I propose that considering future agricultural expansion data and promoting globalized conservation solutions for defining spatial priorities should be included in this toolbox for sustainability. Only by the careful analysis of future scenarios of agricultural expansion and other human activities will it be possible to predict their impacts on biodiversity and, most importantly, act effectively to reduce the worst impacts of human land use on the environment. Water is a crucial resource for life on Earth because it is irreplaceable in its role of sustaining the functioning of environment and societies. Humankind uses water resources for drinking, municipal needs, and a number of economic activities. Among them, agriculture is the most water-demanding, claiming more than 85% of human water consumption . Despite its important impacts on crop production, food security, and rural livelihoods, water often remains hidden in the economic valuation of agricultural assets. Unlike oil, it is seldom treated as a commodity and traded in the marketplace to generate revenues . Rather, it remains underpriced because users do not pay for its real value . Oftentimes farmers do not even pay for the provision costs associated with withdrawal and delivery . Thus, while crops use huge amounts of water, the price of agricultural products seldom accounts for the cost of water consumption. What is the value of water? How can it be determined? The valuation of water remains a difficult task because this natural resource is rarely traded and therefore its value cannot be determined from a market price. Of course, there are exceptions, such as bottled water, which accounts for less than 1% of human appropriation of water resources worldwide , the pricing of municipal water supply , or the few water markets existing around the world . In some of these cases, the market value reflects the extrinsic value of water, expressed both by the users’ willingness to pay and the willingness of water rights holders to accept compensation for relinquishing their water allocations . Water markets and water trading can be found in Australia, the United States, Mexico, Chile, China, Spain, and South Africa .
These are more exceptions than the rule because in most of the world there are no tradable water rights , the “conditio sine qua non” for the emergence of water markets . In other words,blueberry grow pot in many regions there are no water entitlements that can be sold or acquired through market transactions separately from the land. Rather, water is either tied to land’s property rights or treated as a public good, “res nullius” , or a common pool resource . Although not properly priced, water availability shapes the global patterns of agricultural production and trade and the associated flows of embodied or “virtual” water , which is the water consumed in the production of goods such as crops . In fact, water-scarce regions need to import agricultural commodities to meet their food demand . Even when water is not directly commodified, the goods it contributes to produce are. The value of the associated virtual water, however, is seldom accounted for . Likewise, water is implicitly acquired with agricultural land in the form of rainwater and sometimes also irrigation water when blue water resources are inherently appropriated with the land . This happens in regions where land ownership includes water rights or unregulated access to adjacent or underlying freshwater resources . Interestingly, while there are well-established methods to calculate the water resources that are virtually acquired with agricultural land , their economic value remains difficult to assess . Because water pricing is often viewed as a mechanism to promote a more efficient use of water resources, an international agreement on water valuation is sometime considered to be crucial to the achievement of an efficient and sustainable global water use, a point that has been discussed at the World Water Forum in the last two decades . The value of irrigation water in agricultural areas is an important piece of information for investors and financial groups engaged in the acquisition of land and water resources. Even in the absence of a water market,land and agribusiness investors would benefit from knowing more about the potential economic value of the water resources they are virtually acquiring with the land.
Indeed, the decision to invest along the banks of the Nile River or in areas suitable for rain-fed agriculture instead of targeting arid lands within the same regions would benefit from a combined hydrologic and economic analysis of the availability, productivity, and value of irrigation water. On the other hand, it could be argued that the valuation of water may favor its growing transnational control through the acquisition of water and land entitlements by self-interested agribusiness corporations. This may happen if, as a result of the valuation and commodification of land and water resources, peasants decide to sell land and water rights to realize short-term profits without having the opportunity to plan for the long-term economic development of their communities . At the same time, a major factor impeding planning for rural development is lack of awareness of the value of natural resources such as land and water. Indeed, local communities engaged in the negotiation of land and water concessions need to know the current and potential contribution of water resources to the creation of value in their farmland. Unbalanced power relations and asymmetry in the knowledge of the economic value of these assets are often major obstacles to the informed negotiation of land and water deals . Likewise, investments in irrigation infrastructure require an assessment of the increase in production and associated profits resulting from the use of irrigation. Indeed, farmers’ decision to adopt irrigation depends—among other factors—on the value generated by irrigation in the production process . There is a need for reliable and reproducible water valuation methods that—in the absence of markets—can be used to determine the value of water embodied in agricultural land and its products. The estimate of the value of water in the absence of market is often based on the marginal value produced by a unit volume of water . The literature on this subject is often based on inductive statistical/econometric methods determining the value of water from empirical data, or on deductive models that are fitted to the data . Both approaches typically require a wealth of data that are seldom available, particularly in the developing world .
