At that time, the Middle East suffered a dry spell, limiting wild grain harvests. The area's communities began to supplement wild crops with their own plantings, storing the excess to ensure their food supply. They also began to domesticate wild animals of the region. The practices of agriculture and animal domestication arose quickly in different parts of the world, appearing in the Americas by 8000 B.C., Africa and India by 7000 B.C., and in East Asia and Europe by Barley, wheat, rice, and oats were the first to be systematically cultivated. Later-8,000 to 5,000 years ago—humans began planting root crops and legumes, followed by fruit trees and leafy vegetables. Each area of the world grew regional foods, though some spread via traders and migrants. Irrigation, developed in Mesopotamia around 6000 a.c., was critical to agricultural development. Canals, reservoirs, and embankments allowed fresh water and silt deposits from the Tigris and Euphrates Rivers to channel directly into fields. This increase made the soil more fertile, made farmers less dependent on rainfall, and paved the way for the development of cities.