ABSTRACT
The renewable freshwater resources (RFWR) are limited (Table 21.1) and are determined by the global hydrological cycle (Oki and Kanae 2006). With the increase in population from 7 billion in 2011 to 9.2 billion in 2050, there will be a greater competition for water use by agriculture than for industrial and urban uses. There will also be additional water use for improving the environment (i.e., C sequestration) for nature conservancy (i.e., restoration of wetlands, and wildlife habitat) and for recreational purposes. Limiting and decreasing water resources must be judiciously managed for both people and nature (Postel and Richter 2003). The availability of freshwater resources will also be confounded by the projected climate change. The hydrological cycle is likely to be intensi‘ed by climate warming (Huntington 2010), with possible adverse effects on the availability of fresh water for competing uses. Thus, sustainable management of water resources, using the strategies of integrated water management (IWM) (Bouwer 2002) and ecohydrological approach (Falkenmark and Rockström 2005) among others, is essential to meeting the growing demands. While agriculture currently uses about 70% of the total water withdrawal (Molden 2007), decline in its share of the scarce resource is inevitable because of numerous competing but essential uses. Estimates of calories produced per cubic meter of water range from 1000 to 7000 for corn, 1260 to 3360 for legumes, 500 to 2000 for rice, and 60 to 210 for beef (Molden et al. 2007). Therefore, understanding the hydrological processes in agricultural and related ecosystems is essential to improving the use ef‘- ciency by decreasing the losses. The themes of Chapters 1-20 presented in this volume address the scienti‘c processes, technological options, and policy interventions to enhance effective water use. This chapter is focused on addressing the research and development priorities in improving soil water storage for enhancing and sustaining agronomic productivity with the goal to advance the global food security, while improving the environment.
