### 2.12.6.4. Soil Hydrology[¶](#soil-hydrology "Permalink to this headline")

The combined water and ice soil volume fraction in a soil layer \\(\\theta \_{i}\\) is given by

(2.12.67)[¶](#equation-12-62 "Permalink to this equation")\\\[\\theta \_{i} =\\frac{1}{\\Delta z\_{i} } \\left(\\frac{w\_{ice,i} }{\\rho \_{ice} } +\\frac{w\_{liq,i} }{\\rho \_{liq} } \\right) .\\\]

If \\(\\theta \_{i} <\\theta \_{sat,i}\\), the pore volume fraction at saturation (as may occur when ice melts), then the liquid water mass is adjusted to

(2.12.68)[¶](#equation-12-63 "Permalink to this equation")\\\[w\_{liq,i} =\\left(\\theta \_{sat,i} \\Delta z\_{i} -\\frac{w\_{ice,i} }{\\rho \_{ice} } \\right)\\rho \_{liq} .\\\]

Otherwise, if excess ice is melting and \\(w\_{liq,i} >\\theta \_{sat,i} \\rho \_{liq} \\Delta z\_{i}\\), then the water in the layer is reset to

(2.12.69)[¶](#equation-12-64 "Permalink to this equation")\\\[w\_{liq,i} = \\theta \_{sat,i} \\rho \_{liq} \\Delta z\_{i}\\\]

This allows excess ice to be initialized (and begin to be lost only after the pore ice is melted, which is realistic if the excess ice is found in heterogeneous chunks) but irreversibly lost when melt occurs.

