Submitted to: Agricultural and Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/2018
Publication Date: 2/22/2018
Publication URL: http://handle.nal.usda.gov/10113/5931571
Citation: Nielsen, D.C. 2018. Influence of latitude on the US great plains East-West precipitation gradient. Agricultural and Environmental Letters. 3:170040. doi:10.2134/ael2017.11.0040.
Interpretive Summary: Precipitation increases from west to east across the Great Plains of the United States in response to both the rain shadow of the Rocky Mountians and the flow of moisture from the Gulf of Mexico. The number of miles for an inch change in annual precipitation increases from about 13 miles at latitudes below 38 degrees N to 66 miles at the North Dakota border with Canada. This change in precipitation gradient was described well with a quadratic equation (miles per inch = 237.9 - 13.77*LAT + 0.2096*LAT*LAT) where LAT is latitude in decimal degrees. This relationship provides a useful tool for farmers to use as a first assessment in determining the applicability of research results acquired in a location different from their own that may have very different annual precipitation.
Technical Abstract: Precipitation varies greatly from east to west across the US Great Plains as a result of a combination of the rain shadow of the Rocky Mountains and the moisture flow from the Gulf of Mexico. Because of this precipitation gradient, application of research results obtained in one location to other locations can be difficult. Farmers would have a better means of understanding the applicability of cropping systems research done in one part of the Great Plains to their specific location if they had an understanding of the rate of change of precipitation with east-west direction at their latitude. The objective of this analysis was to determine if a consistent, predictive relationship exists between the east-west precipitation gradient (km per mm change in precipitatoin) and latitude in the Great Plains. The east-west precipitation gradient was determined for 15 transects across the Great Plains from Texas to North Dakota. Seven different unctional relationships between precipitation gradient and latitude were determined. The precipitation gradient changed little from 31o N to 38o N (0.85 km for a mm change in precipitation) and then increased in a systematic manner at latitudes north of 38o N to 3.87 km per mm at 48.5o N. A quadratic polynomial relationship fit the data well and was used to create a simple spreadsheet decision support tool to help farmers understand how quickly precipitation changes with east-west direction at a given latitude.