怒江上游流域降雪识别及其演变趋势和原因分析

降水的相态变化直接影响地表能量和水循环过程,有效的识别降水中的降雪量,并量化气候变化对降雪变化趋势的影响,对于提高融雪径流模拟、支撑变化环境下高寒地区水资源管理具有重要意义。本文根据怒江上游流域1979年以前6个气象站点的降雪比例和日平均气温的统计关系,采用指数方程形式的双温度阈值方法对1979年以前有记录的降雪量进行了识别和验证。在此基础上,对1980—2016年各气象站点降雪量进行估计和趋势分析,并量化识别了气温和降水变化对其降雪量变化的影响。结果表明:(1)降雪识别指数方程能够在年和月尺度上较好估计各气象站点降雪量,其相关系数均在0.86以上,相对误差均在5%以内。(2)1979年以后,各气象站点气温均呈显著增加趋势,整体上年降水量和年降雪量分别呈增加和减少趋势,但趋势并不显著。(3)气象站点气温升高具有减少降雪量的作用,且作用强度均从流域东南向西北逐渐增强。气候变化背景下,低温条件下降水概率增加对流域降雪量的增加具有显著促进作用,但1979年以后气温的显著增加对降雪量的影响占据主导作用,使得流域降雪量整体呈减少趋势。

Separation of snowfall from precipitation and its evolution trend and reasons analysis in upper reaches of Nujiang River Basin

Precipitation phase has a direct influence on the surface energy balance and hydrological processes. It is important and necessary to separate the snowfall from precipitation and quantify the impact of climate change on the snowfall for the improvement of snowmelt runoff simulation and the management of the water resources in the alpine area. Based on the relation between snowfall proportion and daily temperature of six meteorological stations before 1979 in upper reaches of Nujiang River Basin, a separation scheme with exponential function structure was applied to estimate the snowfall,which was validated by the precipitation phase data before 1979. Furthermore, the snowfall was estimated and analyzed by the separation scheme from 1980 to 2016, and the impact of temperature and precipitation change on snowfall evolution was explored. The results show that:(1) the separation scheme performs well in snowfall estimation with Pearson correlation coefficient above 0.86 and relative BIAS under 5% in the six stations. (2) Temperatures after 1979 show a significant increasing trend in the six stations, while the annual precipitation and snowfall demonstrate insignificant increasing and decreasing trends overall the basin, respectively. (3) Increase of temperature promotes the decrease of snowfall, and the influence intensity of temperature on the snowfall gradually increases from the southeast to the northwest of basin. Moreover, the precipitation probability increases in the low temperature condition under the climate change,which significantly promotes the snowfall increase in upper reaches of Nujiang River Basin. However, the significant increase of temperature has a dominant effect on the snowfall change after 1979,and the overall snowfall shows a decreasing trend in upper reaches of Nujiang River Basin.