Urban growth modelling and social vulnerability assessment for a hazardous Kathmandu Valley

Abstract

In our rapidly urbanizing world, many hazard-prone regions face significant challenges regarding risk-informed urban development. This study addresses this issue by investigating evolving spatial interactions between natural hazards, ever-increasing urban areas, and social vulnerability in Kathmandu Valley, Nepal. The methodology considers: (1) the characterization of flood hazard and liquefaction susceptibility using pre-existing global models; (2) the simulation of future urban built-up areas using the cellular-automata SLEUTH model; and (3) the assessment of social vulnerability, using a composite index tailored for the case-study area. Results show that built-up areas in Kathmandu Valley will increase to 352 km2 by 2050, effectively doubling the equivalent 2018 figure. The most socially vulnerable villages will account for 29% of built-up areas in 2050, 11% more than current levels. Built-up areas in the 100-year and 1000-year return period floodplains will respectively increase from 38 km2 and 49 km2 today to 83 km2 and 108 km2 in 2050. Additionally, built-up areas in liquefaction-susceptible zones will expand by 13 km2 to 47 km2. This study illustrates how, where, and to which extent risks from natural hazards can evolve in socially vulnerable regions. Ultimately, it emphasizes an urgent need to implement effective policy measures for reducing tomorrow's natural-hazard risks.

Quantifying the potential benefits of risk-mitigation strategies on future flood losses in Kathmandu Valley, Nepal

“…Kathmandu Valley encloses three districts (Bhaktapur, Kathmandu, and Lalitpur), which comprise five municipal areas and several municipalities and rural municipalities (formerly named village development committees, or VDCs) (Mesta et al, 2022b), Figure 1.…”

“…A previous study by the authors (Mesta et al, 2022b) revealed that urban land in Kathmandu Valley could reach 352 km 2 in 2050, almost doubling its current size and covering half the total valley extent. A significant share of this new urbanization is projected to occupy the valley's most hazardous (at least in terms of flooding and liquefaction) and socially-vulnerable regions (Mesta et al, 2022b). Thirdly, other natural hazards such as earthquakes have unveiled the poor state of Nepal's building stock and physical infrastructure, which is caused by a combination of low-quality building materials, deficient construction practices, low compliance with building codes, as well as aging, and deterioration (Bothara et al, 2018;Varum et al, 2018).…”

Strong ground motion data of the 2015 Gorkha Nepal earthquake sequence in the Kathmandu Valley

“…Consequently, the valley is highly susceptible to the risks associated with site amplification 11 . In addition, the explosive population growth that has occurred in recent years has markedly increased the risk of earthquake damage in the valley 12 .…”

Urbanisation and Disaster Risks in the Himalaya

“…The fragile geophysical conditions coupled with haphazardly growing urbanisation and rampant construction activities in mountain geography have triggered multi-hazards 3 (e.g., landslide, flood) and simultaneously elevated exposure of the Himalayan dwellers to the risk of disasters (Tiwari et al, 2018;Walker, 2011;Wester et al, 2019;Poudel et al, 2021;Rusk et al, 2022) which are likely to intensify in the future (Mesta et al, 2022;Wester et al, 2019). In the Nepal Himalaya, an average of 500 natural and non-natural hazards occur annually which on an average kill 900 and affect around 6,40,000 people every year (NPC, 2019).…”

“…Blackburn, 2020). However, not all urban dwellers have received equal attention, leaving some more vulnerable than others (Bhattarai and Conway, 2010;Mesta et al, 2022). Given the nature of Himalayan people's exposure to multi-hazard risks, understanding diverse experiences and perceptions of risks, root causes of risks (biophysical, socio-technical and political-institutional), and the underlying narratives that inform differential responses and abilities to deal with and reduce such risks are crucial.…”