Evaluation and analysis of observed soil temperature data over Northwest China

Abstract

Abstract Soil temperature (ST) is an important land surface factor as a predictor of regional climate change. Based on the ST data from 30 climate stations in Northwest China (NWC) during the period 1960–2000, the trends and distribution of STs at 0, 80, 160, and 320 cm depths were investigated, together with observed atmospheric variables, such as air temperature (AT) and precipitation. The differences between the annual average AT and ST at each layer (0, 80, 160, and 320 cm) in each station was no more than 6°C. In different seasons, the differences were even more remarkable than annual values. Trends in some stations varied during the period 1961–2000, with warming trends appearing at some stations after the mid-1980s. Few warming trends appeared in the west part of NWC, while most warming trends appeared in the east part. There were more warming trends at annual time scales than in season timescales. The fewest warming trends were found in winter, but they had the largest magnitude of increase (1.1°C/decade) for surface ST; the largest magnitudes of increase for 80 and 160 cm ST were in summer, with increase of 0.95 and 0.88°C/decade, respectively. The correlation coefficients between ST and AT were positive and statistically significant at the 95% confidence level in most stations except in winter. The correlation values between ST and precipitation were different at different time scales.