Irrigated agriculture accounts for a substantial portion of global water withdrawals (70%) and consumption (80-90%), playing a vital role in global food security by contributing to 40% of global food production. With growing concerns about climate change and population growth, irrigation is seen as a crucial adaptation strategy to mitigate future food crises. However, current irrigation practices rely heavily on fossil fuel-based energy for pumping, resulting in significant greenhouse gas (GHG) emissions. While numerous studies have assessed GHG emissions in various agricultural aspects (land use, fertilizer production, livestock, etc.), a comprehensive global analysis of energy-related GHG emissions from irrigation remains lacking. This gap in knowledge hinders effective mitigation strategies for achieving net-zero emissions in agriculture. Previous research has focused primarily on improving irrigation water efficiency rather than reducing energy consumption and CO2 emissions directly. This study aims to quantify global energy consumption and CO2 emissions from irrigation (2000-2010), providing a spatially explicit analysis at a 10x10 km resolution. The analysis considers various irrigation systems (surface, sprinkler, drip) and pumping systems (electricity, diesel), including CO2 emissions from groundwater degassing. Furthermore, the study projects future energy and CO2 emissions under a sustainable irrigation expansion scenario in 2050 and evaluates the effectiveness and feasibility of various mitigation interventions. Finally, the study compares the energy and CO2 intensity of irrigation with other farm operations.

Existing literature provides regional and country-specific data on irrigation energy consumption and GHG emissions for regions like China, India, the Mediterranean, Pakistan, and the United States. However, a globally comprehensive dataset detailing the energy-related greenhouse gas emissions from irrigation remains absent. Previous studies have quantified GHG emissions within broader agricultural and food systems, including land use change, fertilizer use, livestock production, and food processing and transportation. Indirect GHG emissions associated with irrigation, such as methane emissions from reservoirs and rice paddies, and nitrous oxide emissions from fertilizer use, have also been studied. These previous efforts highlight the significance of GHG emissions in agriculture, and the need for mitigation strategies within this sector. However, a consistent global dataset, incorporating energy intensity, and detailed breakdown by irrigation and pumping methods, is notably missing, necessitating the current research to address this critical gap.

This study uses a spatially explicit approach to quantify global energy consumption and CO2 emissions from irrigation between 2000 and 2010 at a 10 x 10 km resolution. The analysis incorporates various factors influencing energy use, including the volume of irrigation water, total pressure head, irrigation system type (surface, sprinkler, drip), pumping system type (diesel, electric), and irrigation water source (surface or groundwater). Data on groundwater table depth, the percentage of surface and groundwater used for irrigation, the proportion of different irrigation systems, and irrigation water withdrawal were sourced from various datasets including Fan et al. (2013), Siebert et al. (2010), Jägermeyr et al. (2015), and Huang et al. (2018). Energy requirements were calculated using equations considering water volume, total pressure head (including lift, drawdown, operating pressure, and friction losses), and pump and prime mover efficiency. Energy-related CO2 emissions were calculated by multiplying energy consumption by the appropriate CO2 emission factor, accounting for the carbon intensity of electricity and diesel fuel. CO2 emissions from groundwater degassing were estimated using a separate equation considering groundwater volume, the ratio of groundwater withdrawal for irrigation, and CO2 concentration in groundwater. Future energy consumption and CO2 emissions were projected under a sustainable irrigation expansion scenario in 2050, assuming constant water-use efficiency and projected regional carbon intensity of electricity. The study also assesses the feasibility of mitigation options (drip irrigation, low-carbon electricity) to reduce CO2 emissions, using a feasibility metric and considering country-specific factors. Finally, the contribution of irrigation to overall farm energy use and CO2 emissions is analyzed by comparing irrigation energy and CO2 intensity with those from fertilizers, machinery, and fuel, using data from FAOSTAT.

The study reveals significant variations in energy and CO2 emissions intensity across countries and continents. Asia showed the highest energy (8.0 GJ/ha) and CO2 (1063 kg CO2/ha) intensity, followed by Africa, South America, North America, Oceania, and Europe. Sprinkler irrigation had the highest energy and CO2 intensity (1.8 MJ/m³, 188.4 g CO2/m³), followed by drip (1.0 MJ/m³, 109.0 g CO2/m³) and surface irrigation (0.5 MJ/m³, 58.5 g CO2/m³). Diesel pumping showed higher intensity than electric pumping. Global energy consumption from irrigation was 1896 PJ, with Asia and North America accounting for 72% and 14%, respectively. India, China, the US, Pakistan, and Iran contributed 68% of global energy consumption. Total global CO2 emissions from irrigation were 222 Mt CO2 per year (216 Mt from energy consumption and 6 Mt from groundwater degassing). Asia and North America were the major contributors. Sustainable irrigation expansion in 2050 could increase energy consumption by 28% and CO2 emissions by 7%, primarily in North America, Africa, South America, and Europe. Mitigation through low-carbon electricity and drip irrigation could reduce CO2 emissions by 55% globally; however, the feasibility varies significantly across regions. Groundwater pumping accounts for 89% of total energy consumption, despite only 40% of irrigated agriculture relying on groundwater. The study further shows that irrigation energy and CO2 emissions account for about 15% of total agricultural energy consumption and emissions.

The findings highlight the significant environmental footprint of irrigation, particularly the substantial energy consumption and CO2 emissions associated with groundwater pumping. The study's projections of future energy and emission increases under sustainable irrigation expansion underscore the need for mitigation strategies. The effectiveness of mitigation options varies significantly based on regional contexts and the feasibility of implementing drip irrigation and transitioning to low-carbon electricity. The significant contribution of irrigation to overall farm energy use and CO2 emissions indicates a pressing need to prioritize water-efficient irrigation techniques and low-carbon energy sources in agricultural policies and practices. While the study suggests that a transition to low-carbon electricity and the adoption of drip irrigation, where feasible, have the potential for substantial CO2 reduction, the findings also stress the crucial need for country-specific assessments to understand the economic and practical aspects of mitigation strategies. The economic viability of these changes must consider factors such as initial capital investments, operational costs, carbon pricing, and overall economic return for farmers.

This study provides the first comprehensive, spatially explicit global assessment of energy consumption and CO2 emissions from irrigation. The findings highlight the significant contribution of irrigation to agricultural GHG emissions and energy use, particularly the dominance of groundwater pumping. Future irrigation expansion will likely exacerbate these impacts, necessitating urgent action towards mitigation. While efficient irrigation techniques and low-carbon electricity hold substantial potential for emissions reductions, the practical implementation will require country-specific assessments considering economic and technical feasibility. Further research should focus on developing and implementing tailored mitigation strategies, including policy interventions that encourage the adoption of sustainable irrigation practices and the transition to low-carbon energy sources in agriculture.

The study relies on existing datasets with varying spatial and temporal resolutions, potentially introducing uncertainties in the estimates. The lack of consistent country-level data on irrigation pump types (diesel vs. electric) led to indirect estimations, potentially affecting the accuracy of energy and CO2 emission calculations. The projection of future energy and CO2 emissions assumes constant water-use efficiency and projected regional carbon intensity of electricity, which may not hold true in all scenarios. The feasibility analysis of mitigation options is based on regional targets for low-carbon electricity, which may not represent all country-specific situations. Finally, socioeconomic factors influencing irrigation adoption are not explicitly considered, which may limit the generalizability of the study's findings.