Green and Blue Water Footprints: What Are They & How Do They Relate to Food?
Food security is having reliable access to a sufficient quantity of affordable, nutritious food. One necessity to achieve food security is the availability of freshwater resources for agriculture production.
The Environmental Impact of our Diets
The human population is rising, and our diets ever evolving. It is vital that the impact of food production on water use is fully understood in association with population-level dietary patterns in order to develop sustainable water management. This is vital, as climate change is predicted to change rainfall patterns and lead to an increase in extreme weather conditions, including floods and droughts.
It is known that a change in diet to include a greater consumption of animal based foods resulted in an increased global water use for agriculture. As such, the identification of sustainable diets that promote health with a minimal environmental impact is increasingly important.
Furthermore, research is beginning to suggest that reducing animal based foods in the diet results in a reduced environmental impact. However, this does not always correspond with lower water use as some plant based foods, such as fruits and pulses are dependent on an increased water use in the form of irrigation.
The Water Footprint of our Diets
There is a wide inconsistency worldwide regarding the amount and type of water used in food production, which are dependent on the environmental and agricultural management factors used.
The Water Footprint is the most commonly used metric for assessing water use. This quantifies the volume of water consumed during a particular foodstuff’s production. There are two different types of water footprint:
• Blue Water Footprint: The use of groundwater and surface water. • Green Water Footprint: The use of rainfall.
When a foodstuff, or particular diet has a high blue water footprint larger volumes of irrigation water are used during crop production. This can be problematic in areas where groundwater and surface water reserves are being used unsustainably. This is particularly evident when rainwater is inefficiently used and the water footprint is indicated as low green water and high blue water. In contrast a high green water footprint can indicate that the crop has a low yield or is inefficient in their water use. This is also true for crops with a high total (green and blue) water footprint.
A global systematic review and meta-analysis has been conducted by Harris F et al and published in Advances in Nutrition assessing the water use of diets and quantified the water footprint of diets in countries worldwide. This review has highlighted that, on average, European and Oceanian dietary patterns have the highest green water footprints. This is in contrast to Asian dietary patterns, which have the highest blue water footprint, particularly in areas such as the Middle East where there is limited rainfall and a greater need for irrigation. Water scarcity in Asia is a particular concern as groundwater resources are depleting in some areas, and climate change could disrupt normal patterns of rainfall and irrigation water supply.
Unfortunately, it is thought that simply changing dietary habits in Asia could be insufficient to decrease local water use, unless these changes coincide with improved water management systems in agriculture. Therefore, it is important to educate in this instance to improve the nutritional status of diets, for example by changing to more nutrient-dense and water-efficient crops, such as cereals (maize, millet and sorghum) instead of rice and wheat in India. Importing foods from water-abundant regions could also be a solution.
This review has also highlighted that animal based foods are the main contributor to increasing the green water footprint of diets, particularly in areas such as Europe and Oceania, compared with the global average. Changing to diets with no animals based foods from an average dietary pattern would decrease the total water footprint by 25% and blue water footprint by 12%. Dairy products typically have a lower water footprint than meat. It was also reported that vegetarian diets had lower total water footprints compared with current average diets. Whereas, in contrast, cereals, fruits, nuts, oils and vegetables are the main contributors to increasing the blue water footprint of diets.
Overall, healthier diets have a lower total water footprint and this could be further reduced by further limiting animal based foods from our diets. However, the increase use of blue water in the production of cereals, fruits, nuts, oils and vegetables needs to be further investigated, particularly as the general consensus is to increase the production and consumption of these foods in order to meet health dietary guidelines around the world. This is particularly sensitive in countries with declining groundwater or surface water availability, which might limit the potential for irrigation.
The environmental impact of the water footprint of a particular foodstuff is linked to local water availability. This is particularly important where water demand is growing and climate change in the local environment threatens supply. Hence, future studies must take this into consideration. There is also a need for the development of novel technologies to record the production of foodstuffs and will lead to a more accurate assessment of water footprints in the future.
Ultimately, the changes that are occurring to our dietary patterns are leading to an increase in water security concerns and therefore there is a need to better our understanding of the amount and type of water used in food production for consumers to make educated decisions, and for governments and policy makers to make informed policy decisions.
Harris F (2019). The Water Footprint of Diets: A Global Systematic Review and Meta-analysis. Adv Nutr. Sept 6