| Author: | Qing, Yamin |
| Title: | Advancing the understanding of soil drought dynamics and mechanisms in a warming climate |
| Advisors: | Wang, Shuo (LSGI) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Global warming Droughts Heat waves (Meteorology) Soil mechanics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Land Surveying and Geo-Informatics |
| Pages: | 104 pages : color illustrations |
| Language: | English |
| Abstract: | Global warming is accelerating the water cycle, intensifying soil droughts, and drawing heightened attention from the scientific community to rapidly emerging phenomena known as flash droughts. Furthermore, global warming is also likely to influence soil drought-associated compound events (i.e., drought-hot and drought-pluvial extremes), altering their frequency, intensity, as well as their timing and geographical distribution. Such rapidly evolving soil droughts and soil drought-associated compound events have already resulted in considerable agricultural losses, water shortages, and heightened wildfire risks, leading to significant environmental and socio-economic repercussions. Thus, the imperative for comprehensive, interdisciplinary research into these phenomena becomes more critical, which is useful for hazard management, particularly in regions that are prone to these phenomena, and can inform the development of effective management strategies to mitigate the impacts of these events on ecological and socio-economic systems. Despite significant efforts in detecting soil droughts and drought-associated compound events, most previous studies have limitations, particularly in exploring the dynamic evolutions and underlying mechanisms of these extreme events. To address these issues, I have proposed a new definition that considers both the rapid intensification rate and the existing drought conditions to robustly identify flash droughts. Moreover, I examined the onset phase of flash droughts to reveal how fast flash droughts. As an extension of the flash drought work, I further quantified the dynamics of soil drying rates and the climatic mechanisms driving these changes. Additionally, the soil drying characteristics prior to the occurrence of hot extremes were investigated to identify the dynamic relationship between drought and hot extremes. Lastly, dynamic evolution of drought and pluvial transitions were accessed, particularly employing causal transitive chains to probe the mechanisms behind the occurrence of these transitions from the perspective of land−atmosphere couplings. The main findings are as follows. 1) 33.64−46.18% of flash droughts with 5-day onset of drying, and there is a significant increasing trend in the proportion of flash droughts with the 1-pentad onset time globally during the period 2000−2020. Flash droughts do not appear to be occurring more frequently in most global regions, just coming on faster. 2) Wet regions have witnessed a significant increasing trend in the soil drying rate during 1980−2020, with an average increase of 6.01−9.90% per decade, whereas there is no consistent trend in dry regions. I also identify a near-linear relationship between the annual soil drying rate and its influencing factors associated with atmospheric aridity and high temperatures. 3) The rapidly evolving dry extremes are more likely (54.99−67.76%) to be followed by hot extremes compared to slowly evolving ones, with large disparities observed in the northern middle latitudes (30 °N−60 °N). 4) There is a significant increase in the drought and pluvial transition occurrences (0.24−1.03% per year) globally during 1980−2020. The drought and pluvial transitions can be explained by the indirect transitive causal chain based on causal inference approach. The findings of this dissertation suggest that the soil droughts and drought-associated compound events (i.e., drought-hot and drought-pluvial extremes) are intensifying during recent decades, which poses a serious challenge for the adaptability of ecosystems and agriculture to these extreme events under the global warming. Additionally, by employing comprehensive data analysis, this dissertation has shed light on the underlying mechanisms that drive the onset and progression of these events. These insights contribute to a deeper understanding of the factors governing drought dynamics, offering valuable guidance for the development of more accurate predictive models and effective mitigation strategies in the face of a changing climate. |
| Rights: | All rights reserved |
| Access: | open access |
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