Catalonia faces 18 hours of "intense downpours" with possible rises in rivers and streams

The forecast describes a period of torrential rain across Catalonia, with very strong storms in some areas. It matters because intense rainfall can quickly overwhelm drainage systems and watercourses. The reports also mention possible rises in rivers and small streams, known locally as rieras.

The expected period of intense downpours is about 18 hours. Forecasts also warn that some places could receive more than 100 litres per square metre in the coming hours. Barcelona is specifically mentioned as a place where rain may become intense during the afternoon.

Catalan authorities have raised rain alerts as the episode develops. The forecast linked to DANA Adam indicates that storms may remain very strong. Conditions can vary sharply between locations, so the alert period signals a need for caution near rivers, streams, and areas that collect runoff.

A rainfall total of 100 litres per square metre means that more than 100 litres of water would cover every square metre of ground. Because one litre spread over a square metre equals one millimetre of rain, the forecast exceeds 100 millimetres. That is a substantial rainfall total.

The important detail is the timing. The reports expect more than 100 litres per square metre in the coming hours, during a period described as torrential and intense. If water falls faster than soil, drains, rivers, and streams can absorb or carry it, runoff builds quickly and flooding becomes more likely.

The article does not give a historical comparison or a return period, so it does not establish how rare this amount is in Catalonia. It does show that the forecast is serious enough for authorities to raise rain alerts and warn about possible river and stream rises.

Rivers and small streams rise suddenly when rainfall reaches them faster than water can soak into the ground or move downstream. Torrential rain increases surface runoff, especially when the soil is already wet or hard to absorb more water. The water gathers in channels and raises their level quickly.

For example, a storm dropping heavy rain across a river basin can send water from roads, slopes, and fields into the same river or riera. Small streams may respond particularly quickly because they have narrower channels and smaller catchments. A short burst can therefore produce a sharp rise even when the waterway was low beforehand.

The reports warn of possible rises in rivers and rieras during Catalonia’s 18-hour episode of intense showers. That warning matters because water levels can change faster than people expect. Areas beside channels and places where runoff concentrates require special caution while the storms continue.

DANA is the Spanish acronym for an isolated depression at high levels of the atmosphere, commonly described as a cut-off low. It matters because this type of system can destabilise the air over a region. The article links the forecast to DANA Adam and mentions very strong storms.

When colder air aloft sits above warmer, moisture-rich air near the surface, the contrast encourages air to rise. Rising air cools, water vapour condenses, and clouds grow vertically. If the atmosphere remains unstable and moisture continues arriving, thunderstorms can produce intense bursts of rain.

The source gives no detailed track or temperature data for DANA Adam. It does state that the AEMET forecast involves very strong storms and that Catalonia faces torrential rain. The system’s presence helps explain why rainfall may be concentrated, intense, and capable of producing sudden rises in rivers and rieras.

AEMET is Spain’s national weather agency. Its role is to monitor the atmosphere, produce forecasts, and issue official alerts for hazardous weather. In this episode, the forecast associated with AEMET warns of DANA Adam, very strong storms, and potentially intense rainfall in Catalonia.

When torrential rain is expected, AEMET communicates the risk through its warning system. Alerts are normally shared in official forecasts and bulletins, then relayed by authorities, emergency services, broadcasters, and weather platforms. The reports also note that Catalonia has raised its rain alerts, showing how forecasts become public safety information.

The article does not specify the alert colour, exact warning level, or every communication channel used in this case. It does establish the main sequence: AEMET forecasts the conditions, Catalonia elevates its warnings, and the public receives information about heavy rain and possible river and stream rises.

The greatest danger depends on how water moves through each landscape. River valleys and low-lying land can collect runoff, while coastal streams may rise quickly after intense rain over nearby slopes. Urban areas also face problems because roads, roofs, and pavements shed water instead of absorbing it.

A storm over a small coastal basin can send water rapidly into a stream, producing a sudden rise near its mouth. In a city, the same rainfall may flood streets or underpasses if drains cannot carry the flow. These mechanisms can occur together when a storm affects hills, channels, and built-up areas.

The article specifically warns of possible rises in rivers and rieras and reports intense rain in Barcelona. It does not rank the four settings or identify particular sites. The safest conclusion is that every listed environment can be exposed, with extra caution needed wherever water naturally gathers or flows quickly.

Intense downpours need both moisture and a mechanism that lifts air. Moist air contains abundant water vapour. When it rises, it cools and condenses into clouds. If colder air above makes the atmosphere unstable, the rising motion can accelerate, allowing clouds to grow taller and release heavy rain.

Catalonia’s terrain adds another influence. Hills and mountains can force moist air upward, while slopes channel falling rain toward valleys, rivers, and rieras. In built-up areas, paved surfaces speed runoff. Together, storm development in the atmosphere and water movement on the ground can produce intense rainfall followed by rapid rises in waterways.

The source does not provide detailed measurements of moisture, instability, or terrain effects for this event. It does report torrential rain, very strong storms, possible rises in rivers and rieras, and more than 100 litres per square metre. Those facts show why the episode carries flood-related risks.