Nowadays, mankind is encountering periodic problems to provide necessary water in the fast process of development. This is while the environment and ecosystems based on water resources encounter droughts and shortage of water resources especially in arid and semi-arid areas under critical conditions. Limitations of water resources, fast growth of population, and the requirement to produce more food in such areas have caused the agriculture section to demand for more water than other sections. Iran, with the average rainfall of nearly 252 mm per year, is located in one of the arid regions of the world. 65% of our country consists of arid and semi-arid regions in which the average annual rainfall is less than 150 mm. In most of these regions, the only water resources providing economical and social demands originate from the aquifers, being in poor condition in recent decades due to overuse. Presently, from among the 30 plains in southern Khorasan, 13 plains have been declared as “forbidden” and 3 are in critical conditions. Such a condition is brought about due to more demands for water necessary for agricultural activities, so that 91% of the water extracted is consumed by the agriculture sector. In the plain of Birjand, the decline of water surface has increased from 21 cm to 60. The investigation of farming water consumption in the west of this plain indicates the lowest economical output—thus wasting the most important environmental resource. Producing plants like hay and beet with high water consumption and low economical output is an instance of such a waste. For the stability of water resources in the plain and economical production of the crops, it is necessary to make changes in the pattern and composition of the plants produced in the area.

Key words: watershed; water surface decline; aquifer; plant pattern; productivity; agriculture water.