Turning the clock 360 years back to reveal climate trends in southwest China
“One of the world’s largest biodiversity hotspots is to be found in the Hengduan Mountains located in southwest China. More recently, the region has been suffering the devastating effects of climate change, with increased episodes of drought registered over the last decade,” remarked Dr. Yang of the Chinese Academy of Sciences. “The most extreme drought experienced in 2009-2010 affected about 16 million people and 11 million livestock in Yunnan province. Farmlands were not spared either with about four million hectares left destroyed.”
According to Dr. Aster Gebrekirstos, a scientist at the World Agroforestry Centre, “Dendrochronology, the examination of tree growth rings as a method for scientific dating, offers a means to understanding the tendency of climate changes over time. It is useful to understand the effect of climate variations on tree growth and to assess its responses in centuries. Formation of tree rings may be distinct or less prominent depending on climate seasonality and species.”
By measuring tree ring widths of the Picea likiangensis tree from Jade Dragon Snow Mountain, southwest China, Gebrekirstos and colleagues were able to develop a chronology for the area dating 361 years that captured spring climate variation over centuries, decades and years. They found that the Jade Dragon Snow Mountain has experienced considerable variations in spring drought conditions. Four distinct periods were recognized: (1) 1650–1730 with a relatively humid period; (2) 1730–1860 with greatly fluctuating periods of dryness and intermittent wet periods (1746–1755, 1782–1800, and 1820–1830) and several dry periods (1735–1745, 1756–1780, 1810–1820, and 1830–1860); (3) 1870–1945, a humid period, with the wettest period during 1930–1945; and (4) 1945–2011, a period with decreasing humidity.
“The results are consistent with hydrological studies in nearby regions and related species, as well as historical records of natural disasters,” remarked Ms. Bi of the Chinese Academy of Sciences.
“The recently observed spring drought confirms a trend of decreasing humidity over the past 60 years. The Hengduan Mountains region, in southwest China, is experiencing fast socio-economic transformation, with population growth, intensified farming activity, over-exploitation of water resources, improper forest management, mass tourism and an expanding road network. This has led to ecological alternation over the years resulting in natural hazards such as the more frequent droughts particularly during spring. This suggests that a sound strategy for management and land-use planning is required to secure ecosystem and human well-being,” added Prof. Xu, coordinator for the World Agroforestry Centre in east and central Asia and Professor at Kunming Institute of Botany at the Chinese Academy of Sciences.
This study also sought to evaluate whether large-scale climatic drivers such as El Niño Southern Oscillation (ENSO), Atlantic Multi-decadal Oscillation (AMO), and synoptic anomalies influence tree growth through their effects on local climate. The study suggests that tree growth seems to benefit from an El Niño year and is restrained by a La Niña year.
The study further assesses regional climate trends in line with past studies; the 1930s–1950s were the longest, wettest and most humid period of the past 361 years. Similar results were discovered in northern Vietnam, Thailand, western India, suggesting that this wet period of about 20 years influenced a large area of southeast Asia. Additionally, the period from the 1750s to 1770s overlapped with the so-called ‘Strange Parallels’ (1756–1768), a serious drought across all Asian monsoon areas indicating that a dry climate prevailed over a large area of southeast Asia at that time. On the other hand, northern Vietnam experienced a dry spell from the 1830s to the mid-1860s.
The study by Gebrekirstos and colleagues however found that it was not as serious, indicating that the Jade Snow Mountain area was drier than northern Vietnam. This difference could be attributed to mountainous topography, which can dramatically modify the intensity of the monsoon systems.
In conclusion, recent drought events in southwest China were magnified by agricultural and socioeconomic stresses. The Hengduan Mountains are sensitive to climate change and are being impacted by increased water demand, intensified landscape fragmentation and spatial isolation of species. More attention ought to be paid to a sound ecosystem management approach, including reasonable land-use planning and a regulated urbanization process.
Download the full paper here here. Bi, Y., Xu, J., Gebrekirstos, A., Liang, G., Zhao, M., Liang, E., and Yang, X. Assessing drought variability since 1650AD from tree-rings on the Jade Dragon Snow Mountain, southwest China. International Journal of Climatology 2015.