1.3: Irrigation Development

For thousands of years, irrigation has contributed substantially to world food production. Historians note that irrigation was one of the first modifications of the natural environment undertaken by early civilizations. Several millennia ago, irrigation permitted nomadic tribes to settle in more stable communities with assurance of annual crop productivity. Initial attempts at irrigation were rudimentary, consisting of ponding water in basins enclosed by low earthen dikes.

The earliest societies to rely successfully on irrigation were located in four major river basins: the Nile in Egypt around 6,000 B.C.E., the Tigris and Euphrates in Mesopotamia about 4,000 B.C.E., the Yellow River in China around 3,000 B.C.E, and the Indus in India approximately 2,500 B.C.E. In Mexico and South America, irrigation was practiced by the Maya and Inca civilizations more than 2,000 years ago. In Iran, ganats, 3,000 year-old tunnels to bring water from the mountains to the valley, are used to this day (Kuros, 1984). Earthen dams to store surface water were first constructed in the second and third centuries in Japan to irrigate rice and were constructed as early as the third century B.C.E. in Sri Lanka (i.e., the Abhaya Wewa reservoir). In Central Europe, irrigation was documented as early as the third century C.E. (Csekö and Hayde, 2004).

In North America, irrigation is known to have existed among Native Americans of the southwest as early as 1200 B.C.E. Early Spanish explorers found evidence of irrigation canals and diversion points along rivers. The Spaniards introduced new irrigation methods and irrigated crops such as grapes, fruits, vegetables, olives, wheat, and barley. As in other areas of the world, irrigation made it possible for Native Americans to develop settlements and enjoy a more secure food source.

At the beginning of the 1800s, the total irrigated area in the world was estimated at about 20 million acres (Gulhati, 1973). Up to that time most irrigation works were small systems. Irrigation began to expand in many countries in the nineteenth century and took on new dimensions in terms of the amounts and methods of water diversion and management. The first barrages, short diversion dams, were built in the Nile Delta in about 1850. About the same time in India, several irrigation canal systems were constructed. The Lower Chanab Canal in Pakistan was the first canal system intended strictly for arid land not previously cultivated. In 1847 Mormon colonies began irrigating in Utah. Their efforts expanded into California, Nevada, Idaho, Wyoming, Arizona, New Mexico, and Canada. German immigrants started an irrigation colony in Anaheim, California, in 1857, and an irrigation colony was started in 1870 at Greeley, Colorado. At the end of the nineteenth century, irrigation in the world was estimated at 100 million acres, a fivefold increase during the century (Gulhati, 1973).

Historians sizing up the twentieth century will almost certainly include irrigation as one of the century’s characteristics. During the first half of the century, irrigated area worldwide rose to more than 230 million acres. The surge continued in the second half of the century with over 800 million acres in 2017 (Table 1.2).

Table 1.2 Growth in irrigated land and world population since 1900 (adapted from FAO-STAT, 1999; FAO, 1998, 2021).

Year	Irrigated Area (millions of acres)	Population (billions)
1900	100	1.5
1950	235	2.5
1970	422	3.7
1990	598	5.3
1997	669	5.9
2017	806	7.5

Many countries—such as China, Egypt, India, Indonesia, Israel, Japan, Korea, Pakistan, and Peru—rely on irrigation for more than half of their domestic food production. Countries with 10 million irrigated acres or more are tabulated in Table 1.3. Large areas of irrigated lands in southeast Asia lie in the humid equatorial belt. These areas have monsoon climates with very large totals of annual rainfall, but portions of the year are dry. In these countries, paddy or flooded rice is the dominate irrigated crop. Countries like China, Korea, Japan, Indonesia, and the Philippines have long been noted for this type of irrigated agriculture. Irrigated area in each country (as a percentage of cultivated area) is shown in Figure 1.1.

Figure 1.1 Global Distribution of irrigation as a fraction of cultivated land area. Data from FAO (2021).

Table 1.3 Top 10 irrigated countries in the world in 2017 (adapted from FAO, 2021).

