Overestimation of water pressure by traditional water footprint: Method revision and application

Abstract

The water footprint (WF) is an essential indicator for assessing the pressure of human activities on freshwater resource utilization. The traditional WF model assumes that human water resource occupation comprises a green, blue, and grey WF, which can be linearly summed to the total WF. However, since there are two kinds of human demand for water resources, consumptive occupation and functional occupation, the relationship between them is not exclusive and does not have simple linear addition characteristics. The overlapping relationship between blue and grey WF has long been overlooked in the traditional WF calculation, resulting in a duplicate calculation of water requirement and exaggerating actual water resource demand. This study introduced a new index of blue-grey WF that deducted the overlapping portions of blue and grey WF, thereby calculating a region’s actual freshwater resource utilization. Northern Anhui, an arid region short of water resources with water pollution, was selected as a case study. The traditional WF calculation showed that the multi-year average WF of Northern Anhui was 3.44 × 1010 m3 from 2011 to 2020, with the grey, green, and blue WF accounting for 52.59 %, 27.63 %, and 19.78 %, respectively. The blue and grey WF overlapped each other and the blue WF can be fully covered by grey WF, resulting in a total blue-grey WF of 1.81 × 1010 m3, much lower than the sum of blue and grey WF. Based on the revised WF calculation model, the multi-year average WF of Northern Anhui was 2.76 × 1010 m3, decreased by 19.78 %, indicating a severe issue of duplicate calculation of blue and grey WF. The revised WF model could avoid the repeated calculation issues of water resources used by different functions. It provides a more reliable and accurate research method for regional water resources accounting and management decision-making.