Abstract
Droughts are a recurrent phenomenon in the semiarid forest-steppe ecotone of Mongolia with negative consequences for tree growth and agricultural management. In order to better cope with the uncertainty of a changing climate, the study of historical drought and its effects on forests could provide useful insights into ecosystem responses to climate variability. Siberian larch (Larix sibirica) is a dominant tree species in Western Mongolia that provides a valuable source of proxy data in the form of annual rings. We used dendrochronological techniques to establish a standard master chronology and analyze the relationship between annual ring widths and climatic factors. Correlation analyses revealed that the strongest associations of tree-ring index (TRI) values for the master chronology to direct climate variables were June temperature (r = −0.36, p < 0.01) and precipitation (r = 0.39, p < 0.01). The master chronology was strongly correlated to Palmer Drought Severity Index (PDSI) for June (r = 0.606, p < 0.001), and this variable (PDSIJun) was chosen for reconstruction. A simple linear regression of PDSIJun based on TRI explained 35.4% of the total variance for the period 1965–2016 and based on this model the PDSIJun changes from 1731–2016 were reconstructed. Split–sample calibration–verification tests were conducted to evaluate the quality of the model used for climate reconstruction. In the past 286 years, the number of non-drought years (PDSI > 0) was low, with a frequency of only 14.1% of the total reconstruction years. Extreme drought (PDSIJun < −2.70) occurred frequently in the 19th and early and late 20th centuries. Multi-taper method (MTM) spectra and wavelet analysis showed that the reconstructed PDSI series had high and low frequency periods (2.4–3.3 and 85–92 years). Our findings provide an understanding of the drought history of the semiarid forest-steppe ecotone of western Mongolia.
Highlights
Global warming and an increase in the frequency of extreme weather events has prompted an emerging research emphasis on drought [1]
Palmer (1965) proposed an index to indicate the severity of drought (PDSI) [8], which provides an integrated measure of soil moisture conditions by considering precipitation, temperature and evaporation of soil water [9]
(0.21), mean sensitivity (0.52) and AC1 (0.67), indicated the chronology would be useful for climate reconstruction
Summary
Global warming and an increase in the frequency of extreme weather events has prompted an emerging research emphasis on drought [1]. Droughts occur in most parts of the world, and depending on their frequency and intensity, can strongly affect the water balance of ecosystems, inland Asia and Mediterranean basin [4] in arid and semiarid regions [5]. The severity of drought is driven by potential evapotranspiration, which is an indicator of moisture demand [7]. Palmer (1965) proposed an index to indicate the severity of drought (PDSI) [8], which provides an integrated measure of soil moisture conditions by considering precipitation, temperature and evaporation of soil water [9]. Potential evapotranspiration is a clear indicator of moisture demand and an important factor in determining the severity of drought [10]. The PDSI is the most effective index for monitoring the regional drought and moisture conditions [11] and has been applied widely in studies from different regions around the world [12,13]
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