“…Most of these publications use synthetic (or twin) experiments with assimilation of artificially generated data. Examples include studies with simulated measurements of the groundwater table depth or hydraulic head (Franssen and Kinzelbach, 2008;Bailey and Baù, 2012;Kurtz et al, 2014;Shi et al, 2014;Song et al, 2014;Tang et al, 2015), discharge/streamflow (Bailey and Baù, 2012;Moradkhani et al, 2012;Vrugt et al, 2013;Rasmussen et al, 2015), groundwater temperature (Kurtz et al, 2014), soil moisture (Wu and Margulis, 2011;Plaza et al, 2012;Erdal et al, 2014;Shi et al, 2014;Song et al, 2014;Pasetto et al, 2015), brightness temperature from passive remote sensing (Montzka et al, 2013;Han et al, 2014), and contaminant concentration (Gharamti et al, 2013). These studies use a variety of different methods for joint parameter and state estimation, among which the EnKF (Franssen and Kinzelbach, 2008;Wu et al, 2011;Gharamti et al, 2013;Erdal et al, 2014;Kurtz et al, 2014;Shi et al, 2014;Pasetto et al, 2015), the iterative EnKF (Song et al, 2014), the extended KF (Pauwels et al, 2009), the local ensemble transform KF (Han et al, 2014), the ensemble transform KF (Rasmussen et al, 2015), and the normal score EnKF (Tang et al, 2015).…”