River temperature under change: understanding the potential of riparian forest and landscape properties for climate adaptation

Eardly, Dominic ORCID: 0000-0001-6435-026X (2025). River temperature under change: understanding the potential of riparian forest and landscape properties for climate adaptation. University of Birmingham. Ph.D.

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Abstract

Climate change has driven global stream temperature increases in recent decades and poses a challenge to cold water adapted fish such as Atlantic salmon (Salmo salar) and Brown trout (Salmo trutta) whose populations are in decline. Beyond fish populations, elevated stream temperatures also pose risks to electric power generation (Van Vliet et al., 2013) and the production of drinking water (Delpla et al., 2009), making the mitigation of rising temperatures associated with climate change of socioeconomic importance (Hannah & Garner, 2015). Riparian tree planting is one of a limited number of mitigation strategies available to freshwater fisheries and river management, limiting summer stream temperature increases by providing shade to channels. Research indicates that planting in small headwater streams is most effective, but larger rivers, where adult salmonids are often found in summer, remain vulnerable. Previous studies using process-based stream temperature models have typically been limited to small scale stream reaches and as a result, are unable to capture the impact of cooled tributary inflows on larger rivers. The aim of this thesis was to further inform riparian planting strategies by elucidating the impact of cooled tributary inflows and the influence of heat advection on larger mainstem rivers. These research gaps were addressed by increasing the scale of modelling from reaches and sub-catchments to larger nested catchments with the following four-step methodology: (1), a six-point energy balance study was undertaken within a nested headwater catchment, using high-temporal-resolution hydrometeorological data at a novel spatial resolution of six locations across three sub-catchments to identify spatiotemporal patterns in energy fluxes within and between catchments; (2) these data were interpolated from point observations to 50m intervals along river networks, complemented with hydrometeorological data obtained from a novel roving weather station measuring for discrete 24 hour periods at a higher sub-km spatial resolution within the study area; (3) these newly-developed datasets were then incorporated into process-based stream temperature models to assess their influence on model performances; and (4) three sub-catchment models were combined to assess the immediate and downstream temperature influence of a series of riparian planting strategies across stream networks and at catchment outlets.
The key findings are: (1) within a Scottish headwater catchment, controlled for land-use, observed stream energy fluxes show spatiotemporal variation within and between sub-catchments, with the presence of a shallow loch disrupting longitudinal patterns in stream temperature; (2) inverse distance weighting using Euclidean distances was shown to be the most effective method for scaling micrometeorology within and between nested catchments of a Scottish headwater catchment; (3) the use of scaled micrometeorology improved the performance of process-based stream temperature models when compared with standard model inputs; and (4) within the study area, the largest catchment scale stream temperature reductions were obtained by planting headwaters and upstream tributaries but largest stream temperature reductions at the mainstem outlet were achieved by planting at the mainstem outlet locality itself. Within the scale of study area investigated, the diminishing returns in stream temperature reduction when planting in larger rivers were not large enough to overcome the diminishing stream temperature reductions observed in the advection of upstream cooling. These results represent new insights into the best-use of riparian tree planting when looking to mitigate elevated summer stream temperatures with climate change.

Type of Work:	Thesis (Doctorates > Ph.D.)
Award Type:	Doctorates > Ph.D.
Supervisor(s):	Supervisor(s) Email ORCID Hannah, David M. UNSPECIFIED UNSPECIFIED Krause, Stefan UNSPECIFIED UNSPECIFIED Jackson, Faye UNSPECIFIED UNSPECIFIED Malcolm, Iain UNSPECIFIED UNSPECIFIED Dugdale, Stephen UNSPECIFIED UNSPECIFIED
Licence:	All rights reserved
College/Faculty:	Colleges > College of Life & Environmental Sciences
School or Department:	School of Geography, Earth and Environmental Sciences
Funders:	Royal Society
Subjects:	G Geography. Anthropology. Recreation > GE Environmental Sciences
URI:	http://etheses.bham.ac.uk/id/eprint/16167

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