Correlation of estimated evapotranspiration (ET) and Normalized Difference Vegetation Index (NDVI) with growing degree units (GDU) and precipitation.

We calculated GDU and precipitation from weather-station data and ET and NDVI from landscape blocks containing field sites. “Weekly total” time interval is the response value for ET or NDVI for each week and the corresponding weekly total precipitation and total GDU. “Four-week total” is the sum of the weekly values over a four-week period incremented a week at time. “To-date total” is a running total that is cumulated each week over the growing season each year. The number of weekly observations available (n) for the correlation analyses is the product of the number of field sites, number of years of observation, and number of composite periods from January through August (34 weeks for NDVI or 30 weeks for ET). All correlations have p