PWV versus PWV plots (blue dots) comparing the site measurements and the data obtained by the interpolation of MERRA-2 data at APEX (bottom panel) and LHATPRO (bottom panel) sites. The red line represents the robust linear regression, and the black line represents the 1:1 line. The legend values indicate the Spearman correlation coefficient (ρ), the Pearson correlation coefficient (r), and the slope of the linear regression (m; defined by the equation PWV_site = m* PWV_merra-2).