Opened 21 months ago

Last modified 19 months ago

#720 new enhancement

Review plant water stress

Reported by: luyssaert Owned by: somebody
Priority: major Milestone: ORCHIDEE 4.3
Component: Physical processes Version: trunc
Keywords: Cc:


Around r6831 it became clear that many of the remaining parameter issues come from or seem to be related to the use of the hydraulic architecture to calculate plant water stress. Known issues:
(1) The use of many prescribed parameter values works OK as longs as there is no to little water stress. However, when a drought is building up, the use of prescribed parameter values seems to result in overconsumption of water (the plant behaves as there is no drought building up). Only when the thresholds are exceeded there is suddenly too much water stress.

Proposed solution: calculate the soil water potential of the sleeve around the roots (Following Tuzet et al).

(2) If there is water stress, GPP and the energy budget have to be recalculated. This takes time, adds code and is sensitive to numerical issues. This recalculation inverts the original equations for vbeta3. Some of these inversions results in divides by zeros and small numerical issues.

Proposed solution: include all the soil and plant based conductances in the calculation of GPP in diffuco (Following Tuzet et al)

(3) In diffuco transpiration and latent heat have there own coefficients, i.e. vbeta3 and vbeta. In case of water stress vbeta3 is recalculated. vbeta is not, this is a bug.

Proposed solution: wait for issue (2) to be solved. If the recalculation is no longer needed, this problem may have been solved as well.

(4) copied from #712. Previously SRF_twbr and SRF_water_budget_closure had similar values and a similar trends. In r6826 SRF_twbr was closed but SRF_water_budget_closure had a value of 10-1 compared to ORCHIDEE Tag 2.1 where this variable had a value of 10-7 kg/m2/day.
SRF_water_budget_closure is not calculated in ORCHIDEE but calculated by libIGCM monitoring. The variable is calculated as (((1-nobiofrac[d=1,l=2:100000])*DelSoilMoist_daily[d=2,l=2:100000] + DelIntercept_daily[d=3,l=2:100000] + DelSWE_daily[d=4,l=2:100000] + delstock_routing_daily[d=5,l=2:100000])*Areas[d=1]*Contfrac[d=1] - ((rain[d=6,l=2:100000] + snowf[d=7,l=2:100000] - evap[d=8,l=2:100000])*Areas[d=1]*Contfrac[d=1] - (riverflow[d=9,l=2:100000] + coastalflow[d=10,l=2:100000])*1000*86400 ))/(4*3.14*6370000*6370000*0.26)

Note that monitoring also contains a variable called delta_water_stock that is calculated as ((1-nobiofrac[d=1,l=2:100000])*DelSoilMoist_daily[d=2,l=2:100000] + DelIntercept_daily[d=3,l=2:100000] + DelSWE_daily[d=4,l=2:100000] + delstock_routing_daily[d=5,l=2:100000]). Both tag2.1 and r6826 have a delta_water_stock of 10-3. Which suggest the problem is less likely to be in this variable.

delta_water_stock is used to calculate SRF_water_budget_closure: (delta_water_stock*Areas[d=1]*Contfrac[d=1] - ((rain[d=6,l=2:100000] + snowf[d=7,l=2:100000] - evap[d=8,l=2:100000])*Areas[d=1]*Contfrac[d=1] - (riverflow[d=9,l=2:100000] + coastalflow[d=10,l=2:100000])*1000*86400 ))/(4*3.14*6370000*6370000*0.26).

rain and snowf are identical between tag2.1 and r6826. Given that the difference in delta_water_stock is much smaller (10-3) than the difference we are looking for (10-1), the three most suspicious variables are coastalflow, riverflow and evap. The merge was not supposed to touch riverflow and coastalflow. These are less likely to be the cause of the difference. The first place to start looking is therefore evap. Is evap written before or after it is being recalculated to account for water stress? A previous no stress simulation still has the twbr problem which seems to dominate the imbalance but the imbalance in twbr and water_budget_closure are of the same magnitude. Fixes for twbr touched on vevap variables but not on evap.

Proposed solution: wait for issue (2) to be solved. If the recalculation is no longer needed, this problem may have been solved as well.

Change History (1)

comment:1 Changed 19 months ago by luyssaert

  • Summary changed from Review and plant water stress to Review plant water stress
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