The Influence of Rain Sensible Heat and Subsurface Energy Transport on the Energy Balance at the Land Surface

Abstract

A : CLM, Common Land Model; LSM, land surface model. S S : C S -S MIn land surface models, which account for the energy balance at the land surface, subsurface heat transport is an important component that reciprocally infl uences ground, sensible, and latent heat fl uxes and net radia on. In most models, subsurface heat transport parameteriza ons are commonly simplifi ed for computa onal effi ciency. A simplifi ca on made in all models is to disregard the sensible heat of rain, H l , and convec ve subsurface heat fl ow, q cv , i.e., the convec ve transport of heat through moisture redistribu on. These simplifi ca ons act to decouple heat transport from moisture transport at the land surface and in the subsurface, which is not realis c. The infl uence of H l and q cv on the energy balance was studied using a coupled model that integrates a subsurface moisture and energy transport model with a land surface model of the land surface energy balance, showing that all components of the land surface energy balance depend on H l . The strength of the dependence is related to the rainfall rate and the temperature diff erence between the rain water and the soil surface. The rain water temperature is a parameter rarely measured in the fi eld that introduces uncertainty in the calcula ons and was approximated using the either air or wet bulb temperatures in diff erent simula ons. In addi on, it was shown that the lower boundary condi on for closing the problem of subsurface heat transport, including convec on, has strong implica ons on the energy balance under dynamic equilibrium condi ons. Comparison with measured data from the Meteosta on Haarweg, Wageningen, the Netherlands, shows good agreement and further underscores the importance of a more ghtly coupled subsurface hydrology-energy balance formula on in land surface models.

The improvement of soil thermodynamics and its effects on land surface meteorology in the IPSL climate model

“…where G 1 is the soil heat flux due to heat conduction process; H 1 is the sensible heat flux of rainfall due to the difference of temperature between the rainwater and the soil surface (Kollet et al, 2009); T rain and T S are the temperature of the rainfall and the soil surface, respectively (K); q L,0 is the infiltrated water flux (m s −1 ); F rad , F h 1 , and LF q 1 are the net radiation, sensible heat and latent heat flux respectively (W m −2 ); C S is the "layer" heat capacity per unit area (J m −2 K −1 ) and is related to the thickness of the first soil layer. T rain is estimated by wet bulb temperature (Gosnell et al, 1995).…”

“…Several studies investigated the influence of this process on the land-surface variables based on 1-D (onedimensional) experiments based on site observations (e.g. Kollet et al, 2009). However, to our knowledge, the impact of the heat convection has never been evaluated on the global scale.…”

Infiltration in Arid Environments: Spatial Patterns between Subsurface Heterogeneity and Water‐Energy Balances

“…The coupled model, PF.CLM directly simulates the terrestrial components of the hydrologic cycle under transient conditions, including the diurnal cycle, seasonal trends, and a rapid response to meteorological conditions. Complete details of the equations and coupling between ParFlow and CLM have been discussed previously (Kollet et al, 2009) and are not repeated here for brevity; however, some details of the vegetation processes in CLM that are pertinent to the current study are provided here. The CLM model calculates a complete canopy water and energy balance and represents plant transpiration using a photosynthesis‐based approach.…”

“…Recent modeling studies have demonstrated spatial and temporal variability in land–atmosphere water and energy fluxes for different levels of model integration (fully or loosely coupled), scale (local to regional), and subsurface complexity (heterogeneous or homogeneous). These studies include fine‐scale simulations of uncorrelated heterogeneous systems with shallow water tables (Zhu and Mohanty, 2003; Mohanty and Zhu, 2007; Kollet et al, 2009), as well as fully coupled homogeneous simulations (Maxwell et al, 2007; Kollet and Maxwell, 2008; Maxwell and Kollet, 2008; Kollet et al, 2009). Those studies that included explicit descriptions of heterogeneity, including both simplified, steady‐state simulations (Zhu and Mohanty, 2003; Mohanty and Zhu, 2007) and integrated, fully coupled simulations (Kollet, 2009), demonstrated interdependence between heterogeneity and shallow soil moisture and thus evapotranspiration.…”

Insights on geologic and vegetative controls over hydrologic behavior of a large complex basin – Global Sensitivity Analysis of an integrated parallel hydrologic model

“…The coupled land surface energy and water balance is simulated by a modified version of the CLM which requires hourly atmospheric variables such as precipitation, air temperature, pressure, wind speed, specific humidity, and solar radiation, along with soil moisture estimates (which are provided by ParFlow) to simulate near land surface-atmospheric fluxes such as ET loss (Kollet and Maxwell, 2008a). Details of equations used in CLM to simulate all the water and energy fluxes are provided elsewhere (Dai et al, 2003;Kollet et al, 2009;Maxwell and Miller, 2005). Equations relevant to the work presented here are summarized below.…”