Flood in Semarang, Indonesia: A Lesson in Flood Response

The rainy season has just started in Indonesia, yet one of its major cities has already been hit by a flood. This city is Semarang, the capital city of Central Java. The flood in Semarang has lasted for several days. It started on October 22, 2025, and as of November 1, some areas remained inundated by floodwater.

However, the water level in most areas has receded. Due to this hydrologic hazard, citizens in Semarang experienced many inconveniences. According to a report, this disaster also caused a few fatalities and financial loss.

Flood in Semarang: Impact and Causes

On October 22, heavy rain poured in Semarang. This extreme weather event led to flooding in Semarang. This city is located along the coast of the Java Sea. Moreover, Semarang is a low-lying region. Therefore, it is not surprising that this city experiences flooding each year.

1. The Impact

The Semarang flood at the end of October affected 18 subdistricts.  The flood level varies from 50 cm to 80 cm. One of the badly affected areas is Kaligawe Road, a vital transportation route in northern Java. Every day, numerous trucks carrying logistics pass through this road. 

These trucks typically head to Semarang harbor or to other cities in Java. However, the flooding caused a traffic obstruction on this road, which affected logistic delivery. The flood also inundated railroads in this city. Thus, 16 train journeys were suspended.

Moreover, more than 40,000 people were affected by the Semarang Indonesia flood. Most of them stayed in their house. However, around 130 people must evacuate their houses and stay in shelters. The Semarang flood also killed 2 children.

The flood in Semarang has lasted for more than 10 days. Currently, 16 subdistricts are still inundated. However, the height of the floodwater has receded.

2. The Causes

According to experts, flood hit Semarang due to three factors.

• River Overflow: Heavy rain that lasted for days had caused the upstream of the Tenggang River and the Sringin River to overflow in Semarang. Moreover, the embankment broke in several locations. Therefore, the river water flowed freely to the city.

• Tidal Flood: The Semarang flood occurred at the same time as the tidal flood. This city has a low-lying coastal area. Therefore, tidal floods often hit Semarang’s coastal subdistricts during high tide.

• Bad Drainage System: The drainage system in Semarang is not in good condition due to various factors, including highway construction, sea embankment, and broken flood control pumps.

Flood Response in Semarang

The local government has taken several measures to reduce the floodwater level in Semarang. Below are the response actions taken by the government.

1. Pumping the Floodwater: The government collaborated with BBWS Pemali Juwana and authorized agencies to pump the floodwater into the Terboyo retention pond. BBWS Pemali Juwana’s pumps have a total capacity of 25,000 L of water per second.

2. Weather Modification: Another measure to handle the flooding in Semarang is weather modification. The government agency, BMKG, modified the weather on the upstream of the Tenggang River and the Sringin River to prevent heavy rain that could trigger further overflow.

3. Creating a Diversion Channel: The government also built a diversion channel. This channel is 4 m wide and 137 m long. It lets the floodwater flow to the retention pond without pumping.

4. Humanitarian Actions for the Victims: The local government and the Ministry of Social helped victims of the Semarang flood in several ways, including providing temporary shelters, free meals, and clothes.

The Importance of Flood Early Warning

During the first days of the Semarang flood, many trucks were broken when their drivers recklessly crossed the flooded road. Those drivers didn’t know the height of the floodwater, so they thought it was safe to pass this road. This condition led to traffic congestion on Kaligawe Road and nearby roads.

Authorities can actually prevent traffic congestion during flooding by broadcasting a wireless alert to road users near the inundated road. From this warning, drivers will find out the road condition before they reach the flooded area. Therefore, they can find alternative roads and avoid the hazard.

Wireless alerts are almost similar to SMS, but they are sent via the radio cells of a cellular network. Moreover, a wireless alert system allows authorities to disseminate flood warnings to geotargeted cell phones. The cell broadcast technology also has the ability to send an alert to thousands of cell phones within seconds. 

Therefore, alert recipients can respond to this alert accordingly. Consequently, broadcasting early flood wireless alerts is effective in preventing traffic congestion, minimizing financial loss, and reducing casualties during floods.

The flood in Semarang has lasted for more than a week. Consequently, it caused various disruptions and affected thousands of people. Local governments can actually minimize these disruptions if they disseminate wireless flood alerts. To distribute these alerts, governments can purchase cell broadcast technology on smsbroadcaster.com.