Widespread increases in low-frequency variability of precipitation over the past century

Abstract

PRECIPITATION (rain and snow) provides, through its participation in the global hydrological and energy cycles, most of the heat flux within the atmosphere. For this reason, a knowledge of precipitation variability is important to understanding the behaviour and changes of the Earth's climate system. Precipitation measurements have been made at thousands of sites over the past hundred years or so, and recent efforts have resulted in the compilation of global data sets^1–3 and regional networks^4,17. The latter have been analysed to reveal high-frequency (up to inter-annual) regional trends in precipitation variability over the past century⁴. Here I exploit the global data sets to examine the low-frequency (decadal to multi-decadal) variability of precipitation over a similar time period. In agreement with other analyses⁵,I find that the global mean precipitation has not changed. The fluctuations about the mean, however, have increased significantly (on decadal to multi-decadal timescales). That is, over the past century—during which climate warming has occurred—the global precipitation field has undergone changes on those scales, in which extremes have become more probable. This result is consistent with predictions from model simulations of global climate-warming scenarios^6–8.