In 2006 we wrote an editorial for the Journal that highlighted the urgent need for a shift in thinking in water resources governance and management to improve our understanding of social-ecological water challenges and to correct the assessment of water requirements and investment opportunities necessary to feed a growing world population and meet increasing water demands (Falkenmark and Rockström 2006). We named this a move from a blue (runoff) focus to a broadened green-blue (soil moisture and runoff) focus (Falkenmark and Rockström 2004). The fundamental implication is a shift from seeing runoff to seeing precipitation as the primary water source in governance and management. It furthermore implies a shift from applying integrated water resources management (IWRM) as solely a runoff-based management framework to implementing it as a rain-based water management framework.
Some Core Implications of a Green-Blue Approach
Three fundamental shifts are required when moving from a blue to a green-blue water resources regime: incorporation of land use, focus on multiple scales, and integration of the role of water in terrestrial and aquatic ecosystem functions and ecological resilience.
Land Use
The dominant source of freshwater on the planet—making up on average out of the total of approximately of precipitation over land—is green water flow, i.e., rainfall that infiltrates in the upper unsaturated soil layers and flows back to the atmosphere as vapor/evapotranspiration (Fig. 1). At the ground level, 65% of the continental precipitation forms green water and the remaining 35% forms blue water. Soil management and land use are ways to influence partitioning of rainwater between green water in the soil and blue water in rivers and aquifers. Land use is thus at the heart of managing the use of the largest freshwater source for human well-being on the planet.
Fig. 1. Continental precipitation in terms of green water and blue water
Multiple Spatial Scales
In general terms, green water produces human well-being at the local scale, while blue water generates social benefits at the scales of the larger catchment or river basin. An integrated green-blue approach implies a downward extension of the focal scale in water resources management, from river-basin-based analyzes, governance, and management of streamflow to a stronger emphasis on the smaller catchment in which soil moisture operates and generates a multitude of ecosystem services for humans and nature. This mesoscale focus, above the farmer’s fields but below the river basin, creates choices for partitioning rainfall and allows consumptive use of green water to be properly brought into the water balance and to influence management interventions, from food and bioenergy crops, forests and natural vegetation, and release of blue water to downstream uses. Important, it enables a more explicit analysis of conflicts of interest and trade-offs between green and blue water use, and between upstream and downstream users and uses.
Ecosystem Functions and Ecological Resilience
A green-blue approach also makes it possible to include, for the first time, the water needed to sustain both terrestrial and aquatic ecosystem functions. This in turns enables water resource management to consider water to sustain desirable spatial configurations of catchments in terms of biomes and biodiversity, which are critical in determining the ecological resilience of a catchment, i.e., the capacity to cope with disturbances (such as fire, flooding, or drought) while maintaining structure and function. So far, green water, which sustains all terrestrial biodiversity, has been explicitly addressed in water resources planning and management to a very limited extent. In their future role, water resources planners and managers will have to pay adequate attention also to social-ecological dynamics, such as consumptive water use alterations linked to intensified or expanded food production, reduced return flow back to the river system as an effect of increasing irrigation efficiency, streamflow depletion in response to increased green water flows, effects of upstream rainwater harvesting for dry spell–resilient food production downstream, and effects on streamflow and groundwater recharge of altered forest management.
Water Resources in Dry Climates
A green-blue approach is particularly essential for addressing problems in dry climate regions in low latitudes with increasing pressures on water resources. There, green water flow plays a much larger role in the partitioning of rainfall between green and blue water sources than in the temperate zone. For a country such as Kenya, for instance, green water resources amount to over 90% of total water resources, as compared to 65% for the planet as a whole (see Fig. 1). Fig. 2 shows the relative amount of green water available in areas under different land cover in Kenya. For many poor, semiarid countries like Kenya, a mixture of green and blue water interventions will be essential to produce the food needed for a growing population.
Fig. 2. Estimate of rainfall partitioning over Kenya between green water use in different land types, vapor/green water flow, and blue water flow in rivers and aquifers, plus blue water withdrawals and their partitioning between consumptive water use and return flow back to the river system (darker blue indicates the amount that has to be reserved as environmental flow to support aquatic ecosystems)
Policy Implications
Integrated Land-Water Policies
The green-blue water framework for governance and management will have to be reflected in water planning, policies, and practices. Basically, this shift has to proceed from seeing water resources availability and use as fairly stable, giving all attention to blue water as the source, seeing land use as fairly irrelevant, and limiting ecosystem attention to environmental flows for protection of aquatic ecosystems. A new approach has to be developed around a realization that “stationarity is dead” (Milly et al. 2008), i.e., the realization that amplitude and frequency of water extremes will increase with global environmental change. A green-blue water approach can thereby enable new avenues to build water resilience in the face of growing water turbulence.
