Simultaneous Heat And Water Research Articles

Impacts of spatially and temporally varying snowmelt on subsurface flow in a mountainous watershed: 1. Snowmelt simulation

Abstract The dominant source of streamflow in many mountainous watersheds is snowmelt recharge through shallow groundwater systems. The hydrological response of these watersheds is controlled by basin structure and spatially distributed snowmelt. The purpose of this series of two papers is to simulate spatially varying snowmelt and groundwater response in a small mountainous watershed. This paper examines the spatially and temporally variable snowmelt to be used as input to the groundwater flow modelling described in the second paper. Snowmelt simulation by the Simultaneous Heat and Water (SHAW) model (a detailed process model of the interrelated heat, water and solute movement through vegetative cover, snow, residue and soil) was validated by applying the model to two years of data at three sites ranging from shallow transient snow cover on a west-facing slope to a deep snow drift on a north-facing slope. The simulated energy balances for several melt periods are presented. Snow depth, density, and the m...

Modeling plant canopy effects on variability of soil temperature and water

Vegetative cover affects the spatial and temporal variability of heat and water in the soil. The ability to predict temperature and water conditions enhances our ability to evaluate management options for soil and water conservation, plant establishment and pest control. The simultaneous heat and water (SHAW) model is a detailed process model of heat and water movement in a snow-residue-soil system. This paper describes provisions added to the SHAW model for vegetative cover and simulation of heat and water transfer through the soil-plant-air continuum. The model was applied without calibration to one full year of data on semiarid sagebrush rangeland to simulate vegetation effects on the spatial and temporal variability of soil temperature and water. The model currently has no provisions for plant growth or annual variation in leaf area index, resulting in insufficient shading of the soil surface during summer months. Nevertheless, the model accounted for over 96% of the variation in near-surface soil temperature for sagebrush-covered areas and over 91% of the variation for bare soil surfaces. Simulated water potential and total water use also agreed well with measured values.

SENSITIVITY OF SOIL FREEZING SIMULATED BY THE SHAW MODEL

ABSTRACT Sensitivity analyses conducted on hydrologic models are useful for understanding the complicated interactions of hydrologic processes and for demonstrating the potential errors resulting from incorrect estimation of input parameters. The effects of typical changes (measurement errors or natural variability) in input parameters on soil freezing as simulated by the Simultaneous Heat and Water (SHAW) model were investigated. The SHAW model simulates the interrelated heat and water transfer within snow, residue, and soil using estimated or measured weather data. Simulated frost depth was found to be very sensitive to small changes in air temperature (1° C) and initial snow depth (10 cm). Simulated frost depth was also potentially sensitive to the specified soil temperature for the lower boundary depending on the proximity of frost depth to the depth of the simulated profile. Site, residue soil characteristics having the greatest impact on simulated frost were slope, thickness of the residue layer, thermal conductivity of soil particles, soil bulk density, and a surface roughness parameter. Soil hydraulic parameters had little effect on frost depth, but had a large impact on water movement toward the zone of freezing and ice content of the frozen soil.

Simultaneous Heat and Water Model of a Freezing Snow-Residue-Soil System II. Field Verification

ABSTRACT Frozen soil has a major effect in many hydrologic and erosion situations, but it is very difficult to predict, especially on tilled agricultural soils with crop residue and intermittent show cover. A Simultaneous Heat And Water (SHAW) model to provide this predictability by simulating the interrelated heat, water and solute transfer through snow, crop residue and soil was presented in a companion paper (Part I). Detailed climatic, soil temperature, water content and frost depth data were collected for six diverse tillage-residue conditions during two winters to verify the model predictions. When compared to measured values, simulated soil temperatures were excellent, simulated frost depths were quite good, and simulated soil water profiles were good. Minimal calibration was necessary because the model uses fundamental equations for heat and water transfer with readily definable site parameters.

Modeling Soil Freezing and Thawing on a Rangeland Watershed

ABSTRACT Soil frost can significantly reduce the infiltration capacity of soil, which may result in severe flooding and erosion. Snow cover, precipitation, and frozen soil vary with elevation particularly in mountainous rangelands, and consequently only portions of a watershed typically contribute to runoff. The objective of this research was to extend the applicability of the Simultaneous Heat and Water (SHAW) model to frozen soil prediction on rangeland. The SHAW model simulates heat, water, and solute transfer through a one-dimensional snow-residue-soil system using hourly weather observations. Simulations were conducted for a low, middle, and high elevation site on the Reynolds Creek Experimental Watershed in southwestern Idaho. Simulated frost depths, snow depths, and soil temperatures compared well with measured values at the three sites. For the first year, soil frost was deepest (72 cm measured; 75 cm simulated) at the lower elevation site where snow cover was minimal. The model correctly predicted little or no frost penetration at the upper elevation sites for the same year. Maximum simulated frost depths for the second year were 58 cm, 43 cm, and 31 cm at the low, middle, and high elevation site compared to measured values of 58 cm, 50 cm, and 34 cm, respectively. These results support the use of the SHAW model for simulating soil frost on rangelands.