Changes in agro-meteorological indicators in the contiguous United States: 1951-2000

Mosaic changes in regional and local surface air temperatures and precipitation have occurred along with the increase of the average global surface air temperature in the 20th century, particularly in the recent two decades since 1980. From those changes have emerged these questions: how have the changes altered the local and regional agro-meteorological environment and affected the crop productions? These questions especially their spatially varying aspects have not been well examined. The aim of this study is to examining the effects of regional climate change on agro-meteorological environment, in terms of indicators, such as the thermal time (or Growing Degree Days) and growing season length, and to evaluate the influence of environmental change on crop yield. Major results of this study show a significant trend of increase in the thermal time across the western United States and a trend of decrease in thermal time from the U.S. Great Plains to the east coasts at a rate of 20 Growing Degree Days per 10 years. Results also show a significant trend of decreasing annual number of frost days at a rate of 3 days per decade and a trend of lengthening growing season by 4 days per decade in the western United States. Concurrently, the rainfall patterns in the warm season indicate more persistent weeklong wet spells and fewer dry spells in recent decades. These spatial variations of changes in the agrometeorological environment across the contiguous United States indicate substantial regional effects on crop production from the changing climate in the last 5 decades. Detailed geographical variations of the agrometeorological indicators revealed in this study can be beneficial for updating management decisions and practice routines in local and regional agricultural productions.