## Total Circulation of Lake Biwa

In Lake Biwa, layers of water temperatures are formed in summer because of big differences between the surface water temperatures of 26-28 degrees C and deepest-part water temperatures of 6-8 degrees C. When the lake surface cools down from autumn to winter, the surface water temperatures come down and layers of water temperatures disappear, with shallow water and deep water becoming admixed. This phenomenon is called “total circulation.” However, if the lake surface does not cool down and the surface water does not sink as deeply as before because of rising atmospheric temperatures, the total circulation would decrease and oxygen is not supplied to the lake’s bottom, possibly causing a deterioration of water quality and thus giving an impact on lake ecosystems.

Source: Ministry of Land, Infrastructure, Transport and Tourism, "Water Resources in Japan 2007"

# Section 2 Efforts to Solve Water Problems

## 1 Problems in the Use of Water Resources

As discussed in Section 1, water resources available to humans are limited and unevenly distributed geographically. On top of this, we expect to see an increase in water stress due to global warming as well as further rises in demand for water owing to population growth and economic growth. Then, are we using limited water resources effectively without wasting them? For example, in the case of water for agricultural use, which accounts for about 70% of the total water consumption, water is lost in each stage in the course of irrigation of farmland. For example, there is a report that in Asia, 20% of irrigation water is lost in the stage where water is carried from reservoirs to irrigated areas, another 15% is lost when water is delivered to agricultural fields, and in addition, 25% of water is wasted in agricultural fields (Figure 4-2-1). In this case, as much as about 60% of water is lost and only the remaining 40% is actually used to grow crops. These loss problems can be improved through the averaging of agricultural fields, improvements to irrigation channels, and the “drip infusion” of irrigation water to crop roots.

In developing countries, the nonrevenue water rate (the ratio of the difference obtained by deducting water sold from water produced to water produced) is said to average at 40%. Nonrevenue water rates in major cities of Asian countries show a lot of water is wasted through water leaks, while very little water is wasted in Japan (Figure 4-2-2). Fact-finding surveys on water projects in China and Vietnam, conducted in FY 2008, found that leaks of clean water are big problems in those countries. In Zhejiang Province, China, 20 to 30% of water projects in the province are estimated to suffer water leaks. In water projects in Changxing County of the same province, the quantity of water supply is as much as 36% lower than the quantity of clean water, presenting the authorities there with a major challenge to taking measures to deal with water leaks.

Installation of sanitary facilities remains inadequate in Asian countries as a whole, though the degree of sanitation varies from country to country, standing at 44% in China, 55% in Indonesia, 72% in the Philippines, 61% in Vietnam, 17% in Cambodia, 33% in India, 59% in Pakistan and 39% in Bangladesh. Substantially more effective utilization of water resources is possible if sewage water is adequately treated for reuse as water resources. We need to further promote effective use of water resources through prevention of water leakages and adequate sewage treatment when sewage is discharged into public water areas.