Managing water has to be downscaled from basin to catchments and subcatchments and characterized by complex spatial configurations for land use. Water management must therefore incorporate rainwater partitioning into green and blue water pathways and must include development of policies well adapted to the management of rain as the primary water source (Table 1). For water planners, the fundamental shifts are (1) focus on precipitation as the planning resource and (2) bottom-up application of planning, starting from the local subcatchment, i.e., the small, often ephemeral tributaries forming social-ecological units ranging in size from hundreds of hectares to hundreds of square kilometers, and moving on to catchments, which are generally less than . With growing human pressure on finite water resources in catchments or basins, trade-offs between green and blue water uses will increase (Fig. 3). There are now an increasing number of examples of changes in land use upstream affecting quality and quantity of streamflow in downstream areas. For instance, intensified use of green water in upper catchments in Gujarat, India, has resulted in disputes over blue water resources downstream.
Fig. 3. Blue and green features to be addressed in catchment-based trade-offs
Table 1. Conceptual Differences between the Past Blue Water–Based Management of Water Resources and the New Green-Blue Water–Based Management of Land and Water Resources
New
Conventional
Planning
• forming green water in soil and blue water in rivers/aquifers
• in rivers and aquifer
• Planning of management options as a continuum from rain-fed to irrigated agriculture
• Planning focus on water allocations for irrigation, industry, and domestic water supply
• Cross-scale focus—downscaling from river basin to catchment and local level
• River basin plans
• Integrated land and water resource management (ILWRM)
• IWRM
Policies
• New environmental policies, including green water needs to sustain terrestrial ecosystems
• Environmental impact assessment
• Green-blue trade-offs between up- and downstream (e.g., Water Act, Republic of South Africa)
• Water in aquatic ecosystems, environmental water flow
• Forest plantation fees
• Demand management
• Green water credits (GWCs)
• Water laws regulating blue water distribution
For a river basin with predominantly rural land in its upper catchments, the planning regime will involve questions, including (1) Where do we get the most human well-being and sustainability from water resource investments: from multiple, small-scale water-harvesting storage systems upstream for supplemental irrigation, or from one or a few larger storage and base flow–providing reservoirs in the lower locations in the basin? (2) What are the upstream-downstream trade-offs for different green and blue water intensification scenarios? (3) What are the safe minimum allocations of green water for terrestrial ecosystem functions and services and blue water for aquatic ecosystem functions and services?
Rain-Fed–Irrigated Agriculture Continuum
To rapidly increase agricultural productivity in regions prone to water scarcity, many of the most promising water management interventions are found in various degrees of irrigation-supported agriculture along a continuum between rain-fed and irrigated agriculture (Comprehensive Assessment 2007). This global-scale assessment stressed the need for breaking the sectoral dichotomy between rain-fed and irrigated agriculture; this will be necessary in order to introduce both water resources investments in terms of water storage for supplemental irrigation in small-scale rain-fed systems, and improved soil and moisture conservation practices in irrigated systems.
Green-Blue Payment Schemes
To address these green-blue upstream-downstream water interactions, several payment schemes are being tested and implemented. In the Colorado basin, downstream water users “buy” blue water from upstream water users who forsake withdrawals for downstream use. Such “blue” schemes are now being piloted in a green-blue setting. In the Tana River basin in Kenya, research is currently being carried out to develop a green water credit scheme that involves payment for green water for ecosystem services authorities (Dent and Kauffman 2007).
This green water credit (GWC) concept builds on the growing evidence that improved land and water management upstream cannot only improve green water benefits there (e.g., through increased farm yields) but also release more useful and better quality blue water to downstream uses (base flow replacing storm flow, less sediment). In the Tana case, the downstream stakeholder is a hydropower operator concerned with siltation of reservoirs and streamflow depletion. The GWC initiative focuses on the whole spectrum, from building up the water balances for different land and water management practices (e.g., impacts on runoff generation of conservation tillage and water harvesting) to the development of credit payment and decision support systems for catchment and basin planners.
