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 name	Description
Available Water Storage in Top 100 cm Soil	Maximum available water storage in the top 100 cm of the soil, in mm.
Proportion of Precipitation in January	Proportion of annual precipitation that falls during the month of January, as a value between 0 and 1.
Proportion of Precipitation in February	Proportion of annual precipitation that falls during the month of February, as a value between 0 and 1.
Proportion of Precipitation in March	Proportion of annual precipitation that falls during the month of March, as a value between 0 and 1.
Proportion of Precipitation in April	Proportion of annual precipitation that falls during the month of April, as a value between 0 and 1.
Proportion of Precipitation in May	Proportion of annual precipitation that falls during the month of May, as a value between 0 and 1.
Proportion of Precipitation in June	Proportion of annual precipitation that falls during the month of June, as a value between 0 and 1.
Proportion of Precipitation in July	Proportion of annual precipitation that falls during the month of July, as a value between 0 and 1.
Proportion of Precipitation in August	Proportion of annual precipitation that falls during the month of August, as a value between 0 and 1.
Proportion of Precipitation in September	Proportion of annual precipitation that falls during the month of September, as a value between 0 and 1.
Proportion of Precipitation in October	Proportion of annual precipitation that falls during the month of October, as a value between 0 and 1.
Proportion of Precipitation in November	Proportion of annual precipitation that falls during the month of November, as a value between 0 and 1.
Proportion of Precipitation in December	Proportion 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 Temp	January temperature divided by mean annual temperature.
Ratio of February Temp to Annual Temp	February temperature divided by mean annual temperature.
Ratio of March Temp to Annual Temp	March temperature divided by mean annual temperature.
Ratio of April Temp to Annual Temp	April temperature divided by mean annual temperature.
Ratio of May Temp to Annual Temp	May temperature divided by mean annual temperature.
Ratio of June Temp to Annual Temp	June temperature divided by mean annual temperature.
Ratio of July Temp to Annual Temp	July temperature divided by mean annual temperature.
Ratio of August Temp to Annual Temp	August temperature divided by mean annual temperature.
Ratio of September Temp to Annual Temp	September temperature divided by mean annual temperature.
Ratio of October Temp to Annual Temp	October temperature divided by mean annual temperature.
Ratio of November Temp to Annual Temp	November temperature divided by mean annual temperature.
Ratio of December Temp to Annual Temp	December 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.

T_i = T * RT_i

P_i = P * RP_i

where:

T_i is temperature, in degrees C, for month i
P_i is precipitation, in mm, for month i
P is the annual precipitation, in mm
T is the mean annual temperature, in degrees C
RT_i is the Ratio of [month i] Temp to Annual Temp parameter
RP_i is the Proportion of Precipitation in [month i] parameter

Then PET (monthly potential evapotranspiration) is calculated as:

PET_i = 0.013 * (T_i/(T_i+15) * (R_s+50)

where:

PET_i is monthly potential evapotranspiration in mm
T_i is monthly temperature in degrees C
R_s is the [month i] Radiation (cal/cm2) parameter

If T_i ? 0, then PET_i = 0.

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

sms_i = 0 < sms_i-1 + precip_i - PET_i < MaxAWS

where:

sms_i is the soil moisture, in mm, for the current month
sms_i-1 is the soil moisture, in mm, for the previous month
precip_i is the monthly precipitation (mm) for the current month
PET_i 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, sms_i-1 = MaxAWS.

Monthly actual evapotranspiration (AET) is calculated as:

AET_i = sms_i + precip_i

if sms_i+1 ? 0, or

AET_i = PET_i

if sms_i+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.