Immer wieder haben Dürren in China große Schäden angerichtet und Hungersnöte ausgelöst. Mehrere Arbeiten haben jetzt die historische Dürregeschichte Chinas aufgearbeitet und Hinweise auf die Auslöser gegeben. Im November 2013 erschien im Fachmagazin Climate of the Past Discussions eine neue Arbeit von Cai et al., in der anhand von Baumringen die Dürreentwicklung der vergangenen 300 Jahre für das zentralchinesische Lössplateau rekonstruiert wird. Die Forscher entdeckten einen steten Wechsel von Trocken- und Feuchtperioden. Das 19. Jahrhundert war dabei die trockenste Phase. Auf Basis einer Spektralanalyse der Zyklizität vermuten die Autoren, dass die Regenmengen durch das pazifische El Nino-Geschehen sowie Sonnenaktivitätsschwankungen kontrolliert werden. Im Folgenden die Kurzfassung der Arbeit:
We utilized tree-ring cores, collected from three sites at Lingkong Mountain located in the southeast part of the Chinese Loess Plateau (CLP), to develop a regional ring-width chronology. Significant positive correlations between the tree-ring index and the monthly Palmer drought severity index (PDSI) were identified, indicating that the radial growth of trees in this region was moisture-limited. The March–August mean PDSI was quantitatively reconstructed from 1703 to 2008 with an explained variance of 46.4%. Seven dry periods during 1719–1726, 1742–1748, 1771–1778, 1807–1818, 1832–1848, 1867–1932 and 1993–2008 and six wet periods during 1727–1741, 1751–1757, 1779–1787, 1797–1805, 1853–1864 and 1934–1957 were revealed in our reconstruction. Among them, 1867–1932 and 1934–1957 were identified as the longest dry and wet periods, respectively. On the centennial scale, the 19th century was recognized as the driest century. The drying tendency since 1960s was evident, however, recent drought was still within the frame of natural climate variability based on the 306 yr PDSI reconstruction. The warm and dry phases of Lingkong Mountain were in accordance with changes in the East Asian summer monsoon (EASM) strength, they also showed strong similarity to other tree-ring based moisture indexes in large areas in and around the CLP, indicating the moisture variability in the CLP was almost synchronous and closely related with EASM variation. Spatial correlation analysis suggested that this PDSI reconstruction could represent the moisture variations for most parts of the CLP, even larger area of northern China and east Mongolia. Multi-taper spectral analysis revealed significant cycles at the inter-annual (2.0–7.8 yr), inter-decadal (37.9 yr) and centennial (102 yr) scales, suggesting the influence of ENSO and solar activity on moisture conditions in the CLP. Results of this study are very helpful for us to improve the knowledge of past climate change in the CLP and enable us to prevent and manage future natural disasters.
Zur gleichen Zeit erschien im Magazin Climate of the Past Discussions auch eine Arbeit von Peng et al., in der mithilfe von Klimamodellen versucht wird, die Dürregeschichte Ostchinas nachzuvollziehen. Es zeigte sich, dass die Modelle Dürreperioden von mehr als einem Jahrzehnt sehr gut abbilden konnten. Als Hauptauslöser der Dürren identifizierten die Autoren Schwankungen der Sonnenaktivität. Im Folgenden die Kurzfassung der Arbeit:
We use proxy data and modeled data from 1000 yr model simulations with a variety of climate forcings to examine the occurrence of severe events of persistent drought over eastern China during the last millennium and to diagnose the mechanisms. Results show that the model was able to simulate many aspects of the low-frequency (periods greater than 10 yr) variations of precipitation over eastern China during the last millennium, including most of the severe persistent droughts such as those in the 1130s, 1200s, 1350s, 1430s, 1480s, and the late 1630s–mid-1640s. These six droughts are identified both in the proxy data and in the modeled data and are consistent with each other in terms of drought intensity, duration, and spatial coverage. Our analyses suggest that monsoon circulation can lock into a drought-prone mode that may last for years to decades and supports the suggestion that generally reduced monsoon in eastern Asia were associated with the land–sea thermal contrast. Study on the wavelet transform and spectral analysis reveals six well-captured events occurred all at the drought stages of statistically significant 15–35 yr timescale. A modeled data intercomparison suggests that solar activity is the primary driver in the occurrence of the 1130s, 1350s, 1480s, and late 1630s–mid-1640s droughts. Although the El-Niño–Southern Oscillation (ENSO) plays an important role in monsoon variability, a temporally consistent relationship between the droughts and SST pattern in the Pacific Ocean could not be found in the model. Our analyses also indicate that large volcanic eruptions play a role as an amplifier in the drought of 1635–1645 and caused the model to overestimate the decreasing trends in summer precipitation over eastern China during the mid-1830s and the mid-1960s.
Im Dezember 2011 veröffentlichte eine Forschergruppe um Yong Zhang von der Chinese Academy of Sciences in Peking eine Dürreanalyse der vergangenen 300 Jahre auf dem nordöstlichen Tibetplateau. Die Arbeit erschien im Fachjournal Climate Research. Auch hier fanden die Forscher einen steten Wechsel von Trocken- und Feuchtphasen. Die längste Dürrephase ereignete sich dabei Ende der 1920er bis Anfang der 1930er Jahre. Im Folgenden die Kurzfassung der Arbeit:
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