Water for food: evolution and projections of water transfers through international and domestic agricultural trade

Abstract

Freshwater resources are under increasing pressure from human and environmental constraints. Population growth and socio-economic development have intensified water withdrawals globally, in particular for irrigated agriculture, accounting for 70-80% of global water use. Furthermore, climate change is expected to strengthen water scarcity in some regions. Trade of water-intensive products, corresponding to a transfer of water resources, can reduce the spatial heterogeneity of water availability. As such, domestic or international trade may improve water-use efficiency at a global or national scale, by providing more efficiently produced goods to all consumers. This thesis quantifies, analyzes and models these virtual transfers of water, between the world's nations and among provinces of China. The impacts of future climate, socio-economic and policy changes on these systems are also estimated.

Chapter 1 describes the evolution of international food trade and associated water resources transfers, and provides an assessment of key impacts of policy, economic and biophysical factors on this global system. Chapter 2 develops a fitness model that determines which variables control the global virtual water trade network's structure and temporal evolution, and estimates changes in the network under future scenarios. Chapter 3 presents the construction and analysis of China's inter-provincial and foreign virtual water trade. The connectivity and flow structure of this network, as well as the efficiency of the system in terms of water resources, are quantified and analyzed. In addition, we identify provinces and commodities that could be targeted for improved efficiency. In Chapter 4, specific agricultural policy scenarios in China are considered, and their impacts on domestic and foreign virtual water trade are analyzed.