Reading the flood

What the marks mean

The Ping at Nawarat (gauge P.1) is read in metres against a staff gauge with two lines that matter. Below about 3.50 m the river is comfortably in its channel. At 3.70 m it is bank-full: the warning level, where low spots along the river start to take water. At 4.20 m it is at the top of the flood barrier; past that, the defences are at their limit and water spreads into the streets.

Putting a number in perspective

A reading of "4.5 m" is abstract until you have something to compare it to. When tropical storm Noru pushed the Ping over the barrier in October 2022, the river reached roughly that level and flooded the Night Bazaar and riverside roads. In 2011 it peaked near 4.95 m; in October 2024 it set the record at 5.30 m, more than a metre over the barrier. So the barrier at 4.20 m is not a theoretical line; it is roughly the level at which the parts of town nearest the river go under.

How much warning you actually get

The city gauge tells you the flood has essentially arrived. Your warning comes from the gauges above the city. The river at San Sai (P.67) is six to eight hours upstream of Nawarat, and Chiang Dao (P.20) about eighteen. So a rising San Sai reading tonight is your notice for the morning; heavy rain up at Chiang Dao today is your notice for tomorrow. That is the practical value of watching upstream: it converts an abstract number into hours you can use. (For the fuller picture, see where the Ping comes from.)

Where the city floods first

Chiang Mai does not flood evenly. The riverside roads and the low-lying neighbourhoods go first: the areas along Charoenrat and Charoen Prathet by the Night Bazaar, and the low districts such as Pa Daed and Nong Hoi. If you are in one of these, the same gauge reading means more to you, and sooner, than it does to someone on higher ground. Away from the river, the bigger risk is often not the Ping at all but sudden local rain that overwhelms the drains, a separate hazard the monitor tracks as flash-flood risk.

What to do as it rises

When the season is wet, get in the habit of a glance: the risk verdict and the upstream gauges, once a day. It costs nothing and it is how you avoid being surprised.

As the river approaches bank-full (3.70 m) and the upstream gauges are climbing, act on the hours you have: move vehicles to higher ground, lift valuables off the floor in riverside and ground-floor spaces, charge phones and power banks, and set aside water, medicine and documents. This is the calm-preparation stage; do it before you need to.

As it nears the barrier (4.20 m), low-lying areas should be following official instructions, not their own judgement: move to higher ground if told to, keep away from the water, and never drive or walk through a flooded street, where depth and current are deceptive. Never risk your life to protect property.

This site makes the official numbers readable and gives you earlier notice; it does not issue evacuation orders. Those come from the authorities, and when they do, they override anything you read here.

The map, and the flood poles

The monitor's map carries more than the river line. The CMU Water Center maintains a network of more than two hundred flood-marker poles across the city that record how deep past floods reached at each spot: a street-level memory of where the water goes. The map also shows evacuation shelters and flood-safe parking. Between the live gauges, the forecast, and that local knowledge of where water pools, you have the three things that matter: how high, how soon, and where.

Open the live map ›

Where this comes from

The 3.70 m warning and 4.20 m barrier are the marks used for the P.1 Nawarat gauge. Past peak heights are best-available figures from news reporting and flood histories and can vary slightly by source and by how the peak is timed; treat them as approximate. Neighbourhood flood-proneness is general and local; your own street is the final authority.