Pasternack, Gregory B.; Tonina, Daniele; Casas-Mulet, Roser; Adeva- Bustos, Ana; Vanzo, Davide; John, Andrew; Tinoc, Rafael
Climate Change Prediction and Adaptation in Ecohydraulics
Verfügbar unter/Available at: https://hdl.handle.net/20.500.11970/110902 Vorgeschlagene Zitierweise/Suggested citation:
Pasternack, Gregory B.; Tonina, Daniele; Casas-Mulet, Roser; Adeva-Bustos, Ana; Vanzo, Davide; John, Andrew; Tinoc, Rafael (2023): Climate Change Prediction and Adaptation in Ecohydraulics. In: Hydrolink 2023/1. Madrid: International Association for Hydro-Environment Engineering and Research (IAHR). S. 18-14.
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Climate Change Prediction and Adaptation in Ecohydraulics
By Gregory B. Pasternack, Daniele Tonina, Roser Casas-Mulet, Ana Adeva-Bustos, Davide Vanzo, Andrew John and Rafael Tinoco
thermal regimes with feedback to riparian and aquatic environs, including effects from altered riparian and floodplain vegetation.
This climate-change mechanistic chain will also interact with and likely be amplified by the broad scope of continuing local and regional anthropogenic pressures on inland waters and coasts, such as land-use, land-cover change, water abstraction, flow regulation, fish, and vegetation over harvesting, and exces- sive dispersal of nutrients, toxic chemicals, microplastics, and sediment. Together, local, regional and global pressures pose severe alterations to inland and coastal waters and may cause habitat degradation, shrinkage, and fragmentation8, organism physiological distress, higher risk of stranding, food-web dis- ruptions, increase in excessive riparian vegetation density, and alteration of many ecological functions. While ecohydraulics is spreading to address more species at the population scale and develop methods for community-level dynamics, it is unclear where climate change adaptation will require comprehensive assessment of all organisms or achieve success using a limited number of abiotic and biotic indicators. Nevertheless, ecohy- draulics is posed to provide the tools to quantify the impact of both climate change and anthropogenic needs on inland and coastal ecosystems and to weight different scenarios and alternative solutions including the use of nature based solutions.
Water is typically viewed as the definitive feature of rivers and coasts, but these systems also involve essential sediment dynamics. Traditionally, many ecohydraulics approaches assume a static terrain to evaluate how changes in flow or other controls affect biota. Over time, this will have to change so that sediment dynamics are incorporated. Sediment continuity from river headwater to coast is sensitive to climate, with significant impacts on morphodynamics, ecological processes, and river management and safety11. The quantification and modelling of sediment dynamics and its ecological impacts are critical in ecohydraulic research. Climate adaptation requires under- standing how river habitat responds to morphological changes induced by either natural or artificial floods12, 9 as well as river engineering activities (e.g., Figure 12).
Ecohydraulics is the process-based study of intertwined abiotic- biotic phenomena in aquatic and riparian inland and coastal zones across a wide range of scales. As a community, ecohy- draulicists have been developing a diversity of new environmental observational methods, solving the fundamental science about how many abiotic-biotic interlinks function5 and developing practical tools for both diagnosis and treatment of environmental problems6 typically caused by human impacts to inland and coastal waters. Examples of the latter include procedures and software for predicting spatial patterns of habitat quality for target species in each lifestage, likelihood of occurrence of specific ecological functions, organism migration and behavioral dynamics, and riparian vegetation dynamics. Such tools are available in a rapidly growing plethora of custom algorithms (e.g., FishXing, Dottertools, and Riverconn), and built into ecohy- draulic synthesis suites (e.g., CASiMiR, River Architect, HABBY, and MesoHABSIM) and decision-support systems (e.g., DRIFT and IFIM) for use in river restoration, environmental flows, fish passage, and other such engineering efforts. Despite the caution that emerging practices remain largely unproven, ecohydraulics is a hopeful, forward-looking endeavor tightly coupling scientific exploration, technological development, and engineering practice.
Now and into the future, ecohydraulics will need to quantify the effects of climate-change-induced physical and biological alterations on aquatic habitats and improve the applicability of its tools for climate change adaptation.
