Soil temperature change on the Tibetan Plateau

Abstract:

Increased radiative forcing has resulted in the global warming that includes the warming in air and soil over the past decades. The warming at the Earth’s surface propagates or conducts downward into the ground and modifies the ambient ground thermal regime. In addition to the surface radiation that directly heats the soil, the other soil heat fluxes associated with atmospheric circulations of various scales are important mechanisms as well. The quantification of the causal relationships between the radiation, large scale atmospheric circulations and soil temperature change in the upper few meters on the Tibetan Plateau (TP) is the objective of this study.

Daily soil temperature data during 1980-2013 at various depths from surface down to 3.2 m depth at 88 stations located on the TP obtained from China Meteorological Administration are used to investigate the changes in soil temperature. After the quality control, the Mann-Kendall trend, EOF and regression analyses are applied to analyze the soil temperature and radiation data. The Mann-Kendall test shows that soil temperature at layers above 3.2-m-depth increases from 1980 to 2013 at most stations on the TP, although the warming rate varies among stations. Time series of the EOF analysis shows that a hiatus in the soil temperature warming has occurred since 2004 on the TP, which is several years behind the hiatus of the global warming but is similar to the air temperature change on the TP. Besides, we do not find a clear phase delay from the surface to the 3.2m level. Net surface solar radiation, long wave radiation that partly reflects the greenhouse gases forcing, latent and sensible heat fluxes are examined to understand the underlying mechanisms for the distinct warming of the soil on the TP. Contributions of the atmospheric circulation changes, induced by either internal variability or external forcing or both of the two factors, are also examined. The above analysis results will be presented at the conference.