The forecast of warmer weather, and reduced precipitation and streamflow under climate change makes freshwater biota particularly vulnerable to being exposed to temperature extremes. Given the importance of temperature to regulate vital physiological processes, the availability of discrete cold-water patches (CWPs) in rivers to act as potential thermal refugia is critical to support freshwater ecosystem function. Being able to predict their spatial distribution at riverscape scales is the first step to understanding the capacity to maintain thermal refuges and to inform future river management strategies. Novel Unmanned Aerial Vehicle (UAV)-based Thermal Infra-Red (TIR) imagery technologies provide an opportunity to assess riverscape stream temperature. On the example of a 50 km linear length of the groundwater-dominated Upper Ovens River (Australia), this study presents a methodology addressing critical challenges in UAV-based TIR and optical data acquisition, processing, and interpretation. Our methodological approach generated 49 georeferenced high-resolution TIR and optical orthomosaicked imagery sets. The imagery sets allowed us to identify river-length longitudinal patterns of temperature and to detect, characterize, and classify 260 CWPs. Both stream and CWPs temperatures increased but presented considerable variability with downstream distance. CWPs were non-uniformly distributed along the riverscape, with emergent hyporheic water types dominating, followed by deep pools, shading, side channels, and tributaries. We found associations between CWPs and key physical controls including land use, riparian vegetation, longitudinal and lateral CWP location, and CWP area size, illustrating processes acting at multiple spatial scales. This study provides a basis for future works on the thermal associations with physical controls over a riverscape, and it highlights the major challenges and limitations of the use of UAV-based TIR and optical imagery to be used in future applications. In conjunction with studies of thermally linked ecological processes, the predictions of CWPs can help prioritize river restoration measures as effective climate adaptation tools.

中文翻译：

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基于无人机 (UAV) 的热红外 (TIR) 和光学图像揭示了地下水占主导地位的河景上冷水地区的多空间尺度控制

对气候变暖的预测以及气候变化下降水和流量的减少使淡水生物群特别容易受到极端温度的影响。鉴于温度对调节重要生理过程的重要性，河流中离散冷水斑块 (CWP) 作为潜在的热避难所的可用性对于支持淡水生态系统功能至关重要。能够在河流景观尺度上预测它们的空间分布是了解维持热避难所的能力并为未来的河流管理策略提供信息的第一步。基于新型无人机 (UAV) 的热红外 (TIR) 图像技术为评估河流景观温度提供了机会。在以地下水为主的上奥文斯河（澳大利亚）的 50 公里线性长度的示例中，本研究提出了一种方法来解决基于无人机的 TIR 和光学数据采集、处理和解释中的关键挑战。我们的方法论方法生成了 49 个地理参考高分辨率 TIR 和光学正射镶嵌图像集。图像集使我们能够识别河流长度的纵向温度模式，并对 260 个 CWP 进行检测、表征和分类。溪流和 CWP 温度都增加，但随着下游距离的变化呈现出相当大的变化。CWPs沿河景不均匀分布，以突水下流水类型为主，其次是深水池、遮荫、侧渠道和支流。我们发现 CWP 与关键物理控制之间的关联，包括土地利用、河岸植被、纵向和横向 CWP 位置以及 CWP 区域大小，说明了在多个空间尺度上起作用的过程。这项研究为未来研究与河流景观物理控制的热关联的工作奠定了基础，并强调了在未来应用中使用基于无人机的 TIR 和光学图像的主要挑战和局限性。结合热相关生态过程的研究，CWP 的预测可以帮助优先考虑河流恢复措施作为有效的气候适应工具。这项研究为未来研究热关联与河流景观物理控制的工作奠定了基础，并强调了在未来应用中使用基于无人机的 TIR 和光学图像的主要挑战和局限性。结合热相关生态过程的研究，CWP 的预测可以帮助优先考虑河流恢复措施作为有效的气候适应工具。这项研究为未来研究热关联与河流景观物理控制的工作奠定了基础，并强调了在未来应用中使用基于无人机的 TIR 和光学图像的主要挑战和局限性。结合热相关生态过程的研究，CWP 的预测可以帮助优先考虑河流恢复措施作为有效的气候适应工具。