Abstract
Significant air temperature changes have occurred globally during the 20th century, which are spatially variable to a considerable degree and these changes can have substantial implications in agroecosystem productivity. The agroclimate indicators that are responsible in these contexts are first fall frost (FFF), last spring frost (LSF), climatological growing season (CGS) length, and heat accumulation (growing degree days, GDD). We explore spatial and temporal trends associated with these indices across the continental U.S. (CONUS) during 1900–2014 using datasets collected at 1218 sites. On average, FFF has been occurring later (by 5.4 days century−1), and LSF has been occurring earlier (by 6.9 days century−1), resulting in the average lengthening of the CGS (by 12.7 days century−1). Annual GDD has been increasing by 50 °C century−1. We also report trends for agricultural belts and climate regions. We developed relationships between county-level crop yields vs. agroclimate changes and found that all crops (maize, soybean, sorghum, spring wheat, winter wheat, and cotton) responded positively to a lengthened CGS, while responding negatively to increase in GDD, except cotton. Overall, we find that the observed changes in agroclimate, were beneficial for crop yields in the CONUS, albeit some crop and region specific exceptions.
Highlights
Significant air temperature changes have occurred globally during the 20th century, which are spatially variable to a considerable degree and these changes can have substantial implications in agroecosystem productivity
The agricultural growing degree days (GDD) (AGDD) follows a clear latitudinal pattern with increasing magnitudes as we move from north to south with some exceptions such as Rocky Mountains ranges, which are lower in AGDD magnitudes than their surroundings and Mojave and Sonoran deserts in the west, which are naturally higher in AGDD magnitudes than their surroundings due to high air temperatures
The maps, data, and information, pertaining to the geographic and temporal variability associated with GDD, frost dates, and climatological growing season (CGS) are a resource that can act as one of the longest-term (115-year) climatology and trend information for these indices in the continental U.S (CONUS)
Summary
Significant air temperature changes have occurred globally during the 20th century, which are spatially variable to a considerable degree and these changes can have substantial implications in agroecosystem productivity. Natural and anthropogenic variability and trends in climate during the 20th century have been associated with increases in air temperatures at the earth’s surface, with a recorded global terrestrial warming of 0.74 °C1 These trends are highly variable in terms of geography, and regions have to be individually evaluated for determination of the site-specific impacts on environment, agriculture, public health and a range of areas that are prone to temperature changes. Some studies have investigated the changes in these agro-climatological indices in the recent past for the United States[3,4,5] The results from these studies have been consistent in reporting a general lengthening of the growing season or the frost-free period, by about 2 weeks during the 20th century in the continental U.S (CONUS), by about a week for North America during 1950–2011, and by 0.89 days decade−1 during 1901–2009 for the Northern Hemisphere. Our study attempts to bridge the gap between two interdependent characteristics of crop growing conditions (GDD and frost-free period), by addressing them under a common framework
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