# Controlled Drainage Effectiveness in Reducing Nutrient Outflow in Light of Climate Changes
## 1 Introduction
By implementing effective adaptation measures together with appropriate agro-technical measures, integrated solutions for water management in drained areas can be developed [24]. Drainage systems are typically designed with a lifespan of more than thirty years, making them a significant long-term investment. Consequently, it is crucial to conduct research on the potential impact of projected climate change on the performance of agricultural and drainage water management systems [25; 26]. Simulation modeling of hydrological changes is the prevailing approach employed to evaluate how climate change could affect the efficacy of future adaptation strategies [27]. While numerous field campaigns have been conducted to investigate the effects of CD, challenges arise when attempting to test diverse scenarios involving meteorological conditions and hydrological linkages [17; 28]. Models offer a valuable means of assessing the effectiveness of various water management strategies in both present and future climate scenarios [29; 30; 31]. [PERSON] [32] indicated that the implementation of CD had a minimal effect on subsurface drainage, resulting in a reduction of less than 15% in the outflows during both historic and future periods. Similarly, CD demonstrated consistent changes in nitrogen losses in the drainage outflows, with a slight reduction projected for the future. The CD led to an average decrease of 4.42 kg N ha\({}^{-1}\) yr\({}^{-1}\), equivalent to 17.25% during the historic period, and a further reduction of 7.25 kg N ha\({}^{-1}\) yr\({}^{-1}\), corresponding to 25.75%, during the future period. [PERSON] et al. [33] noticed that CD exhibited enhanced efficacy during summer, with reductions in subsurface drainage outflow increasing to 42.7% for the Representative Concentration Pathway (RCP) 4.5 emission scenario and 81.8% for RCP 8.5 under late-century climate conditions. Such evidence of the advantages of implementing CD practice in current climate conditions will continue to be applicable under projected future climate scenarios. [PERSON] et al. [30], who conducted simulations on the effects of CD, using RCP 4.5, observed a decreased duration of the GWT above the drainage depth in future projections. Consequently, this led to a reduced impact of CD on GWT and drainage outflow. According to [PERSON] et al. [31], when CD is applied in future climate scenarios, it is projected to significantly impact the GWT, leading to an average increase of 1-4 cm compared to historical data. It achieves this by reducing annual drain discharge by approximately 41.3 to 46.2 mm and 22.4 to 26.1 mm in RCP 8.5, as well as 41.3 to 43.2 mm and 21.0 to 24.8 mm in RCP 2.6, respectively. These results highlight the relevance and viability of CD as an effective method for mitigating drainage outflow, particularly in milder winter conditions in the future. The purpose of this study was to determine the effect of CD on the GWT, drainage outflow, and N and P losses from agricultural fields in Greater Poland. Simulations have been carried out, assuming changes in temperature and precipitation in line with the Inter-Sectoral Impact Model Intercomparison Project (ISMIP) simulations, in particular the third round of ISIMIP3b, as part of the international Coupled Model Intercomparison Project 6 (CMIP6). It focuses on regional scale changes in agriculture for three models (Geophysical Fluid Dynamics Laboratory (GFDL), Max Planck Institute Earth Model (MPI), and UK Earth System Model (UKESM)) for predicting the impact of future climate changes. Our study uses the SSP370 scenario with an additional radiative forcing of 7 W m\({}^{-2}\) by the year 2100. This scenario is in the upper-middle part of the full range of scenarios and has been newly introduced, closing the gap between RCP6.0 and RCP8.5. To know the seasonal effects of CD, it is necessary to study long-term simulations with future climate predictions and assess the change in the near future.