Twentieth Century Regional Climate Change During the Summer in the Central United States Attributed to Agricultural Intensification

Abstract

Both land use changes and greenhouse gas (GHG) emissions have significantly modified regional climate over the last century. In the central United States, for example, observational data indicate that rainfall increased, surface air temperature decreased, and surface humidity increased during the summer over the course of the twentieth century concurrently with increases in both agricultural production and global GHG emissions. However, the relative contributions of each of these forcings to the observed regional changes remain unclear. Results of both regional climate model simulations and observational analyses suggest that much of the observed rainfall increase—as well as the decrease in temperature and increase in humidity—is attributable to agricultural intensification in the central United States, with natural variability and GHG emissions playing secondary roles. Thus, we conclude that twentieth century land use changes contributed more to forcing observed regional climate change during the summer in the central United States than increasing GHG emissions.

Spatially Distinct Seasonal Patterns and Forcings of the U.S. Warming Hole

“…In this study, we find mostly insignificant correlations between ocean-atmosphere indices and summer temperature, suggesting that forcings besides aerosols and oceanic and atmospheric modes in the Pacific and Atlantic Basin are contributing to the summer warming hole. Besides aerosols, changes in external forcing could arise from changing land use, irrigation, and agricultural intensification (Alter et al, 2017;Misra et al, 2012;Pei et al, 2016). In support of this hypothesis, we note that there is considerable spatial coherence between the location of the summer warming hole and the region within which cooler extreme temperatures are associated with agricultural intensification (Figure 3 of Mueller et al 2016).…”

“…This suggests that the summer warming hole is not a result of large-scale oceanic-atmospheric modes of variability and that spring represents a period during which processes in the Pacific and Atlantic basins become less influential on temperature in the warming hole region, while the effects of external forcing may become more influential. Besides aerosols, changes in external forcing could arise from changing land use, irrigation, and agricultural intensification (Alter et al, 2017;Misra et al, 2012;Pei et al, 2016). Existing literature suggests that the effect of anthropogenic aerosols is largest during the summer and autumn (Leibensperger et al, 2012;Yu et al, 2014) and could contribute to the summertime warming hole.…”

Enhancing the Predictability of Seasonal Streamflow With a Statistical‐Dynamical Approach

“…One possible explanation for the poor skill (and tendency to overpredict) of NMME summer forecasts ( Figure S1) may be their inability to capture recent decreases in summer surface air temperature in the central United States due to agricultural intensification (alongside increased surface humidity and rainfall; Alter et al, 2018). On average, at the shortest initialization time and when all forecast/observation pairs are pooled across all sites, the NMME precipitation forecasts are better in winter/fall (precipitation R = 0.79/0.58, MSESS = 0.21/0.11, respectively) than in spring/summer (R = 0.57/0.27, MSESS = À0.13/À0.54).…”

“…The climate exhibits average annual temperatures ranging from less than 3°C in northern Minnesota to over 15°C in southeastern Missouri and average annual precipitation from~500 mm to~1200 mm in the same areas (Andresen et al, 2012). The Midwest has also witnessed a notable increase in precipitation (Alter et al, 2018) and flooding (Mallakpour & Villarini, 2015) in recent decades.…”

“…The NMME temperature forecasts tend to be better in the fall/spring (R = 0.87/0.84; MSESS = 0.67/0.66, respectively) than in the summer/winter (R = 0.77/0.81; MSESS = À0.90/0.61, respectively). One possible explanation for the poor skill (and tendency to overpredict) of NMME summer forecasts ( Figure S1) may be their inability to capture recent decreases in summer surface air temperature in the central United States due to agricultural intensification (alongside increased surface humidity and rainfall; Alter et al, 2018). Spatially, however, the skill of NMME precipitation forecasts is extremely variable when considering individual catchments: the regions with high precipitation forecast skill tend to match those where a statistically significant relationship exists between heavy precipitation and certain climate modes of variability ( Figure S2), such as the Pacific Decadal Oscillation in eastern Midwest in the winter or the North Atlantic Oscillation in the northwestern Midwest in the summer (Mallakpour & Villarini, 2016).…”