## 2 Model Description  
This section introduces the current land surface parameterisation operationally used at ECMWF. It describes the representation of the land surface fluxes of energy, water and carbon, and where appropriate, corresponding sub-surface quantities. The main surface scheme parameterisation structures were set with the Tiled ECMWF Scheme for Surface Exchanges over Land [5, 6, 7]. Each grid-box at the interface between the surface and the atmosphere is fractioned into tiles. There are currently seven tiles over land (high and low vegetation, bare ground, shaded and exposed snow, intercepted water and lake) and up to two tiles over sea and freshwater bodies (open and frozen water). Each tile is characterised with its own properties identifying separate water and heat fluxes and allow solving an energy balance equation for the tiles skin temperatures and taking into account physical processes that limit evaporation of vegetated areas and bareground (see the Supplementary Materials for detailed formulation). One of the important characteristics of the ECMWF land surface scheme is the skin layer fast response, that allows for an implicit solving of the skin temperature equation in conjunction with the boundary layer's vertical turbulent transport, as a natural integrated way within the IFS. Given the interdependence of the tiles' skin temperature, the [PERSON] et al. [27] coupling approach is therefore used to jointly solve the skin temperatures equations in a fully implicit way. The uniform global soil texture and the lack of surface runoff are shortcomings that have also motivated a revision of the land surface hydrology. In this context, [PERSON] et al. [8] implemented a new runoff and infiltration parametrizations that are related to the standard deviation of orography and the soil texture. The snowpack is characterised by considering, snow density, thermal insulation properties interception of rain and the evolution of the albedo due to metamorphism aging processes [9; 28]. The skin temperature over land is thermally in contact with a multi-layer soil (currently four layers, Section 3.3) or with a snow layer mantle overlying the soil, if snow is present (Section 3.2). The combined effect of melt energy, basal heat flux and top energy fluxes triggers the snow temperature variation. A modified Fourier diffusion equation that considers the soil water phase changes' thermal effects is used to characterise the soil heat budget. Considering a zero-flux as the bottom boundary condition and a net ground heat flux at the top, allow then to solve the energy equation. The snowmelt contributes to surface runoff and infiltration by depleting the snow mantle that collects the Snowfall. The rainfall is partitioned in fractions that are collected by an interception layer and the snow mantle, and a remaining throughfall fraction. This latter fraction contributes to surface runoff and infiltration. The multi-layer soil discretization which is shared for heat and water budget equations is used to solve [PERSON]'s law that govern the subsurface water fluxes. The bottom layer boundary assumes a free drainage condition and for the top boundary, surface evaporation and infiltration are assumed. While an additional root extraction sink from vegetated areas is considered in each layer. A revised bare soil evaporation enhances the soil-atmosphere water exchange especially over deserts and sparsely vegetated regions [29] and introducing a vegetation growth seasonal evolution allows to better modulate the evapotranspiration [10]. As an important component of the global carbon dioxide (CO\({}_{2}\)) budget, a land surface CO\({}_{2}\) exchange module has been added to ECLand [30] enabling environmental forecasting applications which also involves interaction with atmospheric CO\({}_{2}\) concentration.