Assessment of Surface Energy Balance in Southern Idaho

Proper management of water resources is always a matter of concern in arid regions like southern Idaho such as the Snake River basin where rainfall is limited and the moisture level of atmospheric air is below threshold level most of the time throughout a year. For the proper assessment of water resources it is necessary to quantify the Evapotranspiration (ET) loss in this region and use the available water resources efficiently. A vast quantity of water is moving in the atmosphere under the direct influence of solar energy. So, in order to characterize the behavior of the water cycle, it is important to understand the energy balance of the Snake River basin. ET is an important phenomenon in the water cycle for the estimation and evaluation of the available water resources. If we understand how ET is changing over space and time, then we can more accurately calculate the crop water requirement (CWR) at a high resolution for that region. This study can help water managers and farmers in manage water resources very efficiently. Current research has difficulty projecting how ET is going to change over different locations in the future. Therefore, through this research we are trying to understand the partition of the energy balance components and quantify them to help the water management in southern Idaho. To support this research, we will use the data from both Land Surface Hydrology Model and field observations and present the trends in surface energy balance components. Introduction The driving input in the surface energy balance is the net radiation. The net radiation is partitioned into different components at the earth’s surface. The three major components of net radiation are; latent heat flux, sensible heat flux and ground heat flux. The largest fraction of the net radiation available at the earth’s surface is used to evaporate water from the surface back to the atmosphere. This fraction of net radiation is called latent heat flux (λE). Unlike precipitation (x-mm of rain), rate of evaporation is commonly measured in terms of energy flow leaving the evaporating surface in the form of latent heat of vaporization (Shuttleworth, 2012). A second fraction of net radiation that carries the heat back and forth to the atmosphere from the surface is sensible heat flux. This fraction of net radiation is used by the atmosphere for the direct warming or cooling the atmospheric air. The third component of the energy balance is ground heat flux that conducts through the soil when the net radiation is positive and radiates out of the soil when the net radiation is negative (Gentine, 2012; Shuttleworth, 2012). Although every component of net radiation impacts the hydrological cycle, this study focuses on the quantification of latent heat flux and employs it to understand the anomalies of evapotranspiration (ET). ET is an important process for the water exchange between the land surface and the atmosphere. ET plays an important role in the hydrological cycle, so it is essential to estimate ET accurately for the evaluation and management of available water resources. The difference between precipitation and evapotranspiration is the water available for use by animals and nature. Thus the quantitative assessment of ET is essential to maintain a balance between the available water and its consumption. Global warming and natural changes in climate can highly affect the ET process, so it is necessary to understand the interaction between the hydrological cycle and atmospheric parameters (Dingman, 2002; Brown). The hydrological cycle is a complex process that involves a direct interaction between the atmospheric parameters and surface parameters. It is not yet understood how a reliable prediction can be made in this field (Devonec et al., 2002). One of the approaches researchers use to understand the hydrological behavior is the energy balance approach (Heerwaarden et al., 2010). According to the first law of thermodynamics, for the energy balance closure the sum of latent heat flux (λE), ground heat flux (G), sensible heat flux (S), and other losses (storage) must be equivalent to net radiation (Rn) at the surface (Wilson et al., 2002). Assuming the change in energy storage is zero, the energy balance equation can