The Barometric Pressure Method implements an atmospheric pressure algorithm descibed within Anderson (2006) and Follum et al (2015) that is based on a standard atmospheric altitude versus pressure relationship. The algorithm for atmospheric pressure, P_a, is defined as:
P_a = 33.86(29.9-0.335H_e+0.00022H_e^{2.4})
where
H_e is the elevation (meters) above sea-level.
The Barometric Pressure Method calculates the atmospheric pressure at a specific location (grid cell or subbasin) by altering standard atmospheric pressure at sea-level (101.325 kPa) using a defined Lapse Rate. The elevation of the grid cell or subbasin location is determined from the associated terrain model. If the basin model is not georeferenced and/or does not have an associated terrain model, the calculations proceed assuming that the location is at sea-level. The Lapse Rate is specified in units of Deg F / 1000ft^2 or Deg C / 1000m^2 and, depending on the selected discretization, is applied at a subbasin by subbasin or grid cell by grid cell basis.
Required Parameters
A Lapse Rate must be defined for each subbasin. Although optional, it is recommended that a terrain model is associated with the basin model and that the basin model is georeferenced. Otherwise, pressure will be calculated assuming sea-level elevation.