Submitted to: Hydrology and Earth System Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2012
Publication Date: 7/3/2012
Citation: Alkhaier, F., Z. Su, and G.N. Flerchinger. 2012. Shallow groundwater effect on land surface temperature and surface energy balance under bare soil conditions: modeling and description. Hydrologic and Earth System Sciences. 16:1817-1831. Interpretive Summary: Understanding how groundwater affects surface temperature and energy transfer is important for utilizing remote sensing to locate the existence shallow groundwater and to incorporate the influence of shallow groundwater on land surface models for improved climate research, weather forecasting and water management studies. Using computer modeling, we demonstrated the influence of shallow groundwater on surface temperature and surface energy fluxes, and highlighted the conditions under which remote sensing can best be used to for shallow groundwater detection. The practical utilization of remote sensing data in delineating shallow groundwater effect on land surface temperature and surface energy balance is illustrated in a companion paper.
Technical Abstract: Appreciating when and how groundwater affects surface temperature and energy fluxes is important for utilizing remote sensing in groundwater studies and for integrating aquifers within land surface models. To explore the shallow groundwater effect, we numerically exposed two soil profiles – one having shallow groundwater – to the same meteorological forcing, and inspected their different responses regarding surface soil moisture, temperature and energy balance. We found that the two profiles differed in the absorbed and emitted amounts of energy, in portioning out the available energy and in heat fluency within the soil. We conclude that shallow groundwater areas reflect less shortwave radiation due to their lower albedo and therefore they get higher magnitude of net radiation. When potential evaporation demand is high enough, a large portion of the energy received by these areas is spent on evaporation. This makes the latent heat flux predominant, and leaves less energy to heat the soil. Consequently, this induces lower magnitudes of both sensible and ground heat fluxes. The higher soil thermal conductivity in shallow groundwater areas facilitates heat transfer between the top soil and the subsurface, i.e. soil subsurface is more thermally connected to the atmosphere. In view of remote sensors’ capability of detecting shallow groundwater effect, we conclude that this effect can be sufficiently clear to be sensed if at least one of two conditions is met: high potential evaporation and big contrast in air temperature between day and night. Under these conditions, most day and night hours are suitable for shallow groundwater depth detection.