Integrated assessment of global agricultural land and water resources in a changing world.

摘要

Climate-Water-Food (CWF) system involves numerous interactions and is gaining much attention since last decade. Climate change has generated significant influences on natural resources and agriculture, and the impacts are likely to amplify in the future. Land and water resources are two main constraining factors for agriculture, and the pressure on the natural resources will continue rising due to population growth and economic development. Therefore, it is of great importance to improve the understanding of the CWF system and adopt wise management practices to adapt with the global changes in both the environment and the human society.;This dissertation develops an integrated framework for characterizing interactions within the complex CWF system. The aim of this framework is to optimize agricultural land and water resources at the global scale. To achieve that, a Global Optimization Model of Agricultural Land and Water resources (GOALW) is developed and implemented. GOALW is a partial equilibrium model with a global objective such as global welfare maximization and global security maximization. It is composed of socio-economic and agro-hydrologic components. The model is able to simulate the interactions among price, demand, crop area, productivity, and irrigation water use, and provide valuable insights such as marginal value of water and land.;The marginal value (MV) of agricultural water availability refers to how much the global social welfare increases when local agricultural water availability increases by one unit. Western U.S., north Europe, west Europe and east coast of Australia have relatively high MV, while Amazon area, inland of Africa, Mideast, western area of Asia have lower MV. Nevertheless, marginal cost are high in high plains of U.S., southern China and Ganges area of India, which may offset their advantages in MV. Crop yield and per capita income could explain more than 40% of MV value, and water scarcity index (ratio of the annual irrigation requirement for one FPU (food production unit) over the irrigation water availability) explains 32% of the MV value.;In order to estimate how the CWF system responds to various forcing, a number of scenarios are considered in this dissertation. Climate change is a great concern for agriculture, and its impacts on irrigation water requirements are investigated. Since climate change involves much uncertainty, an ensemble approach is adopted to provide more reasonable projection. It is found that the global irrigation requirement is going to decline although the global mean temperature rises. This might be explained by the decrease in crop evapotranspiration, which is due to the declining diurnal temperature range (DTR), as already observed and/or projected in some regions.;Impacts of climate change on irrigation water use and economic factors are also assessed. Adverse effects of temperature rise are incorporated into the model through a linear function. Global irrigation water use reduces by 3% (A1b_SAM) and 14% (B1_RMS), respectively, compared to the baseline defined as the situation around 2005. The world prices of most crops increase since the adverse impacts of temperature rise outweigh the positive effects from irrigation requirement decline. The trade pattern is also affected: cereal exports are likely to decline in East Europe and North America, while imports are possible to decrease in East Asia, Sub-Saharan Africa, as well as Southeast Asia.;Yield and area requirement considering population growth and economic development are estimated under the integrated framework. Projected population and GDP of 2025 are adopted to represent future socio-economic situations. Three scenarios are constructed: yield increase, land expansion, and yield & area scenario. When only productivity improvement or area expansion is considered, food prices increase and area expansion is expected with the various magnitudes though. If both productivity improvement and area expansion are considered to satisfy demand growth, crop prices decline and moderate area expansion is expected. MV reduces in the yield & area scenario with exceptions in countries/regions including south China, northeast U.S., and western Russia.