Irrigation Overview

Overview of Irrigation What Is Irrigation? Irrigation is the controlled application of water to land to grow crops, maintain landscapes, and restore vegetation in areas where natural rainfall is insufficient. Rather than waiting for rain to fall, irrigation allows farmers and landscapers to actively manage water supply to meet plant needs. This practice is ancient—civilizations have used irrigation for over 5,000 years. Today, irrigation is critical for agriculture worldwide, supporting food production in both dry climates and regions that experience unreliable rainfall patterns. The map above shows the global distribution of irrigated agricultural land, with particularly high concentrations in Asia, the Middle East, and parts of North America. Irrigation has become essential for feeding the world's growing population. Understanding Water Sources for Irrigation Irrigation water can come from different sources, and the source available often depends on local geography and resources: Groundwater is accessed through springs or wells, drawing water from underground aquifers. This source is reliable but depends on sufficient groundwater availability in the region. Surface water comes from rivers, lakes, and reservoirs. This is often the most abundant source but may be seasonal—available primarily during rainy periods. Non-conventional sources are increasingly important as water becomes scarce. These include: Treated wastewater (recycled from cities and industries) Desalinated water (salt removed from seawater) Drainage water (collected from other agricultural areas) Fog collection (capturing moisture from fog in specific climates) The choice of water source affects irrigation system design and cost, making it a critical planning decision. Supplementary vs. Full Irrigation One of the most important distinctions in irrigation is understanding how it relates to rainfall. There are two main approaches: Supplementary irrigation adds water to the rainfall that already falls naturally. This is common in regions with moderate rainfall where plants need extra water during dry spells or critical growth periods. Think of it as "topping off" what nature provides. Supplementary irrigation is used widely in temperate regions with reasonably predictable rainfall. Full irrigation supplies most or all of the water crops need, with little dependence on rainfall. This approach is necessary in arid and semi-arid areas, particularly outside rainy seasons when rainfall is absent. In these regions, irrigation isn't optional—it's the only way to grow crops. The image above shows a rice paddy—an example of full irrigation. The standing water visible indicates intensive water management typical of areas with limited rainfall. Why this matters: The type of irrigation used depends on climate and water availability. A farmer in a semi-arid region relies on full irrigation year-round, while a farmer in a humid climate uses supplementary irrigation only when needed. The Connection Between Irrigation and Drainage Irrigation and drainage are closely related concepts that both affect water balance in an area. Drainage is the removal of surface water and groundwater from land—essentially the opposite of irrigation. Why study them together? When water is added through irrigation, it must go somewhere. Excess water needs to drain away, or it can accumulate and create waterlogging (soil becoming too wet) or raise groundwater levels. Conversely, effective drainage helps create the soil conditions where irrigation can work properly. Understanding both processes is essential for sustainable water management in agricultural areas.