Abstract
Water source is one of the most important concerns for regional society and economy development, especially in the Weihe River basin which is located in the marginal zone of the Asian summer monsoon. Due to the weakness of short instrumental records, the variations of streamflow during the long-term natural background are difficult to access. Herein, the average June–July streamflow variability in the middle reaches of the Weihe River was identified based on tree-ring width indices of Chines pine (Pinus tabulaeformis Carr.) from the northern slope of the Qinling Mountains in central China. Our model could explain the variance of 39.3% in the observed streamflow period from 1940 to 1970 AD. There were 30 extremely low years and 26 high years which occurred in our reconstruction for the effective span of 1820 to 2005. Several common dryness and wetness periods appeared in this reconstructed streamflow, and other tree-ring precipitation series suggested the coherence of hydroclimate fluctuation over the Weihe River basin. Some significant peaks in cycles implied the linkages of natural forcing on the average June–July streamflow of the Weihe River, such as the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) activities. Spatial correlation results between streamflow and sea surface temperature in the northern Pacific Ocean, as well as extremely low/high years responding to the El Niño/La Nina events, supported the teleconnections. The current 186-year streamflow reconstruction placed regional twentieth-century drought and moisture events in a long-term perspective in the Weihe River basin, and provided useful information for regional water resource safety and forest management, particularly under climate warming conditions.
Highlights
Weihe River is the largest tributary of the Yellow River, China, with a basin area of 134,800 km2 .The length of the Weihe River is 818 km, crossing three provinces of Gansu, Ningxia, and Shaanxi in the eastern part of the Northwest China [1,2]
Our results provide the first hydrological reconstruction inferred from tree rings for the Weihe
The responses of tree radial growth to climatic factors showed that the NWTabc chronology was significantly positively correlated with precipitation in June (r = 0.572, n = 31, 1940–1970, p < 0.01), significantly negatively correlated with temperature in June (r = −0.401, n = 31, 1940–1970, p < 0.05), and not correlated with precipitation and temperature in July, indicating that the growth of Pinus tabulaeformis was very sensitive to humidity conditions before the East Asian monsoon season started in July
Summary
Weihe River is the largest tributary of the Yellow River, China, with a basin area of 134,800 km. The length of the Weihe River is 818 km, crossing three provinces of Gansu, Ningxia, and Shaanxi in the eastern part of the Northwest China [1,2]. The upper reaches locate in the semi-arid region of eastern Gansu and southern Ningxia, and the middle and down reaches locate in the semi-humid region of Shaanxi. Hydroclimate in the Weihe River basin is mainly influenced by the Asian summer monsoon, and is sensitive to climate anomalies [3,4]. Total annual precipitation over the basin is about. 573 mm, and most precipitation occurs in the summer rainy season. The mean natural discharge is Forests 2019, 10, 208; doi:10.3390/f10030208 www.mdpi.com/journal/forests
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