Green water footprint: what it is and how it supports sustainability

The green water footprint is the volume of rainwater, temporarily stored in the soil as moisture, that plants consume during their growth. It is one of the three components of the water footprint defined by the Water Footprint Network, alongside the blue footprint and the grey footprint.

When we talk about sustainability we tend to think of the carbon footprint, but green water is decisive: it explains most of the water consumption of rain-fed agriculture and much of irrigated agriculture too. This article explains what it is, how it is calculated and why it matters.

What is the green water footprint?

The green water footprint measures the rainwater that a crop evapotranspires over its cycle, plus the water incorporated into the harvest. Unlike the blue water footprint, which corresponds to surface water or groundwater withdrawn for irrigation, and the grey water footprint, which refers to the water needed to assimilate pollutants, the green footprint comes exclusively from rainfall retained in the soil.

Key characteristics of the green water footprint

• It comes from rainfall: it does not involve withdrawing water from rivers or aquifers, but making use of precipitation stored in the soil.
• It depends on vegetation and climate: plants consume it through evapotranspiration, and it varies with the crop, the soil and the rainfall pattern.
• It is central to agriculture: in many rain-fed crops it is, by far, the main component of the water footprint.

If you want to see how the three colours of water combine in the field, read our article on the water footprint in agriculture.

How is the green water footprint calculated?

The calculation estimates how much rainwater a crop consumes during its growth. To do so, the following factors are analysed, among others:

1. Green crop evapotranspiration: the rainwater that the plant transpires, assessed from soil moisture and limited by the available rainfall.
2. Effective precipitation: the share of rainfall that actually remains available in the soil for the crop.
3. Soil and crop characteristics: the soil's capacity to retain water and the water requirements of each species.

Within the Water Footprint Assessment framework, the green footprint of a crop is obtained by dividing the green water evapotranspired during the season by the crop yield, and it is expressed in litres per kilogram. It is not, therefore, simply the difference between total rainfall and evapotranspiration: it is the rainwater effectively consumed by the crop.

Why is it important for sustainability?

The green footprint helps to manage water efficiently in agriculture, one of the sectors that consumes the most water on the planet. Its value can be seen on several fronts:

Less pressure on blue water sources

Relying on rainwater reduces the need to withdraw water from rivers and aquifers, something especially valuable in areas with water stress.

A boost for sustainable farming practices

Knowing the green footprint makes it possible to choose crops better adapted to the local climate and to improve soil management so it retains more moisture.

Conservation of soil and biodiversity

Efficient use of rainwater supports the health of the soil and its associated ecosystems, the basis of agricultural biodiversity.

If you are interested in the corporate side, you can read our article on strategies to reduce the water footprint of companies.

Examples of green water footprint in crops

According to the Water Footprint Network estimates (Mekonnen and Hoekstra), in many staple crops green water is the dominant component of the water footprint. As a rough guide, cereals such as wheat or maize tend to fall in the region of around 1,000 to 1,800 litres per kilogram of grain, while rice tends to be more demanding. These figures are global averages and vary widely depending on the region, climate and yield, so they should be interpreted as estimates rather than fixed values.

How to reduce the green water footprint?

Rather than "reducing" rainwater, the aim is to make better use of it and produce more food per litre consumed. Some strategies:

1. Choose adapted crops and varieties: species suited to local rainfall and, where appropriate, drought-tolerant.
2. Improve soil management: cover crops, organic-matter inputs and conservation tillage to retain more moisture.
3. Regenerative agriculture: rotations and practices that increase the soil's capacity to store water and improve its fertility.

The green water footprint, key to efficient agriculture

The green water footprint is fundamental to assessing water use in agriculture and promoting more sustainable practices. Understanding how it is calculated helps to make better decisions about crops, soil and water management.

To complete the picture of the water footprint, we also recommend reading about the blue water footprint, the grey water footprint and virtual water.

Frequently asked questions about the green water footprint

What distinguishes the green footprint from the blue one?

The green footprint is the rainwater stored in the soil that plants consume; the blue footprint is the surface water or groundwater withdrawn, usually for irrigation.

Why is the green footprint not usually considered "harmful"?

Because it makes use of rainwater that, for the most part, does not compete with other uses. Even so, it takes up land and shapes land use, so it must also be managed sensibly.

Which sectors depend most on the green footprint?

The agricultural sector, especially rain-fed crop production, where much of the water consumed comes from rainfall.

If you want to measure and manage the water footprint of your activity with traceable data, you can rely on Manglai's water footprint solution.