Water shortage is one of main concerns in today's world. Given that crop irrigation accounts for ~70% of global water consumption, reducing crop irrigation by water-saving technologies is considered as an important method to relieve water shortage. 

However, the growing application of water-saving technologies is found to be rarely accompanied by the increase of water availability because water saved at a field scale does not necessarily reduce water consumption at a regional scale. The regional reassessment of water savings is necessary for better understanding this dilemmas. The difficulty to quantify irrigation variables limits global reassessment. 

In a study published in Agricultural Water Management, a research team from the Center for Agricultural Resources Research (CARR), Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences, reassessed the effect of water-saving irrigation from 1980s to 2010s across the world and in four hot-spot irrigation regions. 

The researcher used satellite-based ET partition data and varied irrigated area, provides a novelty method to quantify irrigation variables. 

Globally, crop irrigation has kept increasing and over 50% of increase has been induced by "new" irrigated lands that expanded over the past four decades. Meanwhile, in "old" irrigated lands, the increase of crop transpiration exceeds the reduced soil evaporation that has been caused by water-saving technologies. 

As consequence, both the increase of crop transpiration in "old" irrigated lands and the expansion of "new" irrigated lands together lead to the paradox of irrigation efficiency across the world. 

The global evidence proves the wide existence of the paradox of irrigation efficiency, and calls for better management considering both the increase of irrigation efficiency and regional water accounting. 

Sprinkler irrigation equipment in potato fields in Zhangjiakou, China. (Image by ZHOU Xinyao)