Water use in cotton farming.



Cotton has a reputation for being a thirsty plant, and the amount of water needed to produce a t-shirt or a pair of jeans is often used as a measure to illustrate the unsustainable practices of cotton farming. However, these calculations do not fully represent the reality. 

Cotton and other plants absorb water through their roots and release it back into the atmosphere through pores in their leaves, with only a small percentage being absorbed into the plant itself. In this cycle, water also evaporates from the soil into the atmosphere, eventually returning as rain and replenishing waterways, the earth, and underground water tables. Irrigation water is drawn from these sources. Water can be used in a way that disrupts this natural cycle or contaminates it, for example, through the use of pesticides, fertilizers, or minerals. Displacement and contamination can interrupt the availability of fresh water for local use, contributing to water stress and, consequently, biodiversity loss due to the alteration of natural water sources. 

Cotton, like other farmed plants, interacts with different types of water. Green water refers to rainwater stored in the root zone of the soil, while blue water denotes irrigation water from lakes and rivers. Grey water is the fresh water needed to dilute pollutants from crop growth in order to maintain groundwater quality standards. 

Cotton water consumption varies significantly based on the region, location, and farming methods used. Some farms rely solely on green water, some use only blue water or a combination of green and blue. According to the ICAC Cotton Data Book 2021, 52% of global cotton is rain-fed, with 95% of cotton farms in Africa using rainwater and 13 African countries having zero blue water footprint. Over 60% of cotton produced in the USA and India comes from rain-fed sources, while Uzbekistan, Pakistan, Mexico, Kazakhstan, Egypt, and China are fully dependent on blue water. However, nearly 50% of global cotton uses irrigation. The amount of irrigation water depends on climate, rainfall, soil type, and other factors. For example, Brazil uses 17 liters/kg, while Turkmenistan uses 13,696 liters/kg. 

The type of irrigation methods and systems can have effects on biodiversity at all levels. The choice of irrigation methods depends on the economic development level of the region, available technologies, and local governance. Efficient irrigation systems such as mobile irrigators, sprinklers, and drip systems, which do not use excessive water and apply irrigation when the soil and air data indicate that it is necessary for a proper yield, are not easily accessible and affordable for all farmers. 75% of irrigated cotton uses surface irrigation methods, such as flood or furrow, leading to potential water loss. 

Mismanagement of irrigation, along with mismanagement of water sources, directly impacts biodiversity. For instance, excessive farming and irrigation demands in Uzbekistan, Kazakhstan, and Turkmenistan led to the Aral Sea catastrophe caused by diverting waters from the two main rivers feeding the Aral Sea, the Amu Darya and Syr Darya, for irrigation. This resulted in the water level of the Aral Sea dropping, becoming too saline for most aquatic life, leading to a collapse of the entire ecosystem due to disrupted food webs and habitats. Similarly, other activities, such as dam constructions, can alter natural ecosystems if mismanaged.