Modernizing Water Legislation
Essentially, no national water legislation in the world currently considers rainfall as water; nobody knows who owns the rain. Instead, water rights, regulation of allocation between water uses and users, target the use of runoff resources. Green water use in forestry is included in the South African Water Act, the most progressive water legislation in the world, through a tax on the timber industry, which conducts “a streamflow reducing activity.” Although still within a blue water resource paradigm, green water use (e.g., in eucalyptus plantations) is, in other words, taxed for reducing what is seen as “the water resource,” namely blue water availability. This is in fact an early attempt of an integrated green-blue water policy, though it is an indirect one.
At present, situations in which local runoff collection and green water consumption is greater in upper catchments, which is increasingly occurring on a large-scale (cases in Gujarat in India, in the upper Murray Darling in Australia, and among commercial grape vineyards in the Cape Province), still fall outside of water legislation. It is now time for new green-blue water policies and legislation to consider precipitation upfront as the basic water resource, fundamentally shifting the legal framework for water regulation.
Building Resilience to Global Change
An early and very significant negative impact of climate change will be reduced water availability and increased water shocks in many regions of the world. A rain-based, integrated approach in water resources planning and management will, in other words, increase in relevance, particularly as warming will increase the volume of green water flows. It is in the green-blue water domain that the social cost of inaction will be largest, since the first and most direct social effects of climate change are related to water (too much, too little, at the wrong time). Our assessment is that adaptation to climate change will have to be centered first and foremost on managing water shocks. As the largest water vulnerabilities are currently felt among tropical rain–fed farmers, and the largest amplification of climate change–induced water shocks are expected to be felt there, our focus on adaptation must also be centered here. As seen in Fig. 4, there is a disturbing correlation between inherent social vulnerability (degree of hunger) and water vulnerability (high degree of dry spells and droughts), future growth in water demand (food water requirements), and the risk of future climate change–induced decline in food production as a result of water shocks. Despite uncertainties, there is little doubt that the frequency and amplitude of water-related shocks—droughts, floods, and dry spells—will increase as a result of climate change (Intergovernmental Panel on Climate Change 2007). Building resilience to global environmental change will therefore have to focus on both adaptation to increasing water shocks and transformation. Integrated green-blue water management is critical in this regard. A green-blue framework approach will make it possible to clarify trade-offs involved and to orchestrate catchment activities for compatibility. It will also improve recognition of local challenges and opportunities, thereby facilitating stakeholder participation in decision making.
Fig. 4. Inherent water vulnerability and poverty (left) shown as (1) undernourishment as percent of population (yellow 5–20%; orange 20–35%; ) and (2) semiarid and dry-subhumid regions according to Koppen climate zones; social water demands (middle) shown as the estimated requirement of increased agricultural water to meet the UN millennium development goals by 2015 of halving hunger (light ; dark ); risk of climate change–induced reduction in food production (right) shown as the Intergovernmental Panel on Climate Change assessment of reductions on food production under business-as-usual conditions (gray zone 0–25% reduction; black reduction)
Resilience against Droughts in Agricultural Landscapes
An increased variability in rainfall will require improved ability to address drought and dryspell–related phenomena. Since management needs differ for short-term and long-term rainfall fluctuations, improved distinctions are called for, especially in terms of frequency. As shown by Barron et al. (2003), dry spells, i.e., periods of no rainfall during crop-growing seasons, cause significant yield reductions in the savanna regions in sub-Saharan Africa. They are essentially annual events, as opposed to meteorological droughts, which occur on average 1–2 times per decade. Already now, the management of frequent intraseasonal dry spells involves the buildup of ecological resilience in smallholder farming by improving infiltration and reducing overland flow; by increasing water holding capacity through mulching, etc.; and by supplemental irrigation to protect plants from dry spell damage to their root systems, thereby improving their water uptake capacity. In contrast, interannual variability, involving shorter or longer sequences of drought years, requires investments in social resilience through insurance systems, secondary employment in the family, and so forth.
Tropical Farmer Vulnerability
Although the potential of in situ soil and water management is limited in view of the rainfall available on the farmer’s field, there is ample evidence to show that in situ green water management—using various practices for soil and water conservation, and conservation farming (noninversion ripping and subsoiling instead of conventional plowing systems)—can function as yield-improving strategies in water scarcity–prone smallholder farming systems (Hudson 1987; Rockström et al. 2009a; Barron 2009). To adapt to larger water fluctuations induced by climate change, however, rain-fed agriculture will need investments in supplemental irrigation, based on larger-scale water harvesting, which have been shown to have a significant potential (Comprehensive Assessment 2007).
