MEGAN BDSNP and NOAH LSM

MEGAN
1

Hello everyone,

I am trying to use BDSNP in MEGAN to estimate soil emissions. I noticed that the user instructions state that the BDSNPmust be used with PX LSM. But I only have meteorological data based on the NOAH LSM. I understand that soil modeling for PX and NOAH is quite different. What I want to know is if I use NOAH LSM and BDSNP together, will the results be reasonable? Thanks for any suggestions.

WXY
2025.4.26

2

If you look in BDSNP_MOD.F you’ll see the variables

  REAL,    INTENT( IN ) :: SOILM ( NCOLS,NROWS )         ! soil moisture [m3/m3] (PX)
  REAL,    INTENT( IN ) :: SOILT  ( NCOLS,NROWS )        ! soil temperature [K] (PX)

This is important because PX assumes a top layer depth of 1 cm versus NOAH’s 10 cm. You can comment out the LSM check

C ! make sure it only runs with PX version
IF( .NOT. PX_LSM ) THEN
MESG = “BDSNP Soil NO is only compatible with PX version”
CALL M3EXIT( PNAME, JDATE, JTIME, MESG, 2)
END IF

And it should run. My guess is that BDSNP with NOAH will produce less soil NO because the deeper top layer will dry out less often. The pulse term will be smaller if the soil doesn’t dry out.

This might be a good thing, though, since BDSNP seems to produce too much soil NO in general.

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3

Dear willison.jeff
Thank you so much! It is very clear.

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