“…These include, for example, the one-, two-, three-and fourdimensional variational algorithms (1D-, 2D-, 3D-, and 4D-VAR, e.g., Seo et al, 2003Seo et al, , 2009Valstar et al, 2004), extended or ensemble Kalman filtering (EKF or EnKF, e.g., Moradkhani et al, 2005b;Slater and Clark, 2006;Weerts and El Serafy, 2006;Shamir et al, 2010), particle filtering (e.g., Moradkhani et al, 2005a;Weerts and El Serafy, 2006;Matgen et al, 2010;DeChant and Moradkhani, 2012), H-infinity filters (Wang and Cai, 2008), hybrid EnKF or 4D-VAR approaches (e.g., Zhang et al, 2009), and other Bayesian approaches (e.g., Reggiani and Weerts, 2008;Todini, 2008;Reggiani et al, 2009). While most DA applications have focused on updating hydrologic model states (e.g., soil moisture and snow water equivalent), recent research has also examined the benefits of estimating model states and model parameters simultaneously (e.g., Moradkhani et al, 2005a, b Vrugt et al, 2005;Lu et al, 2010;Leisenring and Moradkhani, 2011;Nie et al, 2011) as well as the possibility of model structure identification and uncertainty estimation (e.g., Neuman, 2003;Bulygina and Gupta, 2010;Hsu et al, 2009;Parrish et al, 2012).…”