Landslides and Flash Floods in the Monsoon - 23.06.2015

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Landslides and floods during the monsoon season impact lives and livelihoods in Nepal every year. The localised impact of these natural hazards will place an additional burden on earthquake-affected households. In addition, there will be landslides and floods in districts that were not affected by the earthquake, stretching national capacity to respond. This report provides a brief overview of the historical impact of landslides and flash floods in Nepal, as well as mitigation strategies to support contingency planning.


Historic Impact

  • Floods and landslides have caused at least 8,400 deaths in Nepal between 1983 and 2013 (p.7).

  • The monsoon period represents 60–80% of the annual total precipitation, and in the past has accounted for around 90% of landslide fatalities.

  • Past events have caused significant loss of life and damage to vital infrastructure such as roads, hydropower, irrigation and drinking water facilities, agricultural land, and property (p.7).

  • Flooding is, by far, the largest natural cause of building damage in Nepal on an annual basis (p.5).

Expected Upcoming Impact

  • Landslides and flash floods are mostly triggered by monsoon rains, and increase in July and August (p.3).

  • Additional landslides are expected due to the instability of the soil after the earthquake. Over 3,000 landslides were observed after the 25 April earthquake, higher than the number of landslides reported in the past five years combined (p.3).

  • A weaker than usual monsoon is correlated with higher rainfall in the region most prone to landslides (p.3).

  • Steep slopes in narrow valleys destabilized by the earthquake pose a threat of flash flooding when landslides block rivers (p.5).

  • Access to earthquake-affected communities by both land and air will significantly decrease due to impassable roads, landslides blocking mountain footpaths, and stormy weather.

  • Approximately 40% of landslide dams break within a week of formation, and 80% break within 6 months, highlighting the need to monitor landslide occurrence closely and have mitigation measures in place (p.5).

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