The growing pressure on global water resources requires technical tools and rigorous analysis to understand and mitigate the threats associated with scarcity, quality, and access to water. Indicators such as the Water Stress Index (WSI) and Water Risk Indicators (WRI) play a critical role in identifying vulnerable regions and planning strategies for sustainable water management.
The Water Stress Index (WSI): Analyzing Per Capita Availability
The Water Stress Index (WSI) focuses on the basic per capita availability required to meet essential human needs and the availability of renewable water resources (Gleick, 1996). Also known as the Falkenmark indicator, the WSI categorizes a population by its level of water scarcity and is evaluated by the ratio between a country's water footprint and its total renewable water resources. These resources include the blue and green water components, as defined by the Water Footprint Manual (Hoekstra et al., 2011):
- Blue water: Surface and groundwater resources (rivers, lakes, aquifers).
- Green water: Water stored in soil layers and directly used by vegetation.
Water availability is calculated based on a minimum daily human consumption volume of 50 liters (direct consumption, sanitation, personal hygiene, and food preparation). The higher the index, the greater the pressure on a country's water resources. This metric highlights nations with the most difficulty accessing water for these functions, providing a framework to prioritize the development of water infrastructure in these populations.
Key thresholds established by the WSI are:
- Water stress: <1,700 m³/year per capita.
- Chronic water scarcity: <1,000 m³/year per capita.
- Absolute water scarcity: <500 m³/year per capita.
These metrics quantify the impact of population growth, urbanization, and economic activities on water availability. Technically, WSI analysis is crucial for designing evidence-based policies that prioritize investments in water-efficient technologies and aquatic ecosystem restoration projects.
The Water Risk Indicators (WRI): Measuring Water Stress Metrics
Building on the renewable water availability defined by the WSI, the World Resources Institute developed the Water Risk Indicator (WRI). This is a reference index for measuring water stress across various geographical scales. The WRI uses a weighted aggregation methodology to evaluate risks related to water availability at national and watershed levels, focusing on five key indicators: baseline water stress, interannual and seasonal variability, flood frequency, and drought severity. The WRI quantifies the average exposure of users to water stress through the ratio between total withdrawals and total renewable supply in a specific area.
The WRI uses a scale of 1 to 5:
- 0-1: Very low water stress (<10% of renewable water withdrawn annually).
- 1-2: Low water stress.
- 1-2: Moderate water stress (20-40% of renewable water withdrawn annually).
- 3-4: High water stress
- 4-5: Extreme water stress (>80% of renewable water withdrawn annually).
Thirty-seven countries face extremely high levels of water stress (WRI 4-5), where over 80% of available renewable water is withdrawn annually (Gassert et al., 2013). Consequently, these nations experience heightened competition for water resources, extreme vulnerability to climate-related disasters, and a high dependency on alternative solutions (technology, innovation, governance). Besides, this scenario has critical implications for the agricultural, industrial and domestic sector. Countries like India, China, and Morocco are among the most affected, where competition for water resources limits the ability to meet the needs of both populations and productive sectors. Conversely, nations such as Singapore and the United Arab Emirates, with high per capita GDPs, use advanced water technologies like gray water reuse and desalination to compensate for limited renewable water availability.
Figure 1. A global map displaying WRI values for various sub-basins, with colors ranging from yellow to dark red. WRI 1 (white): No stress; WRI 3 (orange): Medium stress; WRI 5 (dark red): Extreme stress. Gray indicates unavailable data.
Limitations of WRI and WSI
The WSI is a relevant metric when it comes to contextualizing a region based on its renewable water availability in relation to consumptive use. This index has been a significant step in investigating and accurately assessing the actual water availability in basins, the challenges they face, and determining whether low water availability truly poses a threat when there is a high capacity for resilience. However, there are several limitations to this index, such as the static nature of its data, which prevents the inclusion of climatic and meteorological variations that could influence water availability, or the possibility that new technologies might lead to changes in water extraction. Nor does it include any analysis of infrastructure and governance, nor does it detail how water resources should be allocated across social, industrial, or agricultural sectors to balance competing demands. Nonetheless, building on this foundation, the most accurate system developed by the World Resources Institute has been achieved, evaluating the WRI.
Specifically in the WRI, the rankings allow comparisons between sub-basins, basins, or countries, but they do not address issues such as water quality, governance, or investments in water solutions. This is because the calculation of the water stress index considers numerous parameters extracted from extensive studies, models, and databases on withdrawals for agricultural, industrial, and domestic use, as well as probabilities of floods and droughts, seasonal variations in water flows, and access to supply. However, there is limited information on issues related to its constraints. Water management regimes or conservation policies at any level are not evaluated. This limits its scope in terms of governance regulation and investments in water technologies, which could enhance populations' resilience to water risks and threats. Furthermore, one of the main factors affecting public health, biodiversity, and access to drinking water—namely, the quality of surface and groundwater—is not assessed. A degradation in water quality can reduce the amount of renewable water available, as populations cannot rely on water volumes that fail to meet human health quality standards. However, this parameter is challenging to quantify, and the quality factor is often neglected when accounting for the water availability of populations.
