In this paper: https://www.tandfonline.com/doi/pdf/10.1080/02664763.2021.1940109, the authors have two actual datasets (e.g., 59 observations showing continuous annual flood data) and the authors want to fit it with a Gumbel distribution.
The authors say that
"it is important to first have an idea of the underlying distribution of the two data sets. To get an idea of the underlying distribution of the two data sets, first construct a Q-Q plot by plotting the observed versus expected magnitudes, see Figure 1. "
Question: why can the author conclude that
It is clear from Figure 1 that the data points fall approximately on the straight line; therefore, it can be concluded that the extreme value distribution is an appropriate distribution for both flood data sets.