  Day-and-night radiative sky cooling has emerged as a potential alternative to
conventional cooling technologies such as refrigeration-based air conditioning
and evaporative wet cooling. Both radiative cooling and evaporative cooling can
passively achieve sub-ambient cooling without consuming electricity. Although
both cooling techniques are subject to impacts from various weather conditions,
the extents of the impacts under the same conditions are not well understood.
In this work, we experimentally and theoretically study the thermal
performances of a passive radiative cooler and a passive evaporative cooler
when exposed to a clear night sky. We show that evaporative cooling is better
suited for high-temperature and low-humidity weather conditions, with the
measured sub-ambient temperatures of the radiative and evaporative coolers
being -13.5{\deg}C and -15.0{\deg}C, respectively, at a low relative humidity
of 13% and a high ambient temperature of 26.0{\deg}C. On the other hand,
radiative cooling is relatively more resilient than evaporative cooling under
high-humidity and/or low-temperature weather conditions, with the measured
sub-ambient temperatures of the coolers being -11.5{\deg}C and -10.5{\deg}C,
respectively, at a slightly higher relative humidity of 32.0% and a slightly
lower ambient temperature of 17.0{\deg}C. Depending on water availability and
weather conditions, both evaporative cooling and radiative cooling can be
adopted as mutually supplemental cooling technologies.
