Date of Award

5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

Committee Chair/Advisor

Dr. Ashok Mishra

Committee Member

Dr. Nigel Kaye

Committee Member

Dr. Charles Privette

Committee Member

Dr. Lawrence Murdoch

Abstract

Severe hydroclimatic extreme events, such as droughts, heatwaves, and heavy rainfall, are occurring with increasing frequency and causing significant impacts on both people and the environment. These events also compound in space and time, leading to even more significant consequences. Therefore, it is essential to comprehend these phenomena' concurrent and time-delayed progression across different temporal and spatial scales to address adaptation and mitigation effectively. To accurately understand and map the co-evolution of extreme events, it's necessary to have a thorough grasp of their spatiotemporal patterns, how they propagate and interact with one another, and the underlying mechanisms driving their occurrence.

Here, we present a novel approach to understanding how different hydrometeorological flows and their extremes, such as droughts, heatwaves, and heavy precipitation, are connected in space and time. Specifically, we employ complex network analysis to explain the spatiotemporal synchronicity and propagation of extreme hydroclimatic events. Our methodology and finding stand steadfast as a cornerstone by simplifying and improving the understanding of the complex phenomena of hydroclimatic extremes. By deriving synchronization and propagation networks, we unlock the potential to characterize spatial synchrony and propagation of extreme events from local to regional and global scales. We also assess the change in such characteristics in future climate scenarios. We delineate independent regimes of hydroclimatic extremes, providing insights into the nature of extreme weather events. Our approach also leverages the concept of synchronization in Kuramato oscillators to assess the influence of spatial connectivity on the emergence of spatially compounding drought. By doing so, we uncover the critical role of spatial connectivity in shaping the hydroclimatic landscape. Our methodology represents a significant leap forward in understanding hydroclimatic dynamics and lays the foundation for disruptive

advancements in this field. We present six articles focusing on the spatiotemporal synchrony and propagation structure of all possible climate extremes (extreme precipitation, heatwave, drought) on a regional to Global scale.

First, we investigated the spatial synchrony and propagation structure of extreme precipitation events and heatwaves over the USA. The analysis for extreme precipitation reveals critical regions of moisture inflow, convergence, and divergence, along with six different regimes of synchronized precipitation over the Conterminous United States (CONUS). In the aspect of heatwaves, network coefficients have been able to conclude that the occurrences of ‘blocking high’ drives spatially compounding heatwaves over the Northern USA. The study also captures the strong convergence of heatwaves over the midwest regions, possibly explaining episodes of amplified heatwaves over Chicago. Using spatial propagation (from source to sink) structure over the USA, we have been able to predict the occurrence of heatwave days with an accuracy of 63% with a lead time of 2 days. Next, we explore the global connectivity of drought events, demonstrating the existence of drought hubs and linkages in driving multi-continental droughts. We also quantify drought's global spatial propagation structure, providing insights into the relationship between circulation cells (i.e., Hadley or Ferrel cells) and drought events' convergence (and divergence zones). We also examine the future evolution of synchrony and propagation structure of droughts under different radiative forcing scenarios. The study reveals a substantial increase in spatial synchrony (in the occurrence of droughts) along with the spatial extent of the drought events over the northern hemisphere subtropics and midlatitude. This finding is crucial to develop effective mitigation for such projected simultaneous breadbasket failure. Finally, we introduce a networked global hydrological cycle that accounts for the intricate interconnections between various hydrological cycle components, such as soil moisture, evapotranspiration, and precipitation. The results indicate that this framework offers valuable insights into significant mesoscale patterns in the global hydrological system that cannot be discerned through conventional statistical approaches. Delineation of such structures is crucial to understanding the large-scale dynamics and improved predictability of hydrological extremes.

Author ORCID Identifier

https://orcid.org/0000-0001-8217-1361

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