Towards an Understanding of the Twentieth-Century Cooling Trend in the Southeastern United States: Biogeophysical Impacts of Land-Use Change

Abstract

11This paper explores the link between the anomalous warming hole in the Southeastern U.S. and 12 a major land use/land cover (LULC) change in the region. Land surface and satellite 13 observations were analyzed to estimate the net radiative forcing due to LULC change. Albedo 14 and latent energy were specifically addressed for the dominant LULC change of agriculture to 15 forests. It was assumed that in the energy limited environment of the region, the partition of 16 changes in available energy due to albedo will mostly impact the sensible heat. The results 17 show that in the Southeastern U.S. for the period of 1920 to 1992 the changes in sensible (as a 18 result of albedo) and latent energies are in direct competition with each other. In the spring 19 Revised Manuscript (non-LaTeX) Click here to download Manuscript (non-LaTeX) Revision2.docx 2 and early summer months, the croplands are in peak production and the latent energy 20 associated with their ET is comparable to that of the forests so the decrease in radiation due to 21 albedo dominates the signal. However, during the late summer and fall months most major 22 crops have matured thus reducing their transpiration rate while forests (particularly 23 evergreens) maintain their foliage and with their deep roots, are able to continue to transpire 24 as long as atmospheric conditions are favorable. This later influence of latent energy appears to 25 more than offset the increased radiative forcing from the spring and early summer. Overall, a 26 mean annual net radiative forcing resulting from a LULC change from cropland to forests was 27 estimated to be -1.06 W/m 2 ; thus, a probable contribution to the 'warming hole' over the 28 Southeast during the majority of the 20th century. 29 30

Modeling the contributions of global air temperature, synoptic-scale phenomena and soil moisture to near-surface static energy variability using artificial neural networks

“…4). This finding is also replicated in the second region of weak or negative air temperature trends described above and centered on MS and AL (Ellenburg et al, 2016). The RMSE is lower in ANN-HL3-SM than ANN-HL3 over all but one grid cell in these two states.…”

“…1a and g; Pryor and Schoof, 2016;Ellenburg et al, 2016). For example, over the period 1950-2000 the region as a whole experienced rapid population growth (though this was not spatially uniform), expansion of area classified as exurban, an overall reduction of land in agriculture (though again this was highly heterogeneous in space) and an increase in the intensity of water management (including expansion of irrigation) (Brown et al, 2005).…”

“…1h). The lack of warming in both regions has been attributed to changing land-surface characteristics and enhanced soil moisture availability (Kalnay and Cai, 2003;Pan et al, 2009;Ellenburg et al, 2016). In the case of MS and AL, up to 60 % of the variance of summer temperatures has been ascribed to soil moisture (and thus an increase in the LE at the surface at the expense of H , Eq.…”

“…In the case of MS and AL, up to 60 % of the variance of summer temperatures has been ascribed to soil moisture (and thus an increase in the LE at the surface at the expense of H , Eq. 2) and cloud cover (reducing the net radiation) (Ellenburg et al, 2016). However, additional factors may account for these warming holes including large-scale climate modes such as the Interdecadal Pacific Oscillation and the associated sea surface temperature anomalies in the tropical Pacific (Meehl et al, 2015), as well as aerosol radiative forcing (Leibensperger et al, 2012;Yu et al, 2014).…”

Winter climate variability in the southern Appalachian Mountains, 1910–2017

“…The southeastern United States (SEUS) has been identified as a 20 th century regional climate anomaly meaning that this region actually experienced a decline in mean annual temperatures while the majority of the planet warmed (Portmann et al, 2009;Ellenburg, 2016). The vast majority of this cooling occurred from the 1930s to the late 1970s, although the region has experienced a slight rebound in temperatures over the last few decades (Hansen et al, 2001;Kunkel et al, 2006).…”