Maximum and Minimum Soil Surface Temperature Trends Over China, 1965-2014

Minimum and maximum soil surface temperatures have shown significant warming trends since the midtwentieth century in China, with minimum temperatures rising at a faster pace than maximums, resulting in a decrease in the soil surface diurnal temperature range. Similar to air temperature, these changes demonstrate spatial coherence, with regions at higher latitudes experiencing relatively more change. While increases in air temperatures in China slowed after 1998, paralleling the global "warming hiatus," soil temperatures at the surface and in shallow layers have continued to rise across China. The increases in soil surface temperatures are fastest at night since 1998, reducing the soil surface diurnal temperature range. Thus, we find that while the decrease in the diurnal air temperature range mainly happened during the earlier "dimming" period ending around 1988, the decrease in the diurnal soil surface temperature range is detectable only during the renewed dimming period after 1998. This has caused soil temperatures at the surface and in shallow layers to diverge from air temperatures since 1998. Although changes in soil temperatures were associated with changes in air temperature, the patterns of change are different. Calculations using only nonurban stations show similar warming rates, indicating that the effects of urbanization are small.