Figure 4 . Scatter plots showing the performance of NN1W and NN2W against SA across all sites. Points above the grey zero line show configurations where the NN configuration improved performance over SA. The “Maximum improvement” line is based on the performance of the SA simulations, and is simply (1-NSE) in subplots a and b, and (1-KGE) in subplots c and d.
We also compared the KGE for different periods of temporal aggregation to evaluate whether performance improvements of the NN configurations persisted across timescales (Figure 5). The KGE score was chosen here because it shows greater variability than the NSE score in Figure 3, though the results are similar for NSE. We see that the sub-daily aggregations, on average, showed better performance for both NN configurations, demonstrating that they were able to capture the diurnal cycle of turbulent heat fluxes. This is mostly due to the strong dependence of turbulent heat fluxes on solar radiation, which we will further explore in section 3.2. Both NN1W and NN2W were able to outperform SA across all timescales for sensible heat.
However, at daily and longer temporal aggregations differences between models were seen in latent heat performance. The NN1W configuration performed better at sub-daily timescales than for daily or longer aggregations, for which performance was similar to SA. In contrast, the NN2W configuration performed better for latent heat than SA across all timescales.