Flow calibration

[jzwart]

Only calibrating for flow and with only flow observations. Calibrating soil_moist_max, gwflow_coef, gwsink_coef, ssr2gw_rate, op_flow_thres, and srain_intcp.

Calibrated on Denali from 1980-10-01 to 2004-10-01, with weights higher for low flow observations. Only calibrating for 42 segment subbasin that Xiaowei used in his PGRGN paper. Reduced discharge RMSE from 6.8 to 6.3 cms, although reduction in RMSE is still highest for high discharge segments.

The lowest flow segment (model_idx == 416) reduced low flow periods even lower, with several 0 flow vals

The highest flow segment (model_idx == 455) reduced low flow periods

PRMS tends to over predict at lower flows and under predict at higher flows