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Harvard Forest Symposium Abstract 2015

• Title: A millennial context of the 21st Century Heat Drought in Mongolia
• Primary Author: Amy Hessl (West Virginia University)
• Additional Authors: Kevin Anchukaitis (Woods Hole Oceanographic Institution); Oyunsanaa Byambasuran (Not Specified); Caroline Leland (Columbia University in the City of New York); Neil Pederson (Harvard Forest)
• Abstract:

  Climate change is expected to have a significant impact on the ecosystems and cultures in semi-Arid Asia. Understanding the links between climate, ecosystems, and people requires robust records of climate history with high temporal resolution. Mongolia experienced a rapid transition away from pastoralism beginning in the late 1990s as many families lost their herds during a drought and severe winter conditions. Though the drivers of this transition were multi-factorial, market forces and overgrazing by herders are thought to be the primary agents of change. However, this change also coincided with a significant reduction in precipitation and rapid warming during the summer, the season where Mongolia typically receives >70% of its total annual precipitation. Using a 1100 year long tree-ring reconstruction of summer drought, derived from live and dead Siberian pine (Pinus sibirica) trees growing on a lava flow in central Mongolia (Fig 1), we ask: how extreme was the 21st century drought in the context of last 1100 years? Growing on dark lava with little soil development, these stunted trees are severely water-stressed. We find that radial growth is correlated with both soil water availability (scPDSI) and grassland productivity (Normalized Difference Vegetation Index (NDVI)). Our reconstruction, calibrated and validated on instrumental June-Sep scPDSI, account for 56% of the annual variability between 1959 and 2009 (Pederson, Hessl et al., 2014). Our examination of tree-ring and meteorological data suggests that the early 21st century drought was the hottest of the last 1100 years. These results are consistent with model projections of warming in semi-arid Asia where rising temperatures will contribute to increased water stress, independent of the forecast increase in rainfall. Future warming is expected to lead to “heat droughts” similar or worse than that of the early 21st Century. These changes are expected to have severe environmental and social consequences for modern Mongolia. We are currently building records that will be 2000 years in length or more (Fig 1). These data will enable understanding of the relative importance of climate versus land management in catalyzing social change by examining multiple empires and help prepare societies for the full range of future climatic extremes.
  
  
  
  Reference:
  
  Pederson N, Hessl AE, Baatarbileg N, Anchukaitis KJ, Di Cosmo N (2014) Pluvials, droughts, the Mongol Empire, and modern Mongolia. Proceedings of the National Academy of Sciences, 111, 4375-4379.
  
  

• Research Category: Historical and Retrospective Studies
  International Research Projects
  Regional Studies


• Figures:
HesslPedersonEtAlMongolDroughtHistoryHFsymposium2015pix.pdf