Evaluating changes in season length, onset, and end dates across the United States (1948–2012)

Abstract

Discussed in a global context, the issue of scale is important to consider as it relates to climate change. As climatological studies utilize temporally and spatially static definitions of seasonal definitions, the understanding of seasonal change may be limited by the way in which seasons are defined. This research serves as a challenge to this perspective by examining the changes in seasons by incorporating variability into the way in which seasons are defined. Temporally and spatially variable seasons were defined based on thresholds of apparent temperature and upper-level circulation patterns for the period 1948-2012. Using 60 US surface stations, two apparent air temperature metrics were used to define seasons that vary spatially and temporally. Stations represented major cities found in the contiguous United States. A large-scale circulation approach utilized synoptic categorizations based on 250-mb geopotential heights from the NCEP-NCAR reanalysis (NNR) as a metric of seasonal delineation. In this method, seasons varied temporally but not spatially. Despite the different methodological approaches, consistent trends were found. Since 1948, late starts of autumn and winter have been observed while earlier onsets of spring and summer have taken place. For the individual stations, the largest shifts occurred along coasts and in larger, more urbanized environments. Individual locations also showed increased variability in start date, and significant changes were found for all four seasons in the circulation approach. Seasons have been shown to be important for a variety of processes including phenological responses and human adaptation to extreme temperature environments; therefore, the consideration of season variability may be appropriate for future climatological research.

Analysis of spatio‐temporal changes in annual and seasonal precipitation variability in South America‐Chile and related ocean–atmosphere circulation patterns

“…These changes are more noticeable in Central and Southern Chile for those rain gauges located around 40 ∘ S, which showed mostly significant negative (positive) trends during austral autumn (winter) (Figure 8(f) and (g)). Seasonal changes have recently been reported for United States by Allen and Sheridan (2015), who analysed temperature data concluding that late starts of autumn and winter have been observed while earlier onsets of spring and summer have taken place between 1948 and 2012.…”

New indices for assessing changes in seasons and in timing characteristics of air temperature

“…Global warming caused by increasing emissions of greenhouse gases is a major concern around the world (Allen et al 2010;Vörösmarty et al 2000). The mean ambient air temperature of the Earth rose by approximately 0.85°C from 1880 to 2012 (Allen and Sheridan 2016;Hartmann et al 2013). This is reported to have caused climate change (Richardson et al 2018), with increasing frequency of droughts, floods, and extreme weather events in many parts…”

Defining frigid winter illuminates its loss across seasonally snow-covered areas of eastern North America

“…The overall shortening of winter that we observed was largely due to an earlier spring onset; 22 of 37 sites exhibited significantly earlier loss of continuous cold conditions as compared with only 6 of 37 sites where the onset of cold conditions occurred later. Other studies have likewise reported that earlier springs drove trends in reduced winter duration (Dye 2002, Allen and Sheridan 2016, Kutta and Hubbart 2016. In addition, proxies for the beginning of spring, particularly phenological data describing budbreak, leaf emergence, and leaf out, have been widely used to document earlier springs (Richardson et al 2006, Schwartz et al 2013, Piao et al 2015, providing further evidence for an advancement of spring onset by −0.8 to −0.9 d per decade in the northeastern US from 1901 to 2012 (Monahan et al 2016).…”