In recent decades, there has been growing concern regarding worsening global climate conditions for agricultural production, especially in Mediterranean climate and other semi-arid areas where the scarcity of water is a major problem. The objective of the study was to estimate the long-term evolution (in Spain, over 1922-2016) of the decoupling between crop´s water requirements and the green water available, and to analyze the causes of the changes. The FA0-56 methodology was followed to estimate the green water, blue water and water stress of crops, via an explicit territorial distribution, using 0.5^o grid cells. We propose a new indicator called Violet Water. This indicator groups together the water stress of the rainfed croplands and the blue water of the irrigated croplands, representing the components of this decoupling. Our results show that crops´ water requirements increased by 21% and violet water by 30% over the study period. The decomposition analysis used to study the drivers of these changes suggests that increasing reference evapotranspiration, caused by global warming, was the major driver triggering the growth of crop water requirements. Meanwhile, the changes in violet water values were mainly driven by the coupling of the cropland´s spatiotemporal structure and climate change. The sensitivity analysis performed showed that the increasing trends in water stress, blue water and violet water were consistent for almost all the tested scenarios, but significant differences on the scale aroused depending on the climate data used (climate normal or each year climate) and specially on the geographical and historical Kc adjustment (crop-fixed Kc versus adjusted Kc). This highlights the importance of considering simultaneously the effect of the different factors, but also the need for refining this type of adjustment in future research.

在最近的几十年中，人们日益关注农业生产的全球气候条件恶化，特别是在地中海气候和其他半干旱地区，在这些地区缺水是一个主要问题。该研究的目的是估计作物的需水量和可用绿水之间的脱钩（在西班牙，1922-2016年）的长期演变，并分析变化的原因。遵循FA0-56方法，通过明确的地域分布，使用0.5 ^o来估计农作物的绿水，蓝水和水分胁迫网格单元。我们提出了一种新的指标，称为紫罗兰色水。该指标将雨养农田的水压力和灌溉农田的蓝色水归纳在一起，代表了这种脱钩的组成部分。我们的结果表明，在研究期间，农作物的需水量增加了21％，紫罗兰色水增加了30％。用于研究这些变化驱动因素的分解分析表明，由全球变暖引起的参考蒸散量增加是触发作物需水量增长的主要驱动因素。同时，紫罗兰色水值的变化主要是由农田时空结构和气候变化的耦合驱动的。进行的敏感性分析表明，水分胁迫的趋势在增加，与调整后的Kc相比）。这突出了同时考虑不同因素的影响的重要性，同时也需要在未来的研究中完善这种类型的调整。