Water Footprint of Forest and Orchard Trees: A Review

Abstract

The measurement of water consumption by trees is fundamental for detecting potential opportunities to mitigate water resource depletion. The water footprint (WF) is a tool to address the environmental effects related to water use, identifying ways to reduce overall water consumption. This work presents a review, updating the information on how WF is being addressed when applied to forest and orchard trees, identifying the methodological trends of the WF studies, and highlighting the main challenges that deserve further research for a consistent WF assessment of these trees. A sample with 43 publications selected based on keyword screening criteria was comprehensively reviewed, showing that most of the studies focus on orchard trees (mainly olive and citrus trees). The bulk of the studies only presented accounting or inventory results (i.e., water volumes consumed) and disregarded their sustainability or impact. This review highlights that a robust WF assessment of forest and orchard trees requires further research for harmonising the quantification of the green water scarcity footprint, and puts key challenges to the WF practitioners, such as the selection of the most adequate method to estimate ET considering trees specificities and climatic parameters, and the adoption of high spatial and temporal resolution for the WF assessment.