Changes in Annual Land-Surface Precipitation Over the Twentieth and Early Twenty-First Century

Abstract

Time trends in annual land-surface precipitation during the twentieth and early twenty-first centuries and their spatial patterns are estimated from gridded (at a 0.5° × 0.5° spatial resolution) rain-gauge-based precipitation data sets available from the Climatic Research Unit (CRU), the Global Precipitation Climatology Centre (GPCC), and at the University of Delaware (UDel). Our analyses of these precipitation data sets make use of spatially weighted (geographic) percentiles as well as of join-point and simple linear regression. A consistent increase in annual land-surface-average precipitation (of approximately 0.2 and 0.5 mm/year) occurred during the first half of the twentieth century. This increase was followed by nearly a half-century (approximately forty-four years, from 1949 through 1993) of decreases in annual land-surface-average precipitation (on the order of 0.3 to 0.6 mm/year). Trends, once again, reversed themselves in the early 1990s and increased (at rates of approximately 0.75 to 2.1 mm/year) over the decade from 1992 through 2002. Maps of precipitation change during these alternating periods of increasing and decreasing precipitation show considerable spatial variability.