Improved water retention and irrigation efficiency in agricultural areas
Description
Soil moisture is the component of the water cycle that is accessible by the roots of plants and the quantity of water available is a major steering factor for plant growth. Soil moisture content is a factor of rainfall, evapotranspiration, surface run-off and deep percolation, and is therefore sensitive to changes in temperature and precipitation patterns and intensity (EEA, 2016b). As drying of soil moisture has already been observed (EEA, 2016a) and is projected to continue in the Mediterranean region (IPCC AR5 WGI, 2014), some measures can be taken to protect soil moisture and ensure agricultural productivity. Adaptation options include water retention measures to store water in the soil or at the wider landscape level. Storing water in soil decreases the negative impacts of droughts and the need for additional irrigation, and when rainfall is not sufficient to ensure crop productivity, additional water can be applied via irrigation.
Several measures based on the use of technology in agriculture can increase the water retention of soil by decreasing runoff. Runoff, depending on soil characteristics, can be reduced by tillage methods combined with plants having a high root density and lush surface cover. Conservation tillage, including both no-tillage and minimum tillage, is the practice of limiting or eliminating tillage practices (ploughing in particular), leaving some of the previous season’s crop residues on the soil surface. It reduces evaporation from the soil surface, preserving soil organic matter in the upper soil layers and, consequently, increasing water retention capacity of the soil. Terracing and contour ploughing are other methods of soil conservation to slow or prevent rapid surface runoff. Contour ploughing is the farming practice of ploughing across a slope following its contours, which have the effect of slowing water run-off during rainstorms so that the soil is not washed away, and allows the water to percolate into the soil. The rows made by the plough run perpendicular rather than parallel to slopes, generally resulting in furrows that curve around the land (Climate-ADAPT, 2015b).
At a wider landscape level, increasing water storage can either aim to increase the natural water retention capacity of an entire landscape or with human-made structures. The water retention capacity of an agricultural landscape can be improved by maintaining drainage systems; establishing a variable water flow regime; rehabilitating and reconstructing/adapting morphological structures in rivers; adopting ad hoc crop rotations and other agricultural practices (tillage systems, soil cover management, etc.); and setting up flood control reservoirs (Climate-ADAPT, 2015b).
Some measures applied to protect and manage water resources and address water-related challenges are multi-functional measures that work by restoring or maintaining ecosystems as well as natural features and characteristics of water bodies using natural means and processes. These Natural Water Retention Measures (NWRMs) are able to enhance, as well as preserve, the water retention capacity of soil, aquifers, and ecosystems with a view to improve their status. NWRMs for the agriculture sector include: meadows and pastures, buffer strips and hedges, crop rotation, strip cropping along contours, intercropping, no-till agriculture, low-till agriculture, green cover, early sowing, traditional terracing, controlled traffic farming, reduced stocking density, and mulching. They provide multiple benefits including the reduction of risk of floods and droughts, water quality improvement, groundwater recharge and habitat improvement. The application of NWRMs support green infrastructure, improve or preserve the quantitative status of surface water and groundwater bodies, and can positively affect the chemical and ecological status of water bodies by restoring or enhancing natural functioning of ecosystems and the services they provide (NWRM, 2015).
While improving water retention can lessen the water demand for agriculture, irrigation has long been a practice of European agriculture. In Europe, there has historically been a mix of rain-fed and irrigated agriculture, with agriculture accounting for approximately 40% of total water withdrawal, reaching 80% in some regions. In particular in southern Europe, irrigation demand is projected to increase in the coming years, while water availability is expected to decrease, due in part to climate change. However, significant water savings of over 40% of the volume of water abstracted could be achieved with improvements in irrigation infrastructure and technologies, such as improving the delivery and application efficiency of irrigation systems, changing practices, planting drought-resistant crops, and reusing treated water (EPRS, 2019).
Techniques to improve the efficiency of irrigation, optimize water use and in turn reduce water demand include shifting from gravity irrigation to modern pressurized systems (e.g., drip and sprinkler irrigation) and improving conveyance efficiency (note: pressurized systems require an energy source to pump the water, therefore the use of non-pressurized systems better mitigate climate change). Deficit irrigation, where irrigation is applied during drought-sensitive growth stages of a crop and limited outside these periods if rainfall provides a minimum supply of water, can also be applied. Water productivity increases under deficit irrigation, but the application of this technique requires adjustments in the agricultural systems, imposing changes at different levels (Climate-ADAPT , 2015a).
Costs and benefits
The multi-functionality of NWRMs contributes to their cost-efficiency, positioning them as good options for sustainable climate adaptation measures. NWRMs therefore may offer the best return in terms of societal benefits from flood control and other ecosystem services such as water quality regulation and water provisioning, food or material production, biodiversity protection, recreation, air quality and climate regulation (European Commission). For example, crop rotation or changes in tilling and ploughing practices come at little to no cost but provide significant benefits in terms of groundwater recharge.
Regarding irrigation, pressurized irrigation is more efficient than gravity irrigation in terms of water use, yet has additional costs associated with electricity use. However, consideration is being given to the use of photovoltaic systems to power irrigation (see H2020 project MASLOWATEN), shifting away from reliance on the energy grid or diesel generators, thereby reducing long-term energy costs and contributing to mitigation of greenhouse gas emissions.
Implementation time and lifetime
Implementation Time: Variable, approximately 1-5 years
Lifetime: 1-25 years
Source for more detailed information
Climate-ADAPT, 2015a, Improvement of irrigation efficiency, https://climate-adapt.eea.europa.eu/metadata/adaptation-options/improvement-of-irrigation-efficiency
Climate-ADAPT, 2015b, Improved water retention in agricultural areas, https://climate-adapt.eea.europa.eu/metadata/adaptation-options/improved-water-retention-in-agricultural-areas
EEA, 2016a, Indicator assessment: Soil moisture, https://www.eea.europa.eu/data-and-maps/indicators/water-retention-4/assessment
EEA, 2016b, Indicator specification: Soil moisture, https://www.eea.europa.eu/data-and-maps/indicators/water-retention-4
European Commission (EC), Environment: Natural water retention measures, https://ec.europa.eu/environment/water/adaptation/ecosystemstorage.htm#:~:text=Natural%20water%20retention%20measures%20are,courses%20and%20using%20natural%20processes.
IPCC, 2014, AR5 WGI Long-term Climate Change: Projections, Commitments and Irreversibility, https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter12_FINAL.pdf
MArket uptake of an innovative irrigation Solution based on LOW WATer-ENergy consumption (H2020 project MASLOWATEN), https://maslowaten.eu/?page_id=122&lang=en
Natural Water Retention Measures (NWRM), http://nwrm.eu/