The role of ecohydraulics for climate change research For a global problem like climate change, ecohydraulics is the final set of links in the mechanistic chain by which oceanic- atmospheric-terrestrial systemic drivers force intertwined local physico-chemical environmental conditions and biotic function- ing. For example, climate change is expected to alter aquatic physical quantities globally via increases in global air temperature and altered precipitation and wind patterns. These climate con- ditions will in-turn modify water flow, sediment transport, water
Figure 1 | Map of river depths at 10 m3/s without dredging (left) and after dredging (right). Dredging of the riverbed may reduce flood damages and impact habitat diversity2.
Ecohydraulic remote sensing of climate change
Remote sensing (RS) is likely to play a decisive role in climate change progression and adaptation by society and nature itself.
This holds true for ecohydraulic responses to climate change.
A key RS advantage is its use for repeated surveys through time. Ecohydraulicists have been developing workflows for change detection and analysis that can be deployed to track and quantify ecohydraulic effects of climate-changed flow regimes, sediment regimes, and civil infrastructure.
RS customized for ecohydraulics is expected to provide the tools and methodologies to map spatial and temporal distributions of aquatic and riparian physical aspects as well as potentially the distribution of habitat directly. RS measurements will quantify the input parameters for modeling the spatial and temporal quality of habitats. Further, overwater and underwater RS measurements are already used to map the morphology and behavior of plants and animals, and RS systems will be essential to characterizing and tracking climate change impacts on eco- hydraulic patterns and dynamics.
Advances in overwater RS include passive imagery and ac- tive topo-bathymetric LiDAR enable direct mapping of vegeta- tion, terrain, water, snow and ice surfaces topping rivers, and infrastructure as well as changes in all of these. Satellite RS can measure discharge and bathymetry in large rivers. Video or repeat-image analysis is being used to map patterns of water surface velocity and monitor streamwood fluxes. Normalized Difference Vegetation Index methods and multispectral cameras provide vegetation distribution and their status.
Ecohydraulicists were early adopters of unoccupied aerial vehicles (aka drones) as low-cost tools for mapping and moni- toring rivers and coasts, and continue to explore novel applica- tions. For example, drone-mounted thermal infrared imagery technologies are effective for cold-water-refugia (CWR) assess- ment and prediction, and further progress in this domain will be critical to inform long-term adaptation measures that main- tain resilient cold-water habitats to support key organisms’
persistence. Drones have also been used to map riparian and aquatic vegetation, especially where invasive species are a problem and may expand with climate change.
Meanwhile, underwater ecohydraulics technologies include side scan and multibeam sonar, dual frequency identification sonar (DIDSON), videography, stationary cameras, and infrared scanners. For one of the important topics in ecohydraulics, fish passage, DIDSON has been used to monitor passage rates and behavioral responses to passage infrastructure besides to quantify behavior and path selection by migrating fish when they arrive at a river confluence. Stationary cameras and scan- ners have become instrumental to management of fish passage structures, because users cannot only quantify passage rates, but also determine organism species, identify wild versus hatchery origin, and measure size and shape attributes. Acoustic telemetry may also be considered a form of RS; it is used to map organism movements in two or three dimensions (i.e., 2D or 3D). Once organism tracks are georeferenced within water bodies, results inform on organism individual and group behaviors
as well as responses to external drivers. Current telemetry ad- vances continue to miniaturize transmitters that are surgically implanted in organisms and improve the processing of the mas- sive amount of data these systems yield (e.g., ACTEL, fishtrack3d, and YAPS on GitHub).
Spatial variations of stream temperature and the processes governing thermal heterogeneity within the riverscape are of key concern for managers. Thermal heterogeneity is increasingly considered a key aspect of river habitat structure (e.g., Figure 23), given its potential to provide CWR in some areas of the world and warm water refugia in others. Thus, it will be an important water management target in climate adaptation strategies. Rivers are complex dynamic ecosystems with a physical structure that can be represented as a hierarchical organization of interconnected spatial scales. Whilst river tem- perature is driven by climatic, topographic, land cover and hy- drological controls at the air-water interface, such an array of multi-scalar physical features will play a key role in determining how heat is distributed, including groundwater inputs, hyporheic flows, in-channel physical complexity, and shading.
Figure 2 | Changes in stream thermal habitats between present and future (with a predicted 4 °C warming) water temperatures, in different river morpho- logies of the River Ovens, Australia. Modified from Kuhn et al. (2021).
