soil_moisture_index#

hydrometlib.cosmos.soil_moisture_index(cosmos_vwc, wilting_point, field_capacity, saturation)[source]#

Calculate soil moisture index (SMI) [unitless, 0-2]

SMI is a normalised measure of soil wetness relative to the wilting point, field capacity and saturation of the soil:

  • 0, when VWC is at or below the wilting point

  • between 0 and 1, when VWC is between the wilting point and field capacity

  • between 1 and 2, when VWC is between field capacity and saturation

  • 2, when VWC is at or above saturation

\[\begin{split}SMI = \begin{cases} 0 & \theta_v \le \theta_{wp} \\[2pt] \dfrac{\theta_v - \theta_{wp}}{\theta_{fc} - \theta_{wp}} & \theta_{wp} < \theta_v \le \theta_{fc} \\[6pt] 1 + \dfrac{\theta_v - \theta_{fc}}{\theta_{sat} - \theta_{fc}} & \theta_{fc} < \theta_v \le \theta_{sat} \\[6pt] 2 & \theta_v > \theta_{sat} \end{cases}\end{split}\]

where \(\theta_{wp}\) is wilting_point, \(\theta_{fc}\) is field_capacity and \(\theta_{sat}\) is saturation. A null \(\theta_v\) gives a null result.

Reference:
COSMOS-UK User Guide; Appendix H Soil Moisture Index

https://cosmos.ceh.ac.uk/sites/default/files/2024-12/COSMOS-UK_User_guide_v3_08_0.pdf

Parameters:

  • cosmos_vwc (Expr) – Volumetric Water Content (soil moisture) [%]

  • wilting_point (Expr) – Site attribute - volumetric water content at the wilting point of the soil [%]

  • field_capacity (Expr) – Site attribute - volumetric water content at field capacity [%]

  • saturation (Expr) – Site attribute - volumetric water content when the soil is fully saturated [%]

Return type:

Expr

Returns:

Expression or Series calculating soil moisture index [unitless, 0-2]