“…Streamflow is one of the most commonly observed hydrologic variables. Its earliest measurements date back to the late 19th century (Ashman et al, 2004). In more recent decades, the assimilation of streamflow observations into hydrologic models has followed various DA approaches and covered the gamut of applications (e.g., Wood and Szöllösi-Nagy, 1978;Kitanidis and Bras, 1980;Moradkhani et al, 2005;Weerts and El Serafy, 2006;Clark et al, 2008;Pauwels and De Lannoy, 2009;Seo et al, 2009;DeChant and Moradkhani, 2012;Noh et al, 2013;McMillan et al, 2013;Rafieeinasab et al, 2014;Lee and Seo, 2014;Sun et al, 2015;Ercolani and Castelli, 2017;Abbaszadeh et al, 2018;Ziliani et al, 2019, and references therein).…”