很抱歉，由于出海，昨天写好的文稿今天未能及时发布，未来一周我会尽量不断更，像我的沉闷学科的掘墓人老师学习，做到日更。

In studies of the potential effects of global climate change on freshwater ecosystems, water temperature is a primary factor.Linear regressions of stream temperature versus air temperature are attractive for this purpose, because they require only oneinput variable (air temperature) which can be simulated by General Circulation Models (GCMs) better than other climatevariables. Under a warmer climate scenario, high stream temperatures must be projected by extrapolation. The question ariseswhether linear extrapolation is valid.

To answer the question, the heat exchange processes that contribute to surface water temperature have been analyzed and related to air temperature on a weekly time scale. The equilibrium temperature concept introduced by Edinger has been used. In stream reaches with large drainage area, stream temperature can be approximated by equilibrium temperature. At elevated air temperatures, the vapor pressure deficit above a water surface increases drastically (even in humid regions) causing strong evaporative cooling and hence a flatter stream temperature/air temperature relationship. At low air temperatures, stream temperatures often reach 08C as an asymptote. If an upstream flow control (dam, reservoir release) or a waste heat input is present, the lower asymptotic value can be larger than 08C. As a result of these upper and lower constraints for stream temperatures, the stream temperature/air temperature relationship resembles an S-shaped function rather than a straight line. Linear extrapolations to high and low air temperatures are therefore not justified.

在研究全球气候变化对淡水生态系统的潜在影响时, 水温是一个主要因素。流体温度与空气温度的线性回归在这方面非常具有吸引力，因为它们只需要输入一个变量（空气温度）通过一般环流模型(GCMs) 来模拟就可以得到比其他气候变量更好的结果。在气候变暖的大背景下，必须通过模拟来预测流体高温。问题的关键是验证这种线性预测是否有效。

为了回答这个问题, 我们对影响地表水温度的热交换过程进行了分析, 并研究了其在周时间尺度上与气温的关系。平衡温度概念由 Edinger 引入使用。在水流量大的区域，流体温度可以通过平衡温度近似来计算。在空气温度高的情况下，水表层的蒸汽压不足会急剧增强（即使在潮湿地区），导致强烈的蒸发冷却，因此形成一种平缓的流体温度和空气温度变化关系。在空气温度低的情况下，流体温度常接近0摄氏度。如果存在上游流量控制 (水坝、水库) 或余热输入，则流体温度渐进值可能会大于0摄氏度。由于这些流体温度的上限和下限约束, 流体温度与空气温度的关系类似于 s 形函数, 而不是一条直线。因此, 对高和低温的线性外推法是不合理的。

参考文献：Stream temperature/air temperature relationship:a physical interpretation