Principal components of thermal regimes in mountain river networks

摘要: Abstract. Description of thermal regimes in flowing waters is key to understanding physical processes, enhancing predictive abilities, and improving bioassessments. Spatially and temporally sparse data sets, especially logistically challenging mountain environments, have limited studies on regimes, but inexpensive sensors coupled with crowd-sourced collection efforts provide efficient means developing large sets for robust analyses. Here, are assessed using annual monitoring records compiled from several natural resource agencies in the northwestern United States that spanned a 5-year period (2011–2015) at 226 sites across contiguous montane river networks. Regimes were summarized with 28 metrics principal component analysis (PCA) was used to determine those which best explained variation reduced set orthogonal axes. Four components (PC) accounted for 93.4 % the temperature metrics, first PC (49 % variance) associated represented magnitude and variability second PC (29 % metrics representing length intensity winter season. Another variant of PCA, T-mode analysis, applied to daily values revealed two distinct phases spatial variability – homogeneous phase during winter when temperatures at all were ∘C and a heterogeneous throughout year's remainder among sites more pronounced. Phase transitions occurred March November, and coincided abatement onset subzero air across the study area. S-mode PCA conducted same matrix daily temperature after transposition indicated two PCs accounted for 98 % temporal among sites. The was responsible 96.7 % variance correlated air temperature ( r=0.92 ), whereas for 1.3 % residual discharge r=0.84 ). Thermal these networks relatively simple responded coherently external forcing factors, so sparse monitoring arrays small summary may be adequate their description. provided computationally extracting key information elements set here could be applied broadly facilitate comparisons diverse stream types and develop classification schemes regimes.