Rain-fed agriculture, the converse of irrigated agriculture, has traditionally meant cultivation of plants without adding additional water beyond that which falls naturally on them from the sky or flows to them as surface water. Obviously, there is a spectrum of human intervention between minor flood control management and massive irrigation works, as well as a spectrum in scale between typical surface flows and the traditional floods of major river systems. A third spectrum relevant to understanding the role of water in agriculture involves the energy needed for supplying the water to the fields, which ranges from low in some gravity-fed systems to high in systems requiring additional energy inputs for raising water to the level of fields well above the water table.
It is possible that the first crops cultivated by irrigation were small flood control systems on alluvial fans in arid regions, such as Jericho, circa 9000 BC, but it is just as likely that small flood control management works were built along river systems having a natural flood, and it is unlikely we will ever know when or where the earliest such systems were built, since alluvial soils in flood plains are rearranged annually and the likelihood of the earliest such works leaving a trace down to the present are slim. Significant irrigation works in the Middle East date at least to 5000 BC in the Nile, and an early major irrigation project was completed there around 3100 BC during the 1st dynasty.
If we leave unsolved the question of who was first to irrigate, we can concentrate on the broader ramifications of irrigation technology. Modern measuring systems tempt researchers to believe that irrigation is required where less than a particular amount (e.g., 250 mm) of rainfall occurs. Premodern measuring systems were generally more sophisticated and allowed for temperature, orientation to the sun, soil characteristics, temporal distribution of rainfall, and evapotranspiration by evaluating rain-fed fields not in terms of area and precipitation, but in more direct terms of the optimal amount of seed they would support. Even small gravity-fed watershed-harnessing systems can concentrate rainfall from a larger area onto a smaller one, and nature does a fair job of this in many circumstances. Thus, precipitation requirements for annuals like grains (trees can survive on the water table if it is high enough) make sense only as guidelines, and the ethnographic literature is full of the expected exceptions (e.g., the Hunza, in Northern Pakistan, who require only 180 mm for rain-fed agriculture).
Karl Wittfogel developed the idea that irrigation works were both the products of centralized states and, via the control possible by monopolizing the water supply, the basis for the development of a particular (oriental) version of state despotism. This theory was taken up by many scholars but is now not seen as fitting well many of the very areas it was thought to explain best, such as Bali, where a strong case has been made that vast irrigation systems were constructed and regulated without any significant role for the state. If it does not have the broad relevance claimed for it by Wittfogel, some scholars, such as Sidky, claim it has explanatory value for 18th-century irrigation among the Hunza. Stanish suggests that part of the argument may be valid if reworked in terms of linking political complexity to labor intensification and declining returns to labor in areas largely under local control.
Because many early civilizations developed in riverain areas and also developed irrigation systems, archaeologists have focused a lot of attention on irrigation. In a classic work, Butzer attributes the repeated elaborations of the irrigation infrastructure in the Nile during dynastic times to local communities rather than to centralized state initiatives but notes the extensive efforts under state control to develop the Faiyum during the Hellenistic period. It may be that this model of early local development usurped only in much later times by a central state will fit far more premodern situations.
Irrigation systems, whose infrastructure is durable, both significantly improve the efficiency of human labor, through the multiplier impact of the infrastructure, and enable more labor to be used effectively in a given unit of area. At some level of effort (the margin in terms of labor efficiency), there begins to be a general trade-off, under ceteris paribus conditions, with intensification leading to higher returns per unit area and declining returns per unit of labor. Many irrigated systems pass beyond an optimal point where both returns to labor and to unit area increase and sacrifice the former for the latter. They often operate in this suboptimal area, from the perspective of returns to labor, because the sociopolitical system has prioritized returns to unit of area or water or even some combined unit of land and water.
It is normal in many irrigation-based societies for the labor of many to be constrained in some measure by the will of the few. Varied explanations for how this comes about have been proffered. Inefficient uses of human labor, which are inevitable where the other factors of production (land, water, and capital, understood broadly) are unevenly distributed, may well have reached an early nadir in large-scale irrigation contexts.
The modern era of high-tech dams and irrigation projects has brought to the fore issues of environmental damage; displacement of peoples by new lakes, with a host of associated social and health issues; a regular prioritization of the energetic needs of urban areas over the needs of farmers; and a plethora of opportunities for corruption by elites, companies, and international organizations. Large-scale irrigation projects promise more predictable yields, greater independence from world market fluctuations in crop prices, and local sources of energy. Only in rare cases where the climate and ecology are already optimal for the crops in question do such projects provide crops at competitive world market prices if all costs are considered. Despite typical inter-national advice to the contrary, modern decisions to undertake large-scale irrigation stand or fall on political and social considerations, not economic efficiencies, and would do well to be so understood.
- Butzer, K. W. (1976). Early hydraulic civilization in Egypt: A study in cultural ecology. Chicago: University of Chicago Press.
- Caufield, C. (1996). Masters of illusions: The World Bank and the poverty of nations. New York: Henry Holt.
- Hammoudi, A. (1985). Substance and relation: Water rights and water distribution in the Dra Valley. In A. E. Mayer (Ed.), Property, social structure, and law in the modern Middle East. Albany: State University of New York Press.
- Lansing, S. (1991). Priests and programmers: Technologies of power in the engineered landscape of Bali. Princeton, NJ: Princeton University Press.
- Park, T. K. (1992, March). Early trends toward class stratification: Chaos, common property, and flood recession agriculture. American Anthropologist, pp. 90-117.
- Sidky, H. (1997). Irrigation and the rise of the state in Hunza: A case for the hydraulic hypothesis. Modern Asian Studies, 31, 995-1017.
- Stanish, C. (1994). The hydraulic hypothesis revisited: Lake Titicaca basin raised fields in theoretical perspective. Latin American Antiquity, 5, 312-332.
- Wittfogel, K. A. (1957). Oriental despotism: A comparative study of total power. New Haven, CT: Yale University Press.