Ecohydraulic modeling as a bridge across scales
Because many aspects of ecohydraulics cannot be directly observed, ecohydraulicists use spatially explicit (2D or 3D) mechanistic numerical models to produce meter-resolution, spatially explicit maps of aquatic and riparian “micro-habitat”
over increasingly long kilometers of river as well as for coasts and estuaries. Micro-habitats are coherent areas with charac- teristic physical attributes where organisms perform ecological functions. Beyond hydraulics, landforms, and physical habitats, ecohydraulicists have increasingly been using algorithms to extend simulations to address bioenergetic, individual-organism behaviors, and a growing list of diverse ecological functions.
Mechanistic ecohydraulic models enable understanding of, prediction of, and adaptation to the effect of physical drivers such as water, streamwood, and sediment management and climate change on aquatic habitat quantity and quality distri- bution.
Studies and forecasts of the effects of climate change on regional to local environments often link together a series of models and analysis tools to enable simulation of alternative future scenarios. As ~1-m resolution topo-bathymetric river
and coast datasets are collected and made available, spatially explicit hydrodynamic and possibly morphodynamic modeling could be driven by climatic-hydrological forecasting models, taking the existing practice to a whole new level of direct rele- vance to environmental stewardship and provision of ecosystem services to society. The hope is to obtain reduced risk and dam- ages for society by using early warning systems, river rehabili- tation (including connectivity), and environmental flow regimes, thereby reducing the need for traditional engineered flood measures that have been widely shown to negatively impact riverine and coastal ecosystems.
Organism physiology, behavior response, and survival can be predicted with a cascade of models. A recent study by Reeder et al.7 used a cascade of models, from climate change to hydrological model, to ecohydraulic model and to a statistical fish growth model, to understand the impact of climate change on Chinook salmon (Oncorhynchus tshawytscha) size before migrating to the ocean. The study showed that climate change may increase fish size, and potentially their fitness, negligibly limit rearing habitat but significantly reduce spawning habitat (Figure 3).
Figure 3 | Rearing habitat distribution at 2 m3/s discharge along a section of Bear Valley Creek (Idaho, USA) bankfull width of 15 m (a), effect of climate change on mean summer temperature, mean annual weighted usable area for rearing and spawning habitat (b) and their effect on fish mode length (c).
Environmental flows are river operating rules and/or reservoir releases for environmental benefits. They have been an important tool in addressing freshwater ecosystem degradation due to historic human influences and they will be for addressing the threat imposed by climate change. In drying climates, competition for water resources has increased and securing and providing adequate high flows for wetlands and floodplains is more difficult.
In wetter climates, more intense floods can scour riverbanks and high flows can drown out streamside vegetation. Rivers may also alternate between long periods of low flows and short periods of intense extreme flood flows. Researchers are respond- ing to these threats by using mechanistic models to understand impacts on the flow regime and pursue a more predictive envi- ronmental flows science to better manage available resources.
This includes using ecological models to understand how fresh- water ecosystems dynamically respond to specific flow events and longer-term flow regimes. In addition, potential conflicts between different water users, mean social impacts, co-benefits and barriers are increasingly important for environmental flow management and implementation (Figure 41). The continued implementation of environmental flows worldwide will help adapt rivers to a changing climate.
Climate adaptation challenges
Imminent changes in global climate are driving a shift in discus- sions from mitigation to adaptation strategies for human popula- tions in at-risk communities. Likewise, changes in inland and coastal ecosystems might need to be assessed from a new angle, to reconsider, for instance, the role of prevention and management strategies for both native and invasive species, and whether efforts should be directed to help existing communi- ties survive under new adverse climate scenarios or find a ba- lance with new communities able to thrive under future conditions.
Climate change is fundamentally changing the functional relationships among abiotic and biotic conditions. As a result, the widespread practice of quantifying functional relationships by either assuming idealized equations or generating statistical
equations may simply be unusable in the future and may already not apply in some cases, because both approaches are based on experience and data from past and current conditions. There- fore, simple functional relationships that connect relatively distant causal drivers to local ecohydraulics responses are very risky to assume and use in climate adaptation, just as they have proven risky for use in river rehabilitation and environmental flow regime design.
