Observational variations in the seasonal freezing depth across China during 1965-2013

Abstract

Long-term changes in the soil freezing-thawing depth are an important indicator of climate change. Based on data from 764 meteorological stations across China, we analysed the climatology and variability in the seasonal freezing depth (SFD) during 1965-2013 and investigated the connections among changes in the SFD, meteorological factors (temperature, precipitation, snow depth, freezing index and thawing index) and atmospheric circulations (East Asian winter monsoon [EAWM] and North Atlantic Oscillation [NAO]) in each of 4 sub-regions: northwestern China (W), the Tibetan Plateau (TP) and eastern China (E1 and E2). In addition, the contributions of 2 different factors to variation in the SFD were quantified. The results revealed that during 1965-2013, the SFD noticeably changed from positive to negative anomalies in approximately 1988 for all of the studied regions, exhibiting a significant decreasing trend at rates (mean ± SE) of 0.23 ± 0.03, 0.08 ± 0.01, 0.26 ± 0.03 and 0.24 ± 0.03 cm yr-1 in E1, E2, W and TP, respectively. The air freezing index was strongly correlated with the SFD in the E2 and TP regions, and accounted for 82.6 and 84.9% of the change in SFD, respectively. Snow depth showed a significant association with the variability in SFD only in the E1 region. Compared to the NAO, the EAWM plays an important role in changes in SFD. These findings have implications for further understanding the mechanisms of cold environment changes across China.