Figure 4.
The image consists of four heatmaps arranged in a two-by-two grid. Each heatmap spans a time range from 1980 to 2020 along the horizontal axis, which represents the periods. The vertical axis indicates a different variable related to the data. The colour gradients in the maps depict varying values, with specific patterns visible across the years. Contour lines are also present, emphasizing distinct data ranges. Each heatmap carries a label in the upper area, indicating specific measurements or conditions corresponding to the visual representation in that section, identified by letters (m, n, o, p, q, r) for reference.(Continued)