Like other fields, ecohydraulics has seen an increasing up- take of artificial intelligence. Given the abundance of observations possible using RS, such methods are very promising, not only to describe conditions but also to reveal underlying variables driving temporal dynamics. However, these methods based on current and past conditions may be susceptible to improper extrapolation to future conditions in the facing of changing functional relationships. Therefore, mechanistic models provide the best promise for not only predicting future ecohydraulic conditions under climate change scenarios, but also testing alternative adaptation strategies at local to regional scales4, 10. As the intensity and recurrence of extreme weather events increase, interest on nature-based solutions and ‘building with nature’ has grown generally, but also as a climate adaptation strategy. Given the still unknown feedbacks on flow-biota interactions, the efficacy of such projects on flood-prone regions and at-risk coastal communities will need to be assessed under a comprehensive ecohydraulics framework. Such a framework requires combined efforts from physical and numerical modeling to yield a better understanding of mid- and long-term effects on the modified ecosystem. Overall, ecohydraulics is an emerging transdisciplinary field that can help climate change scientists and climate adaptation practitioners move beyond the physical understanding of the environment to get at essential intertwined abiotic-biotic conditions and dynamism.
Time spent writing this article was partly supported by the USDA National Institute of Food and Agriculture, Hatch project number #CA-D-LAW-7034-H.
Figure 4 | Key elements of environmental flow management that consider non-stationary environments, such as climate change from Horne et al. (2022).
The overall approach is based on participatory modelling.
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3 | Kuhn J, Casas-Mulet R, Pander J, Geist J. Under review. Assessing stream cold-water patches from UAV-based imagery: a matter of classification method and metrics. Remote Sens. 2021, 13(7), 1379; https://doi.org/10.3390/rs13071379
4 | Lane, B. A., Pasternack, G. B., Sandoval-Solis, S. 2018. Integrated analysis of flow, form, and function for river management and design testing. Ecohydrology.
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6 | Pasternack, G. B. 2019b. “Applied Fluvial Ecohydraulics”. Oxford Bibliographies in Environmental Science. Ed. Ellen Wohl. New York: Oxford University Press, Entry Launch Date 2019-10-30. DOI: 10.1093/OBO/9780199363445-0124.
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Gregory Pasternack is a Professor in Land, Air, and Water Resources at University of California, Davis. He leads a combi-nation of (i) basic physical and ecological science to understand how the naturally complex landscape works, (ii) development of methods and software for designing more natural, functional environments, and (iii) technology transfer to get concepts, methods, and results into the hands of practitioners, regulators, and stakeholders.
Daniele Tonina is a Professor at the Center for Ecohydraulics Research. He held post-doctoral research positions at the University of California at Berkeley (USA) and at the University of Trento (Italy). He received engineering degrees from the University of Trento (BS, MS, 2000) and the University of Idaho (PhD, 2005). His research focuses on the interaction between surface and subsurface waters, riverine aquatic habitat and use of remote sensing in monitoring stream hydraulics. He is an IAHR, ASCE and AGU member. He serves as Associate Editor for the scientific journals of Water Resources Research, Hydrological Processes and Hydraulic Engineering.
Roser Casas-Mulet is research fellow at the Aquatic Systems Biology Unit, Technical University of Munich (Germany); and an honorary fellow at the University of Melbourne (Australia). She is a hydrogeoecologist with interdisciplinary experience in fluvial geomorphology, hydraulic engineering, freshwater ecology and remote sensing. Her research interests aim at understanding how physical habitat drives freshwater diversity and supports long-term river resilience in the context of climate change and global anthropogenic changes: particularly those caused by hydropower.
Ana Adeva-Bustos is a Researcher at SINTEF, Norway. She works applying and integrating models (e.g., hydraulic, hydro- power optimization and habitat models) to support a more environmental and sustainable management in regulated rivers and reservoirs, under current and future climate. She works evaluating management alternatives and using decision support tools for generating results that are end-user/stakeholder oriented.
Davide Vanzo is Senior Research Assistant at the Laboratory of Hydraulics, Hydrology and Glaciology at the Swiss Federal Institute of Technology (ETH), Switzerland. His research mainly focuses on (i) the investigation of river eco-morphodynamic processes such as sediment dynamics, thermal transport, vegetation and habitat dynamics, river alterations due to hydropower, (ii) the development of numerical modelling strategies to simulate river processes.
Andrew John is a Research Fellow at the University of Melbourne, Australia. His research aims to identify robust climate change adaptation strategies for environmental flows in large, complex river basins. This requires integrated ecohydrological and water resource modelling that supports decision making under deep uncertainly.
Rafael Tinoco is an Assistant Professor at the Department of Civil and Environmental Engineering at the University of Illinois Urbana-Champaign. His research group at the Ecohydraulics and Ecomorphodynamics Laboratory investigates flow-biota- sediment interactions across scales, to address challenges from invasive and endangered species, assessment of nature-based infrastructure, and resilience of fluvial and coastal communities.