This indicator describes trends in average precipitation for the United States and the world.
This indicator examines U.S. and global precipitation patterns, based on rainfall and snowfall measurements from land-based weather stations worldwide. This indicator starts at 1901 except for the detailed map of Alaska, where reliable statewide records are available back to 1925. The indicator extends through 2015.
This indicator shows annual anomalies, or differences, compared with the average precipitation from 1901 to 2000. At each weather station, annual precipitation anomalies were calculated from total annual precipitation in inches. Anomalies for the contiguous 48 states and Alaska have been determined by calculating average precipitation anomalies for areas within each state based on station density and topography. These regional anomalies are then averaged together in proportion to their area to develop national results. Similarly, global anomalies have been determined by dividing the world into a grid, averaging the data for each cell of the grid, and then averaging the grid cells together.