Water-saving technologies have long been seen as an effective method to reduce irrigation water use and alleviate regional water shortage. However, growing reports of more severe water shortage and increasing application of water-saving technologies across the world have necessitated reassessment of agricultural water-saving. This study develops a simple method based on satellite-based ET partitions to estimate water withdrawal, water consumption and return flow from the 1980s to 2010s, and quantifies water-savings across globe and four hot-spot irrigated areas at both field and regional scales based on water accounting framework. The results show that global irrigation water flows keep increasing from the 1980s to 2010s, with over 50% increase from the expansion in irrigated lands. While water-saving technologies are found mainly applied in originally old irrigated lands, traditional flooding irrigation is still dominant in newly-developed irrigated lands. Non-beneficial water consumption (soil evaporation) is effectively reduced by water-saving technologies, but return flow has increased at the same time. At field scale, water-saving technologies fail to save water because the accumulated increased return flow is more than the accumulated decreased non-beneficial water consumption. At regional scale, however, water is saved because the return flow percolated to fresh aquifers is seen as beneficial rather than loss. At the same time, the accumulated increase of beneficial water consumption (crop transpiration) exceeds regional water savings, which explains the paradox between wide application of water-saving technologies and more severe regional water shortage. This study provides key new evidence for the paradox of irrigation efficiency and helps reconsidering water-saving technologies and their impacts on regional water resources.

长期以来，节水技术一直被视为减少灌溉用水和减轻区域水资源短缺的有效方法。但是，越来越多的关于严重缺水的报道和节水技术在世界范围内的日益广泛应用，都需要对农业节水进行重新评估。这项研究开发了一种基于卫星ET分区的简单方法，以估算1980年代至2010年代的取水量，水消耗量和回流量，并根据实地和区域规模对全球和四个热点灌溉区的节水量进行量化。关于水核算框架。结果表明，从1980年代到2010年代，全球灌溉水流量一直在增加，其中灌溉土地的扩张增加了50％以上。虽然发现节水技术主要应用于原始的旧灌溉土地，但传统的洪水灌溉在新开发的灌溉土地中仍然占主导地位。节水技术有效地减少了非有益的水消耗（土壤蒸发），但与此同时回流却增加了。在田间规模上，节水技术无法节水，因为累积的回流增加量大于累积的非受益用水量减少量。然而，在区域范围内，节水是因为渗入新鲜含水层的回流被认为是有益而不是损失。同时，有益用水（作物蒸腾）的累积增加量超过了区域节水量，这解释了节水技术的广泛应用与更严重的区域水资源短缺之间的矛盾。这项研究为灌溉效率悖论提供了重要的新证据，并有助于重新考虑节水技术及其对区域水资源的影响。