way to measure how much water collects on a flat surface. This takes into account evaporation, percolation, and runoff. Meteorologists usually measure rainfall in millimeters (mm) and record it with one decimal place in their observations. It provides a straightforward indicator of the intensity of rainfall.Rainfall measurement is a crucial aspect of meteorology. Here’s an explanation of how rainfall is measured and the concept of 1 mm of rainfall:
24-Hour Rainfall Amounts:
– Light Rain: 0.1-9.9 mm
– Moderate Rain: 10.0-24.9 mm
– Heavy Rain: 25.0-49.9 mm
– Stormy Rain: 50.0-99.9 mm
– Heavy Stormy Rain: 100.0-249.9 mm
– Very Heavy Stormy Rain: ≥250.0 mm
Millimeter of Rainfall:
Imagine 1 mm of rainfall as a depth of water accumulated on a flat surface. It’s roughly equivalent to pouring two 500-milliliter bottles of water onto one square meter of level glass. For 50 mm of rainfall, it would be about 100 bottles.
If we look at an area of one mu (666.7 square meters), 1 mm of rain gives about 0.667 cubic meters of water. This water weighs around 667 kilograms because 1 cubic meter of water weighs 1000 kilograms. Researchers have calculated that a rainfall of 5 mm can saturate droughty soil by 3 to 6 centimeters.
Importance of Rainfall Measurement:
Rainfall is a key factor in calculating regional water resources. It is essential to have an accurate and convenient method to predict rainfall for effective water resource management.
Rainfall Measurement Tools:
The main tools for measuring rainfall are bucket rain gauges. Weather and water agencies often use these. These gauges consist of a funnel-shaped collector that directs the rainwater into a container or ‘bucket’. When the bucket fills to a certain level (e.g., 0.1 mm), it tips over, recording the rainfall event. Each tip of the bucket sends a pulse to a recording device, which tallies the rainfall depth.
Working Principle of Bucket Rain Gauge:
The rain gauge works by letting rainwater enter a funnel at the top. The water then flows into a measuring bucket. When the water reaches a certain height, like 0.1 mm, 0.2 mm, or 0.5 mm, the bucket tips over. This tipping sends a signal through an electrical circuit to the recorder. This process continues, providing a measure of the entire rainfall event.
Measuring rainfall is important in weather science.
1 mm of rainfall is the amount of water that gathers on a flat surface. This is after considering evaporation, percolation, and runoff. Typically, people measure it over a 24-hour period and record it in millimeters.
For example, 1 mm of rain is about the same as pouring two 500-milliliter bottles of water on one square meter. In agriculture, 1 mm of rain equals about 667 kilograms of water for every mu, which is 666.7 square meters. This shows how important rainfall is for calculating water resources in a region. It also emphasizes the need for a simple and accurate way to predict rainfall. This is essential for managing water resources effectively.
Meteorological and hydrological agencies primarily use bucket rain gauges to measure rainfall. These gauges collect rainfall in a funnel. They measure the amount that spills over when it reaches a certain level, like 0.1 mm. Each time the measuring bucket tips over, it sends a pulse to a recording device, which calculates the total rainfall depth.