Country	Irrigated Area (millions of acres)	Population (millions)
India	174	1,339
China	173	1,453
United States	66	325
Pakistan	49	208
Iran	22	81
Indonesia	17	265
Thailand	16	69
Mexico	16	125
Turkey	13	81
Brazil	11	208

At the beginning of the twentieth century, irrigation in the western United States amounted to about 3 million acres. Early Caucasian settlers in the western United States were no different than people of ancient civilizations. They developed cooperative irrigation practices and formed communities, especially in southern California and Utah. Irrigation development in the west in the twentieth century was tied closely to the 1902 Reclamation Act which provided capital and the expertise to construct major water supply facilities. During the first three decades of the twentieth century, large multipurpose federal water projects were designed and built for irrigation, flood control, power generation, wildlife and fish habitat, and water-based recreation. Examples include the Colorado River, the Columbia Basin, Central Utah, the Missouri Basin, the Minakoka Project of Idaho, and the Salt River Project of Arizona. Following these projects, private development of pump irrigation from extensive natural underground reservoirs (aquifers) in the plains states, ranging from the Dakotas south to the high plains of Texas, permitted a major increase in irrigation from 1950 to 1980. In the last decades of the twentieth century, irrigation in southeastern states like Florida, Georgia, and South Carolina, where crops grown extensively on sandy soils are at risk during periods of drought, increased rapidly.

Figure 1.2 Irrigated farmland by state in the United States in 2017 (data from USDA, 2019).

The distribution of irrigation in 2017 in the United States from the USDA Farm and Ranch Irrigation Survey is shown in Figure 1.2. The irrigated areas of 20 leading states are presented in Table 1.4, as well as the percentage change in irrigated area for these states over a 15-year period (2002 to 2017). The data for several western states, like California, Arizona, Wyoming, Colorado, Montana, Idaho, Texas, and Utah, indicate that the size of the irrigated area either increased slowly or decreased. This indicates that land and water resources were developed near the maximum possible area under the socioeconomic conditions of the time. Areas with large increases in irrigation were near or just east of the hundredth meridian, the line on the globe that roughly divides the semiarid West from the subhumid Midwest in the United States. The states of Arkansas, Georgia, Louisiana, Michigan, Mississippi, Missouri, and Nebraska had large percentage increases in irrigation during the 15-year period. This increase, in large part, was a consequence of groundwater being tapped by irrigation wells. As you review the 20 leading irrigation states, you will also notice the amount of irrigated lands in southeastern states, like Georgia, Mississippi, and Louisiana, increased dramatically during the 15-year period. By 2017 there were over 58 million irrigated acres in the United States (Table 1.4).

Table 1.4 Irrigated land in the United States in 2017 and the percent change over the previous 15 years. The 20 leading irrigation states are listed along with data by region and nationally (adapted from USDA, 2014, 2019).

	Irrigated Land (acres)	Percent Change Since 2002
State:
Arizona	911,000	-2
Arkansas	4,855,000	17
California	7,834,000	-10
Colorado	2,761,000	7
Florida	1,519,000	-16
Georgia	1,288,000	48
Idaho	3,398,000	3
Kansas	2,503,000	-7
Louisiana	1,236,000	32
Michigan	670,000	47
Mississippi	1,815,000	54
Missouri	1,529,000	48
Montana	2,061,000	4
Nebraska	8,588,000	13
Nevada	790,000	6
Oregon	1,665,000	-13
Texas	4,363,000	-14
Utah	1,097,000	1
Washington	1,689,000	-7
Wyoming	1,568,000	2
Region:
19 Western states	41,234,000	-2
9 Southeastern states	11,393,000	20
22 Northeastern states	5,387,000	41
Nation:
U.S. total	58,014,000	5

The type of irrigation system (Chapter 5) in the United States has also changed with time. Table 1.5 summarizes the percent of irrigated land using surface, sprinkler, and microirrigation since 1950. After a maximum of 98% surface irrigation (Chapter 10), this type of irrigation system has declined to 35% of the irrigated area in 2018. Meanwhile, the amount of sprinkled land has increased from 2%of the irrigated land in 1950 to 55% 2018. The amount of sprinkle irrigation (Chapters 11-13) now surpasses that of surface irrigation in the U.S. Microirrigation (Chapter 14), which includes drip/trickle, microspray, and similar systems, has increased from its infancy in the 1960s to 3 million acres at the turn of the century. Microirrigation accounted for 10% of the irrigated area in the U.S. in 2018.

Table 1.5. Comparisons among irrigation methods in the United States since 1950 (adapted from Irrigation Journal, 1971,2000,2001; USDA, 2014, 2019).

Year	Irrigation Method (percent of total irrigated area in U.S.)
	Surface	Sprinkler	Microirrigation
1950	98	2	-
1970	81	19	-
1990	56	42	2
2000	45	50	5
2008	39	54	7
2018	35	55	10