These classes of methods fail to capitalize on process-based understanding of the underlying hydrological processes determining the role of water as a factor of production . More recently, some studies have proposed a mixed model in which one of the factors of production is estimated with biophysical models while the shadow price of groundwater is determined either by fitting a function of production to empirical data or by simulating the dynamics of crop growth accounting for their dependence on soil moisture and irrigation technology . Here we use a completely mechanistic biophysical method for the valuation of water in agriculture that can be used even when tradable water rights do not exist. We carry out this valuation analysis for the 16 major crops at the global scale on a 10-km grid and then map and critically analyze the results. Our approach allows for the worldwide valuation of water in agriculture and can be used to determine water’s contribution to the value of both crop production and agricultural land.ently planted in each location allows for an estimate of the maximum price farmers might accept to pay for irrigation water. If we look at the four major staple crops , we find that the global mean water values are $0.05, $0.16, $0.16, and $0.10/m3 for wheat, maize, rice, and soybean, respectively . The value of water for the production of maize, soybean, and rice is consistently higher than for wheat. These differences are the result of the combined effect of differences in crop price and in crop water use efficiency . The values of water for maize and rice are substantially higher in East Asia than in other regions of the world . Interestingly, for maize and rice the within-region variability in water value tends to be smaller than the variability among regions, potted blueberries while for wheat and soybean the water value variability tends to be relatively small both within region and across regions . Results presented in this manuscript refer to water withdrawals because farmers are more likely to be allocated—and consequently account for and keep track of—volumes of water withdrawals than water consumption . Values of water based on consumption are presented in SI Appendix as well as in Fig. 1B. As expected, the water values determined with reference to water withdrawals are lower than those determined with reference to water consumption and the difference depends on the efficiency of the irrigation system .
Expanding the analysis to the 16 major crops [≈70% of global food production ], we see that for all of them the global median and mean roughly range between $0.05 and $0.25/m3. The only exception is represented by potatoes, which consistently exhibit a much greater water value than the other crops with a median value of $0.67/m3 . The higher values of water for potatoes is due to their higher yields per unit volume of water application and their higher price compared to the other crops; however, despite their widespread use, potatoes contribute to only 2.1% of the global food calorie production and account for only 1.1% of the global irrigated areas . Variability in the mean water value across regions is overall smaller than that across crops and ranges from $0.09/m3 in South Asia to $0.42/m3 in Europe . With the current crop distribution, the global median and mean water values are $0.13 and $0.23/m3, respectively . Interestingly, even though the within-region water value can substantially vary , globally, the spread around these median and mean value is relatively small, with the 25% and 75% quartiles being $0.08 and $0.42/m3 smaller and greater than the median, respectively . We also provide an estimate of the maximum water values obtained considering—among all of the crops currently cultivated in every 10-km × 10-km pixel—the crop associated with the maximum local water value. These results show that the current crop distribution does not maximize water value . In this analysis we have considered the global areas cultivated with the 16 major crops. Each crop has its own irrigation water requirements, yield, and price, which leads to different water values, depending on the crop. In Fig. 4B we show the results for the crop that realizes the maximum value. Thus, while with the current crop distribution the median water value is $0.13/m3 , if we consider only the crops with the maximum value, the median of the maximum values around the world becomes $0.54/m3 . Interestingly, the variability in water value is greater for the maximum values than for the median values both across regions and within regions . The crops that maximize water value are potatoes in many regions of the world and sugarcane in South and Southeast Asia .The economic valuation of water is a sensitive matter because it can be the premise to water pricing, commodification, and privatization, which are often contentious issues . In fact,a large part of the public tends to think that water should be publicly owned because it is a natural resource that, like air, is essential for human life . Therefore, the valuation of water becomes particularly difficult when this resource is used not only for economic activities but also for environmental needs or the fulfillment of human rights such as drinking or sanitation. Instead of dealing with these uses, here we explicitly focused on the value of water in agriculture. In fact, in many cases they do not even pay for costs of water infrastructures and their maintenance and operation , which are often subsidized by governmental agencies . In addition to costs associated with the supply, treatment, storage, and distribution of freshwater resources, it is often argued that water itself should be sold to its users to avoid that it goes wasted or is used in economically inefficient ways .