  The relationship between the peak velocities of high-speed solar wind streams
near Earth and the areas of their solar source regions, i.e., coronal holes,
has been known since the 1970s, but it is still physically not well understood.
We perform 3D magnetohydrodynamic (MHD) simulations using the European
Heliospheric Forecasting Information Asset (EUHFORIA) code to show that this
empirical relationship forms during the propagation phase of high-speed streams
from the Sun to Earth. For this purpose, we neglect the acceleration phase of
high-speed streams, and project the areas of coronal holes to a sphere at 0.1
au. We then vary only the areas and latitudes of the coronal holes. The
velocity, temperature, and density in the cross section of the corresponding
highspeed streams at 0.1 au are set to constant, homogeneous values. Finally,
we propagate the associated high-speed streams through the inner heliosphere
using the EUHFORIA code. The simulated high-speed stream peak velocities at
Earth reveal a linear dependence on the area of their source coronal holes. The
slopes of the relationship decrease with increasing latitudes of the coronal
holes, and the peak velocities saturate at a value of about 730 km/s, similar
to the observations. These findings imply that the empirical relationship
between the coronal hole areas and high-speed stream peak velocities does not
describe the acceleration phase of high-speed streams, but is a result of the
high-speed stream propagation from the Sun to Earth.
