ECONOMY

Arabia is more likely to conjure up images of desolate deserts than fertile fields, yet agriculture was, and still is, of great importance in certain parts (Pl. 13). However, since there are no permanent rivers or lakes in Arabia and rainfall is limited to certain times of the year (spring and summer in south Arabia, autumn/winter and spring elsewhere), careful management of water is everywhere necessary. Moreover high temperatures mean high evaporation rates, and when the rains do come they may be heavy but brief. Runoff is then immediate and often devastating. After a short time all the surface water has disappeared and the valleys become dry again. Methods had therefore to be devised for the effective catchment, distribution and storage of this precious resource. Terracing, the conversion of valley slopes into stone shelves, broke the pace of the floodwater, causing it to cascade gently down the step-like shelves, part of it sinking into the ground at each shelf, depositing in the process some of the soil and organic debris which it bore along (Pls. 1d, 7). Canals were cut to smooth out flooding irregularities, to circulate water evenly around fields and to convey it to areas lying beyond the reach of the floods. Small dams of compacted earth or loose stone were constructed at an angle to the banks of a valley to divert some of the floodwater to plots of land on either side. Across valleys more substantial dams would be built which served to calm the turbulence of the water, sometimes with the additional aid of stilling basins, and contain it until the desired level of water was reached, when it would be led off by canals to the awaiting fields. Finally, wells were dug and cisterns hollowed out in order to store water, chiefly for household consumption, but also to supplement irrigation sources in dry years.