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Sloan Coats, Jason E. Smerdon, Benjamin I. Cook, and Richard Seager

1. Introduction A stark feature of multidecadal hydroclimate variability in the North American Southwest (NASW; 25°–42.5°N, 125°–105°W) is the occurrence of widespread drought conditions lasting decades to centuries [see Cook et al. (2007) for a review]. Understanding the causes of these so-called megadroughts is critical for assessing their likelihood of occurrence in the future and whether their risk probabilities will be influenced by greenhouse gas forcing. The limited (~150 yr

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Andrew J. Newman and Richard H. Johnson

1. Introduction The North American monsoon (NAM) has the typical characteristics of a monsoon: a seasonal wind reversal and areas receiving a significant portion of their annual precipitation during the NAM ( Carleton et al. 1990 ; Badan-Dangon et al. 1991 ; Douglas et al. 1993 ; Douglas 1995 ; Stensrud et al. 1995 ; Adams and Comrie 1997 ; Anderson et al. 2000a ; Vera et al. 2006 ; Johnson et al. 2007 ). Regions in the core of the monsoon (northwest Mexico) receive up to 80% of their

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Nicole J. Schiffer and Stephen W. Nesbitt

1. Introduction Portions of northwestern Mexico and the southwestern United States receive in excess of 70% of their annual precipitation during July, August, and September ( Douglas et al. 1993 ). The circulation changes associated with this boreal summer precipitation maximum in this region have been termed the North American monsoon [NAM; see Adams and Comrie (1997) for an overview of the NAM]. The large-scale circulation changes associated with the NAM modulate precipitation within and

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Neil P. Lareau and John D. Horel

Hemisphere storm tracks have been studied in depth for better than half a century ( Petterssen 1956 ; Klein 1957 ; Blackmon 1976 ; Sickmöller et al. 2000 ; Hoskins and Hodges 2002 , hereafter HH02 ; Wettstein and Wallace 2010 ). Storm tracks are also of manifest regional importance. The occurrence and progression of storms across western North America have a significant impact on the region’s hydrologic cycle during the cool season (October–April), particularly in terms of the development of

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Mizuki Iida, Shusaku Sugimoto, and Toshio Suga

; Overland et al. 2015 ), such as central Eurasian cooling attributable to sea ice loss in the Barents–Kara Seas ( Honda et al. 2009 ; Petoukhov and Semenov 2010 ; Inoue et al. 2012 ; Nakanowatari et al. 2014 ; Sato et al. 2014 ; Mori et al. 2014 , 2019 ; Chen et al. 2016 ) and eastern Asian cooling from an ice-free Chukchi Sea ( Tachibana et al. 2019 ). North America also has experienced extreme cold winters over the past 10 years ( Wallace et al. 2014 ). These extreme conditions are related to

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Joshua P. Heyer, Simon C. Brewer, and Jacqueline J. Shinker

1. Introduction Tropical Pacific sea surface temperature (SST) forcing impacts hydroclimate variability globally in areas of the tropics, extratropics, and western North America (NA) ( Ropelewski and Halpert 1986 ; Cayan and Peterson 1989 ; Kiladis and Diaz 1989 ; Cayan 1996 ; Myneni et al. 1996 ; Trenberth et al. 1998 ; Gershunov and Barnett 1998a , b ; Trenberth et al. 1998 ; Dettinger et al. 2000 ; Castro et al. 2001 ; Gershunov and Cayan 2003 ; Verdon et al. 2004 ; Seager et al

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Melissa S. Bukovsky, Carlos M. Carrillo, David J. Gochis, Dorit M. Hammerling, Rachel R. McCrary, and Linda O. Mearns

; Cook and Seager 2013 ). Statements about precipitation associated specifically with the North American monsoon (NAM) season for these regions are more uncertain, however. In the CMIP3 suite of GCMs, a decrease in summertime-mean precipitation was projected for the SWUS and northwestern MX, but model agreement on that projection was weak ( Christensen et al. 2007 , their Fig. 11.12). In the CMIP5 ensemble, decreases in monsoon season rainfall are small and insignificant overall, given a shift in the

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Giovanni Forzieri, Fabio Castelli, and Enrique R. Vivoni

1. Introduction The North American monsoon (NAM) region in the southwestern United States and northwestern Mexico experiences seasonal greening of a range of ecosystems due to the synchronized availability of precipitation and solar radiation in the summer, July–September (JAS). Vegetation dynamics in parts of the NAM region have been explored using remote sensing observations and related to precipitation and soil moisture ( Mora and Iverson 1998 ; Watts et al. 2007 ; Pennington and Collins

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Tristan Ballard, Richard Seager, Jason E. Smerdon, Benjamin I. Cook, Andrea J. Ray, Balaji Rajagopalan, Yochanan Kushnir, Jennifer Nakamura, and Naomi Henderson

1. Introduction The Prairie Pothole Region (PPR) contains between 5 and 8 million wetland basins in small depressions left behind by the most recent Pleistocene glaciation. The PPR provides immense biological and ecosystem services to our society ( Johnson et al. 2010 ). First and foremost, the region acts as an ideal waterfowl breeding habitat, producing 50%–80% of North American ducks in late spring and summer ( Batt et al. 1989 ). This 800 000 km 2 region spans five states (Montana, North

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Tyler P. Janoski, Anthony J. Broccoli, Sarah B. Kapnick, and Nathaniel C. Johnson

eastern North America, mean snowfall decreases but the average intensity of snowfall events increases. Kawase et al. (2016) found similar results, including decreases in mean snowfall but increases in extreme daily snowfall in some areas of Japan, using an ensemble of high-resolution climate models. Although these recent studies indicate progress in understanding how both mean and extreme snowfall will change with increasing greenhouse gases, it remains uncertain how these results would apply to

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