Abstract
Soil moisture is an important parameter in land surface processes, which can control the surface energy and water budgets and thus affect the air temperature. Studying the coupling between soil moisture and air temperature is of vital importance for forecasting climate change. This study evaluates this coupling over China from 1980–2013 by using an energy-based diagnostic method, which represents the momentum, heat, and water conservation equations in the atmosphere, while the contributions of soil moisture are treated as external forcing. The results showed that the soil moisture–temperature coupling is strongest in the transitional climate zones between wet and dry climates, which here includes Northeast China and part of the Tibetan Plateau from a viewpoint of annual average. Furthermore, the soil moisture–temperature coupling was found to be stronger in spring than in the other seasons over China, and over different typical climatic zones, it also varied greatly in different seasons. We conducted two case studies (the heatwaves of 2013 in Southeast China and 2009 in North China) to understand the impact of soil moisture–temperature coupling during heatwaves. The results indicated that over areas with soil moisture deficit and temperature anomalies, the coupling strength intensified. This suggests that soil moisture deficits could lead to enhanced heat anomalies, and thus, result in enhanced soil moisture coupling with temperature. This demonstrates the importance of soil moisture and the need to thoroughly study it and its role within the land–atmosphere interaction and the climate on the whole.
Highlights
The summer of 2013 was unprecedentedly hot in Eastern China, causing substantial societal and economic impacts [1]
The coupling strength appears to be highest in Northeast China and part of the Tibetan Plateau, where the climate is neither too wet nor too dry, showing that soil moisture has the strongest impact on temperature over the annual average in these regions
The results are consistent with previous studies which have suggested that such hot spots of soil moisture–temperature coupling occur most in transitional regions between wet and dry climate [9,39,40]
Summary
The summer of 2013 was unprecedentedly hot in Eastern China, causing substantial societal and economic impacts [1] Such a phenomenon has drawn widespread concerns, and the physical mechanism behind such heatwave is gradually being discovered [2,3,4]. Based on the energy balance, the decline of latent heat flux causes an increase of the sensible heat flux, enhancing the air temperature. These conditions indicate a negative feedback between soil moisture and air temperature: Soil moisture deficit results in the rise of air temperature [11,12,13]
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