“…[2] It is commonly agreed that the quality of real-time hydrologic forecasts depends on the adequacy of the rainfall runoff model structure and parameters as well as the accuracy of space-time representation of rainfall input [e.g., Kitanidis and Bras, 1980;Georgakakos and Hudlow, 1984;Georgakakos, 1986;Georgakakos and Smith, 1990;Krajewski et al, 1991;Pessoa et al, 1993;Michaud and Sorooshian, 1994;O'Connell and Todini, 1996;Winchell et al, 1998;Bell and Moore, 2000;Ogden et al, 2000;Borga, 2002;National Research Council, 2002;Syed et al, 2003;Smith et al, 2004;Ajami et al, 2007;Gabellani et al, 2007]. While errors due to both factors have received much recent attention in the literature [e.g., Finnerty et al, 1997;Butts et al, 2004;Carpenter and Georgakakos, 2004;Wagener and Gupta, 2005;Borga et al, 2006;Huard and Mailhot, 2006;Kavetski et al, 2006aKavetski et al, , 2006bKuczera et al, 2006;Oudin et al, 2006], data assimilation and ensemble forecasting frameworks are considered effective means of improving forecasts in the face of uncertainty [e.g., Kavetski et al, 2002;Vrugt et al, 2005;Carpenter and Georgakakos, 2006a;Kavetski et al, 2006a;Moradkhani et al, 2005aMoradkhani et al, , 2005bMoradkhani et al, , 2006Oudin et al, 2006;Russo et al, 2006;…”