EN 
DE 
For the long-term planning of water management issues in the Central German lignite mining area [LMBV mbH (2010): Zwei Jahrzehnte Braunkohlesanierung - Eine Zwischenbilanz; Leipzig], large-scale groundwater models are operated and updated on the basis of the PCGEOFM software (https://www.ibgw-leipzig.de/index.php/haupt-pcgeofim). The post-mining lakes currently being flooded and the receiving water systems are taken into account as time-varying boundary conditions in order to model the interactions with the groundwater balance. Long-term forecasts have so far been made on the basis of long-term climatic averages over the past 40 years. This approach is based on the assumption that future climatic conditions will develop in the same way as previous ones.
Current climate projections for Saxony (ReKIS), which indicate increasingly drier and warmer conditions in the future [http://rekis.hydro.tu-dresden.de/], have not yet been taken into account in the model forecasts. However, there is a concrete need for realistic estimates of future lake water levels, surplus and discharge volumes in the course of currently pending water legislation procedures.
In order to fulfil these requirements in a targeted manner, a methodically simplified approach was chosen as an example to take future climatic developments into account.
To this end, the model forecasts were carried out on the basis of the 10-year series 2011 to 2020 and the 3-year series 2018 to 2020. Due to their brevity, these series are only suitable as a basis for long-term forecasts to a limited extent. However, the scenarios are highly relevant insofar as they depict the trend towards increasingly drier and warmer conditions in a methodologically simplified manner. According to the responsible approval authority, the 2011 to 2020 series roughly corresponds to the political climate target (RCP2.6, +1.5 K compared to the 1961-1990 climate series) in terms of the average temperature increase, while the 2018 to 2020 series (+2.2 K) is still significantly colder than projected in the "continue as before" scenario (RCP8.2, +5 K in 2100) [LfULG Sachsen, Deutscher Wetterdienst (2021)].
The simplified methodological approach of basing the model forecasts on various time series measured in the past represents an initial pragmatic and expedient approach.
IBGW Engineering office for groundwater
Links to sources:
https://www.bayceer.uni-bayreuth.de/FH-DGGV-2022/de/prog/bayconf/beitrag_detail.php?id_obj=20857
