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CESM1.2.z: for CLM4.5: Important Bad interpretation of maximum rate constant for soil water content in SoilbiogeochemDecompCasc

erik

Erik Kluzek
CSEG and Liaisons
Staff member

Code:
The following reference was interpreted wrongly in terms of the maximum rate of soil respiration. This issue goes back to the introduction of CLM4.5

Code:
! calculate the rate constant scalar for soil water content.

Code:
! Uses the log relationship with water potential given in <br />! Andren, O., and K. Paustian, 1987. Barley straw decomposition in the field: <br />! a comparison of models. Ecology, 68(5):1190-1200. <br />! and supported by data in <br />! Orchard, V.A., and F.J. Cook, 1983. Relationship between soil respiration <br />! and soil moisture. Soil Biol. Biochem., 15(4):447-453. <br /><br />The max rate was interpreted as... maxpsi = sucsat * -9.8e-6 (for 50%clay/50% loam it's -0.0070) <br /><br />Whereas the new code reads in the max rate as a parameter and uses it. Currently using the value of -0.03MPa. <br /><br />The files are in models/lnd/clm/src/clm4_5/biogeochem and named CNDecompCascadeMod_CENTURY.F90/CNDecompCascadeMod_BGC.F90. <br />So previously psi was never capped and it should have been. Dr. Charlie Koven gives this note "it replaces the hard-coded assumption present <br />in prior versions of the model that soil respiration was water-limited whenever it fell below saturation." So now it's only water-limited until it <br />reaches the maxpsi_hr parameter, from that point to saturation it's not water-limited.
http://bugs.cgd.ucar.edu/show_bug.cgi?id=2324
 
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