Increasing river temperatures are a threat to cold water species including ecologically and economically important freshwater fish, such as Atlantic salmon. In 2018, ca. 70% of Scottish rivers experienced temperatures which cause thermal stress in juvenile salmon, a situation expected to become increasingly common under climate change. Management of riparian woodlands is proven to protect cold water habitats. However, creation of new riparian woodlands can be costly and logistically challenging. It is therefore important that planting can be prioritized to areas where it is most needed and can be most effective in reducing river temperatures. The effects of riparian woodland on channel shading depend on complex interactions between channel width, orientation, aspect, gradient, tree height and solar geometry. Subsequent effects on river temperature are influenced by water volume and residence time. This study developed a deterministic river temperature model, driven by energy gains from solar radiation that are modified by water volume and residence time. The resulting output is a planting prioritization metric that compares potential warming between scenarios with and without riparian woodland. The prioritization metric has a reach scale spatial resolution, but can be mapped at large spatial scales using information obtained from a digital river network. The results indicate that water volume and residence time, as represented by river order, are a dominant control on the effectiveness of riparian woodland in reducing river temperature. Ignoring these effects could result in a sub-optimal prioritization process and inappropriate resource allocation. Within river order, effectiveness of riparian shading depends on interactions between channel and landscape characteristics. Given the complexity and interacting nature of controls, the use of simple universal planting criteria is not appropriate. Instead, managers should be provided with maps that translate complex models into readily useable tools to prioritize riparian tree planting to mitigate the impacts of high river temperatures.
Bibliographical noteFunding Information:
Contributions from Marine Scotland Science Freshwater Fisheries Laboratory were funded under Service Level Agreement FW02G. Some map features are based on digital spatial data licensed from CEH, NERC ? Crown Copyright and database right (2020), all rights reserved. Ordnance Survey Licence number 100024655. The authors would like to thank Steve Ormerod and an anonymous reviewer for constructive and useful comments during the first round of manuscript revisions. Colleagues at SEPA and NRFA are thanked for providing hydrometric data. Velocity and flow data for river gauging stations were provided by SEPA ? Scottish Environment Protection Agency and database right 2020. All rights reserved. Daily flow summaries (Q95) for all gauging stations in Scotland were provided by National River Flow Archive; National River Flow Archive (2020) https://nrfa.ceh.ac.uk, NERC CEH, Wallingford.
© 2021 Crown copyright. Hydrological Processes © 2021 John Wiley & Sons Ltd. This article is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.
- deterministic modelling
- riparian woodland
- river temperature
- solar radiation
ASJC Scopus subject areas
- Water Science and Technology