Growing season relative humidity variations and possible impacts on Hulunbuir grassland

A relative humidity series of April-August during 1825-2009 AD was reconstructed based on tree-ring width of Pinus sylvestris var. mongolica for the Hulunbuir area. During the past 185 years, 25 humid years and 26 arid years were identified in the reconstruction, as well as 6 wet periods and 6 dry periods. The relative humidity has decreased since approximately the 1950s, suggesting a warm and dry climate trend in the study area. The reconstruction can be compared with those of the surrounding tree ring reconstructed precipitation and relative humidity series at the decadal scale, reflecting the consistency of the regional climate variations. Besides, significant positive correlations are revealed between the reconstruction and the normalized difference vegetation index of the Hulunbuir grassland. And the decrease in relative humidity will cause negative impacts on the Hulunbuir grassland. Comparisons between the sandstorm records and the relative humidity of the study area indicate that strong sandstorms occurred more frequently in Hulunbuir when the relative humidity was low. Therefore, under the downward trend in relative humidity, more effort should be made to protect the grassland ecology and treat the bare sand land for the local and surrounding areas.