COLOMBIA · CARIBBEAN COAST · EXPLAINER
Floods on Colombia’s Caribbean coast build fast because steep rivers, rain-fed street streams called arroyos, high tides and blocked drains all work against the cities at the same time.
Key Facts
- —Main cause Steep mountain rivers and rain-fed city streams called arroyos fill quickly when heavy rain arrives.
- —The mountain The Sierra Nevada de Santa Marta rises to 5,775 metres only 42 kilometres from the coast.
- —The seasons Two rainy seasons a year, and the second peaks in October and November.
- —Weak points High tides slow drainage in Cartagena, and rubbish blocks canals and drains in Barranquilla.
- —Latest case Heavy rain on Saturday, 24 October 2026 put Santa Marta on red alert and flooded Cartagena.
- —Power Index Colombia ranks 6th of 14 in The Rio Times Latin America Power Index, with 51.9 points (October 2026 edition).
Caribbean Colombia floods so fast because several quick causes meet at once: steep rivers that fall from a very high mountain to the sea in a few dozen kilometres, rain-fed streams called arroyos that turn streets into channels, high tides that hold back drainage and rubbish that blocks canals. The latest case came on Saturday, 24 October 2026, when heavy rain put Santa Marta on red alert and flooded neighbourhoods in Cartagena, as our news report on the Santa Marta red alert describes.
The causes matter to foreign readers because the coast has large cities and tourist towns that US travellers visit, and because floods there can build within hours even in a year when El Niño is expected to bring less rain overall. Local and national authorities issue colour-coded alerts, and this explainer also shows how to read them.
In Plain English
- Arroyo: a rain-fed stream or channel that fills during storms, including along city streets; IDEAM warns of arroyos forming around Cartagena.
- Flash flood (creciente súbita): a rapid rise in a river or stream after heavy rain.
- IDEAM: Colombia’s national weather and river-monitoring institute.
- Sierra Nevada de Santa Marta: a mountain range, separate from the Andes, that rises beside the Caribbean coast.
How Caribbean Colombia Floods Start
The Sierra Nevada de Santa Marta is independent of the Andean chain and rises to 5,775 metres only 42 kilometres from the coast, UNESCO says in its biosphere-reserve file. That averages roughly 140 metres of height for every kilometre inland, our calculation from UNESCO’s figures, so rain that falls high up reaches the lowlands quickly.
IDEAM’s bulletin of 25 October lists rivers that descend from the mountain, including the Sevilla, Tucurinca, Frío, Orihueca, Aracataca and Fundación, among those with a probability of flash floods. It also names the Piedras, Gaira and Manzanares, which discharge into the Caribbean and underpin Santa Marta’s red alert, and it notes flooding in Zona Bananera on 24 October.
A flash flood is a rapid rise in a river or stream after heavy rain, and IDEAM’s bulletins use the term creciente súbita for the warning. The institute’s red alert is described in the same bulletins as “to take action”, a level that calls for immediate attention from residents and rescue services.
Arroyos, Tides and Blocked Drains
On this coast an arroyo is a rain-fed stream that can fill streets, and IDEAM’s bulletin of 25 October warns of the formation of arroyos around Cartagena, Santa Catalina in Bolívar and Luruaco, Piojó, Juan de Acosta, Tubará and Puerto Colombia in Atlántico. After Saturday’s downpour, Noticias RCN described streets in Santa Marta turned into streams that swept everything along.
Barranquilla’s infrastructure agency says one trash trap on the Arroyo León collects waste from 68 arroyos in 18 sub-basins of the city’s western basin, which drains to the Mallorquín lagoon and the Caribbean. Its director, José Luis Romero, told El Heraldo that crews generally clean the channels twice a year, around the April and October rains, and the paper reports that one cleaning round of 50 storm channels removed 5,800 tonnes of waste over 32 kilometres.
In Cartagena, the city hall said high tide can slow the exit of rainwater to the sea, and El Universal notes that Bocagrande and Castillogrande have historically flooded when strong rain coincides with high tide. Its drainage project for those districts, which includes four pumping stations, is still under construction, and the final pumps are not yet working.
Rubbish makes each of these problems worse, because waste blocks grates, culverts and channels, as Caracol Radio noted in Santa Marta on Saturday. Barranquilla’s city hall says it has removed 14,200 tonnes of waste from arroyos, canals and the trash trap so far this year.
Two Rainy Seasons and a Strange Year
Colombia’s second rainy season starts in late September and peaks in October and November in the Andean and Caribbean regions, IDEAM says. Barranquilla’s infrastructure agency likewise describes two wet seasons a year in the city, around April and October.
El Niño does not switch rain off, according to IDEAM, which declared the phenomenon on 8 October 2026 yet expects below-normal totals and warns of storms and flash floods. The institute adds that rain varies by region and by day as tropical waves pass, so a wet spell can strike in a dry-leaning season.
