There are 4 contributions submitted to 51r1 that concern land surface hydrology improvements:
- The orogaphic runoff fix consists in calibrating the orographic runoff generation retuning its sigma_min and sigma_max parameters using a CDF matching technique applied to the standard deviation of orography that ensures an equal area is assumed saturated in orographic terrain. This is necessary because the distribution of standard deviation of orography is skewed towards lower values at higher resolutions. Therefore the values of sigma_min and sigma_max conserving the runoff generation over orography are calculated to be:
This fix is shown to improve locally the river-discharge downstream of orographic areas and it preserves the runoff behaviour across resolutions. - The frozen soil runoff fix consists in avoiding an infiltration shut-down for frozen layers in presence of a partially frozen soil column. This situation happen in Spring when the upper soil layers are melting and hydrologically active while the deepest layer is still frozen. The soil moisture infiltrates into the bottom layer but cannot runoff since the layer is still frozen. This cause saturation to be reached in the deepest layer. Combined with the upward scheme used for the infiltration rates (calculating the maximum infiltration across two adjacent layers) this leads to a rapid dry-out of the upper-layers resulting in an unrealistic large runoff and dry topsoil. The frozen soil fix consists in calculating the frozen soil fraction based on the whole soil column volume, instead of each layer separately. This avoids the build-up of a saturated barrier in deep layers (when the soil column is already melting) while still preserving the impermeable characteristics in the permafrost regions (where the entire soil column is frozen). This fix is shown to be effective in eliminating the runoff-bombs operationally observed, and improves the river discharge on large part of northern hemisphere.
- The inundation 2-way coupling between the CaMa-Flood river discharge scheme and the ecLand surface scheme to enable re-evaporation from flooded areas. This development improves the realism of surface water distribution particularly in the tropics and the river basins of Amazon, Gange-Brahmaputra-Meghna, and Mekong. This opens-up to model re-infiltration to better simulate temporary flooded areas (e.g. Lake Eyre in Australia). The representation of inuntation areas is shown to improve atmospheric temperature temperatures up to T850 particularly in the tropics.
- The representation of irrigation processes coupling via a monthly climatology of irrigation fraction and a potential irrigation formulation that is based on optimal soil moisture deficit. The irrigation is shown to improve atmospheric variables (temperature and winds) in the areas more extensively irrigated (eg. South East Asia and Central US).
Jira ticket https://jira.ecmwf.int/projects/IFS/issues/IFS-4664
Branches: pad_CY50R1.0_dynamic_water_for_51R1.IFS-4664