A tree-ring-based reconstruction of the Yimin River annual runoff in the Hulunbuir region, Inner Mongolia, for the past 135 years.

Based on the relationships between the regional tree-ring chronology (RC) of moisture-sensitive Pinus sylvestris var. mongolica and the monthly mean maximum temperature, annual precipitation and annual runoff, a reconstruction of the runoff of the Yimin River was performed for the period 1868&ndash;2002. The model was stable and could explain 52.2% of the variance for the calibration period of 1956&ndash;2002. During the past 135 years, 21 extremely dry years and 19 extremely wet years occurred. These years represented 15.6% and 14.1% of the total study period, respectively. Six severe drought events lasting two years or more occurred in 1950&ndash;1951, 1986&ndash;1987, 1905&ndash;1909, 1926&ndash;1928, 1968&ndash;1969 and 1919&ndash;1920. Four wetter events occurred during 1954&ndash;1959, 1932&ndash;1934, 1939&ndash;1940 and 1990&ndash;1991. Comparisons with other tree-ring-based streamflow reconstructions or chronologies for surrounding areas supplied a high degree of confidence in our reconstruction. Power spectrum and wavelet analyses suggested that the reconstructed annual runoff variation in the Hulun Buir region and surrounding area could be associated with large-scale atmospheric-oceanic variability, such as the Pacific Decadal Oscillation (PDO) and El Ni&ntilde;o-Southern Oscillation (ENSO), and sunspot activity.</p

Tree-ring based runoff reconstruction of the upper Fenhe River basin, NorthChina, since 1799 AD

To acquire long-term perspectives on the history of droughts, we have presented the first runoff reconstruction from March to July in the upper Fenhe River basin, based on Pinus tabulaeformis tree-ring width indices from the Guancen Mountains, headstream of the Fenhe River, North China. The reconstruction explains 54.8% of the instrumental runoff variance over the period from 1952 to 2008. An analysis of interannual runoff variability indicated that AD 2001 was not only the driest year for the instrumental period, but also the driest year since AD 1799 in the upper Fenhe River. More extreme single-year droughts existed in the 20th century than in the 19th century in the region. Multiyear and decadal scale dry regime analyses demonstrated that the instrumental runoff underestimated the potential severe and prolonged droughts in the Fenhe River basin in future, such as droughts similar to the multiyear pre-instrumental droughts from 1831 to 1842 and 1919 to 1929. Comparisons between the Fenhe River runoff reconstruction and other nearby precipitation reconstructions showed that drought occurrence has been synchronous in parts of north and northwestern China to some extent for the last 211 years. Spatial correlation analyses between runoff data and the gridded Palmer Drought Severity Index dataset indicated that the average runoff reconstruction from March to July in the upper Fenhe River represents the regional moisture variations in North China, especially in the entire Fenhe River basin. As for the highest frequency and severity of spring drought in Shanxi province, the runoff reconstruction can provide base data for historical drought analysis and water resource planning and management in the Fenhe River basin or even to entire Shanxi province.</p