Decadal co-variability of the summer surface air teimperature and soil moisture in China under global warming

The self-calibrating Palmer Drought Severity Index (PDSI) is calculated using newly updated ground observations of monthly surface air temperature (SAT) and precipitation in China. The co-variabilities of PDS,I and SAT aro examined for summer for the period 1961-2004. The results show that there exist decadal climate co-variabilities and strong nonlinear interactions between SAT and soil moisture in many regions of China. Some of the co-variabilities can be linked to global warming. In summer, significant decadal co-variabilities from cool-wet to warm-dry conditions are found in the east region of Northwest China, North China, and Northeast China. An important finding is that in the west region of Norlthwest China and Southeast China, pronounced decadal co-variabilities take place from warm-dry to cool-wet conditions. Because significant warming was observed over most areas of the global land surface during the past 20-30 years, the shift to cool-wet conditions is a unique phenomenon which may deserve much scientific attention. The nonlinear interactions between SAT and soil moisture may partly account for the observed decadal co-variabilities. It is shown that anomalies of SAT will greatly affect the climatic co-variabilities, and changes of SAT may bring notable influence on the PDSI in China. These results provide observational evidence for increasing risks of decadal drought and wetness as anthropegenic global warming progresses.