Browsing by Author "Porkka, Miina, Assoc. Prof., University of Eastern Finland, Finland"

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Freshwater change in the Earth system - A qualitative-quantitative outlook and implications for planetary boundaries
(2024) Virkki, Vili
School of Engineering | Doctoral dissertation (article-based)
Human actions currently put many life-supporting Earth system processes at risk. The planetary boundaries framework illustrates how this environmental change is pervasive throughout the Earth system and demarcates biophysical boundaries to keep the Earth system stable. Although the framework conceptualisation is sound, especially the definitions of boundaries describing changes in the biosphere and the hydrosphere have been criticised. This thesis provides a comprehensive analysis of global freshwater change and relates this to the planetary boundaries framework. The freshwater cycle supports hydroecological (sustaining ecosystems) and hydroclimatic (regulating climate) functions, which integrally embed freshwater in the Earth system. However, the planetary boundary for freshwater has not captured many of these interconnections, and global-scale approaches have often been limited in analysing and interpreting human-driven freshwater change. Thus, the aim of this thesis is to address the research gap of capturing freshwater change in the Earth system in a way that enables a better representation of freshwater in the planetary boundaries framework. The results of this thesis comprise a thorough qualitative-quantitative assessment of global freshwater change. Using expert knowledge elicitation, blue and green water are shown to strongly interact with other Earth system processes, with variable roles in mediating these interactions. Moreover, associations between common changes in streamflow regimes and their direct and indirect drivers are analysed, using streamflow observations and multivariate global data of the drivers. In-depth analyses of modelled hydrological data further demonstrate the widespread extent and considerable degree of global freshwater change, first through the concept of environmental flow envelopes and then by assessing streamflow and soil moisture deviations beyond pre-industrial reference conditions. This leads to introducing a new planetary boundary for freshwater change, which is defined based on the work conducted for this thesis and parallel studies. Safeguarding freshwater as an integral part of the Earth system requires integrated approaches. The interactions between freshwater and other Earth system processes form a dense and complex network where changes – often anthropogenic in nature – affect more than one component of the freshwater cycle at a time. Thus, setting planetary-scale limits or aggregating freshwater change globally should use the knowledge on the role of freshwater in the Earth system as widely as possible. The findings of this thesis provide a solid background for further advances on understanding the causes and consequences of freshwater change – at local to global scales.