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During growing periods, precipitation is especially small. From July to September there is almost no rainfall, perhaps Just one to six per cent of the yearly
amount. Rains fall mainly in spring (30-50%) and winter (25-40%). Precipitation in autumn ranges from 10 to 20% of the yearly amount. Surface waters are extremely irregularly located in the
Republic. Vast plains accounting for two-thirds of the territory contain little water. At the same time, the mountains in the east of Uzbekistan are densely cut by an extensive network of
thousands of rivers. Such irregularity of surface water is due to geographic characteristics of Uzbekistan.
The rivers taking their source from the territory of the Republic originate mainly in the mountains, where precipitation is the highest and evaporation is the
lowest. Snow and glaciers are the main sources of water that feed the rivers of Contra! Asia, including Uzbekistan. The largest rivers both in Uzbekistan and in Central Asia are the
Amudarya and the Syrdarya. The Amudarya is 1,437 km long and the Syrdarya 2,137 km long. The rivers and their tributaries begin outside Uzbekistan. The Amudarya is formed by the confluence
of the rivers Pyandj and Vakhsh, and the Syrdarya by the confluence of the rivers Narin and Karadarya. The Syrdarya is longer than the Amudarya, but has less water. The Syrdarya Basin
includes the rivers: Narin, Karadarya, Chirchik, Akhangaran, Sokh, Isfara, Akbura, Isfayramsay, Shakhimardan, Gavasay and Kasansay. The Amudarya Basin includes the rivers: Zarafshan,
Kashkadarya, Surkhandarya, Tupolangdarya and Sherabad. Only the middle and lower reaches of the Amudarya and Syrdarya tributaries flow through the territory of the Republic. The average for
many years flow of the Amudarya and Syrdarya is 119 cubic kilometers, while the region consumes 133 cubic kilometers of water. The Republic's share of flow is 41 cu km, but every year it
spends, for economic purpose 62-65 cu km. The resulting shortage of water is compensated by small rivers and underground water. Water from the Amudarya is used for the irrigation of farm
land, mainly, in the Khorezm Oasis and Karakalpakstan. Some water from the middle reaches of the Amudarya is taken into the Amudarya Canal for the irrigation of land in the Bukhara and
Kashkadarya Oases.
Cultivated land in Uzbekistan is artificially irrigated, which accounts for the huge importance of rivers and water reservoirs both for available oases and
for the development and irrigation of new land. Due to this, the ancestors of the Uzbek people had already earned out extensive irrigation work by the 6th century BC Irrigation facilities
on those days possessed no water-lifting technologies and depended on floods.
The Abdullakhanbandy Dike in the Samarkand Region serves as an example of an irrigation structure of the 16th century. Only the rums of many irrigation
systems remain, however, some old systems have been modernized and are still operational. Ancient irrigators of the past built, with amazing expertise, many canals in Uzbekistan and
throughout the whole of Central Asia. The methods of artificial irrigation provoked the admiration of many travelers, scholars, historians, archaeologists and ambassadors from different
countries. Many canals have been and still are being built to take water from large (Amudarya, Zarafshan, Syrdarya) and small rivers (Isfara, Sokh and Kuvasay). The water from the canals is
used not only to irrigate land but also to drive hydropower stations, for instance, Narpay, Southern Ferghana, Northern Ferghana, Big Ferghana, Eskiangar, Amu-Bukhara, Big Namangan Canals
and others.
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