Stream drying patterns – including duration, timing, and dry-down rates – affect aquatic ecosystems and nutrient exports in non-perennial streams. Because hydrologic processes are often nonlinear, changes in drying may also be nonlinear, but analyses of historical changes in stream drying to date have not characterized the frequency or functional forms of nonlinear change. Understanding the extent of nonlinear change in non-perennial streams is essential for advancing our fundamental knowledge of hydrological processes, aquatic ecosystems, and watershed functioning under a warming climate. This paper uses a polynomial-based trend detection technique (PolyTrend) to analyze the linear and nonlinear trend behaviors of three intermittency signatures ( specifying longer or shorter drying duration, specifying timing of stream drying, and specifying dry-down rates) at 540 non-perennial gage stations over 38 years (1980–2017) across the continental United States (CONUS). Additionally, we carried out a breakpoint analysis to characterize the discontinuities in the time series of each intermittency signature. Analysis of shows that about 37 % of the total streamflow stations are drying for longer each year, whereas about 22 % are wetter for longer than in the past. The analysis shows that 10 % of the streams are drying earlier, and 19 % are drying later. On the other hand, analysis of shows that 14 % of streams are drying faster, and 17 % are drying more slowly. For all these metrics, among the significant trends, at least half of the relationships were nonlinear. For , the breakpoint analysis shows more discontinuities in the second half of the analysis period (1999 to 2017) than in the first half, with more discontinuities in the Southern Great Plains than in other regions. The other two signatures demonstrate less frequent discontinuities in the second half of the analysis period, suggesting decreased nonlinear dynamics in recent years. Nonlinear no-flow duration trends are common in Mediterranean California, and the dry-down rate has increased in recent decades. Our findings indicate that nonlinear change in stream drying is widespread and must be accounted for in watershed planning and management.

中文翻译：

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表征非常年美国流的签名的非线性趋势

溪流干涸模式（包括持续时间、时机和干涸率）影响非常年溪流的水生生态系统和养分输出。由于水文过程通常是非线性的，干燥的变化也可能是非线性的，但迄今为止对河流干燥历史变化的分析尚未表征非线性变化的频率或函数形式。了解非常年河流非线性变化的程度对于增进我们对气候变暖下水文过程、水生生态系统和流域功能的基础知识至关重要。本文使用基于多项式的趋势检测技术 (PolyTrend) 来分析 540 个非连续条件下的三个间歇性特征（指定更长或更短的干燥持续时间、指定流干燥时间以及指定干燥速率）的线性和非线性趋势行为。 38 年来（1980-2017）遍布美国大陆（CONUS）的常年监测站。此外，我们还进行了断点分析来表征每个间歇性特征的时间序列中的不连续性。分析表明，大约37%的总水流站每年干燥时间更长，而大约22%的水流站湿润时间比过去更长。分析显示，10% 的河流干燥较早，19% 的河流干燥较晚。另一方面，分析表明，14% 的河流干燥得更快，17% 的河流干燥得更慢。对于所有这些指标，在重要趋势中，至少有一半的关系是非线性的。对于 ，断点分析显示分析期后半段（1999 年至 2017 年）的不连续性比上半年更多，其中南部大平原的不连续性比其他地区更多。另外两个特征表明，在分析期的后半段，不连续性的出现频率较低，这表明近年来非线性动力学有所下降。非线性无流持续时间趋势在地中海加利福尼亚州很常见，并且近几十年来干涸率有所增加。我们的研究结果表明，河流干燥的非线性变化很普遍，必须在流域规划和管理中加以考虑。