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


Erik Kluzek
CSEG and Liaisons
Staff member

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

! calculate the rate constant scalar for soil water content.

! 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.