Environment and Remote Sensing Laboratory, Graduate School of Water Resources, Sungkyunkwan University, Suwon 440-746, Gyeonggi-do, Republic of Korea.
Sci Total Environ. 2020 Apr 20;714:136719. doi: 10.1016/j.scitotenv.2020.136719. Epub 2020 Jan 15.
Irrigated agriculture is important for satisfying the increasing world food demand, but it interrupts the natural hydrological cycle by applying additional water to crops. Accurate information regarding irrigation water use (IWU) is a prerequisite to exploit land surface modeling and to quantify the uncertainty of climate projections. In this study, the global IWU was estimated for 2000-2015 by combining satellite-based soil moisture (SM) observations from the European Space Agency's Climate Change Initiative (ESA CCI) and the model estimated SM from European ReAnalysis-5 (ERA5). Considering irrigation as an unmodeled hydrological process in ERA5 and the ability of ESA CCI SM to capture the irrigation patterns, the global IWU was estimated by solving the water balance equations for ESA CCI and ERA5 SM. Owing to the global absence of ground-truth data for IWU, the IWU estimates were compared with the reported irrigation water withdrawals (IWWs) provided by Food and Agriculture Organization. The results indicated that satellite-based SM observations have the potential to identify global irrigation. All three ESA CCI products (active, passive, and merged) discerned the global irrigated areas satisfactorily, and the estimated IWU captured the pattern of the country-level IWWs (R = 0.77, 0.72, and 0.81 for active, passive, and merged products, respectively). However, the estimated IWU substantially underestimated the reported IWWs (bias of -76.55, -76.01, and -73.93 km for active, passive, and merged products, respectively) due to the coarse spatial resolution (0.25° × 0.25°) of the microwave remote sensing products and the inclusion of supplemental water in the IWWs, which was lost during distribution to crops. Trend analysis of the IWU indicated an increasing trend of the IWU in the first decade of the 21st century. However, in recent years the trend has reversed due to advances in agriculture technology and the adoption of water-efficient irrigation methods.
灌溉农业对于满足不断增长的世界粮食需求至关重要，但它通过向作物额外供水来打断自然水文循环。准确的灌溉水用量（IWU）信息是利用陆面模型和量化气候预测不确定性的前提。在本研究中，通过结合欧洲航天局气候变化倡议（ESA CCI）的卫星土壤湿度（SM）观测和欧洲再分析-5（ERA5）模型估算的 SM，估算了 2000-2015 年的全球 IWU。考虑到 ERA5 中将灌溉视为未建模的水文过程，以及 ESA CCI SM 捕捉灌溉模式的能力，通过求解 ESA CCI 和 ERA5 SM 的水量平衡方程来估算全球 IWU。由于全球缺乏 IWU 的实测数据，将 IWU 估算值与粮农组织提供的报告灌溉取水量（IWW）进行了比较。结果表明，卫星 SM 观测有潜力识别全球灌溉。ESA CCI 的所有三种产品（主动、被动和合并）都能很好地识别全球灌溉区，估算的 IWU 捕捉到了国家层面 IWW 的模式（主动、被动和合并产品的 R 值分别为 0.77、0.72 和 0.81）。然而，由于微波遥感产品的空间分辨率较粗（0.25°×0.25°），以及 IWW 中包含的补充水在分配给作物时会流失，因此估算的 IWU 大大低估了报告的 IWW（主动、被动和合并产品的偏差分别为-76.55、-76.01 和-73.93km）。IWU 的趋势分析表明，21 世纪前十年 IWU 呈上升趋势。然而，近年来，由于农业技术的进步和采用了节水灌溉方法，这一趋势发生了逆转。
