SORTIE-ND
Software for spatially-explicit simulation of forest dynamics

Seasonal Water Deficit

This behavior changes the value of the Seasonal Water Deficit parameter of the SORTIE plot in response to changes in the mean annual temperature and precipitation of the plot. Seasonal water deficit is the difference between potential evapotranspiration in the presence of limitless water and actual evapotranspiration based on available precipitation. As such, it is an index of the degree to which actual supply of moisture fails to meet "demand" for moisture. This assumes that monthly temperature and rainfall patterns do not change along with changes in mean annual temperature and precipitation.

Parameters for this behavior

Parameter nameDescription
Available Water Storage in Top 100 cm SoilMaximum available water storage in the top 100 cm of the soil, in mm.
Proportion of Precipitation in JanuaryProportion of annual precipitation that falls during the month of January, as a value between 0 and 1.
Proportion of Precipitation in FebruaryProportion of annual precipitation that falls during the month of February, as a value between 0 and 1.
Proportion of Precipitation in MarchProportion of annual precipitation that falls during the month of March, as a value between 0 and 1.
Proportion of Precipitation in AprilProportion of annual precipitation that falls during the month of April, as a value between 0 and 1.
Proportion of Precipitation in MayProportion of annual precipitation that falls during the month of May, as a value between 0 and 1.
Proportion of Precipitation in JuneProportion of annual precipitation that falls during the month of June, as a value between 0 and 1.
Proportion of Precipitation in JulyProportion of annual precipitation that falls during the month of July, as a value between 0 and 1.
Proportion of Precipitation in AugustProportion of annual precipitation that falls during the month of August, as a value between 0 and 1.
Proportion of Precipitation in SeptemberProportion of annual precipitation that falls during the month of September, as a value between 0 and 1.
Proportion of Precipitation in OctoberProportion of annual precipitation that falls during the month of October, as a value between 0 and 1.
Proportion of Precipitation in NovemberProportion of annual precipitation that falls during the month of November, as a value between 0 and 1.
Proportion of Precipitation in DecemberProportion of annual precipitation that falls during the month of December, as a value between 0 and 1.
January Radiation (cal/cm2)Global radiation received during the month of January, in cal / cm2.
February Radiation (cal/cm2)Global radiation received during the month of February, in cal / cm2.
March Radiation (cal/cm2)Global radiation received during the month of March, in cal / cm2.
April Radiation (cal/cm2)Global radiation received during the month of April, in cal / cm2.
May Radiation (cal/cm2)Global radiation received during the month of May, in cal / cm2.
June Radiation (cal/cm2)Global radiation received during the month of June, in cal / cm2.
July Radiation (cal/cm2)Global radiation received during the month of July, in cal / cm2.
August Radiation (cal/cm2)Global radiation received during the month of August, in cal / cm2.
September Radiation (cal/cm2)Global radiation received during the month of September, in cal / cm2.
October Radiation (cal/cm2)Global radiation received during the month of October, in cal / cm2.
November Radiation (cal/cm2)Global radiation received during the month of November, in cal / cm2.
December Radiation (cal/cm2)Global radiation received during the month of December, in cal / cm2.
Ratio of January Temp to Annual TempJanuary temperature divided by mean annual temperature.
Ratio of February Temp to Annual TempFebruary temperature divided by mean annual temperature.
Ratio of March Temp to Annual TempMarch temperature divided by mean annual temperature.
Ratio of April Temp to Annual TempApril temperature divided by mean annual temperature.
Ratio of May Temp to Annual TempMay temperature divided by mean annual temperature.
Ratio of June Temp to Annual TempJune temperature divided by mean annual temperature.
Ratio of July Temp to Annual TempJuly temperature divided by mean annual temperature.
Ratio of August Temp to Annual TempAugust temperature divided by mean annual temperature.
Ratio of September Temp to Annual TempSeptember temperature divided by mean annual temperature.
Ratio of October Temp to Annual TempOctober temperature divided by mean annual temperature.
Ratio of November Temp to Annual TempNovember temperature divided by mean annual temperature.
Ratio of December Temp to Annual TempDecember temperature divided by mean annual temperature.

How it works

The first step is calculating monthly temperature and precipitation based on the latest values for the plot.

Ti = T * RTi

Pi = P * RPi

where:

  • Ti is temperature, in degrees C, for month i
  • Pi is precipitation, in mm, for month i
  • P is the annual precipitation, in mm
  • T is the mean annual temperature, in degrees C
  • RTi is the Ratio of [month i] Temp to Annual Temp parameter
  • RPi is the Proportion of Precipitation in [month i] parameter

Then PET (monthly potential evapotranspiration) is calculated as:

PETi = 0.013 * (Ti/(Ti+15) * (Rs+50)

where:

  • PETi is monthly potential evapotranspiration in mm
  • Ti is monthly temperature in degrees C
  • Rs is the [month i] Radiation (cal/cm2) parameter

If Ti ? 0, then PETi = 0.

In order to calculate actual evapotranspiration, we need monthly soil moisture values. Monthly soil moisture storage is calculated as:

smsi = 0 < smsi-1 + precipi - PETi < MaxAWS

where:

  • smsi is the soil moisture, in mm, for the current month
  • smsi-1 is the soil moisture, in mm, for the previous month
  • precipi is the monthly precipitation (mm) for the current month
  • PETi is potential evapotranspiration for the current month
  • MaxAWS is the Available Water Storage in Top 100 cm Soil

It is assumed that the soil is saturated on the last day of the year, so for January, smsi-1 = MaxAWS.

Monthly actual evapotranspiration (AET) is calculated as:

AETi = smsi + precipi

if smsi+1 ? 0, or

AETi = PETi

if smsi+1 > 0.

Annual AET is the sum of the monthly AET values, and annual PET is the sum of the monthly PET values; and Seasonal Water Deficit = PET - AET.

This value is then given to the Plot object which makes it available to other behaviors in the run.

How to apply it

Add this behavior to the run. You do not need to assign this behavior to trees.