Climate-change driven increases in water temperature pose challenges for aquatic organisms. Predictions of impacts typically do not account for fine-grained spatiotemporal thermal patterns in rivers. Patches of cooler water could serve as refuges for anadromous species like salmon that migrate during summer. We used high-resolution remotely sensed water temperature data to characterize summer thermal heterogeneity patterns for 11,308 km of second–seventh-order rivers throughout the Pacific Northwest and northern California (USA). We evaluated (1) water temperature patterns at different spatial resolutions, (2) the frequency, size, and spacing of cool thermal patches suitable for Pacific salmon (i.e., contiguous stretches ≥ 0.25 km, ≤ 15 °C and ≥ 2 °C, aooler than adjacent water), and (3) potential influences of climate change on availability of cool patches. Thermal heterogeneity was nonlinearly related to the spatial resolution of water temperature data, and heterogeneity at fine resolution (< 1 km) would have been difficult to quantify without spatially continuous data. Cool patches were generally > 2.7 and < 13.0 km long, and spacing among patches was generally > 5.7 and < 49.4 km. Thermal heterogeneity varied among rivers, some of which had long uninterrupted stretches of warm water ≥ 20 °C, and others had many smaller cool patches. Our models predicted little change in future thermal heterogeneity among rivers, but within-river patterns sometimes changed markedly compared to contemporary patterns. These results can inform long-term monitoring programs as well as near-term climate-adaptation strategies.

中文翻译：

---

河流和冷水物种避难所的纵向热异质性：规模和气候变化的影响

气候变化驱动的水温升高给水生生物带来了挑战。影响的预测通常不考虑河流中细粒度的时空热模式。较凉的水域可以作为夏季迁徙的鲑鱼等溯河物种的避难所。我们使用高分辨率遥感水温数据来表征整个太平洋西北部和加利福尼亚州北部（美国）的 11,308 公里二级至七级河流的夏季热异质性模式。我们评估了 (1) 不同空间分辨率下的水温模式，(2) 适合太平洋鲑鱼的凉爽热斑的频率、大小和间距（即连续延伸 ≥ 0.25 km、≤ 15 °C 和 ≥ 2 °C，比相邻的水更冷），(3) 气候变化对冷斑可用性的潜在影响。热非均质性与水温数据的空间分辨率呈非线性关系，如果没有空间连续数据，则难以量化高分辨率（< 1 公里）的非均质性。冷斑一般> 2.7 和< 13.0 公里长，斑块间距一般> 5.7 和< 49.4 公里。河流之间的热异质性各不相同，其中一些河流有长期不间断的 ≥ 20 °C 温水，而另一些则有许多较小的凉爽斑块。我们的模型预测未来河流之间的热异质性几乎没有变化，但与当代模式相比，河流内部模式有时会发生显着变化。这些结果可以为长期监测计划以及近期气候适应战略提供信息。