3.1.2. Salinity Data

Several modeling steps were followed to generate salinity data necessary to calibrate pre-development relationships between annual Delta outflow and seasonal average X2. First, the daily outflow time series from the aforementioned 93-year simulation [25] was transformed into a daily "antecedent outflow" time series to represent flow timehistory in the estuary [14,84]. This transformed outflow time series was used to generate a daily X2 time series using a pre-development flow–salinity relationship reported by Andrews et al. [26]. Finally, this synthetic daily X2 time series was averaged to develop seasonal (February–June and July–October) average X2 calibration time series.

For internal consistency, rather than using historical data, we followed a similar methodology to generate salinity data necessary to calibrate contemporary relationships between annual Delta outflow and seasonal average X2. Specifically, we used a subset of the daily contemporary Delta outflow time series [27,82] spanning WYs 1920–2018 and a contemporary flow–salinity relationship reported by [26]. The initial years of the contemporary period (WYs 1912–1919) were excluded from model calibration due to lack of historical Delta outflow data at a daily resolution.
