The study looked at how water stress affects the efficiency of using water for growing wheat in a dry area of China. They compared wheat grown with irrigation to wheat grown only with rainwater. They found that irrigated wheat had higher yields than rainfed wheat. As water stress increased, the efficiency of using water for growing wheat decreased more for rainfed wheat than for irrigated wheat. This shows that how well wheat uses water depends on both the crop yield and the amount of water the plants use.