A fully coupled regional reanalysis framework
Dr. Jan Keller
Deutscher Wetterdienst | +49 69 8062 2859 |
Prof. Dr. Harrie-Jan Hendricks-Franssen
Forschungszentrum Jülich | +49 2461 614462 |
Dr. Arianna Valmassoi
Deutscher Wetterdienst | - |
Reanalyses of various compartments of the terrestrial system have become an important tool in climate monitoring. Although the water cycle and its variations play a crucial role in the effects of climate change, the terrestrial water cycle has not been realistically represented in reanalyses. Further, the impact of human water use and especially irrigation have not yet been accounted for in reanalyses. Project D03 therefore aims to establish a fully coupled reanalysis system to provide estimates in a comprehensive and consistent framework.
Contribution to the CRC
Our main contribution to the CRC is through the establishment of the IMS and the production of the reanalyses. Specifically, the IMS should allow for an otherwise unfeasible assessment of the impact of human land management, land, and water use changes on the regional atmospheric circulation and related water transports. Therefore, this project provides a prerequisite to answering the CRC’s central hypothesis. Furthermore, the explicit consideration of irrigation in the IMS enables a closer analysis of the role of the anthropogenic impact on the water cycle.
In order to implement a comprehensive monitoring system, we make use of the existing coupled modelling framework TerrSysMP that consist of the ICON, CLM and ParFlow model components. This fully coupled terrestrial modelling framework describes the spatio-temporal evolution of the complete subsurface/land surface/atmosphere system. In order to better represent the anthropogenic influence on the terrestrial system, we include an explicit representation of irrigation processes as a main component of the anthropogenic water use. To ensure that the system’s estimates are as close to reality as possible, we employ a data assimilation cycle. Therefore, we develop a strongly coupled data assimilation (DA) scheme that aims to update the initial state of the coupled system for all components at once.
Main results in 2022 and 2023
We have set up and tested the data assimilation system on JUWELS, the Supercomputer at JSC (Jülich Supercomputing Centre), a necessary prerequisite for starting the reanalysis runs. After running several performance and scaling tests, we now have a working setup and started the first version of the reanalysis. Initially, this is run with just ICON alone while we work on the steps needed for the coupled setup (static fields, spin-up). For setting up this first version, cooperation with the Z3 and Z4 projects was vital, as this enabled us to efficiently retrieve ERA5 boundary data which drives the simulation at the upper and lateral boundaries.
In the first figure we can see a comparison of 2m Temperature between the ERA5 reanalysis, which has a typical resolution of 30km, and our own. They agree well on large scales (a good result, given the shown quality of ERA5 on those scales), but our simulation adds a lot more detail, especially in mountainous regions where individual valleys can be resolved.
Other advantages of the high resolution can be seen when looking at wind speed. Here, not only are Fronts much more pronounced, the complicated wind systems near and induced by mountains are much more clearly visible (for example near the Adriatic sea), but also over the oceans, where the storm fields of mid-latitude lows show greatly enhanced detail.
In addition, work has started to implement irrigation in “TERRA”, the land surface model that is included with ICON. This will provide a baseline simulation to compare against once the coupled system is running.