Mass fluxes and budgets at catchment and continental scales
Prof. Dr. Jürgen Kusche
University of Bonn | +49 228 73-2629 |
In project D07, we analyze terrestrial/atmospheric and surface water fluxes and associated budget contributions from model simulations, reanalyses and remote sensing observations for all larger river basins in Europe. Modelling results are combined with catchment-integrating observations like GRACE/-FO derived water storage variability and river discharge. We compare the budgets from the CRC’s modelling system to global reanalyses and CMIP6 climate simulations. The project will quantify to what extent regional changes of land and water use contribute to observed budget changes. It will also quantify the terrestrial-atmospheric contribution of the modelling region to sea level budgets.
Contribution to the CRC
Our main contribution to the CRC is a systematic integrated analysis of components of the terrestrial water budget: we will feed information about fluxes and biases from our budget analysis back to the modelling and observation instances and jointly discuss these results in view of potential causes on the technical and interpretative side. One major asset is our expertise in GRACE/-FO satellite gravimetry post-processing and evaluation, i.e. we provide tempo-spatial observations of gravity changes, which can be interpreted as total integrated water mass change over the assessed region. Furthermore, we assist the CRC with geospatial vector data of rivers and their catchment areas, and we organize cross-cluster consistent use of GRDC river discharge data in close collaboration with several other projects.
For total water mass change (dS/dt), we primarily use spherical harmonic coefficients of unconstrained gravity models of GRACE/-FO satellite observations, analyzed at basin-scale. We compare this total change to the integrated sum of observed and modelled in- and out-flux of water masses such as precipitation (P), evapo(transpi)ration (E) or river runoff (Q). In this way, we are able to identify biases in contributions by a weighted combination with the remaining components and dynamically feed this information back to involved partner projects. A similar approach lets us assess energy budgets over the same targets by comparing incoming short wave radiation and advection with albedo and long wave radiation.
Main Results in 2022 and 2023
We investigated the monthly averaged water flux budget over the dedicated Rees Station kernel (Rhine River catchment as shown in the mini-map with tributary streams). In this example, it involved (1) central differences of NASA GSFC GRACE mascons for total water storage change, (2) GRDC river discharge, (3) IMERG precipitation, and (4) GLEAM 3.6 satellite-derived evaporation data. A direct comparison of the budget terms “P-E” (blue) and “dS/dt+Q” (orange) shows good agreement even with seasonal variation and flux-trends retained.
The same data plotted in a scatter diagramme with temporal colour coding provides insights regarding seasonal behaviour and “character” of the basin, e.g. during warm summer months (brownish colours) total water losses and evaporation tend to dominate compared to winter months. When we switch to the integration of TSMP model runs from the CRC, this type of analysis helps to systematically assess the impact of changes in land- and water use.