Thanks for your response. I agree with you. less rainfall over an extended period of time can make an area arid.
But, as I worked with higher manager in ministry of energy and got involved in IWRM (Integrated Water Resources Management) project, I think the current water shortage can be a result of water resources mismanagement rather than drought
Policy makers should change current strategies for water management specially in agriculture sector. ( about 92 percent the water is used in agriculture but up to 70 percent of water used in the agriculture sector is being wasted), also, there are wrong irrigation plans that should be improved
By the way, I live in Tehran :) for 2.5 years I have been in Isfahan with great memories in this historic city