| 13 | | == Standard protocol == |
| | 11 | The principle is to start from a priori initial conditions, and run the model for a certain amount of time with boundary conditions (weather, land cover, CO2, etc.) which are representative of the period preceding the initialization of the simulation. We often speak of |
| | 12 | - warm up if we create initial conditions by a simulation using the preceding meteorological forcing (for example 1960-1979 to initialize a simulation starting on Jan 1st 1980), |
| | 13 | - spin up if we recycle a meteorological forcing to get a longer preceding period (for instance, to start Jan 1st 1980 after a 20-yr spinup, you can use 20 times 1979, or 5 times 1976-1979, depending on the availability of the meteorological forcing). |
| | 14 | A priori, the closer you are to a warm up, the more realistic your initial condictions, but it's not always possible, especially if you need a long initialization period. |
| | 15 | |
| | 16 | The required length of the initialization period (either spin up or warm up) depends on the components of ORCHIDEE you are interested in. The goal is to bring the corresponding stocks to an equilibrium with the mean climate of the period, and the required period is all the longer as the corresponding residence time are larger: |
| | 17 | |
| | 18 | - The equilibrium of the physics of the land surface (SECHIBA part of ORCHIDEE, for water and heat stocks) should be reached in less than 10 years with a constant climatology and a prescribed LAI. If you spin up, pay attention to the selected years because El Niño or La Niña specific years may give bad results for a global spinup. The spin up can also lead to accumulate ou melt the snow cover in an unrealistic way if the recycled period is short and includes an extreme year in some regions. |
| | 19 | |
| | 20 | - The equilibrium of the LAI (seasonal variation of the vegetation) takes less than two decades to converge. |
| | 21 | |
| | 22 | - The carbon stocks and fluxes take a much longer time to reach an equilibrium when starting from zero. |
| | 23 | - Vegetation C stocks/fluxes: The spinup needs to bring the vegetation above and below ground carbon stocks at equilibrium. This is relatively short for the LAI: few decades or even just one decade are enough. For the other C pools it is linked to the turnover of the !Sap/Heart/wood C pools: usually 100 to 200 years are sufficient. |
| | 24 | - Soil C stocks/fluxes: These pools take a much longer time to be in equilibrium as the passive C pool has a turnover on the order of one thousand years. Usually we need several thousand years to reach the equilibrium. Using the in-built iterative pseudo-analytical spinup configuration reduces this step as we then only need to have the input of C to the soil in equilibrium. |
| | 25 | |
| | 26 | Finally, the length of the initialization period should be dictated by the slower active component influencing your simulations: |
| | 27 | - If you use ORCHIDEE with STOMATE, use a 20-yr initialization even if you are not interested in LAI, because there is a big feedback between the LAI and the hydrology and energy budgets. And if you're interested in !Sap/Heart/wood C pools, use a 100 to 200 period. |
| | 28 | - If you're interested in the soil carbon, you need a longer initialization. But it is not required for the moment if you're not interested in the soil carbon, since there is no feedback between the soil carbon pools and the LAI and the hydrology yet. |
| | 29 | |
| | 30 | == Standard protocol for Carbon-related variables== |
