Food Sources: Earth, Water, and Air - Food Culture and Health in Pre-Modern Islamic Societies - page 39

6. Irrigation in Persia
The distribution and density of popula-
tion and the development of agriculture
in Persia throughout history have been
closely dependent upon the availability
of water, and the nature of the irrigation
systems has influenced both the siting of
settlements and the pattern of society.
Precipitation is scanty and seasonal; it
is concentrated on the periphery of the
country, as also are the major perennial
rivers.
As a general rule, rainfall, which occurs
between October and May, decreases
from the north to the south of the coun-
try and from west to east, but in a number
of areas the high relief of the Alburz and
the Zagros mountains has modified this
pattern. Along the Caspian Sea coast and
the northern flanks of the Alburz, pre-
cipitation reaches more than 1,800 mm.
near the mouth of the Safīd Rūd; annual
totals fall to less than 500 mm. on the
east side of the Caspian near Gunbad-i
ābūs. Along the western flanks and sum-
mits of the Zagros Mountains, precipita-
tion amounts are thought to exceed 800
mm. on some of the higher peaks, and
large areas to the west of · īrāz receive
more than 400 mm. In the north-western
highlands, between the two belts of high
precipitation, there is a zone of moderate
precipitation of 250-400 mm. In the cen-
tre of the country occupied by the Da ª t-i
Kawīr and the Da ª t-i Lū, great sterile
deserts, precipitation totals almost every-
where less than 100 mm., though a higher
precipitation is found on the eastern bor-
ders of the kawīr in the highlands around
Bīr ¡ and and Zāhidān. Everywhere, with
the exception of the Caspian littoral, low
and episodic rainfall is a major constraint
on agriculture, hence the importance of
artificial irrigation.
Dependable supplies of surface water
exist only in isolated districts around

the margins of the country, but there is
nowhere an annual surplus of water, and
seasonal surpluses, except in the north
and west, are insignificant. Run-off is
episodic, and occurs only because pre-
cipitation momentarily exceeds the infil-
tration capacity of the surface. The flow
of water in streams and rivers throughout
the country is seasonal and highly vari-
able from year to year. Peak flows are too
late for winter crops and the minimum
discharge occurs when summer crops are
in greatest need of moisture. The control
of water by artificial irrigation is therefore
immensely important for agricultural pro-
duction and prosperity. Without artificial
irrigation the cultivation of plants native
to regions where summer rainfall is nor-
mal, such as cotton, millet, rice and sugar
would not be possible.
There are few great rivers in Persia—
the great hydraulic civilisations have no
place there. The largest are the Kārūn and
the Kar ¶ a which flow into the Persian
Gulf, draining almost all the area between
Ābādān and Kirmān ª āh. Further south
are the basins of the Mand and the · ūr,
which also drain into the Persian Gulf and
the Gulf of Oman respectively. The Safīd
Rūd flows into the Caspian, as also do the
Aras and the Atrek. The water of the two
last-named, which flow along the modern
Russo-Persian border in the north-west
and the north-east respectively, is shared
with Russia. The central zone of Persia,
covering the largest part of the country,
is an area of internal drainage. Small riv-
ers flow into the closed basins of Lake
Urumiyya (Riāiyya) in Ā £ arbāy ¡ ān,
into the Hāmūn in Sīstān and into dry
lakes and saline marshes in structural
basins in the East Zagros, the depression
between the Zagros and the volcanic axis
extending from umm to Kirmān, the
⁄ az Muriyān basin, the southern Lū,
Balūčistān, the eastern highlands north