Estimating blue, green and grey water of paddy rice in Korea

The degree of grain self-sufficiency is currently about 27% in South Korea which is why Korea is one of the largest net virtual water import countries. Agricultural water resources have been heavily developed from early 1970 for rice self sufficiency and agricultural water use is 48% to the total fresh water resources in Korea. Tracing the water footprint is quite important to set up the national water resources policy because agriculture for crop cultivation consumes a large amount of water. Thus, when considering the low food self-sufficiency and high portion of water use in agriculture, estimation of virtual water for paddy rice in Korea is required to analyze the national water balance. The aim of this study is to estimate the green, blue and grey water footprint of rice, using a higher spatial resolution than earlier studies and applying local data on actual irrigation. Green and blue water from rice fields is calculated using the water balance model in paddy field. The grey water footprint is estimated by referencing the several researches regarding discharge of T-N and T-P in paddy field. The total national water footprint for rice production was 9,275.9 m³/yr, and the direct and indirect water use accounted for 5,358.6 m³/yr and 3,917.3 m³/yr, respectively. Green, blue and grey water for rice production were estimated to be 1,865.4 m³/yr, 3,184.3 m³/yr, and 308.9 m ³/yr except for indirect water use including percolation and residual soil moisture. The total volume of water used for one ton of rice was 840.8 m³/ton, and the green, blue, and grey water accounted for 292.8 m³/ton, 499.5 m³/ton, and 45.5 m³/ton, respectively. The results of this study are expected to be used as basic data for national agricultural water footprint and to assist the national water resources policy.