Sierra Nevada Research Institute, University of California, 5200 North Lake Road, Merced, CA, 95343, USA.
Department of Earth System Science, University of California, Croul Hall, Irvine, CA, 92697-3100, USA.
Sci Rep. 2018 Jan 12;8(1):690. doi: 10.1038/s41598-017-19007-0.
Mountain runoff ultimately reflects the difference between precipitation (P) and evapotranspiration (ET), as modulated by biogeophysical mechanisms that intensify or alleviate drought impacts. These modulating mechanisms are seldom measured and not fully understood. The impact of the warm 2012-15 California drought on the heavily instrumented Kings River basin provides an extraordinary opportunity to enumerate four mechanisms that controlled the impact of drought on mountain hydrology. Two mechanisms intensified the impact: (i) evaporative processes have first access to local precipitation, which decreased the fractional allocation of P to runoff in 2012-15 and reduced P-ET by 30% relative to previous years, and (ii) 2012-15 was 1 °C warmer than the previous decade, which increased ET relative to previous years and reduced P-ET by 5%. The other two mechanisms alleviated the impact: (iii) spatial heterogeneity and the continuing supply of runoff from higher elevations increased 2012-15 P-ET by 10% relative to that expected for a homogenous basin, and iv) drought-associated dieback and wildfire thinned the forest and decreased ET, which increased 2016 P-ET by 15%. These mechanisms are all important and may offset each other; analyses that neglect one or more will over or underestimate the impact of drought and warming on mountain runoff.
山区径流量最终反映了降水（P）和蒸散（ET）之间的差异，而这种差异受到生物物理机制的调节，这些机制加剧或减轻了干旱的影响。这些调节机制很少被测量，也不完全了解。2012-15 年加利福尼亚暖旱对装备精良的金斯河盆地的影响提供了一个极好的机会，可以列举出控制干旱对山区水文影响的四种机制。有两种机制加剧了这种影响：（i）蒸发过程首先利用当地的降水，这减少了 2012-15 年分配给径流量的降水比例，与前几年相比减少了 30%，以及（ii）2012-15 年比前十年温暖 1°C，这增加了相对于前几年的蒸散量，并减少了 5%的 P-ET。另外两种机制缓解了这种影响：（iii）空间异质性和来自较高海拔的持续径流供应使 2012-15 年的 P-ET 比同质流域预期的增加了 10%，以及（iv）干旱相关的枯枝落叶和野火使森林变薄，蒸散量减少，这使 2016 年的 P-ET 增加了 15%。这些机制都很重要，可能相互抵消；忽略一个或多个机制的分析会高估或低估干旱和变暖对山区径流量的影响。
