A new perspective of urban-rural differences: The impact of soil water advection

Urban-rural contrast is central to many urban environmental problems, a prominent example being the urban heat island effect. To ameliorate urban thermal stress, extensive research work has been focused on the mitigation of critical environmental temperatures, while the timing of excessive heating was largely overlooked. Advection of soil water flux plays a critical role in determining the soil thermal field, which in turn modulates surface energy fluxes and land-atmosphere interactions. In this paper, we formulate the wave phase differences between soil temperatures and soil heat fluxes due to soil water advection based on harmonic function method. It has been found that phase lags, viz. hysteresis effects, exist among all land surface energy budgets and the land surface temperature. More generally, the difference of phase and time evolution of the land surface temperature and the ground heat flux is also manifested in annual cycles. In the context of urban-rural differences, the temporal difference in peak surface temperatures and peak turbulent fluxes has profound implication to human thermal comfort and building energy efficiency. (C) 2014 Elsevier B.V. All rights reserved.