EXPLAINER: What do color-coded rainfall warnings mean?

CEBU CITY, Philippines – When bad weather prevails, people often receive text alerts from the National Disaster Risk Reduction and Management Council (NDRRMC) about the volume of rainfall expected.

In most cases, the NDRRMC sends Emergency Alerts to warn the public about heavy or intense rainfall, ranging from yellow to red color.

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But what do the color-coded rainfall advisories mean, and why do we have to pay attention to these?

Color-coding

The state weather bureau has been implementing color-coded heavy rainfall warning system to categorize the intensity of rain.

It has three colors – yellow, orange, and red. The darker the color, the more dangerous the rains can be.

Yellow: Heavy rains

Areas under a Yellow Heavy Rainfall Warning will experience rainfall between 7.5 millimeters (mm) and 15 mm within one hour and this will continue in the next two hours.

At maximum, this is equivalent to 6,300 liters of water, or 30 drums, in an hour, the Philippine Atmospheric Geophysical and Astronomical Services Administration (Pagasa) said.

When Yellow Rainfall Warning is in effect, slight flooding, especially in low-lying areas, is possible. The public is also advised to continuously monitor weather conditions.

Orange: Intense rains

The next level of rainfall warning is Orange Intense Rainfall Warning.

If rains reach this level, the public is advised to stay alert and be ready for any actions from the local and disaster units in their place.

This is because areas under orange warning will receive rainfall between 15 mm and 30 mm within an hour, and this will continue in the next two hours. In an hour, this volume of rainfall can fill four, 20-gallon water containers per square meter.

Effects of orange rainfall warning. | Screenshot from Pagasa-Visayas PRSD

With this amount of rainfall, landslides and floodings are likely. Evacuation may also be required.

Red: Torrential rains

The most intense and dangerous of all heavy rainfall warning colors is red.

The amount of rainfall under this category is 30 mm or more within an hour. For scale, it can fill up eight, 20-gallon water containers per square meter in one hour.

Screenshot from Pagasa-Visayas PRSD video

Red rainfall warning or torrential rain also means serious flooding, flooded and unpassable roads, and life-threatening landslides, particularly in hazardous areas.

Once authorities issue the red heavy rainfall warning, emergency measures such as preemptive and mandatory evacuation will be conducted.