Abstract
Soil heat flux is an inseparable component of the surface energy balance. Accurate estimation of regional soil heat flux is valuable to studies of meteorology and hydrology. Conventional measurement of using soil heat flux plates at the site scale is impractical to estimate large-scale flux. Other approaches generally require soil temperature to be measured in at least two soil layers, which is also difficult to implement at the regional scale. In the last decade, single-layer based approaches were developed to fulfill the regional requirement. This study used a simple but more general approach for estimating soil heat flux solely with surface temperature. The generalized approach can be conditionally linked to two existing single-layer based approaches but has fewer restrictions or assumptions. Error analysis revealed that measurement error in surface temperature would have limited effects on soil heat flux estimated from the new approach. Model simulations showed that soil heat flux estimated from the approach agreed with those simulated from the heat transfer equation. Furthermore, case examinations at two sites with contrasting climate regimes demonstrated that the generalized approach had better performance than the existing single-layer approaches. It achieved the highest correlation of determination and the lowest mean, standard deviation, and root mean squared error of the differences between the estimates and the field measures at either site. The generalized approach can estimate soil heat flux at a depth but it requires only surface temperature data as input, which is an advantage to remote sensing applications.
Highlights
In daytime, solar radiation warms the land surface
Results demonstrated that surface soil heat fluxes estimated from Equation (11) agreed well with that simulated from the heat transfer model (Figure 1(a))
The approach can estimate soil heat flux at any depth but it requires only surface temperature data as input, which appears to be an advantage to remote sensing applications
Summary
Solar radiation warms the land surface. Except for evaporation loss and turbulent heat exchange with air, a part of this heat is transferred into the soil. Horton and Wierenga [5] described an approach to determine soil heat flux at different depth only from the upper boundary temperature, based on Van Wijk’s Fourier series [16] This approach can be used to estimate soil heat flux at regional scale [17]. Wang and Bras [18] used a half-order derivative solution of the heat flow equation and proposed a method to estimate soil heat flux using time series data of soil temperature at the corresponding depth. It performed well in estimating ground or soil heat flux [18,19,20,21,22]. The strength and weakness of each approach were discussed for their possible application to large-scale monitoring of soil heat flux
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