Figure 4.
The image consists of four graphs arranged in a two-by-two grid layout. Each graph shows a time series analysis across the years from 1980 to 2020, with the horizontal axis representing years and the vertical axis displaying 'Period' values. The title of each graph indicates different methodologies or categories, such as PWC and MW, and specific analytical frameworks like ECI or NaR. The graphs depict colour gradients representing varying values, predominantly shades of blue and red, with black contour lines highlighting particular value ranges. The border lines create a triangular shape in each graph, and there are small annotations or labels in the top left corners (s, t, u, v, w, x) corresponding to each figure. The contour lines and colour variations suggest complex data changes across the specified timeline.(Continued)