Why are the waters of the tigris and euphrates rivers important to the people of the middle east?

Because the region is a dry climate which makes water scarce.
The Tigris and Euphrates are one of the only major rivers in that region. Since its impossible to live without water and the diversity of various groups in the region and dirty atmospheres, these factors make the rivers even more important. There have even been wars in the past for the rivers because they are so valuable.

The Tigris and Euphrates rivers are very important to the people of the Middle Easy because it is responsible for the fertility of the soil in the Middle East. There fertility of the soil will make farming very successful and thus having successful agriculture in the area. Also the Middle East has a dry and low precipitation average and the two rivers are also known as a major water source. 

81 is a composite number