1975-2011年渭河上游径流演变规律及对气候驱动因子的响应

为探讨渭河上游径流的变化特征及其对气候变化的响应，选取1975-2011年河流实测径流量进行计算和分析. 结果表明：近40 a来，渭河上游径流总体呈明显下降趋势，其中，20世纪90年代前处于丰水期，90年代后进入枯水期，进入21世纪有明显增多趋势. 径流年际丰枯变化激烈，枯水年的发生概率高、持续性强，最长的连枯年份达8 a. 径流量集中在汛期，各年代的分配峰型有所不同，在70、80年代为7、9月双峰，之后变为单峰型分布. 流域内气候增暖明显，降水减少，蒸发加剧；90年代为明显的暖干型气候，21世纪初期气候向暖湿型转变的过程对径流的增加十分有利. 径流对气候变化有较强响应，但响应程度随时间变化而变化. 通过定量分析气候因子对径流变化的贡献值，发现由于气候增暖导致潜在蒸散量的加剧对径流变化的负贡献达60%以上，绝对值高于降水量的正贡献.

Features and response to climate-driven factors of the runoff in the upper reaches of the Weihe River in 1975-2011

As the largest tributary of the Yellow River, the Weihe River provides a great deal of water sources to the Gansu Province and Shaanxi Province, China, having strategic significance in regional development, ecosystem health and sustainability of socio-economic development in the Yellow River basin. The catchment area of the upper reaches of the Weihe River is 2.579 km², which occupies 19.1% of the total area of the Weihe River watershed. In this paper, the runoffs at Beidao and Wushan Hydrologic Stations of the upper reaches of the Weihe River from 1975 to 2011 were calculated and analyzed in order to understand the runoff features and their response to climate-driven factors. The climate change characteristics were analyzed using the data of monthly precipitation and potential evapotranspiration, which were estimated by using FAO Penman-Monteith method. After selecting the representative stations, the correlation coefficients between the annual, seasonal runoff and climate-driven factors were calculated, and the sensitivity of runoff to the climate change was analyzed. The following conclusions can be drawn: (1) Annual runoff of the river has obviously decreased as a whole, especially in the 1990s, but shifted to increase in the early 21st century. (2) Runoff concentrates in the flood season, and had different distribution forms in different decades. (3) Runoff is affected by climate change; runoff decreases when climate is warm, precipitation decreases, potential evapotranspiration increases and water consumption increases. (4) The response of runoff to climate-driven factors is not stable, changing with time. (5) Both precipitation and potential evapotranspiration contribute to the change of runoff, and the contribution rate of potential evapotranspiration has increased from the 1990s, becoming the major factor to the runoff decreasing.