Green-Blue Approach Critical to Avoid Crossing Thresholds
Adaptation to climate change, particularly in tropical developing regions of the world, is thus largely a question of managing water resources. Within this domain, investments in integrated green-blue water management will be critically important (Rockström et al. 2007). This will not be enough, unfortunately. Under additional pressure from socioeconomic and demographic change (Gordon et al. 2008), particularly in the regions of the world predicted to be worst hit by climate change–induced reductions in water availability, we cannot exclude the potential for crossing a threshold that could cause abrupt loss of water resilience in the agricultural landscape (Arnell 2004; Rockstörm et al. 2009b). This has happened before, e.g., with the shift from a wet to a drier state in the Sahel (Scheffer et al. 2001). Under such circumstances, water adaptations may not be enough to cope with global change: rural societies may have to transform by taking new social trajectories. The ability to come out of such deep water crises on a positive development trajectory will depend on social resilience, from diversity in income sources at the household level to knowledge systems and support from local, national, and regional institutions.
Thus, however we twist and turn the water challenges facing humanity, there is no doubt that urgent action will be needed, through adaptation to steer away from the gradual decline of water availability and through transformations in response to potentially abrupt shifts in water availability. Both will require water resilience. Both will benefit tremendously from an integrated green and blue water framework.
References
Arnell, N. W. (2004). “Climate change and global water resources: SRES environmental and socio-economic scenarios.” Global Environ. Change, 14(1), 31–52
Barron, J., ed. (2009). “Rainwater harvesting: A lifeline for human well-being.” A Rep. Prepared for UNEP by Stockholm Environment Institute, United Nations Environment Program, UNEP, Nairobi, Kenya, 69.
Barron, J., Rockström, J., Gichuki, F., and Hatibu, N. (2003). “Dry spell analysis and maize yields for two semi-arid locations in east Africa.” Agric. For. Meteorol., 117(1–2), 23–37.
Comprehensive Assessment of Water Management in Agriculture (2007). Water for food, water for life: A comprehensive assessment of water management in agriculture, International Water Management Institute, Earthscan, London.
Dent, D. L., and Kauffman, J. (2007). “The spark has jumped the gap: Green water credits proof of concept.” Green Water Credits Rep. 7, ISRIC—World Soil Information, Wageningen.
Falkenmark, M., and Rockström, J. (2006). “The new blue and green water paradigm: Breaking new ground for water resources planning and management.” J. Water Resour. Plann. Manage., 132(3), 129–132.
Gordon, L. J., Peterson, G. D., and Bennett, E. M. (2008). “Agricultural modifications of hydrological flows create ecological surprises.” Trends Ecol. Evol., 23(4), 211–219.
Hudson, N. W. (1987). “Soil and water conservation in semi-arid areas.” FAO Soils Bulletin No. 57, Food and Agricultural Organization of the United Nations, Rome.
Rockström, J., et al. (2009a). “Conservation farming strategies in East and Southern Africa: A regional synthesis of crop and water productivity from on-farm action research.” Soil Tillage Res., 103(1), 23–32.
Rockström, J., Falkenmark, M., Karlberg, L., Hoff, H., Rost, S., and Gerten, D. (2009b). “Future water availability for global food production: The potential of green water for increasing resilience to global change.” Water Resour. Res., 45(W00A12).
Rockström, J., Lannerstad, M., and Falkenmark, M. (2007). “Assessing the water challenge of a new green revolution in developing countries.” Proc. Natl. Acad. Sci. U.S.A., 104(15), 6253–6260.
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.
WR.1943-5452.0000118/asset/0eec2560-7ff8-4396-9bba-06ed4f2c738e/assets/images/large/1.jpg)
WR.1943-5452.0000118/asset/8782e5cd-d3d4-4716-9055-19113714475d/assets/images/large/2.jpg)
WR.1943-5452.0000118/asset/4a38ff3c-b4b5-4e16-81cf-50ba82cb0b8b/assets/images/large/3.jpg)
WR.1943-5452.0000118/asset/f2971cd8-bded-489f-a8cc-3b6e6ab61e77/assets/images/large/4.jpg)
