Quantitative analyzes of virtual water net exports under the impacts of natural changes and human activities in the last 20 years in Shandong Province, China

Virtual water trade in a region is affected by both nature and by humans. To study the contribution of human activities on virtual water trade quantitatively, an innovative method of quantitative comparison and analysis is put forward. At first, climates are adjusted into a unified standard. Then the impacts of increment and reduction of foreign water are studied. Additionally, the impacts of water management policy are studied according to the comparable water quotas. Results show that with the development of the economy, an N-shaped trend and inverted U-shaped trend exist with regard to the net exports of agricultural and industrial virtual water, respectively. The net imports of virtual water have beneficial effects to water environments in water deficient areas, while net exports have negative effects. In 1997, the net exports of agricultural and industrial virtual water reduced by 20.13% and 49.67% respectively due to the cut-off of the Yellow River channel compared with that under average Yellow River water diversion. In 2017, they increased by 1.32% and 41.99% respectively because of the South-to-North Water Transfer (SNWT) project and reduced by 10.01% and 20.39% respectively under the effects of the most stringent water management policy.