Issues on Water Resources

Occurrence of Water Shortage

Occurrence of Water Shortage
Previously, Japan repeatedly experienced major water shortages; for example, 1939 in Lake Biwa, 1964 in the year of Tok yo Olympics, 1967 in Nagasaki, 1973 in Takamatsu, 1978 in Fukuoka, and so on. Though occurrence of water shortages has become rare in recent years the shortage in 1994 covered almost all Japan, when approximately 16 million people were affected at least once by suspended or reduced water supply, and agriculture suffered production losses of 140 billion yen.
Effects of Water Shortage
Modern society offers comfortable lifestyles and high quality servicesbased on stable water supply. Therefore, suspended or reduced water supply would have a serious impact oneveryday home life and social activities as it disables people from preparing meals, using flush toilets and doing other everyday activities. Also, shortage of industrial water results in damages such as reduction or suspension of operations. When shortages of agricultural water occur, farmers save water by means of "water-sharing (method of distributing water in accordance with designated times and turns)", intensification of repeated use and so on, though this requires a lot of labor and cost. For example, at the time of water shortage in 1994, the cost was about three times as much as that in an average year. In addition, when the whole amount of water becomes insufficient, crop growth is reduced or completely hindered.

Securing Stable Water Supply

Fluctuation of Precipitation due to Climate Change
As the long-term trend of temperature change in Japan, the average annual surface air temperature has increased by approximately 1oC over the past 100 years. Concerning precipitation, years of low rainfall have become frequent since around 1970, and the amount of precipitation was much below average in 1973, 1978, 1984, 1994, and 1996, when water shortages caused damage. Recently an increasing trend of fluctuation between extremely low rainfall and extremely high rainfall has been observed. In addition to the above-mentioned decrease in precipitation and frequent occurrence of extremely low rainfall years, due to climate changes accompanying global warming, trends of decreasing snowfall, and increasingly earlier thaw have been recognized.
Changes in Precipitation over the past 100 Years by Area and Season
Trend of Annual Precipitation by Area

Dividing the entire country into 14 areas, changes in annual precipitation over the past 100 years were analyzed. The result showed decreasing trends in almost all the areas with the exception of Hokkaido and San-in which show a slightly increasing trend.

Changes in Precipitation by Season

At many spots precipitation in spring and summer is on an increasing trend. However, at many spots outside Hokkaido precipitation in autumn and winter is on a rapidly decreasing trend.


Estimation of the increase or decrease from the angle of the trend(regression line) for annual precipitation over the period of 1900-2006, after obtaining the arithmetic average for the annual precipitation of each region.

  1. With respect to the precipitation by season at 51 spots for the period between 1900 and 2006, annual increase or decrease was calculated from the inclination of the trend (by regression line) for each spot.
  2. Winter: December (of the preceding year) to February; spring: March to May; summer: June to August; autumn: September to November.
Decline in Water Supply Stability
When constructing dams in Japan, they are designed so as to secure the necessary water supply even in a year of relatively low rainfall (base year for water supply) (see ① in the diagram below). When annual precipitation is much lower than in the base year, the river flow also decreases more than in the base year. On the other hand, since the storage capacity of water remains fixed, it would be impossible to secure stable intake of water throughout the year, even with replenishment from dams (see ② in the diagram on the right). For 60 % of the dams now in operation, the base year is selected from between 1956 and 1975 (see "Changes of Annual Precipitation in Japan" on theprevious page). Assuming that 1960 is the base year for water supply, in 9 out of about 40 subsequent years, annual precipitation was lower than that in the base year. It means that water short ages occurred frequently. It is thus considered to be a problem that stable water supply has been impaired in many places in recent years.
Examples of Decline in Water Supply Stability
Water resources development facilities in the Kiso River System include Tokuyama Dam (under construction), Nagara River Estuary Barrage, Miso River Dam, Aki River Dam, Iwaya Dam and MakioDam. At present, when all of these facilities are in operation, 88 m3 of water per second is planned to be supplied. However, the calculation using flow rate in the year of the second lowest rainfall during the 20-year period from 1979 to 1998 showed that only about 59% of the planned amount (equivalent to 1/10 water shortage) can be stably supplied. Further, in the calculation using the flow amount in 1994 when serious water shortage occurred, the water amount suppliable reduces to about 30% of the planned amount.

Securing Safe and Tasty Water

Growing Interest in Safe and Tasty Water
Water is essential to humans for their physical needs. Looking back on the past, there have been instances where mercury, cadmium and other harmful minerals carried by water were accumulated in rice and fish, and then harmed health of people who ate them; for example, Minamata disease and ouch-ouch disease. Thus, water pollution leads to health damage. In Japan, the spread rate of water supply systems is about 97%, which means that Japan has achieved a reasonable supply of safe and drinkable water. In recent years, however, increased consumption of mineral water and popularization of water purifiers for domestic use reflect a growing social interest and demand for "safe and tasty water" for drinking.
Preservation of Water Quality at Sources
Approximately 78% of drinking water supply (actual record in the fiscal year 2004) is taken from rivers, lakes, marshes and so forth. It is also supplied to each house after filtering. For this reason, water quality deterioration in these water bodies leads to bad-tasting tap water with foul smells like mold or chlorine. Besides that, deterioration increases the risk of generating trihalomethane, which is suspected to be a cancer causing substance that can be formed through chemical reaction between organic matters like humic materials and chlorine injected in the process of purifying raw water for drinking. Various types of efforts made by water supply utility operators including introduction of advanced water purification techniques have reduced problems of smelling and bad-tasting tap water in recent years. With respect to water quality, the attainment rate of environmental standards in river exceeds 80%, for example, 87% in Fiscal 2005, indicating that the quality of river water has improved, but the same cannot be said of lakes and marshes, where the attainment rate of environment standards has remained low, barely exceeding 50% only. In order to secure “safe and tasty water”, it is important to improve water quality in the main water sources including rivers, lakes, and marshes, as well as to further promote efforts of the preservation of water quality at water sources.

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