When comparing the results of our calculations to the Field Capacity Model from Sorooshian et al., the calculated ETc represented 97% of the model prediction, reaffirming that ETc plays an important role in contributing to the majority of the water consumed in irrigation and that agricultural irrigation adds to the increase in surface evapotranspiration. The overall exported water for all 50 crops was calculated at 2.88 x 1010 m3 yr-1 , representing approximately 68% of the total water used in irrigation. When compared to the estimate associated with California agricultural production reported by Fulton et al., 2012, our total exported water was approximately 26% higher than the estimated 2.28 x 1010 m3 previously reported. The difference could be that Fulton et al., 2012 used California data from 1998-2005, whereas, the data analyzed in this study was from 2000-2012. Export production reported in recent years has increased approximately by 26.5% since 2005. Taking this difference into account, our results are consistent with the outcome of the virtual water footprint previously reported. Quantitative research in the field of exported water and virtual water footprint is still very much underdeveloped despite the many virtual water studies conducted over the years. Data presented in this research should be considered as estimates. The work presented here shows the importance of including induced evapotranspiration and contained water content as exported water in trade analysis when drafting water policies.

These results highlight the need to consider water use efficiency in agricultural irrigation to prevent further loss of evapotranspiration. The findings suggest that California’s water resources are being exported outside its borders in magnitudes greater than that of the water consumed in state by the people of California. Thus,blueberry containers the state might be vulnerable to water-supply constraints if the trend continues indefinitely into the future. It further suggests that California has the potential of exacerbating the local environment by exporting more water than it can naturally regenerate through its hydrologic cycle. The figures and methodology developed in this study are intended to be useful to managers, policy makers, planners, researchers, educators and to all those who are concerned with California water use. With better water management practices and sound public policies and increased investment in water infrastructure and efficiency, farmers and other water users can get more use out of each unit of water. Continuing the practice of business as usual in the current water use scenario will likely lead to a long-term devastating effect that will only produce environmentally-damaging consequences for California and the global agricultural market in which California is a major player. California’s unique geography and climate have allowed the state to become one of the most productive agricultural regions in the world. Situated across an arid and semi-arid region, California’s agricultural industry benefits from its naturally warm and dry summers, and mild winters, with average yearly temperature ranging between 13°C and 21°C . The local government reported a record $43.5 billion in cash receipt in 2011 for overall agricultural production, making it the largest agricultural producer in the United States.

The history of California’s agricultural industry and the limit of its growth are connected to the current water shortage created by a prolonged drought . Although there exist extensive water resources within the state boundaries, like in most mediterranean climatic regions the majority of population resides along the water-scarce coastal region, which in California corresponds to the southern region. Today, California’s water resources support over 38 million people as shown in Figure 4-2, a 2.2 USD yr-1 trillion economy and the agricultural region with largest cash receipt in the United States . In a typical year, the Californian agricultural land is irrigated using approximately 4.2 x 1010 m3 of groundwater . To accommodate the growth in population, the State of California and the US Federal Government built a complex hydraulic infrastructural network to harness the inland water supply and deliver it to the cities and agricultural areas . Reduced water supply and growing population are exacerbating the effects of multi-year droughts in many regions, threatening the already stressed and fragile water systems. This is the case where the water to meet demand from urban areas, industry, ecosystems, agriculture and other sectors is nearing its limit under current management practices . In the coming decades, the agricultural throughput is projected to match the population expansion both within California and in North America . For these reasons, the cost of providing water continues to rise as municipalities seek to create and expand capital-intensive infrastructure to secure a reliable water supply . In many parts of California, the growing demand for water is outstripping the available supply, thus it is imperative to take proactive steps in conserving and augmenting the limited water supply resources .

Increasing attention has been directed in recent years to the use of reclaimed urban wastewater . In fact, with advances in technology, reclaimed water is expected to meet the stringent potable quality requirements at a competitive cost providing a more sustainable resource for the industry in a drought-resilient fashion . The potential uses for reclaimed water in urban landscaping and agricultural irrigation provide an effective way to relieve the water resource demand in arid and semi-arid regions . Many studies have also confirmed the benefits of using reclaimed water for crop irrigation . The goal of this research is to analyse the energy advantage of applying reclaimed water for crop irrigation, and to quantify the associated carbon footprint reduction of using reclaimed water versus traditional groundwater pumping in arid and semi-arid areas. Using California as a case study, the water, energy, and carbon-equivalent flows were quantified. In addition, the monetary advantage of substituting traditional water supply sources with reclaimed water, where possible, was assessed. The results show that from 1998 to 2010, the annual average water used in crop irrigation was 4.2 x 1010 m3 , 46.8% of which came from groundwater, 52.2% from surface water, while only 1% came from reclaimed urban wastewater. During the same period, the authors found that the average annual urban water use was approximately 19.4% of the total 5.21 x 1010 m3 used for the entire state, while 80.6% was used for crop irrigation. The time domain of the available data is set by the release schedule of public records. Within much smaller spatial domains, it is conceivable that direct measurements can be carried out with any desired frequency,best indoor plant pots however the modelling effort at the regional scale must rely on public programs for data collection and compilation in published repositories. Urban water reclamation can be used for landscape and crop irrigation without the need for membrane filtration or reverse osmosis treatment, both of which are required to address public health concerns . In areas where groundwater recharge was practiced to replenish aquifers for potable end use , reverse osmosis and membrane filtration were used. In these instances, the calculated energy intensity for water reclamation to meet the potable water standard was 0.640 kWh m-3 . In fact, where microfiltration membranes or reverse osmosis have energy intensities of 0.52 kWh m-3 and 0.64 kWh m-3 , respectively, gravity filtration has an energy intensity of 0.32 kWh m-3 . Since reverse osmosis is not required for the production of reclaimed water suitable for irrigation, the energy intensity value for gravity filtration was selected as comparison term with the current groundwater scenario. The authors found that for Southern California the average energy requirement for groundwater pumping was 0.770 kWh m-3 while reclaimed water production with gravity filtration was 0.324 kWh m-3 . Hence, the energy advantage of applying reclaimed urban wastewater for crop irrigation over groundwater pumping within this spatial domain would be 0.446 kWh m-3 .

