Projecting future global discharge signals with kilometer-scale earth system simulations combined with river routing

Traditionally, to simulate future river discharge on a global scale, a global hydrological model would be forced with atmospheric input data from a climate model. However, this approach does not consider any coupling effects between earth system model components such as the ocean, sea-ice, and most importantly in this case: the land-surface. Nowadays, these components are often integrated in earth system models (ESMs), allowing to directly study the interaction between precipitation, evaporation and surface and subsurface runoff. Since very recent, ESMs are capable of performing multi-decadal simulations globally at kilometer-scale  (9 by 9 km spatial resolution), allowing to (partly) resolve convection, improve orographic precipitation, and include the impact of land surface heterogeneity, while also capturing all large-scale drivers. Given these accomplishments, we are asking the questions: 1) Can we assess future discharge changes by linking a kilometer-scale ESM directly to a river routing scheme? And 2) Do we see the impact of kilometer-scale resolved processes in the atmosphere and on land reflected in the discharge representation?

Here, we use kilometer-scale earth system simulations with the Integrated Forecasting System (IFS) model for past (1990-2020) and future climate (2020-2050; SSP3-7) as input for the river routing Catchment-Based Macro-scale Floodplain (CaMa-Flood) model. This provides global high-resolution historical and future river discharge simulations. Our modelling set-up allows to study how the water balance components react and interact; from atmospheric precipitation, to land-surface feedbacks including evaporation and runoff, to river routing generating streamflow. For the analysis, we first focus on the well-studied and well-observed Rhine basin. Thereafter, we extend our analysis to a diverse set of catchments of varying size globally. With the main goal to assess the impact of kilometer-scale resolved weather and land-atmosphere interactions on future discharge signals, and specifically during floods and droughts.