Understanding the temporal variability of agricultural parameters derived from historical climate data is important for planning in agriculture. Therefore, this study assessed the magnitude and recent trends of the transpiration ratio defined as the crop water use per harvested yield for the period from 1980 to 2010. The crop water use was estimated using the Food and Agriculture Organization’s Crop Wat model for eight administrative provinces in Korea. The temporal trends and spatial uncertainty were explored using the Mann-Kendall and Theil Sen’s methods. The regional average rice yield was 6.31 t ha-1(range 5.9 to 6.9 t ha-1). The results showed that the rice yield in Korea increased by 26 kg ha-1yr-1. Overall, the regional average transpiration ratio was 1,298 m3 t-1 (range 1,162 to 1,470 m3 t-1). From 1980 to 2010, the transpiration ratio decreased by 8.2 m3 t-1 (range 2.7 to 14.4 m3 t-1), largely as a result of the increasing yield. The statistical approach to historical data used in this study also provides a basis for simulating the future transpiration ratio.