The state of water resources in Iran is summarized as follows. The main source of water is precipitation, which normally amounts to 252 mm or 413 billion cubic meters (bcm) annually. This precipitation depth is less than one-third of worldwide average precipitation (831mm) and about one-third of the average precipitation in Asia (732mm). About 30 percent of the precipitation is in the form of snow, and the rest is rain and other forms of precipitation. While 1 percent of the world population lives in Iran, our share of renewable freshwater is only 0.36 percent. Of the 413 bcm of annual precipitation, 296 bcm are lost as evapotranspiration, 92 bcm runs as surface flows, and 25 bcm infiltrates into groundwater resources. Annually, about 13 bcm of water flows into Iran from neighboring countries. So, total renewable water resources are 130 bcm annually. From these sources, about 88.5 bcm is withdrawn, of which 82.5 bcm (93.2 percent) goes to agriculture, 4.5 bcm (5.1 percent) is for drinking, and 1.5 bcm (1.7 percent) is allocated for industry, mines, and miscellaneous uses. While the world uses 45 percent of its freshwater resources, Iran uses about 66 percent.
Precipitation in Iran does not have spatial and temporal uniformity. Part of the country receives less than 50 mm, while the northern part receives more than 850 mm of rain annually (Figure 1). More than 50 percent of the rain falls in winter, and less than 18 percent falls in summer. From the middle of the spring, river and stream discharges start to decrease, and groundwater is the only water source for summer and fall seasons. Statistics show that in 1996 and 2000 about 59.41 and 61.2 bcm, respectively, were withdrawn from the aquifers. Nonuniform temporal distribution of precipitation causes droughts in the years when most annual rainfall occurs in a short time and runs off quickly.
On the basis of studies performed by United Nations (UN) experts, the per capita water resources of Iran are projected to be about 726-860 m3 in 2025, compared with 2,200 m3 in 1990. Overpopulation in an arid and semiarid country causes diverse problems, including increased demand for scarce water and intensified competition between different sectors (agriculture, human consumption, and industry). Overpopulation in Iran will contribute to the country reaching a state of water crisis before the year 2025. Unplanned and irregular expansion of the main and satellite cities in the past 100 years has increased the population six-fold and contributed to water shortage problems. In the last 40 years, the population of Iran has increased by 45 million people, 30 million of whom have been added in the last 20 years. The water crisis and water scarcity will intensify in the future.
Water balance of many countries is in desperate straits, since aquifers are exploited severely, water is diverted from the agricultural sector to drinking and industrial supplies, and demand for more food and better diets is increasing. So, water is scarce, and as the studies of the International Water Management Institute (IWMI) show, it will get scarcer (Figure 2). The countries in dark grey in