Five people, including two children, have been confirmed dead after a landslide hit the village of Cibenda in West Java, Indonesia, slightly before midnight on Sunday 24 March 2024, with another five still unaccounted for. The landslide is reported to have destroyed about 30 houses, and came after weeks of heavy rain in the area, associated with the onset of the Southwest Monsoon. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.
Landslides are a common problem in Java, particularly during the two Monsoon seasons, with parts of the island receiving 4000 mm of rain per year. This problem has been made worse as expanding populations has led to people farming higher on hillslopes, in an area where soils tend to be volcanic in action and poorly consolidated (i.e. lack much cohesion), making them more prone to landslides when trees are removed.
Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry seasons, the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate.
Java has two distinct Monsoon Seasons, with a Northeast Monsoon driven by winds from the South China Sea that lasts from November to February and a Southwest Monsoon driven by winds from the southern Indian Ocean from March to October. Such a double Monsoon Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest.
This year the rains in Indonesia and Southeast Asia have been particularly heavy, due to a prevailing el Niño weather-system over the Pacific Ocean, which is typically linked to more extreme weather patterns in Southeast Asia.
The El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.
The development of an el Niño weather-system this year is considered particularly alarming by climate scientists, as the world has had several consecutive years in which average global sea-surface temperatures have equalled or slightly surpassed the hottest previous average temperatures recorded, despite the climate being in a la Niña phase. As sea surface temperatures are typically significantly warmer during an el Niño phase than a la Niña phase, the development of such a phase could push temperatures into areas not previously encountered on Earth since Modern Humans first appeared, potentially triggering or accelerating other climatic problems, such as glacial melting, droughts in tropical forests, and changes in ocean circulation, which might in turn take us further into unfamiliar climatic territory.
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