Understanding the Asymmetry of Annual Streamflow Responses to Seasonal Warming in the Western United States
Understanding the Asymmetry of Annual Streamflow Responses to Seasonal Warming in the Western United States
复制标题
了解美国西部年度径流对季节性变暖响应的不对称性
DOI：
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发表时间：
2020
影响因子：
5.4
通讯作者：
D. Lettenmaier
中科院分区：
文献类型：
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作者：
Z. Ban;T. Das;D. Cayan;M. Xiao;D. Lettenmaier
年径流量对次年气候变暖的响应是高度不确定的，其控制机制仍然知之甚少，这给适应性水管理带来了挑战。一个典型的例子是美国西部，那里的气候模型预测暖季（4月至9月）的变暖明显大于冷季（10月至3月）。利用四种陆地表面（水文）模型，研究了美国西部四个区域重要流域的年和季节流量变化对暖季和冷季变暖的不对称响应。结果表明：(1)季节和年流量对不对称变暖响应的总体特征在不同模式下是一致的，尽管幅度不同。多模式平均值显示，在暖季升温3℃下，4个流域的年径流量从2.0%下降到7.5%，在冷季升温3℃下，从2.2%下降到4.7%。（ii）季节蒸散发对温度敏感性的不对称性制约了年流量对季节增暖响应的不对称性；③冷暖季总来水比高、夏冷冬冷等特征的流域，暖季增温相对于冷季增温的年流量减少幅度最大。（iii）中的模式可以通过响应一系列复合过程的蒸散发-温度敏感性的变化来解释，这些过程包括持水量随温度升高而增加的速率，与温度相关的融雪-反照率反馈，以及随温度升高而增强的地表阻力。
The response of annual runoff volume to sub‐annual climate warming is highly uncertain, and the governing mechanisms remain poorly understood, challenging adaptive water management. A typical exemplar is the Western United States, where climate models project substantially stronger warming in the warm season (April to September) than in the cool season (October to March). We investigate the asymmetrical responses of annual and seasonal streamflow changes to warm season and cool season warming for four regionally important basins in the Western United States using an ensemble of four land surface (hydrological) models. Our results show that (i) the general features of seasonal and annual streamflow responses to asymmetrical warming are consistent across models, although the magnitudes vary. The multi‐model mean shows annual runoff declining from 2.0% up to 7.5% under 3°C warm season warming, and from 2.2% up to 4.7% under 3°C cool season warming across the four basins. (ii) The asymmetry of the seasonal evapotranspiration sensitivity to temperature constrains the asymmetry of annual streamflow responses to seasonal warming; and (iii) basins with characteristics such as high ratios of warm to cool season gross incoming water, cooler summers, and colder winters have the strongest relative annual streamflow decreases for warm season warming relative to cool season warming. The pattern in (iii) is explained by the variation of evapotranspiration‐temperature sensitivity in response to a compound set of processes, including the enhanced rate of water holding capacity increase with warmer temperatures, temperature‐related snowmelt‐albedo feedback, and enhanced surface resistance with warmer temperatures.