For Saturday’s event, Cartagena’s city hall pointed to a trough and two low-pressure areas in the Caribbean influenced by a stationary front north of the Greater Antilles. The private forecaster iClima added a favourable phase of the Madden-Julian Oscillation, which NOAA describes as an eastward-moving tropical disturbance of clouds and rainfall, and forecast a 63% chance of rain in Cartagena on Sunday, with 10 to 20 millimetres (0.4 to 0.8 inches) possible.
Santa Marta in 2026, Three Floods
- February: after a cold front, the city hall’s preliminary census counted 410 affected families, 20 destroyed homes and 87 uninhabitable ones.
- 26 September: an afternoon storm flooded streets and trapped vehicles, Publimetro reported.
- 24 October: red alert for flash floods and flooded streets, with the Gaira river overflowing.
What It Means for You
For US travellers, the practical lesson is to treat any heavy rain on the Caribbean coast as a flood risk, since streets can turn into streams within hours and the road to Minca, a hill village inland from Santa Marta, flooded on Saturday. The US State Department’s Colombia advisory is Level 3, “Reconsider Travel”, issued on 31 March 2026, and it lists natural disasters among its reasons.
How to Read IDEAM Alerts
- Red, “to take action”: an imminent threat that needs immediate attention from residents and rescue services.
- Orange, “to prepare”: a phenomenon is present or conditions favour one, with no immediate threat, and continuous monitoring is advised.
- Yellow, “to be informed”: an official notice about observed events, with some forecast.
IDEAM publishes its bulletins on its website and river levels on its FEWS viewer at fews.ideam.gov.co, and city halls issue local alerts based on them, as Santa Marta’s did on Saturday. Tayrona National Park near Santa Marta is closed to visitors from 19 October to 2 November for a planned conservation break and reopens on Tuesday, 3 November.
What Is Not Known
No source we read measures how much of Saturday’s flooding came from the weather and how much from drains, rubbish or building on flood paths. Whether climate change is making Caribbean downpours heavier is not addressed in the IDEAM material we read.
It is not yet known whether Cartagena’s drainage works in Bocagrande and Castillogrande will cut flooding once finished, because the city says the project cannot be judged until all its parts operate. Damage totals for Saturday’s floods in Santa Marta, Cartagena and other towns have not been published in the accounts we read.
IDEAM expects below-normal rain in the coming months, but it also says that local storms can still bring flash floods, so the number of further events this season is unknown. The bulletin of 25 October was updated at 00:00 and its alerts were valid until 06:00 local time, so readers should check the latest edition.
Connected Coverage
Frequently Asked Questions
Why does the Caribbean coast of Colombia flood so quickly?
Steep rivers fall from a mountain that rises to 5,775 metres only 42 kilometres from the coast, and rain-fed streams called arroyos fill city streets. High tides and blocked drains then slow the water’s exit.
What is an arroyo?
On Colombia’s Caribbean coast it is a rain-fed stream or channel that fills during storms, sometimes along city streets. IDEAM’s bulletin of 25 October warns of arroyos forming around Cartagena and in several Atlántico towns.
Does El Niño mean less flooding on the coast?
IDEAM expects below-normal rain over much of Colombia in the coming months. It does not stop the October and November rainy season, so local flash floods can still happen.
What does a red alert mean in Colombia?
IDEAM describes its red alert as “to take action”, meaning residents and rescue services should respond at once. Santa Marta’s city hall declared one on 24 October 2026 for the Piedras and Manzanares rivers.
Is it safe to visit Cartagena or Santa Marta in the rainy season?
Visitors can go, but should treat heavy rain as a flood risk, avoid flooded streets and follow local alerts. None of the official accounts we read closes either city to visitors.
Where can I check river and rain alerts?
IDEAM publishes its bulletins on ideam.gov.co and river levels on its FEWS viewer. City halls then issue local alerts based on them, as Santa Marta’s did on Saturday.
Sources: UNESCO, Sierra Nevada de Santa Marta Biosphere Reserve, IDEAM, hydrometeorological bulletin 892, 25 October 2026, 00:00, IDEAM, second rainy season and El Niño, IDEAM, El Niño declaration of 8 October 2026, El Heraldo, rubbish in Barranquilla arroyos, 25 October, El Heraldo, Arroyo León trap, 19 October, El Universal, Bocagrande and Castillogrande drainage project, El Universal, city hall on the weather systems, El Universal, iClima forecast, Caracol Radio, Santa Marta red alert, Noticias RCN, Alcaldía de Santa Marta, census of 4 February 2026, Publimetro, 26 September 2026, Parques Nacionales Naturales, Tayrona closure, US State Department, Colombia travel advisory, US National Weather Service glossary, flash flood, NOAA Climate.gov, Madden-Julian Oscillation. All retrieved 25 October 2026. Photos: sergejf and Mark Koester via Flickr, archive images.
This article was produced by The Rio Times’ automated newsroom system. How we use AI · Report an error · Editorial responsibility: Matthias Camenzind, Editor-in-Chief