Background, Aim and Scope. It is vital to quantify the potential impacts of water consumption for sustainable development. Since water has uneven distributions with time, place, and origin, simple summation of water consumption may mislead as an indicator of the environmental impacts. This paper proposes a concept for weighting uneven distribution of water and characterizing water consumption into potential impacts from viewpoints of hydrology and life cycle assessment.
Materials and Methods. The concept for weighting water resources and converting water consumption into potential impacts on freshwater availability was proposed, based on an assumption that the impact is proportional to the catchment land area or time period required to obtain a unit amount of water from each water source. The Water Availability Factor (fwa) was defined based on global mean precipitation by a global hydrological modeling system to reflect the variability of maximum renewable water resources with location and source of water at global resolution 0.5×0.5 degrees. This concept can be understood instinctively and provide various types of characterization factor based on user’s demands.
Results and Discussion. The fwa for precipitation (fwa_p) tended to be smaller than that for surface or groundwater, based on the principle of water balance. Higher values of fwa_p were found in dry areas such as the Sahara, Arabian Peninsula, South Africa, interior China, the American Midwest and Australia. Three types of weighted average fwa were presented by country, for entire countries, rainfed cropland, and irrigated cropland. Values of fwa_p for agricultural use tended to be lower than those for entire countries in arid countries. It can be thought that croplands appear more selectively distributed in areas with sufficient water accessibility.
Conclusions. The current work showed that the Water Availability Factor can be estimated based on land area or time period required for obtaining a unit amount of water from each source. It can be provided with any spatial resolution such as by grid, continent, country, or basin. The grid-scale data permits local conditions to be depicted and potential impacts evaluated in exacting detail. The result of proposed characterization can be understood intuitively by using the concept of land area or time period required and the global annual precipitation. It is applicable in terms of robustness of the factors, and can be adopted in life cycle impact assessment of freshwater use.
Recommendations and Perspectives. There is room for argument regarding the validation of fwa uncertainties, because it is possible that fwa varies considerably with different meteorological forcing data or hydrologic models. Further study to increase temporal resolution of fwa is expected to reflect seasonal differences of renewable water resources. Actual midpoint characterization on a global scale should be performed using this concept. It will facilitate clarification of locations and magnitudes of potential impacts caused by nations, products, and individuals.