Multidecadal Regime Shifts in U.S. Streamflow, Precipitation, and Temperature ...
- Multidecadal Regime Shifts in U.S. Streamflow, Precipitation,
and Temperature at the End of the Twentieth Century
Steven A. Mauget
U.S. Department of Agriculture�Agricultural Research Service,
USDA Plant Stress and Water Conservation Laboratory,
Lubbock, Texas ( 13 May 2003)
Journal of Climate: Vol. 16, No. 23, pp. 3905�3916.
Intra- to multidecadal variation in annual streamflow, precipitation, and
temperature over the continental United States are evaluated here through
the calculation of Mann�Whitney U statistics over running-time windows of
6�30-yr duration. When this method is demonstrated on time series of
nationally averaged annual precipitation and mean temperature during
1896�2001, it reveals that 8 of the 10 wettest years occurred during the
last 29 yr of that 106-yr period, and 6 of the 10 warmest years during
the last 16. Both of these results indicate highly significant departures
from long-term stationarity in U.S. climate at the end of the twentieth
century. The effects of increased wetness are primarily evident in the
central and eastern United States, while evidence of warmth is found
throughout the Rocky Mountain region and in the West. Analysis of annual
streamflow records across the United States during 1939�98 shows broadly
consistent effects. Initial evidence of the recent wet regime is most
apparent in eastern streamflow, which shows a clear pattern of
high-ranked mean annual values during the 1970s. Over the midwestern
states, a coherent pattern of high-ranked annual flow is found during
multidecadal periods beginning during the late 1960s and early 1970s and
ending in either 1997 or 1998. During the late 1980s and early 1990s, a
significant incidence of low-ranked annual flow conditions throughout the
West was roughly
coincident with the onset of western warmth during the mid-1980s.
Evidence of highly significant transitions to wetter and warmer
conditions nationally, and consistent variation in streamflow analyses,
suggests that increased hydrological surplus in the central and eastern
United States and increased hydrological deficit in the West may be
representative of the initial stages of climate change over the
continental United States.
USDA - Agricultural Research Service
3810 4th Street
Lubbock, Texas, 79415
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