Water temperature (Tw) is a primary determinant of river ecosystem health and function that is strongly controlled by climate variability and change but mediated by catchment properties. We apply a nested analysis to: (1) evaluate how annual and seasonal mean Tw varied across England during the period 2000–2018; (2) assess the extent to which these regional-temporal dynamics correlate with the North Atlantic Oscillation (NAO); and (3) quantify the impact of local climate variability on modelled daily maximum Tw for open, shaded and spring-fed river reaches. Such information is used to identify sentinel locations for long-term monitoring and reporting, to evaluate the true benefit of riparian shade management, and to assess the impacts of climate change on Tw. We draw on a national archive of nearly 1 million Tw values and data from a high-resolution field experiment in central England. Nationally, annual mean Tw changed by −0.4 °C/decade over the period 2000 to 2018, broadly in line with Central England Temperatures, although summer Tw changed by +0.6 to +1.1 °C/decade in parts of central and northern England. There were significant associations between summer Tw and NAO (rho = 0.64, p < 0.05), especially at sites above 300 m altitude (rho = 0.70, p < 0.01). The regional analysis reveals strongest links between summer Tw and NAO in northeast England and weakest associations in lowland regions of southern and east England with major aquifers. Hence, places with significant groundwater flows offer the greatest chance of detecting long-term signals in Tw that are not being driven by the NAO. Site-specific, logistic regression models of daily maximum Tw are found to be sensitive to the prevailing NAO phase during calibration periods. Such models show a thermal benefit for shaded sites compared with open sites that is one average 0.2 °C under negative NAO but 2.8 °C under positive NAO. Based on the findings from our nested analysis we suggest ways of optimising monitoring networks plus improving the appraisal of measures intended to keep rivers cool. In particular, we call for the creation of a national indicator of Tw for use in UK Climate Change Risk Assessments.

水温（Tw）是河流生态系统健康和功能的主要决定因素，其受到气候变化和变化的强烈控制，但受流域特性的调节。我们将嵌套分析应用于：（1）评估2000-2018年期间整个英格兰的年度和季节性平均Tw变化；（2）评估这些时空动态与北大西洋涛动（NAO）相关的程度；（3）量化局部气候变化对开阔，阴凉和春季喂养的河流河段的日最大Tw建模的影响。这些信息用于识别哨点位置，以进行长期监控和报告，评估河岸遮阳管理的真正益处，并评估气候变化对Tw的影响。我们利用英格兰中部近百万个Tw值的国家档案和来自高分辨率中场实验的数据进行提取。在全国范围内，尽管英格兰中部和北部部分地区的夏季Tw变化了+0.6至+ 1.1°C /十年，但2000年至2018年期间的年平均Tw变化了-0.4°C /十年，与英格兰中部温度基本一致。夏季Tw和NAO之间存在显着的关联（rho = 0.64，p <0.05），尤其是在海拔300 m以上的站点（rho= 0.70，p <0.01）。区域分析显示，英格兰东北部夏季Tw和NAO之间的联系最强，而英格兰南部和东部低地地区与主要含水层之间的联系最弱。因此，地下水流量很大的地方提供了最大的机会来检测Tw中不受NAO驱动的长期信号。发现每天最大Tw的针对特定地点的逻辑回归模型在校准期间对主要的NAO阶段敏感。与开放位置相比，此类模型显示了阴影位置的热效益，在负NAO下平均为0.2°C，在正NAO下为2.8°C。基于我们的嵌套分析结果，我们建议了优化监测网络以及改进旨在保持河流凉爽的措施的评估方法。尤其是，