# water (or hydrological) year around the world, does it change?

Following the commonly-known USGS definition of Water Year (or Hydrological Year) we know that it starts on the 1st October and ends on the next 30th September.

Is this definition valid only for temperate/mid-latitudes? What's the water year e.g. in the Equatorial, Polar and Arid regions?

Can I keep using the USGS definition for these areas or shall I just use the calendar year (1st January-31st December)?

Thanks