Detection and Attribution of Spatiotemporal Trends of Climatic Disaster Mortality in Nepal

Abstract

The socioeconomic impacts of climatic disasters are increasing globally. Some studies have argued that this increasing trend results from the growing population and assets exposed to hazardous events. Other studies have reported that it is caused by the increased frequency, intensity, and duration of extreme weather and climate events owing to climate change. Therefore, the reasons behind the increasing impact of disasters remain elusive. Limited information is available on future scenarios of extreme climate indices and their implications in various sectors, including disasters. Although disaster impacts relative to the country’s economy are felt more acutely in low-income countries, existing studies focus primarily on developed countries or at the cross-country level. Therefore, this dissertation addresses the issue of detecting and attributing trends of climatic disaster impacts in the context of low-income countries using Nepal as a case study. Furthermore, this dissertation investigates future climate extremes scenarios and their potential impacts on climate-sensitive sectors in the Karnali river basin in western Nepal. <br /> First, this study assessed the spatiotemporal trends of the frequency, impacts, and vulnerability of multiple climate disasters using the observed 30-year (1992–2021) disaster data at the scale of the 753 subnational units of Nepal. Loss of human life is the most extreme consequence of disasters. Therefore, this study employed human mortality as a measure of disaster impacts and mortality normalized by the exposed population as a measure of vulnerability. Second, the attribution of flood and landslide mortality to indicators of climatic hazards, exposure, and vulnerability was assessed. Floods and landslides were selected for the attribution study because they account for 70% of all climatic disaster mortality in Nepal. This study employed a disaster-specific mixed-effects zero-inflated negative binomial regression model to study the causality of the observed mortality. As explanatory variables, this study used mean and extreme precipitation indices, population density, and per capita income and a social vulnerability index as indicators of hazards, exposure, and vulnerability. Finally, this study provided future projections of 26 mean and extreme climate indices in western Nepal for the near (2021–2045), mid (2046–2070), and far (2071–2095) future for low- and high-emission scenarios (RCP4.5 and RCP8.5, respectively) using bias-corrected ensembles of 19 regional climate models from the COordinated Regional Downscaling EXperiment for South Asia. In addition, a qualitative analysis based on expert interviews and a literature review of the potential implications of the projected climate extremes on the climate-sensitive sectors are performed. Western Nepal was selected to study the future scenario where the strongest rise in precipitation extremes, disaster frequency, and mortality was observed in the past decades. <br /> Results show that ~5,000 fatal climatic disasters were recorded from 1992–2021 in Nepal, killing >10,000 people. The frequency of disasters has increased by about seven incidences per year, and mortality has increased by nearly nine persons per year. However, vulnerability has decreased, most likely owing to economic growth and progress in disaster risk reduction and adaptation. The spatiotemporal trends of disaster mortality closely follow the trend of precipitation extremes. An increase in one standardized unit in maximum one-day precipitation has increased flood mortality by 33%, and heavy rain days have increased landslide mortality by 45%. A one-unit increase in per capita income has decreased landslide and flood mortality by 30% and 45%, respectively. Population exposure does not show significant effects. Hence, this study concludes that the observed rise in climatic disaster mortality, mainly in western Nepal, is primarily attributable to the increased precipitation extremes caused by climate change. Temperature and precipitation patterns in western Nepal are projected to deviate significantly from the historical reference in the near future with an increase in extreme events. Low-intensity precipitation events will decline, but the magnitude, frequency, and duration of extreme precipitation events will increase. This projected rise in precipitation extremes will most likely increase climate-related disaster mortality if actions are not taken to strongly reduce the vulnerability. Similarly, the compounding effects of the increase in extreme temperature and precipitation events will have largely negative implications for the six climate-sensitive sectors in the Karnali region, namely water resources and energy, climate induced disasters, agriculture and food security, forest and biodiversity, tourism, natural and cultural heritage, and public health.