Due to Taiwan's subtropical location, this study investigates the water footprint of four energy crops
(corn, sweet potatoes, sugarcane and sweet sorghum), and one food crop (rice), in order to establish the
water footprint data of a subtropical region. Research results indicate that sweet potatoes have the
smallest water footprint, followed by sugarcane and sweet sorghum, and corn has the largest water
footprint of energy crops, though the water footprint of rice is much larger, which results are consistent
with the average global water footprints for these crops. The green water component accounts for more
than 50% of the overall water footprint for all energy crops except of corn, indicating that the cultivation
processes of these energy crops relies more on rainwater, thus, fulfilling low input selection criteria. The
water footprint of rice is about 13 times larger than that of sweet potatoes and 8.8e10.4 times that of
sugarcane, indicating the relative resource inefficiency of cultivating rice as a food crop. Water footprint
for Taiwan-grown sugarcane, corn, and sweet potatoes compare favourably to those in the top 3 producing
countries (Brazil, United States and China), as the water footprint for Taiwan-cultivated corn is
only 62% of that for corn planted in the United States. A comparison of energy crop water footprints in
temperate, subtropical, and tropical climate zones indicates that sugarcane cultivation is relatively more
efficient in tropical and subtropical regions, due to its heavy reliance on rainwater, while corn and sweet
sorghum perform better in temperate and subtropical regions.