Why Sept 28, 2024 Bagmati river flood in Kathmandu, Nepal?

The Bagmati River flood that claimed more than 101 lives on September 28, 2024, was caused by relentless monsoon rains that began earlier in the week. The heavy rainfall led to rivers, including the Bagmati, bursting their banks and inundating nearby settlements, particularly in the Kathmandu Valley. The intense flooding and associated landslides were exacerbated by climate change, which has been increasing the frequency and severity of such events in recent years. Rescue efforts are ongoing, with hundreds of people still missing and displaced.

The Bagmati River in Nepal has experienced several significant floods over the years. Some of the major floods occurred in:
1. July 1993 – One of the most devastating floods in the Bagmati River’s history. This flood caused widespread destruction in the Kathmandu Valley and surrounding areas, with landslides and inundation leading to the loss of hundreds of lives and severe damage to infrastructure.
2. August 2004 – Another significant flood event occurred, impacting both Nepal and parts of northern Bihar, India, where the Bagmati River also flows. This flood displaced thousands of people and caused widespread agricultural and property damage.
Flooding in the Bagmati River typically occurs during the monsoon season, which spans from June to September, when heavy rainfall leads to swollen rivers and flash floods.

The recent development of dense cloud cover causing heavy rainfall in Nepal can be attributed to several interconnected climate factors:
1. Monsoon Circulation: Nepal’s heavy rains are primarily driven by the South Asian monsoon, where moist air from the Bay of Bengal moves northward.
2. Low-Pressure Systems: These systems over the Bay of Bengal can enhance moisture transport.
3. Global Warming: Increased ocean surface temperatures due to climate change amplify moisture evaporation, leading to denser clouds.
4. Jet Stream Shifts: Changes in upper-atmosphere winds may direct storm systems toward Nepal, enhancing precipitation.
These factors together intensify rainfall, causing floods and landslides.

While the monsoon season in Nepal typically tapers off by late September, this year’s heavy rainfall on September 27-28 could indeed be influenced by climate change, but it’s not the sole factor. The monsoon can sometimes extend beyond its usual period due to lingering low-pressure systems or anomalies in atmospheric circulation. However, climate change has been linked to increasing the intensity and unpredictability of weather events, causing more severe downpours and altering monsoon patterns, which may have amplified this particular rainfall event.
This combination of climate change and delayed monsoonal effects likely led to the unexpected heavy rain.

Yes, it seems likely that Nepal is experiencing a delayed monsoon effect this year. Typically, the monsoon season begins to taper off by late September, but persistent low-pressure systems or disruptions in global atmospheric patterns can prolong it. Climate change may also contribute to these changes, making monsoon seasons more erratic. In this case, the heavy rainfall toward the end of September suggests a continuation of the monsoon beyond its usual end, which could be attributed to these combined influences.