The Grand Canyon receives an average of 15 inches (38 centimeters) of rainfall per year. However, this average is spread unevenly throughout the year and across the canyon itself.

Here's a breakdown:

* South Rim: The South Rim, which is the most popular area for visitors, receives slightly more rain than the North Rim, around 18 inches per year.

* North Rim: The North Rim receives around 12 inches of rain per year.

* Inner Canyon: The inner canyon, which is the deepest part of the canyon, receives even less rainfall, often less than 10 inches per year.

Rainfall is also very seasonal:

* Summer Monsoon Season (July-September): The Grand Canyon experiences a short but intense monsoon season, during which the majority of the annual rainfall occurs.

* Rest of the year: The rest of the year is generally dry, with infrequent rainfall.

It's important to note that these are just averages, and actual rainfall can vary significantly from year to year.