The spatio-temporal variability of green and blue water footprint of maize

The management of water resources for human purposes is a central theme to the challenge of improving food security worldwide. The great majority of freshwater is used for agriculture; therefore, it is important to find a way to assess and quantify water consumption for the production of agricultural goods. The indicator of unit Water Footprint (uWF) identifies the volume of water required to produce a unit of product. This indicator may refer separately to green and blue water, which are respectively the rainwater component (green water footprint) and the irrigation contribution (blue water footprint). In this study, the spatial and temporal variability of green and blue water footprint of maize is investigated, exploring its evolution in the years 1970 – 2019 across the world, with the creation of high-resolution global maps (5 x 5 arc min resolution), and highlighting the spatial heterogeneities of this variable as dependent on crop yield and climatic conditions. To reach this result, the global temporal variability of harvested areas, irrigated areas and crop yield has been reconstructed, together with the hydrological soil water balance through an appropriate model, which joins vegetation growth with local soil and hydroclimatic conditions. From the results, it can be noticed that the green component is usually greater than the blue one and, in the majority of countries, green and blue uWF are progressively reducing through the years, mainly due to technological developments, better irrigation strategies and water management which allow to increase the crop yield. In fact, the main factor influencing the trend of uWF is crop yield, which along the time-interval of the analysis, exhibited significant changes. However, despite the increment of water use efficiency, the estimated overall volume of green and blue water shows a mild variation, mostly due to the effect of climate change and modification of agricultural and irrigated areas.