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Rutgers University (2010)

Reconstructed drought variability across Mongolia based on tree-ring records

Davi, Nicole K.

Titre : Reconstructed drought variability across Mongolia based on tree-ring records

Auteur : Davi, Nicole K.

Université de soutenance : Rutgers University

Grade : Doctor of Philosophy PhD 2010

Our understanding of climate in Mongolia is hindered by the extremely limited meteorological data in the region. Longer records, and insight into temporal drought patterns could aid greatly in anticipating extreme events and agrarian planning. Tree-ring reconstructions can provide longer, high-resolution records of climate variability in regions where recorded data are limited. In central Mongolia, streamflow for the Selenge River (1637-1997), the largest river in Mongolia, was reconstructed. Regression models resulted in a reconstruction of streamflow that explains 49 percent of the flow variation. The wettest 5-year period was 1764-1768 and the driest period was 1854-1858. The most extended wet period is 1794-1802 and an extended dry period is 1778-1783. Spectral analysis, a method for identifying periodicities within a time series, indicated significant variation in the frequencies common to Pacific Ocean variations (PDO and ENSO) and also some quasi-solar and lunar-nodal periodicities. In the far west, a grid cell of the Palmer Drought Severity Index (PDSI) was reconstructed (1565-2003) and explains 41 percent of the total variance in the instrumental PDSI. The reconstruction shows that starting in the 20th Century and continuing into the 21st Century there was a large-scale regional increase in growing-season moisture conditions compared to the prior centuries, a trend not seen in central or eastern Mongolian tree-ring reconstructions. Spectral analysis shows significant periodicities at approximately 22 (99% significance level), 11 (90%), 7 (99%), and 5 (99%) years. Also presented is a summer drought reconstruction for all of Mongolia, based on a network of 34 tree-ring chronologies that span the country. The PDSI model explains 61% of the variance over the most replicated period (1703-1993) and nested model methods were used to create the longest reconstruction possible (1520-1993). The reconstruction shows that droughts from 1999-2002, felt across central and eastern Mongolia, were extreme compared to the past 500 years. Significant periodicities are found at 40 (90%), 19.3 -25 (99%), 11.6 (95%), 6.4-7.2 (95%), and 2.8 years (99%). These high-resolution drought reconstructions supplement and extend the sparse meteorological data in Mongolia and allow for a long-term perspective of drought across Mongolia. As temperatures continue to rise in Mongolia, and much of the Northern hemisphere, drought may be an increasingly dire issue for human and environmental well being. Future predictions of drought and forecast capabilities are summarized, as are current climate risk management program.

Mots Clés : Geography, Climatic changes—Mongolia, Droughts—Mongolia


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