error in macav2 ea calculation

[cpearson1]

~Line: 351
#estimate sat. vapor press and use vpd
es = 0.6108np.exp(17.27self.data.tavg_c/(self.data.tavg_c+237.3))
self.data['ea_kpa'] = self.data.vapor_pres_def + es
***VPD = es - ea; ea_kpa calc is incorrect

Calculation should follow ASCE standardized refet Table 3 Preferred Procedure Order:
https://www.uidaho.edu/-/media/UIdaho-Responsive/Files/cals/centers/Kimberly/water-resources/ASCE-Standardized-Reference-Evapotranspiration-Equation-draft-report-without-appendices.pdf?la=en&hash=F4E3EB1290A7971E172F23A2A3B660B237D727D0

Proposed Fix (use maca provided specific humidity):
if product == 'macav2':
self.data['wind_mean'] = np.sqrt(
self.data['eastward_wind']**2 + self.data['northward_wind']**2
)
self.data['pa'] = np.full(length, refet.calcs._air_pressure(elev))
self.data['ea_kpa'] = refet.calcs._actual_vapor_pressure(
self.data.specific_humidity, self.data.pa
)

[jhuntington]

Also, es should be computed using equation 6 and 7 in https://www.uidaho.edu/-/media/UIdaho-Responsive/Files/cals/centers/Kimberly/water-resources/ASCE-Standardized-Reference-Evapotranspiration-Equation-draft-report-without-appendices.pdf?la=en&hash=F4E3EB1290A7971E172F23A2A3B660B237D727D0 we should not be using Tmean to compute es… we should be using Tmax and then Tmin, and then taking the average of es at Tmax and es at Tmin… the Temp and es function is an exponential… not linear. Justin From: Chris Pearson <notifications@github.com> Sent: Sunday, June 7, 2020 10:19 PM To: WSWUP/MACA-ETr <MACA-ETr@noreply.github.com> Cc: Subscribed <subscribed@noreply.github.com> Subject: [WSWUP/MACA-ETr] error in macav2 ea calculation (#1) ~Line: 351 estimate sat. vapor press and use vpd es = 0.6108np.exp(17.27self.data.tavg_c/(self.data.tavg_c+237.3)) self.data['ea_kpa'] = self.data.vapor_pres_def + es ***VPD = es - ea; ea_kpa calc is incorrect Calculation should follow ASCE standardized refet Table 3 Preferred Procedure Order: https://www.uidaho.edu/-/media/UIdaho-Responsive/Files/cals/centers/Kimberly/water-resources/ASCE-Standardized-Reference-Evapotranspiration-Equation-draft-report-without-appendices.pdf?la=en&hash=F4E3EB1290A7971E172F23A2A3B660B237D727D0 Proposed Fix (use maca provided specific humidity): if product == 'macav2': self.data['wind_mean'] = np.sqrt( self.data['eastward_wind']**2 + self.data['northward_wind']**2 ) # estimate sat. vapor press and use vpd es = 0.6108np.exp(17.27self.data.tavg_c/(self.data.tavg_c+237.3)) self.data['ea_kpa'] = self.data.vapor_pres_def + es self.data['pa'] = np.full(length, refet.calcs._air_pressure(elev)) self.data['ea_kpa'] = refet.calcs._actual_vapor_pressure( self.data.specific_humidity, self.data.pa ) — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub<#1>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/ACYYVWHDBKBBAP2EQRTZKPTRVRYDHANCNFSM4NX7T6CA>. PUBLIC RECORDS NOTICE: In accordance with NRS Chapter 239, this email and responses, unless otherwise made confidential by law, may be subject to the Nevada Public Records laws and may be disclosed to the public upon request.