Hydrological modelling on atmospheric grids; using graphs of sub-grid elements to transport energy and water

Abstract

Abstract. Land Surface Models (LSMs) use the atmospheric grid as their basic spatial decomposition because their main objective is to provide the lower boundary conditions to the atmosphere. Lateral water flows at the surface on the other hand require a much higher spatial discretization as they are closely linked to topographic details. We propose here a methodology to automatically tile the atmospheric grid into hydrological coherent units which are connected through a graph. As water is transported on sub-grids of the LSM, land variables can easily be transferred to the routing network and advected if needed. This is demonstrated here for temperature. The quality of the river networks generated, as represented by the connected hydrological transfer units, are compared to the original data in order to quantify the degradation introduced by the discretization method. The conditions the sub-grid elements impose on the time step of the water transport scheme are evaluated and a methodology is proposed to find an optimal value. Finally the scheme is applied in an off-line version of the ORCHIDEE LSM over Europe to show that realistic river discharge and temperatures are predicted over the major catchments of the region. The simulated solutions are largely independent of the atmospheric grid used thanks to the proposed sub-grid approach.

Budyko Framework Based Analysis of the Effect of Climate Change on Watershed Evaporation Efficiency and Its Impact on Discharge Over Europe

“…Over the course of several years, the model has been tested and validated on many aspects of the land surface processes (hydrology, vegetation, and carbon cycle processes). This attests to its quality to reproduce the water and energy balance and also discharge over different areas over the globe (Guion et al, 2022;Nguyen-Quang et al, 2018;Polcher et al, 2022;Tafasca et al, 2020;F. Wang et al, 2018).…”

“…Over the course of several years, the model has been tested and validated on many aspects of the land surface processes (hydrology, vegetation, and carbon cycle processes). This attests to its quality to reproduce the water and energy balance and also discharge over different areas over the globe (Guion et al., 2022; Nguyen‐Quang et al., 2018; Polcher et al., 2022; Tafasca et al., 2020; F. Wang et al., 2018). Comparing the LSM outputs directly to observations for discharge is challenging, mainly due to the absence of certain processes in the models, including those resulting from direct human activities and the extensive water and river management (F. Wang et al., 2018), as it is the case in our area of interest.…”

“…The hydrological network of the ORCHIDEE LSM is constructed from the hydrological elevation model HydroSHEDS (Lehner et al., 2008), which covers the area studied with the resolution of 30 arc s (approximately 1 km at the equator). The hydrological information is then upscaled to the resolution of the atmospheric grid, the hydrological coherence being preserved by the construction of hydrological transfer units at the subgrid level (Polcher et al., 2022). From a database of gauging stations, upstream basins are reconstituted on the hydrological elevation model grid and then projected on the atmospheric grid during the process.…”

Modeling hydropower operations at the scale of a power grid: a demand-based approach

“…In the initial version of ORCHIDEE (Polcher et al, 2023), each HTU i contains three natural water stores, characterized by their time constants (slow aquifer, fast aquifer, and stream storage). To represent water management we add a fourth store to the https://doi.org/10.5194/egusphere-2023-3106 Preprint.…”

“…3, the fast aquifer is filled by local runoff generated in the HTU, the slow aquifer by local drainage generated in the HTU and the stream store by the discharge from upstream HTUs. The equations of these natural water stores are detailed in previous publications (Zhou et al, 2021;Polcher et al, 2023). They introduce the respective time constants of the natural stores g stream , g f ast and g slow (in unit h.m −1 ) and the topographic index calculated for each HTU τ i (in unit m 2 ).…”