Northwestern China experiences frequent droughts and weather disasters due to its low and variable precipitation.The Qilian Mountains(36° 30'～33°28'N,93°30'～103°30'E)on the northeastern Qinghai-Tibetan plateau are a critical water resource for the Hexi Corridor oasis.Understanding the spatial and temporal variations in extreme droughts between the southern and northern sides of the Qilian Mountains is crucial for effective climate risk management,especially in the context of global warming.In this study,five precipitation-sensitive tree-ring-width series were analyzed:ZMSK(38.15° N,99.95° E;3314～3491 m a.s.1.)and QYG28(38.18° N,100.44°E;3336～3409 m a.s.1.)from the southern Qilian Mountains,and YQ(39.61° N,97.88° E;3100～3500 m a.s.1.),KL3(38.81° N,99.96° E;3000～3300 m a.s.1.),and LY(37.98° N,101.26° E;3162～3350 m a.s.1.)from the northern Qilian Mountains.Residual(RES)chronologies were developed using a cubic spline with a 50％frequency-response cut-off at 67％of the series length,covering the period from 1701 A.D.to 2005 A.D.Correlation analysis with nearby meteorological data explored the climatic implications of each chronology from the prior June to the current September and with different combinations of the monthly meteorological series.All five RES chronologies showed significant positive correlations(p＜0.05)with total precipitation over a 12-month period from the previous July to the current June(p7～c6).Drought intensity levels were classified based on the ring-width index,and a distribution table of extreme drought years was created to examine inter-annual and inter-decadal patterns over the past 300 years.Superposed Epoch Analysis(SEA)was used to investigate potential causes of extreme droughts,particularly the relationship between the tree-ring index and El Nino-Southern Oscillation(ENSO)and North Atlantic Oscillation(NAO)indices.The findings revealed a universal extreme drought year in 1714 A.D.across the entire study area,with five regional extreme drought years(1706 A.D.,1721A.D.,1727 A.D.,1824A.D.,and 1960 A.D.)recorded by four series.Although extreme drought in the 18th century affected the entire Qilian Mountains,there were distinct regional variations in extreme drought events between the southern and northern sides.The southern side experienced the most droughts during the 18th and 19th centuries,showing a dry-dry-wet pattern over the past three centuries(1701～2005 A.D.),which coinciding a dry-wet transition after the 1960s in the Northwestern China.In contrast,the northern side had significant drought periods in the 18th and 20th centuries,showing a dry-wet-dry trend with numerous extreme droughts in the 1920s～1930s and 1990s.On a 10-year scale,the southern side had a high-frequency drought period from 1761 A.D.to 1770 AD,while the northern side experienced more frequent droughts from 1711～1720 A.D.,1721～1730 A.D.,and 1921～1930 A.D.On a 30-year scale,high-frequency droughts occurred from 1701～1730 A.D.and 1761～1790 A.D.on the southern side,and from 1701～1730 A.D.and 1911～1940 A.D.on the northern side.Notably,the period 1701～1730 A.D.was a coincidental drought period for both sides.The extreme drought in Northwestern China during the 1920s～1930s is consistently reflected in the northern chronologies,but discrepancies are observed in the southern chronologies.While initial observations suggest a potential influence of El Nino events on regional extreme droughts,further research is needed to fully understand the response mechanisms of regional drought to ENSO and NAO.
the Qilian Mountainstree-ring width indexextreme drought eventsatmospheric circulation index
NETL
NSTL
万方数据
