## 4 Discussion
It has been shown that water budget components of Scots pine forests could be influenced by forest management [7; 75]. Tree species selection is an important management tool to mitigate the consequences of climate change [89]. Scots pine plantations in northeast Germany are subjected to forest conversion toward more diverse forests with higher broad leaf percentages [90]. This will help to increase seepage discharge and thus improve the hydrological status of the region. On the other hand, the vulnerability of the different tree species toward climate change must be considered [91]. Modeling stand water budgets are considered an important tool to reconsider species-specific thresholds in drought tolerance and future prospective, e.g., [92]. For the state of Brandenburg, a concept is developed, based on species-site relationships, which makes suggestions about tree selection under climate change scenarios [19]. In respect to the climate projections considered, we obtained a significant positive trend in actual evapotranspiration for three of the four cases. Despite bias adjustment by the means of quantile mapping, the results reveal a non-significant bias in dry days between historical time series and future climate scenarios. This indicates a higher drought toward the end of the historical time period than at the beginning of the climate change simulations. Indeed, during the last decade, a high number of record-breaking temperature anomalies could be observed globally [93] and regionally for northeast Germany [94]. The current temperature increase fits well with the projected temperature increase under RCP8.5. Therefore, this scenario seems to be more likely to realize than RCP2.6. Our study comes to the result that under RCP8.5 drought, in terms of dry days, it will increase with both models, while drought in terms of climatic water balance and soil moisture content will increase only with ECE/RCA4 under RCP8.5. MPI/Remo show increasing precipitation under RCP8.5, which partly compensates for increasing water losses due to evapotranspiration and leads to an increase of seepage. Due to the dependency of precipitation to atmospheric circulation and their changes, e.g., [11; 95], uncertainty in the simulation of regional precipitation in climate change models is high, and the models show high variability in simulated precipitation, e.g., [46; 97; 96]. Furthermore, hydrological models do not account for the effects of rising CO\({}_{2}\) concentrations on plants [25]. The gas exchange of CO\({}_{2}\) and water are closely interrelated; therefore, water budgets of plants interact with rising CO\({}_{2}\) concentrations [98]. Vegetation is expected to counteract increasing drought, e.g., by changes in allocation patterns. In consequence, this could lead to an overestimation of drought stress by hydrological models, which did not account for CO\({}_{2}\). Therefore, we conclude that it is highly uncertain to which extent climate change will affect the water budgets of forests in northeast Germany. Forest planters must take account of the current trend toward driz climate and of uncertain future conditions. Moreover, the current trend of an increase in canopy mortality in Europe will cause demographic changes in European forests [99], thus altering the properties and water relation of the soil-plant-atmosphere continuum in forests. Nevertheless, the predicted increase of actual evapotranspiration and number of dry days shown in this study and the widely observed tree damages as a result of the last two drought years (2018 to 2019) demonstrate a high vulnerability of the forest trees in northeast Germany. Forest water budget modeling should hence accompany the ongoing effort of the establishment of mixed stands for risk-sharing in climate change, revealing species-specific thresholds of drought tolerance. Both the susceptibility toward drought of mature forests stands and the understory need to be considered in forest management strategies mitigating the consequences of climate change.