Risk assessment on natural disasters in densely populated Himalayan regions

A new study focuses on the multi-hazard susceptibility of a densely populated region in the Himalayas.

Until recently, most of the studies are focusing on the individual effect of a natural disaster (e.g., landslides, floods, wildfires). Nonetheless, it is evident that one natural disaster may trigger or prevent another one and in fact, those phenomena are interconnected. For example, heavy rainfalls and floods tend to trigger landslides and debris flows. Wildfires devastate forests and precipitation leads to more intense floods. In addition, climate change has exacerbated those phenomena and the need to study them as a whole is urgent. For this reason, new research aims at investigating the effect of more than one natural disaster by performing what is known as a compound hazard evaluation. This approach takes into consideration the impact and the interaction of more than one natural disaster in a given region. 

The new study, funded by NASA, investigates the aforementioned multiple hazards in Hindu Kush Himalayan, a populated region that is exposed to overlapping natural disasters. The conditions in the region have also been impacted by climate change making it a great case study. In particular, the temperature rise has caused more fires which contribute to further landsliding as the ground loses support from the vegetation. Landslides may impact rivers and canals or break dams which leads to flooding. Moreover, the area is earthquake-prone therefore, major earthquakes shape its natural disaster regime. The aim of the study was to derive the patterns of compound hazards in the region and to find patterns in the population exposed to them.

The researchers collected and processed satellite imagery data on ground deformation, wildfires and floods to find out that the greater risk is concentrated in mid-elevation regions where the soils are saturated. Saturated soils are generally more prone to landsliding as their shear strength is reduced compared to dry soils. The data suggest that only a small proportion of the region is prone to this multi-hazard threat. “It’s often stated that the Himalaya is a high-risk environment. But contrary to studies that describe the entire region as highly hazardous, our study shows that the highest risk areas are relatively small,” Jack Rusk, lead author of the study, said. 

However, about 50% of the region's total population (more than 72 million) live in these areas. This is due to the fact that they are beneficial for settlement and agriculture due to warmer temperatures, moist soils and flat elevation. Moreover, the study found that population growth is also concentrated in susceptible regions and, in particular, in a corridor with productive agricultural areas. Hence, urbanization processes increase the exposure to natural hazards.

The authors of the study emphasize the urgent need to address natural hazards as an interconnected phenomenon to derive their actual impact on populated regions. Regarding, the Hindu Kush Himalayan, it is suggested that further research will result in more advanced results regarding the dynamic character of the area.