Observational evidence of summer precipitation deficit-temperature coupling in China

Partition of the energy between sensible heat and latent heat indicates that surface temperatures are affected by soil moisture deficits. Since transpiration by plants is the largest contributor to the land's total latent heat, the coupling of temperature and soil moisture will depend on the response of vegetation to soil moisture deficit and those are influenced by the soil moisture regimes. Utilizing daily precipitation and temperature data from China for a period of 1961-2010, this study computes average annual climatic water balance (AACWB) for defining soil moisture regimes and then quantitatively investigates the summer soil moisture-temperature coupling. With precipitation deficits (indicated by standardized precipitation index with the selected optimal timescale of 3 months) as proxy of soil moisture deficits, results indicate that the relationship between summer precipitation deficits and hot extremes tends to be enhanced when the negative AACWB draws closer toward zero while tends to be weakened with the increase of positive AACWB. For the region with the negative AACWB closing zero, the enhanced relationship should be attributed to the increase of the proportion of latent heat compared to the absorbed total energy. However, the weakened relationship with the increase of positive AACWB may be owing to the different responses of vegetation to precipitation deficit that the transpiration in the region with lower positive AACWB is less when responding to precipitation deficit. However, the physiological mechanisms behind vegetation response to soil moisture deficits still need to be further analyzed. By quantifying relevant biological and hydrological processes and their interaction, it is expected that the uncertainties in future climate scenarios be reduced, which would then allow the development of early warning and adaptation measures prior to the occurrence of hot extremes. Further, the summer precipitation deficit-temperature coupling is strongest along the strip stretching from southwest to northeast in China.