Changes in Global and Regional Precipitation Patterns under the Impact of Climate Warming: Human Influences, Extremes and Seasonality
Creators: Zhao, Jin
Publisher: name: University of Alberta Library
Year: 2023

<p>Climate variability and human activities exert significant influences on various components of the hydrologic cycle worldwide. Changes to the global climate system may affect the magnitude and frequency of both mean and extreme hydrological events, thereby changing the risk to critical infrastructure. To mitigate the potential damage, it is crucial to elucidate why and how high-impact precipitation events could develop, to predict representative future precipitation events under a changing climate, and to assess their potential societal impacts. These insights will provide the scientific basis essential for decision-makers in developing effective mitigation policies and adaptation strategies against the impacts of global warming on future precipitation events.This dissertation aims to fill this research gap by 1) investigating the spatiotemporal changes in observed extreme precipitation over the Northern Hemisphere land and possible human influences to observed changes; 2) projecting changes in ten extreme precipitation indices under the impact of global warming, and 3) quantifying changes in precipitation seasonality across the global land under the influence of climate warming, and the impact of seasonal precipitation changes on future water availability.Chapter 1 - General IntroductionChapter 2 - Detection and attribution analysis is conducted on seasonal precipitation extremes using HadEX3 datasets and simulations from five CMIP6 Global Climate Models (GCMs) in 1950-2014 over the Northern Hemisphere land (NHL), two risk regions (LR and HR) and 16 CMIP6 domains. Results indicate that GHG forcing dominates the increase in observed Rx1day indices across most NHL. Positive trends are more pronounced in fall and winter than in spring and summer. However, due to the cooling effect of anthropogenic aerosols, a weakened Rx1day is evident in the winter of India and southern China. Using the optimal fingerprinting method, results show that anthropogenic forcing is detectable in at least one season over 80% of CMIP6 domains, with more than 60% of attributable contribution, especially in northern Eurasia. Individual AER signal is most detectable in East Asia. Even though seasonal natural forcings are undetectable in one-signal analysis, they contribute to observed changes in certain regions in the two- and three-signal analysis, which suggest the combined impact of anthropogenic and natural forcings on extreme precipitation patterns.Chapter 3 - Ten extreme precipitation indices based on datasets of CMIP6 global climate models and two observed datasets over North America (NA) are evaluated, and their projected changes are assessed (e.g., temporal variations, spatial distributions, seasonal patterns, and model agreement) over the 21st century under different climate warming scenarios of the Intergovernmental Panel on Climate Change (IPCC). Results indicate that the CMIP6 ensemble median (CMIP6-EnM) generally performs better than individual GCMs across most regions of NA and more accurately captures observed patterns of extreme precipitation in NA. The frequency and severity of extreme precipitation events are predominantly projected to increase, particularly in latitudes above 55°N and coastal areas of NA. In contrast, dry conditions in southern NA are projected to intensify throughout the 21st century. Seasonal changes are projected to be more pronounced in winter compared to summer in northern NA, while in Central America, precipitation extremes will likely be less severe in both seasons. However, unlike strong model agreements in high (100%) and mid-latitudes (80%) of NA, there is a wide disparity between the signs of projected changes between GCMs in southern NA.Chapter 4 - A non-parametric precipitation seasonality index (SI) is used to evaluate changes in precipitation seasonality across global land monsoon regions (GLM) and its subregions under a warmer climate, and the impact of SI variations on the seasonal water availability (AW). By conducting a detection and attribution analysis, observed changes in SI are shown to be attributable to anthropogenic influence with high confidence. Anthropogenic aerosol contributed to decreased SI before the 1980s, while greenhouse gas forcing led to an increase in SI after the 1980s at about 5.67%/K. Future changes in SI are projected to increase across most global monsoon regions, indicating an increased contrast in the AW between wet and dry seasons, largely attributed to the wet seasons projected to be wetter. SI changes in the 2080s are expected to affect seasonal water availability (AW) across the GLM, with &#39;wet (dry) get wetter &#39; mechanism in regions projecting a higher (lower) SI and more AW, while with dry (wet) get drier &#39; mechanism in regions projecting a higher (lower) SI and lower AW.Chapter 5 - Conclusions are summarized and recommendations for future work are proposed to better understand the impact of climate warming on future precipitation extremes globally.</p>