Changes in river temperature, discharge and heat flux based on new observational data for Yenisei basin and modeling

River temperature plays an important role in numerous biological and ecological processes within the Yenisei River basin and it is very sensitive to changes in climatic characteristics and anthropogenic disturbances. Water temperature and river discharge characterize heat or energy flux, which is important in northern latitudes for river freeze-up and ice break-up processes and thermal riverbank erosion. The changes in heat flux in river estuary can also significantly impact various biophysical processes in coastal ocean waters.We use new water temperature data and river discharge records for 12 observational gauges in the Yenisei River basin to analyze changes in water temperature and heat flux from upstream to downstream over 1950-2018. Preliminary results show significant increases for most gauges in maximum annual water temperature as well as in 10-days mean water temperature during May-June and September-October. There were no significant changes in river temperature during July-August unless the gauges were impacted by reservoir regulations. The river heat flux has significantly increased in central and northern parts of the Yenisei basin and decreased in the south, mainly due to discharge variability.The gridded hydrological Water Balance Model (WBM) developed at the University of New Hampshire, that takes into account various anthropogenic activities, was used to simulate river discharge and water temperature for entire Yenisei basin with a 5 minute spatial resolution river network using several climate reanalysis products (MERRA2, ERA5 and NCEP-NCAR).  The modeled results were verified with observational data and simulations using the MERRA2 climate drivers demonstrated the best match with observations (Nash-Sutcliffe model efficiencies coefficients were greater than 0.5 for both river temperature and discharge). Maps of modeled changes in runoff, river temperature and heat flux show the opposite changes in the southern and northern parts of Yenisei basin. The model simulations correspond well with observational data even for heavily disturbed river reaches. For example, they show unfrozen water with positive temperatures during the winter below large dams and reservoirs.       The WBM was also applied to project changes in water temperature, discharge and heat flux up to 2100 for several SSPs and GCMs from CMIP6. In spite of heterogenous projected changes in these parameters across Yenisei basin, significant increases in discharge and heat flux to the Arctic Ocean are expected.