Unlike most other natural resources, water flows readily across and through landscapes in complex ways that affect its availability and opportunities to manage it. Understanding these water flows is critical to the design of investment programmes and policies necessary to support a transition to a green economy.
2.1 Services from natural infrastructure
Water makes an irreplaceable contribution to ecosystem services that stem from the earth’s natural capital and vice versa. Protecting the natural ecosystems of river basins and restoring degraded catchment areas is crucial to securing the world’s water supplies, maintaining their quality, regulating floods and mitigating climate change (Khan 2010; TEEB 2008, 2009a, b, c). The role of other ecosystems, such as forests, wetlands and floodplains in providing access to water also needs to be recognised and quantified. Gauging the true value that these ecosystems provide is a key part of charting a course to a green economy.
Recent analysis is showing a close global correlation between the threats to biodiversity and threats to water security. As shown in Figure 2, regions where threats to
human water security is high, but the threat to biodiversity is low, are rare. When the threat to human water security is high, usually the threat to biodiversity is high. This suggests that there may be considerable opportunities for governments to improve biodiversity outcomes by investing in water security (Vörösmarty et al. 2010). Water- dependant ecosystems also play an important role in the provision of cultural benefits (Millennium Ecosystem Assessment 2005).
2.2 Water accounting
As water flows through and across land, it is used and reused. This makes information about water difficult to assemble and use for management. When, for example, a policy promotes a more efficient irrigation system, it is critical to decide whether or not the savings are to be used to expand irrigation or returned back to the river or aquifer from which the water was taken (Molden 1997). Gains in one area can be associated with losses in another area. When the savings are not returned back to the river or aquifer, the result can be a significant reduction in the quantity of water available to the environment and to other users (Independent Evaluation Group 2010).
Biodiversity threat Low
High
Figure 2: Prevailing patterns of threat to human water security and biodiversity. Adjusted human water security threat is contrasted against incident biodiversity threat. A breakpoint of 0.5 delineates low from