Surface runoff
Internal renewable water resources are estimated at 128.5 billion cubic meters (BCM)/year (average for 1977–2001). Surface runoff represents a total of 97.3 BCM/year, of which 5.4 BCM/year comes from drainage of the aquifers and thus needs to be subtracted from the total. Groundwater recharge is estimated at about 49.3 BCM/year, of which 12.7 BCM/year is obtained from infiltration in the river bed and also needs to be subtracted. Iran receives 6.7 BCM/year of surface water from Pakistan and some water from Afghanistan through the Helmand River. The flow of the Arax river, at the border with Azerbaijan, is estimated at 4.6 BCM/year. The surface runoff to the sea and to other countries is estimated at 55.9 BCM/year. Per capita, water availability in the pre-Islamic Revolution era was about 4,500 cubic meters. In 2009, this figure was less than 2,000 cubic meters.