Agricultural Water Consumption in an Era of Climate Change

Introduction

Agriculture is a water-intensive economic activity - irrigation accounts for 70% of worldwide water consumption. With the aggravating state of climate change expected to negatively impact the availability and supply of freshwater resources, agrarian countries and communities have to adapt by finding ways to improve water efficiency in food production.

Greenhouse Farming Versus Open-field Farming

Currently, open-field farming remains the normative method that farmers utilise to cultivate their crops, especially those living in land-abundant or economically less-developed countries. Open-field farming has many drawbacks in terms of water used to maintain and grow crops. Water has to be provided over a large area of land, which makes targeted delivery difficult, and as such is often achieved via surface irrigation (flood irrigation) or crop sprinkler system. When employed, these methods of irrigation result in excess water spent. In addition, direct exposure to the elements (wind and sun) increases evaporation and plant transpiration rates, amplifying water loss from farmland soils to the atmosphere. These factors greatly raise the water costs of crop production via open-field farming. This is exemplified by the fact that 250 litres of water are needed to produce a kilogram of lettuce. Comparatively, only 20 litres of water is required for the same amount of harvest, when crop cultivation takes place within greenhouse environments. This reduction in water use is attributed to the microclimate created within the greenhouses. By providing an enclosed environment, greenhouses help to maintain a high level of internal humidity. Furthermore, greenhouses fitted with shade materials help to filter out infra-red radiation from sun rays whilst allowing visible light to pass through, preventing excessive heating and hence reducing water losses to evapotranspiration. Therefore, a shift from conventional open-field farming to greenhouse farming can be an effective solution to reduce agricultural water consumption.

Controlled Environment Agriculture(CEA) Technology and Water Conservation

Commonly, it is a practice for controlled environment agriculture (CEA) technology to be employed in greenhouse farming. CEA technology refers to systems used within indoor environments to regulate growth parameters such as temperature, water, carbon dioxide level and light intensity, with the aim of improving farming efficiency, crop yield and quality. These systems often involve the use of sensors, processors and actuators to optimise critical environmental parameters. With respect to controlling water delivery and consumption, the automation of micro-irrigation devices helps to temporally target the amount of water provided per crop. Drip irrigation devices coupled to a timer, provide a small amount of water at spaced out timings to ensure plants get the water they need while reducing water wastage. In aeroponics, where crops are cultured without a planting medium, mists of nutrient solution are sprayed periodically onto the exposed roots, hence cutting water costs involved in farming. The harnessing of CEA technologies could therefore serve as an adaptation to climate change, where crops can continue to be grown despite reduced water supply.

Rainwater Harvesting for Urban Farming

In the context of farming in urban environments, water used for irrigation is often drawn from the municipal system, as the sites of food production are located distally away from the source. Furthermore, in areas that receive consistent rainfall, precipitation is converted to overland flows by impervious surfaces and redirected by drains and canals into sewage systems or reservoirs. This water requires further processing and purification before it is suitable to be used for irrigation. This presents an opportunity for technology to be harnessed to harvest rainwater and use it directly for irrigation in urban farming. Rainwater harvesting technology involves the use of physical systems to collect, convey, store and treat rainwater for human use. Retrofitting urban farming facilities and rooftop gardens with such systems, optimises the use of rainwater as a resource, and provides an in situ water source for irrigation.

Conclusion

A multilayered approach involving the modification of farming environments and the use of technology for irrigation is required to improve the security and efficiency of water use in agriculture. This serves as an adaptation strategy to maintain food security despite the onslaught of climate change