Structure and Detectability of Trends in Hydrological Measures over the Western United States
Structure and Detectability of Trends in Hydrological Measures over the Western United States
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DOI：
10.1175/2009jhm1095.1
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发表时间：
2009-08-25
影响因子：
3.8
通讯作者：
Mirin, A.
中科院分区：
文献类型：
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作者：
Das, T.;Hidalgo, H. G.;Mirin, A.
本研究探讨了1950-99年期间，在美国西部（1）/（8）度空间分辨率的关键水文相关变量的观测趋势的地理结构。确定了这些趋势在统计上与自然气候变化相关趋势显著不同的地理区域、纬度带和海拔等级。分析的变量包括冬末和春季温度，冬季总降雪日数作为冬季总湿日数的一部分，4月1日雪水当量（SWE）作为3月至3月（ONDJFM）总降水量的一部分[precip（ONDJFM）]，季节性[JFM]累积径流作为水年累积径流的一部分。观测到的变化进行了比较，自然内部气候变率模拟的850年控制运行的有限体积版本的社区气候系统模式，版本3（CCSM 3-FV），统计缩小到（1）/（8）度网格使用的方法构建的类似物。观测和降尺度模型的温度和降水数据，然后驱动可变入渗能力（维克）水文模型，以获得在这项研究中分析的水文变量。大趋势（在长期控制运行中发现的震级不到5%）在观测中很常见，并占据了美国西部山区的很大一部分（37%-42%）。这些趋势与89%的区域出现的大规模变暖密切相关。水文变量的最强变化不太可能仅与自然变率相关，发生在中等海拔[JFM径流部分为750-2500 m，SWE/Precip（ONDJFM）为500-3000 m]，变暖将温度从略低于冰点推到略高于冰点。使用选定的集水区的数据进一步分析表明，水文气候变量必须有显着变化（在95%的置信水平）超过至少45%的总集水区，以实现可检测的趋势，在措施积累到集水区规模。
This study examines the geographic structure of observed trends in key hydrologically relevant variables across the western United States at (1)/(8)degrees spatial resolution during the period 1950-99. Geographical regions, latitude bands, and elevation classes where these trends are statistically significantly different from trends associated with natural climate variations are identified. Variables analyzed include late-winter and spring temperature, winter-total snowy days as a fraction of winter-total wet days, 1 April snow water equivalent (SWE) as a fraction of October-March (ONDJFM) precipitation total [precip(ONDJFM)], and seasonal [JFM] accumulated runoff as a fraction of water-year accumulated runoff. Observed changes were compared to natural internal climate variability simulated by an 850-yr control run of the finite volume version of the Community Climate System Model, version 3 (CCSM3-FV), statistically downscaled to a (1)/(8)degrees grid using the method of constructed analogs. Both observed and downscaled model temperature and precipitation data were then used to drive the Variable Infiltration Capacity (VIC) hydrological model to obtain the hydrological variables analyzed in this study. Large trends (magnitudes found less than 5% of the time in the long control run) are common in the observations and occupy a substantial part (37%-42%) of the mountainous western United States. These trends are strongly related to the large-scale warming that appears over 89% of the domain. The strongest changes in the hydrologic variables, unlikely to be associated with natural variability alone, have occurred at medium elevations [750-2500 m for JFM runoff fractions and 500-3000 m for SWE/Precip(ONDJFM)] where warming has pushed temperatures from slightly below to slightly above freezing. Further analysis using the data on selected catchments indicates that hydroclimatic variables must have changed significantly (at 95% confidence level) over at least 45% of the total catchment area to achieve a detectable trend in measures accumulated to the catchment scale.