Traditional energy sources (fossil fuel) are facing rapid depletion, and have been producing serious threats to environment. Therefore, people are paying more and more attention to new energy sources. Biomass energy is considered to be a potential clean energy source with great benefits to air quality and CO₂ sequestration (climate mitigation). For example, unprecedented increases in biofuel production are ongoing in the US: ethanol are produced from <2 billion gallons (<0.06 billion tons) in 2001 to 13 billion gallons (0.41 billion tons) in 2010. A total of 189 ethanol plants were operational as of January 2010, with 15 more under construction (Renewable Fuels Association 2012). The Energy Independence and Security Act (EISA 2007) mandates 36 billion gallons (1.13 billion tons) of ethanol by 2022 with 15 billion gallons (0.47 billion tons) from corn. The remaining 21 billion gallons (0.66 billion tons) are expected to be derived from second generation technologies (e.g., cellulosic and lipid-based feedstocks). However, biofuel production would also produce big threats to water and food security.

A recent study, led by Prof. XU Xianli, in Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) and his colleagues in US, found that biofuel demand and production has resulted in significant change in landscape pattern in US Midwest, and thereby significantly influenced hydrologic cycle. In US Midwest, prairies and forest land were rapidly converted to croplands after the 1850s and cropland area continued to expand through the early half of the 20th century. Small grain crops (wheat and oats) and hay decreased from the 1920s to 1970s ~ 1980s, while biofuel crops such as corn and particularly soybeans increased. Cropping systems converted from a mixture of crops (e.g., oats, wheat, hay and corn) to a predominantly corn and soybean rotation. In order to improve crop production, land management practices (e.g. terraces, conservation tillage, farm ponds, and soil drainage improvement) have changed substantially in this area accordingly. All of these changed the way how land surface partitions precipitation in US Midwest in the duration of ~1930s–2010: Decrease of evaporated water but increase of groundwater recharge and thereby increase of baseflow.

Noticeably, once ethanol production from cellulosic biomass becomes commercialized and energy crops (second generation biofuel crops such as miscanthus and switchgrass) become viable, there will be another shift in land use and land cover with more areas occupied by perennial grasses (miscanthus and switchgrass). This will be expected to have another significant impact on the hydrologic cycle because perennial grasses demand much more water than annual crops. This suggests that future biofuel expansion need to consider its impacts on water resources.

The related findings of this research have been published on Journal of Hydrology (X. Xu et al. Journal of Hydrology 497 (2013) 110–120). http://www.sciencedirect.com/science/article/pii/S0022169413004186