This repository contains the dataset linked to the following publication: Article title: Reservoir water quality deterioration due to deforestation emphasizes the indirect effects of global change Journal title: Water Research Article Number: WR_118721 doi: https://doi.org/10.1016/j.watres.2022.118721 Abstract: Deforestation is currently a widespread phenomenon and a growing environmental concern in the era of rapid climate change. In temperate regions, it is challenging to quantify the impacts of deforestation on the catchment dynamics and downstream aquatic ecosystems such as reservoirs and disentangle these from direct climate change impacts, let alone project future changes to inform management. Here, we tackled this issue by investigating a unique catchment-reservoir system with two reservoirs in distinct trophic states (meso‑ and eutrophic), both of which drain into the largest drinking water reservoir in Germany. Due to the prolonged droughts in 2015–2018, the catchment of the mesotrophic reservoir lost an unprecedented area of forest (exponential increase since 2015 and ca. 17.1% loss in 2020 alone). We coupled catchment nutrient exports (HYPE) and reservoir ecosystem dynamics (GOTM-WET) models using a process-based modeling approach. The coupled model was validated with datasets spanning periods of rapid deforestation, which makes our future projections highly robust. Results show that in a short-term time scale (by 2035), increasing nutrient flux from the catchment due to vast deforestation (80% loss) can turn the mesotrophic reservoir into a eutrophic state as its counterpart. Our results emphasize the more prominent impacts of deforestation than the direct impact of climate warming in impairment of water quality and ecological services to downstream aquatic ecosystems. Therefore, we propose to evaluate the impact of climate change on temperate reservoirs by incorporating a time scale-dependent context, highlighting the indirect impact of deforestation in the short-term scale. In the long-term scale (e.g. to 2100), a guiding hypothesis for future research may be that indirect effects (e.g., as mediated by catchment dynamics) are as important as the direct effects of climate warming on aquatic ecosystems. Data description by Xiangzhen Kong (xiangzhen.kong@ufz.de; xzkong@niglas.ac.cn) 2022-06-20 1. Discharge in the streams from 2010 to 2021 at YRZ site, and from 2010 to 2020 at YHZ_Q site. File name: dat_discharge_stream_YRZ_YHZ_2010_2021_daily.csv Note: The data is at daily basis but also available at 15-min high frequency basis, which can be requested from the authors. 2. Nitrate concentration in the streams from 2011 to 2019 at both YRZ and YHZ_Q sites. File name: dat_nitrate_stream_YRZ_YHZ_2011_2019_daily.csv Note: The data is at daily basis but also available at 15-min high frequency basis, which can be requested from the authors. 3. Water quality data in the inflows from 2010 to 2021 at biweekly basis, from YRZ and YHZ_WQ sites. File name: dat_waterquality_stream_YRZ_YHZ_2010_2021_biweekly.csv Note: The data is at biweekly basis, measured at the depth of 0.5m under water surface, from both probe and lab. 4. Water quality data in the predams from 2010 to 2021 at biweekly basis, from YR1 and YH1 sites. File name: dat_waterquality_predams_YR1_YH1_2010_2021_biweekly.csv Note: The data is at biweekly basis, measured at the depth of 0.5m under water surface, from both probe and lab. 5. Water quality data in the predams from 2010 to 2015 at biweekely basis, from YR3 and YH3 sites. File name: dat_waterquality_predams_YR3_YH3_2010_2015_biweekly.csv Note: The data is at biweekly basis, measured at various water depth, only from lab. 6. CTD and BBE probe profile data in the predams from 2010 to 2015 at biweekely basis, from YR3 and YH3 sites. Note: Data stored in the folder "probe_profiles_predam_YR3_YH3_2010_2015_biweekly". The data is at biweekly basis, measured at various water depths. The measurements include water temperature (Celcius), DO (mg/L), Chl-a (mg/m3), bluegreen, green and diatom (all in Chl-a, mg/m3)