Table 3 shows the initial Pa calculated by DM and the real-time correction results modified by GA, respectively. Pa values are corrected by GA at each period according to the RMSE using the observed and simulated discharge. As can be seen in Table 3, compared with the initial values computed by DM, the majority of the Pa values optimized at 23:00 on June 20 are obviously changed with a reduction to be consistent with the forecasting rainfall–runoff process. The value of WU decreases from 17.3 to 16.8 mm, WL with a reduction of 11.6 mm, and WD derives a lower value of 44.0 mm and the total value of WU, WL, and WD reduces from 126.3 to 112.2 mm after the real-time correction. Such reduction demonstrates that Pa modified by GA turns out to conform better to the actual process. Consequently, the simulated rainfall–runoff process with a lower deviation matches better with the actual process, as shown in Figure 5 and Table 4.