Abstract
Based on runoff data collected at the Zhimenda station, reanalysis data from the National Centers of Environmental Prediction/National Centers of Atmospheric Research (NCEP/NCAR), and observation data from ground stations in China, this study analyzes the characteristics of changes in runoff in the source region of the Yangtze River (SRYR) during the flood season (from July to September), the relationship between runoff and antecedent rainfall, and the impact of the westerly jet (WJ) on rainfall in the coastal zone of the SRYR. The results show the following. The runoff in the SRYR displays a significant interannual and interdecadal variability. The runoff in the SRYR during the flood season is most closely related to 15-day (June 16 to September 15) antecedent rainfall in the coastal zone of the SRYR. In turn, the antecedent rainfall in the coastal zone of the SRYR is mainly affected by the intensity of the simultaneous WJ over a key region (55–85°E, 45–55°N). When the intensity of the WJ over the key region is greater (less) than normal,the jet position moves northward (southward), and the easterly (westerly) wind anomalies over the region to the west of the SRYR become unfavorable (favorable) to the transport of water vapor from high-latitude regions to the SRYR. In addition, the southerly wind over the equatorial region cannot (can) easily advance northward, which is unfavorable (favorable) to the northward transport of water vapor from the low-latitude ocean. Hence, these conditions result in a decrease (increase) in the water vapor content in the SRYR. Furthermore, the convergence (divergence) anomalies in the upper level and the divergence (convergence) anomalies in the lower level result in the descending (ascending) motion over the SRYR. These factors decrease (increase) the rainfall, thereby decreasing (increasing) the runoff in the SRYR during the flood season.
Highlights
Introduction e YangtzeRiver originates at the terminuses of the glaciers on Geladaindong Mountain in the middle section of the Tanggula Mountain Range in Qinghai Province. e headwaters consist mainly of three rivers, namely, the Dangqu River, the Tuotuo River, and the Chumar River. e Tuotuo River converges with the Dangqu River to form the Tongtian River, which flows southeastward and converges with the Batang River near Yushu County in QinghaiProvince to form the Jinsha River
Based on runoff data collected at the Zhimenda station, reanalysis data from the National Centers of Environmental Prediction/ National Centers of Atmospheric Research (NCEP/NCAR), and observation data from ground stations in China, this study analyzes the characteristics of changes in runoff in the source region of the Yangtze River (SRYR) during the flood season, the relationship between runoff and antecedent rainfall, and the impact of the westerly jet (WJ) on rainfall in the coastal zone of the SRYR. e results show the following. e runoff in the SRYR displays a significant interannual and interdecadal variability. e runoff in the SRYR during the flood season is most closely related to 15-day (June 16 to September 15) antecedent rainfall in the coastal zone of the SRYR
A precipitation increase could cause the runoff in the SRYR to increase, whereas an evaporation increase could cause the runoff in the SRYR to decrease. e heating of the Tibetan Plateau (TP), enhanced plateau monsoon, and enhanced glacier melting could increase the runoff in the SRYR [2, 5, 11,12,13]
Summary
In this correlation calculation, the runoff in the flood season is the sum of monthly runoff from July to September, the rainfall is the sum of daily rainfall from 16 June to September, and the circulation is the average of the daily data from June to 15 September. A new value is calculated for each grid point based on a correction factor that is determined by looking at each station within the radius of influence. For each such station, an error is defined as the difference between the station value and a value arrived by interpolation from the grid to that station. R2 + r2 where W is the influence radius and r is the distance between the station and the grid point
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