Additionally, the WRI is based on averages at the national or basin level. These average values can mask significant local variations, which means that these regions may be overshadowed by the average needs indicated for the entire watershed or country. As a result, it becomes more challenging to carry out high-impact and necessary activities in those areas.
Another challenge of the WRI, similar to the WSI, is the static nature of its data. This indicator is built based on data recorded at a given moment. However, in the current context of the climate crisis, we cannot assume that risks remain static. There is increasing evidence that climate change affects the climate and weather patterns of a region, leading to prolonged droughts and frequent floods in areas unaccustomed to such events. As a result, civil infrastructure is often unprepared to withstand these threats. This translates into thousands of deaths, a severe impact on human health, and devastating economic costs for countries. If the data were dynamic and predictions of WRI values were made using collected climatic, meteorological, and historical data, combined with vast amounts of information, advanced models could identify countries, basins, sub-basins, or communities with higher WRI values. These values would not only be linked to basin stress but could also be connected to resilience.
However, the WRI is currently the most reliable indicator available to focus water management policies, guide innovation activities, and make compensations in regions based on the threats they face. Despite its limitations, as mentioned, it remains the reference value that promotes and drives new strategies for water management and sustainability.
Perspectives for the future
To address these limitations, there are various cutting-edge technologies that allow for better analysis of these indicators. For example, the data on which the WRI is built could be integrated into predictive models using continuous learning and simulation tools to anticipate scenarios of water stress. The creation of predictive models would allow for the calculation of the relationship between water demand and supply, taking into account extractions, consumptive use, availability, along with climatic, demographic, economic variables, and the existing system of regulations and policies in a region.
Additionally, the inclusion of data on regulations, infrastructure, innovation capacity, and investment could incorporate a resilience aspect into the models, enabling the direction of water management activities toward regions that truly experience water stress in a contextualized manner.
Technical Implications for Spain and Global Context
When a corporation operates in a highly stressed watershed, it is presented with the opportunity to lead projects focused on the implementation of advanced technologies and integrated management strategies. This includes a variety of activities outlined in international methodological documents (Reig et al., 2019). However, it is important to understand the challenges faced by a watershed in order to tailor these activities to a result that truly impacts the natural and social ecosystem. For this, water planning based on data is necessary, such as incorporating the WRI into regional hydrological plans, ensuring decisions are based on scientific evidence.
For example, Spain is facing a water crisis primarily due to the scarcity affecting the territory in general (WRI of 4). On the other hand, the country's economy heavily relies on agronomic systems, especially agriculture. It is the leading exporter of plant-based foods in Europe. Water contributes to the growth, development, and productivity of these foods; it also determines very specific market parameters, such as caliber. It is important to understand this limitation in order to direct water-saving activities in Spain's river basins, knowing that its water footprint in agriculture is 75%, one of the highest in Europe. Therefore, the focus should be on activities that allow for the reduction of this water footprint, such as:
- Irrigation optimization: Technologies like drip irrigation, precision irrigation, and fertigation can reduce consumption by up to 50%.
- Improved agronomic practices: Enhance soil health and water retention capacity while boosting productivity.
- Reducing chemical usage: Minimize the leaching of fertilizers and pesticides into groundwater or surface water, preserving water quality.
Agrow Analytics' Role in Collective Action
The water crisis is a technical, environmental, and humanitarian challenge that requires an interdisciplinary and collaborative approach. Addressing it with scientific rigor and innovative tools is not only possible but necessary to ensure water sustainability.
Synergy is key: farmers, corporations, and tech companies working together toward the same goal, water sustainability.
Sources:
Gassert, F., Reig, P., Luo, T., and Maddocks, A. 2013. Aqueduct country and river basin rankings: a weighted aggregation of spatially distinct hydrological indicators. Working paper. Washington, DC: World Resources Institute.
Gleick, P.H. Basic water requirements for human activities: Meeting basic needs. Water International, 21, 83-92.
Hoekstra, A.Y., Chapagain, A,K., Aldaya, M.M. and Mekonnen, M.M. (2011). The water footprint assessment manual. Setting the global standard. Water Footprint Network, 2011. ISBN 978-1-84971-297-8
Reig, P., Larson, W., Vionnet, S., and Bayart, J.B. 2019. Volumetric Water Benefit Accounting (VWBA): A Method for Implementing and Valuing Water Stewardship Activities. Working Paper. Washington, DC: World Resources Institute.