Rising estimates of terrestrial and global precipitation

Estimates of long-term average terrestrial and global precipitation that have been made in the 1900s from raingage observations are examined. Raingage undercatch is documented and evaluated. Bias-producing influences that irregularly-spaced station networks and commonly-used spatial interpolation procedures have on large-scale spatial averages of precipitation also are investigated, primarily using computer-intensive statistics. Interpretation of each of these sources of bias as well as their interaction suggests that long-term average global precipitation has risen even more than the existing record indicates.