There is a very interesting new paper with respect to climate trends in the southwestern United States (h/t to ICECAP and World Climate Report ). It is
McCabe, G. J., D. R. Legates, and H. F. Lins. 2010. Variability and trends in dry day frequency and dry event length in the southwestern United States, Journal of Geophysical Research, 115, D07108, doi:10.1029/2009JD012866.
The abstract reads
“Daily precipitation from 22 National Weather Service first‐order weather stations in the southwestern United States for water years 1951 through 2006 are used to examine variability and trends in the frequency of dry days and dry event length. Dry events with minimum thresholds of 10 and 20 consecutive days of precipitation with less than 2.54 mm are analyzed. For water years and cool seasons (October through March), most sites indicate negative trends in dry event length (i.e., dry event durations are becoming shorter). For the warm season (April through September), most sites also indicate negative trends; however, more sites indicate positive trends in dry event length for the warm season than for water years or cool seasons. The larger number of sites indicating positive trends in dry event length during the warm season is due to a series of dry warm seasons near the end of the 20th century and the beginning of the 21st century. Overall, a large portion of the variability in dry event length is attributable to variability of the El Niño–Southern Oscillation, especially for water years and cool seasons. Our results are consistent with analyses of trends in discharge for sites in the southwestern United States, an increased frequency in El Niño events, and positive trends in precipitation in the southwestern United States.”
The conclusion contains the text
Little evidence of long‐term positive trends in dry event length in the southwestern United States is apparent in the analysis of daily WBAN precipitation data. During the mid‐1990s to late 1990s, drought conditions began in the southwestern United States and persisted in the 21st century. This drought has resulted in positive trends in dry event length for some sites in the southwestern United States. However, most of the statistically significant trends in the number of dry days and dry event length are negative trends for water years and cool seasons.
In addition, correlation and spectral analyses indicate that a substantial portion of the variability in dry event characteristics in the southwestern United States is attributable to ENSO variability, particularly for water years and cool seasons. Since the mid‐1970s, El Niño events have been more frequent, and this has resulted in increased precipitation in the southwestern United States, particularly during the cool season. The increased precipitation is associated with a decrease in the number of dry days and a decrease in dry event length.
This paper reinforces two issues that have repeatedly been made on my weblog:
- The multi-decadal IPCC global climate models, which have predicted more-or-less perpetual drought in the southwestern United States, are failing in their regional prediction. These predictions, for example, are discussed in the post
where the paper
Barnett, T. P, and D. W. Pierce, 2008: When will Lake Mead go dry? Water Resour. Res., 44, W03201, doi:10.1029/2007WR006704,
that is discussed in that post, includes their forecast
“A water budget analysis shows that under current conditions there is a 10% chance that live storage in Lakes Mead and Powell will be gone by about 2013 and a 50% chance that it will be gone by 2021 if no changes in water allocation from the Colorado River system are made.”
In another post
the paper
Richard Seager, Mingfang Ting, Isaac Held, Yochanan Kushnir, Jian Lu, Gabriel Vecchi,Huei-Ping Huang, Nili Harnik, Ants Leetmaa,2 Ngar-Cheung Lau, Cuihua Li, Jennifer Velez, Naomi Naik Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America Richard Seager, et al., Science 316, 1181 (2007); DOI: 10.1126/science.1139601
is discussed in which they write
“…there is a broad consensus among climate models that this region will dry in the 21st century and that the transition to a more arid climate should already be under way. If these models are correct, the levels of aridity of the recent multiyear drought or the Dust Bowl and the 1950s droughts will become the new climatology of the American Southwest within a
time frame of years to decades.”
The Barnett and Pierce 2008, and Seager et al 2007 papers (and other such papers and reports) have misled policymakers on the reality of how the climate system behaves, as illustrated in the new McNabe et al 2010 paper.
and
- The dominance of the regional climate feature of ENSO, as reported in the McNabe et al 2010 paper, further documents why the use of a global average surface temperature trend (or global average radiative forcing) is a grossly inadequate metric to diagnose climate variability and change.