The calculated energy intensities for other supply sources such as imported water from Northern to Southern California and from the Colorado River Aqueduct system, ocean desalination, and impaired groundwater recovery were also calculated . Reclaimed water required the least amount of energy, whereas ocean desalination had an energy intensity approximately 11 times higher. When compared to traditional groundwater pumping, the energy intensity associated with water reclamation was discounted by 58%, highlighting the importance of reclaimed water as a potential competitive source. When considering the energy requirements for water distribution along a 10 km of horizontal conveyance and 100 m of vertical lift , the energy contributions for conveyance and lift were 0.026 kWh m-3 and 0.34 kWh m-3 , respectively. Therefore, to account for the full energy requirements from point of treatment to point of use, the energy intensities for horizontal and vertical conveyance must be added to the calculated data presented in Table 4-3. The authors recognize that there may exist infrastructural and administrative limitations among water agencies and agricultural users within a region as to the extent in which reclaimed water can be produced, conveyed, applied, and accepted. Also, locations without proper infrastructure or with cultural incompatibility with reclaimed water may be unable to consider water reclamation as an option for their water supply portfolio. However, it is important to frame the transition to reclaimed water within the context of energy savings and monetary benefits. At the present moment, California would be unable to substitute all its groundwater use for reclaimed water, due to limits in existing infrastructure for both production and conveyance. Furthermore, the majority of population within this spatial domain is located in the Southern coastal region, hence investments in infrastructure would be necessary to deliver reclaimed water from urban areas to places where agricultural activity is abundant, such as in the Central Valley, Coachella Valley, and the Imperial Valley farming areas. However, when the water source for water reclamation is brackish agricultural runoff or brackish groundwater from areas near or corresponding to the agricultural production, the energy requirements for conveyance and lift may be substantially abated. It is important to recognize the long-term benefits of matching water quality with the actual end use application. Reclaimed water should be used for crops irrigation while pristine groundwater should remain reserved for potable consumption. Given that water demand for urban, agricultural, and environmental needs is projected to rise , resource allocation efficiency and demand management must be taken into consideration during the policy making. Thus, decision makers should consider the energy intensity of water as quantitative metrics to support the other factors in the evaluation of projects. Moreover, by requiring end users to apply the least energy-intensive source of supply, whenever feasible, the regulatory framework would not only promote monetary savings but also accomplish the goal of placing the appropriate value to all water sources, a task impossible to achieve when differential pricing, incentives and subsidies, and lack of regulation are applied to some but not all water sources. When examining the average energy requirements for agricultural harvest and crop processing in California, the California Energy Commission reported 3.7 x 103 GWh y-1 . However, future research should revisit this value to discriminate between crops and final product. In contrast, the energy consumed to provide an estimated 1.9 x 1010 m3 of groundwater pumping for crop irrigation was calculated here at 1.5 x 104 GWh yr-1 , making the energy requirement for groundwater irrigation the largest energy contributor in the food production chain, at approximately 4.1 times higher than the energy required to harvest and process all crops. Further examination of other energy uses in California indicated that the energy consumed in agriculture, predominantly in food production , was approximately 7% of the total energy produced in California, 2% higher than the energy used in transportation, communication, and utilities combined, and 6% higher than the annual electricity required for all street lightings in California . In 2012, the California agricultural industry reported an export value of 18.18 billion USD, a record 42.7% cash receipt for all crops produced in the state . As the country’s sole exporter of many agricultural commodities, supplying >99% of almonds,artichokes, dates, figs, raisins, kiwi, olives, peaches, pistachios, plums, pomegranates, rice, and walnuts, California’s agricultural export is expected to continue to rise . One area of knowledge gaps is the quantification of the water embedded in agricultural exports. Further research in this area is needed to determine how the agricultural exports from one region affect the overall water portfolio for that region and the region receiving its water-bearing produce.