| 109 | | === Bare soil (r6614) === |
| 110 | | The flag '''ok_bare_soil_new''' controls how the bare soil is perceived and calculated. If set to FALSE the total bare soil is still calculated as a function of veget. When a deciduous PFT sheds its leaves, the gaps in the forest will contribute to bare soil fraction in the grid. Although this approach was introduced a long time ago to get acceptable evaporation estimates from forest, the approach also resulted in using the albedo of deserts as the background albedo of forest gaps. The new albedo scheme (see Albedo and Background albedo) considers a specific background albedo for each PFT and calculates the albedo of the PFT including the canopy gaps. Moving gaps to the bare soil is no longer needed. So, if '''ok_bare_soil_new''' is set to TRUE, canopy gaps no longer contribute to the bare soil. It needs to be tested what will happen with the evaporation in the single-layer model. The multi-layer energy budget should be able to correctly deal with the gaps in the canopy because the diffusivity will increase when the canopy is becoming sparser. |
| 111 | | |
| 112 | | At present the default settings combine the new albedo scheme with the single layer energy budget (enerbil) and '''ok_bare_soil_new''' = n. The consequences of this combination of settings should be evaluated against observations. |
| | 109 | === Bare soil (r6783) === |
| | 110 | The flag '''ok_bare_soil_new''' controls how the bare soil is perceived and calculated. If set to FALSE the total bare soil is still calculated veget_max_1 + sum(veget_max_i - veget_i) with i from 2 to the number of PFTs. When a deciduous PFT sheds its leaves, the gaps in the forest will thus contribute to the bare soil fraction in the grid. Although this approach was introduced a long time ago to get acceptable evaporation estimates from forest, the approach also resulted in using the albedo of PFT1 deserts as the background albedo of forest gaps. In ORCHIDEE v2.1 the background albedo has been reparameterized and this issue may have been largely resolved now if '''alb_bg_modis''' = y ([https://forge.ipsl.jussieu.fr/orchidee/wiki/Documentation/TrunkFunctionality4#Albedobackgroundr6614 more details]). From many points of view a dynamic bare soil fraction is strange, e.g., bare soil has its own water column so when moving the forest gaps from to forest to PFT1 the soil water content, soil carbon content, litter layer, etc all changes temporary. If '''ok_bare_soil_new''' is set to TRUE, canopy gaps no longer contribute to the bare soil. The new albedo scheme (see Albedo and Background albedo) considers a specific background albedo for each PFT and calculates the albedo of the PFT including the canopy gaps but the calculation of bare soil evaporation underneath a canopy would be problematic. For that reason ok_bare_soil_new is recommended only to be used with the multi-layer energy budget (when run with more than 1 layer). The multi-layer energy budget accounts for within canopy turbulence and can therefore deal with evaporation from beneath a canopy. At present the settings for ok_bare_soil_new are included in the energy_control flag ([https://forge.ipsl.jussieu.fr/orchidee/wiki/Documentation/TrunkFunctionality4#Singlevsmultilayerenergybudgetr6614 more details]). The default settings of ORCHIDEE 4.0 combine the new albedo scheme with the single layer energy budget (enerbil) and '''ok_bare_soil_new''' = n. |
