04 Nov What makes Nepal vulnerable to extreme weather?
Nepal, characterized by its mountainous topography and diverse climatic zones, is highly susceptible to the impacts of climate change. Its geographic and environmental features, including the Himalayan range to the north and complex river systems navigating steep gradients, contribute to a heightened vulnerability to climate-induced disasters. Over recent decades, Nepal has experienced an increased frequency and severity of natural hazards, particularly floods and landslides, trends that are closely associated with changing climate dynamics. This analysis explores how climate change intensifies these hazards, with an emphasis on hydrological shifts, accelerated glacial melting, extreme rainfall events, and landslide risks.
Hydrological shifts and altered riverflow patterns
Climate-induced changes are significantly impacting Nepal’s river systems through modifications in precipitation patterns and seasonal water cycles. Rising global temperatures and shifts in weather patterns have introduced unpredictability into rainfall cycles. The monsoon season, typically spanning from June to September, now exhibits variability in its onset, duration, and rainfall intensity. Such variability often results in extended dry periods punctuated by intense precipitation, overwhelming soil absorption capacity and leading to flash floods and river inundation. Intense rainfall events further exacerbate the conditions within Nepal’s river basins. Many rivers in Nepal rely on both monsoon rainfall and runoff from melting snow and glaciers. As temperatures rise, snow cover and glacial masses are diminishing, altering the seasonal flow regime of these rivers. Instead of a gradual release, the snow and glacial melt now occurs more abruptly, often aligning with peak monsoon periods, thus exacerbating flood risks.
Intensified monsoon patterns and flash floods risk
Nepal is witnessing more frequent and severe rainfall events linked to climate change. Research indicates that higher atmospheric temperatures enhance the moisture-holding capacity of air, resulting in intensified rainfall episodes. These heavy rainfall events lead to flash floods, particularly in the hilly and mountainous regions, where rapid water flow in narrow river valleys can cause sudden inundations. Flash flooding is exacerbated by the steep terrain in these regions, as water rapidly converges in rivers and streams rather than being absorbed into the soil. The Terai plains, where rivers from the hills converge, are especially susceptible to such rapid flooding due to upstream runoff. Additionally, extreme rainfall destabilizes riverbanks and associated infrastructure, increasing erosion and heightening flood risks.
Landslides
Landslides are a prevalent hazard in Nepal, attributed to its steep slopes and fragile geological structure. Climate change intensifies landslide risks by increasing soil saturation and destabilization. Intense rainfall events cause the soil to become oversaturated, which reduces its cohesion and structural stability. This effect is particularly pronounced on steep slopes or areas where human activities, such as deforestation and road construction, have further compromised the landscape. During heavy rains, water infiltrates soil particles, increasing the weight and reducing the soil’s adherence to slopes, ultimately triggering landslides. Additionally, shifting vegetation patterns due to climate change have led to reduced natural slope stabilization, as vegetation that would normally help anchor the soil is diminished.
Soil erosion and sedimentation processes
Climate change also accelerates soil erosion and sediment deposition, both of which exacerbate flood risks and disrupt river dynamics in Nepal. Intense rainfall combined with reduced vegetation cover increases soil erosion on slopes. The eroded material is transported by runoff into rivers, where it accumulates as sediment. Sedimentation reduces river channel capacity, heightening the likelihood of overflows during intense rainfall events. Furthermore, sedimentation alters river flow patterns, potentially causing the formation of new channels and redirecting water flow. These disruptions impact agricultural areas, settlements, and natural ecosystems and necessitate costly interventions to manage river channels and mitigate flood risks.
Glacial Lake Outburst Floods (GLOFs)
A pressing concern in the Himalayan region, exacerbated by climate change, is the rising incidence of glacial lake outburst floods (GLOFs). With warming temperatures accelerating glacial melt, there is a consequential expansion of glacial lakes, many of which are held in place by unstable natural moraine dams. As glacial lakes expand, the likelihood of sudden breaches increases, particularly under conditions of heavy rainfall or seismic activity. A breach in these moraine dams can release large volumes of water, sediment, and ice downstream, causing catastrophic flooding. Nepal currently hosts over 3,000 glacial lakes, with a significant proportion classified as potentially hazardous. GLOFs have become more frequent in recent decades, posing ongoing risks to downstream communities, infrastructure, and agricultural areas.