Retrieving baseflow of large rivers from space with the future SWOT mission.

The quantification of aquifer contribution to river discharge is of primary importance toevaluate the impact of climatic and anthropogenic stresses on the availability of waterresources. Several baseflow estimation methods require river discharge measurements, whichcan be difficult to obtain at high spatio-temporal resolution for large basins. The SWOTsatellite mission will provide water level values from which discharge estimations will bederived for large rivers (> 50 - 100 m wide) even in ungauged basins with a maximumfrequency of 21 days. We develop a methodology to estimate baseflow over a whole mission lifetime. To thisaim, an algorithm based on hydrograph separation using the Chapman’s filter was developedto automatically estimate the baseflow in a river network at regional scale (> 10 000 km2).The algorithm was applied to the Seine River basin (75 000 km2, France) using the dischargetime series simulated at daily time step by the coupled hydrological-hydrogeological modelCaWaQS to obtain the reference baseflow estimations. The same algorithm is then forcedwith discharge time series sampled at SWOT observation frequency. The average baseflow isestimated with good accuracy for all the reaches which are observed at least once per cycle(relative bias less than 8 %). The time evolution of baseflow is also rather wellretrieved, with a Nash-Sutcliffe coefficient above 0.7 for 96 % of the network length(Baratelli et al., 2018). Based on former estimations of uncertainties on dischargesthat will be estimate by the mission, it appears that baseflow estimates are alwaysslightly lower than those on discharge. This work provides new potential for thehydrological community to better close the water cycle using forthcoming spacebornedata. Reference : Baratelli, F., Flipo, N., Rivière, A., Biancamaria, S. (2018) Retrieving riverbaseflow from SWOT spaceborne mission, Remote Sensing of Environment, 218, 44-54.doi:10.1016/j.rse.2018.09.013 [ABSTRACT FROM AUTHOR]