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Over the past 50 years, greenhouse gas emissions resulting from agriculture, forestry and other land uses have nearly doubled, and projections suggest a further increase by 2050 (FAO, 2014). 

Climate change mitigation practices in agriculture will have both positive and negative impacts on water resources.  For instance, the cultivation of bio-energy crops, or afforestation and forestation activities that may have mitigation benefits will often translate into more water use and can reduce streamflow or groundwater resources, particularly in arid and semi-arid regions. Land management practices implemented for climate change mitigation may also affect  water resources. For example, soil carbon conservation practices such as reduced tillage, prevent erosion and improve the soil's capacity to retain water. More efficient use of fertilizers can also improve water quality. 

At the same time, water management can have an impact on greenhouse gas emissions and mitigation. Some examples are listed below.

Irrigated agriculture accounts for only 20 percent of the total cultivated land, but irrigated lands are more intensively managed. On average, irrigated agriculture uses greater amounts of inorganic fertilizer and other agrochemicals than most rainfed systems. Irrigated lands can enhance carbon storage in soils and enhance yields by using crop residues to cover the soil surface. 

Irrigation also affects energy consumption, as energy is needed to pump and treat water. Water scarcity and irrigation development are expanding the use of groundwater resources both in absolute and relative terms (Siebert et al., 2010). Water scarcity is also causing the agricultural sectors to tap into non-traditional means, such as desalination and wastewater reuse, to obtain water for irrigation. All these water sources have high energy requirements, which are often met by burning fossil fuels. Groundwater is used for irrigation on 38 percent of all irrigated land, and energy consumption for groundwater irrigation can be significant. For instance in China, it accounts for 16 to 25 million tonnes of carbon dioxide emissions, and in India, it is responsible for 4 to 6 percent of the total national emissions (Shah, 2009). Modern irrigation technologies, such as drip irrigation also increase energy demand. In Spain, irrigation modernization reduced water consumption by 21 percent between 1950 and 2008, but energy demand soared by 657 percent (Corominas, 2010). 

The use of solar energy for irrigation is a potential option for reducing the emissions associated with irrigation. Solar irrigation is an increasingly reliable, relatively low-cost, clean-energy solution for agricultural water management in areas with high incident solar radiation. In many rural areas where reliable access to electricity is lacking or diesel fuel is expensive, solar irrigation initiatives can be a way of providing broader access to energy for agriculture and other uses (FAO and GIZ, 2015). Some countries are promoting solar irrigation in their national action plans on climate change as a way of reducing agricultural greenhouse gas emissions. However, given their low cost of operation, solar irrigation systems also have the potential to encourage farmers to overuse groundwater. Appropriate policies and regulations should be put in place to control water use. 

On balance, the options for directly mitigating climate change through irrigation are the same as those for agriculture as a whole. The mitigation potential is likely greater in areas with intensive groundwater irrigation. The possibilities are determined mostly by the increased intensity of irrigation, which will allow for a greater potential for carbon sequestration in tropical conditions and greater productivity. However, the mitigation benefits may be offset by more intensive use of inputs (Turral et al., 2011).

Agricultural methane emissions account for more than 50 percent of methane emissions from human activities. One-third of these emissions come from flooded rice production (28 to 44 million tonnes of methane per year). More than 90 percent of global rice production is concentrated in the monsoon area of South and Southeast Asia. Since the area of irrigated rice is growing relatively slowly, future increases in methane missions from rice fields are expected to be small. Furthermore, rice fields are converted, at least partially, from natural wetlands, which also emit methane, and extend over a much larger area at the global level. The effective increase in net emissions from transforming wetlands into irrigated rice has not been well studied. However, when emissions from natural wetlands are taken into account, gross emission estimates from rice cultivation are probably substantially smaller than effective net emissions (HLPE, 2012).

Emissions during the growing season can be reduced by using various water management practices, such as cultivating aerobic rice and, where conditions allow, alternate wetting and drying. Avoiding water saturation when rice is not grown and shortening the duration of continuous flooding during the rice-growing season are effective options for mitigating methane emissions from rice fields. Currently, aerobic rice yields tend to be poor (less than 2 tonnes per hectare), which is a strong disincentive for adoption even when natural drainage conditions are favourable (Comprehensive Assessment, 2007). The System of Rice Intensification, which is promoted in many rice-producing countries, can increase the productivity of irrigated rice by adjusting the management of plants, soil, water and nutrients. Because the System of Rice Intensification reduces the amount of flooding of irrigated rice, it also likely reduces methane emissions. It also saves water and may possibly reduce nitrous oxide emissions (HLPE, 2012). However, well-quantified data on reductions in methane emissions achieved by adopting this system are not yet available. The System of Rice Intensification is usually more labour-intensive than paddy rice, and not easily adoptable in countries where labour is scarce.

In some areas of the world, irrigated pastures are an important part of livestock production systems, As the demand for animal feed increases, their importance is growing. Better pasture management, combined with the use of feed additives that suppress methane fermentation in ruminants, can substantially reduce livestock methane emissions (Turral et al., 2011). 

In inland fisheries and aquaculture, the restoration or creation of riparian habitats can absorb carbon and create suitable environments for capture fish production. The modernization of fishing and aquaculture facilities also has the potential to contribute towards low-impact fuel-efficient (LIFE) production systems (see module B4 on fisheries and aquaculture).