Agriculture and Water Consumption in the Changing Future

Agriculture—including the production of food, livestock, aquaculture, and naturally grown materials—accounts for 70–80% of water consumption globally.  In the United States, this number is on the order of 34% of our national consumption.  As climate change increases the uncertainty of available water sources, agricultural producers will have to look for new and sustainable methods of maintaining their crop yield. In addition, projected rapid population growth over the next 25 years will increase demands for food and agricultural products worldwide.  An expanding population will also increase water stress by demanding water for products other than agriculture, such as for domestic, energy, and industrial use.  In the United States and many other countries, new trends towards healthier eating have significantly increased the demand for fruits and vegetables, crops that require a high amount of water input.  Additional pressures on water supply come from conservationists who wish to protect flows in order to maintain aquatic habitats for dependent species.  An increase in demand for agricultural products and simultaneous decrease in supply of water will certainly create many difficulties for farmers and agricultural managers in the near future, and it is imperative to begin planning now to find sustainable solutions to these challenges.  Increases in technology and irrigation efficiency, research regarding drought triggers and preparedness, and genetically engineered crops are likely the best solutions to help agricultural producers in a time of increasing water stress.  Each of these solutions also has challenges and risks involved, but the time for action is now, before global food crisis or water conflict erupts.–Nora Studholm
O’Neill, M. P., and Dobrowolski, J. P., 2011.  Water and Agriculture in a Changing Climate.  HortScience 46, 155-157. 

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O’Neill and Dobrowolski suggest several possible solutions for agricultural producers facing water stress, and assert that it is essential to find responses that encompass the physical, biological, social, and economic issues of water resources.  Some of the most promising technological advancements are systems for recycling or reuse of water.  However, these are not without their challenges.  Wastewater, which is in fairly constant supply, cannot keep up with irrigation demands of farmers, and so these systems would be only a partial solution.  In addition, upstream wastewater facilities can have damaging impacts further downstream, including decreases in downstream flows.  In addition, there is a certain amount of stigma surrounding the idea of eating crops grown with recycled water, and the authors propose that educational outreach programs will be necessary to remove these fears from the public perception. 
Another possibility is the creation of water storage ponds to decrease uncertainty of water sources.  These, however, may gather pathogens from wildlife that use them as a water source, and could introduce dangerous diseases into the human population.  Improved irrigation efficiency and an increase in effective global markets for water will also certainly be key components of the solution.  There is also great promise in genetically modified crops, which may be engineered to be drought- or salt-tolerant, decreasing the impact of water uncertainty.  Not only may genetically modified crops increase yield under uncertain conditions, they may be higher quality and more nutritious as well. 
Finally, in this time of growing uncertainty and increases in severe drought, farmers need to have increased drought preparedness.  An unexpected drought could cost over 1 billion dollars in the US alone, and would certainly have other drastic human impacts as well.  Research is currently under way to determine what “triggers” show severe drought approaching, so that agricultural producers can predict them and be ready to implement changes to minimize damage.
            There is no single answer to the challenges facing agricultural producers in the near future.  As population grows and water supply becomes more uncertain, farmers and managers will have to work with all sectors to ensure that global climate change does not spell disaster for agricultural production.

Effects of Climate Change on Precipitation: A Summary

Precipitation is the result of an intricate atmospheric global process, and a disruption at any step can lead to dramatic alterations.  Global climate change will almost certainly cause such a disturbance, and many individual scientists have studied the possible impacts that such a change might produce.  In this paper, Trenberth (2011) summarizes the various conclusions of researchers who have explored the effects of climate change on global water resources, and uses their studies to draw some inferences of his own.  The most probable consequence is increased and more intense drought worldwide.  Sea surface temperature change and wind shifts will also likely disrupt storm patterns, leading to more extreme events in certain regions of the world.  In addition, more precipitation falling as rain instead of snow will decrease water “storage” in ice and snow and may lead to severe water shortages in some areas dependent on spring runoff.  Like Min et al. (2011), Trenberth claims that the probability of human impact on these results cannot be ignored, and that further studies must be conducted in order to determine exactly the nature of our impact, and how we might be able to mitigate it before the consequences on global water sources become too severe.  Nora Studholm
Trenberth, K. E., 2011.  Changes in precipitation with climate change.  National Center for Atmospheric Research.  Symposium manuscript of Technical Conference on Changing Climate and Demands for Climate Services for Sustainable Development.

            The global water cycle depends on the heat of the sun and the composition of the atmosphere.  As these factors continue to change, the character and amount of precipitation globally will alter as well.  Increased heating of the earth leads to greater evaporation and surface drying, which will likely lead to increased intensity and duration of drought.   Already, droughts have been observed to be increasing in frequency and severity over the 20th century, and regions defined as “very dry” on the Palmer Drought Severity Index have more than doubled in extent since the 1970s. 
Redistribution of rainfall worsens this phenomenon.  The water-holding capacity of air goes up by approximately 7% per 1°C increase in temperature.  As sea surface temperatures rise faster than atmospheric temperatures over land, the water vapor in the air above the oceans increases more than that over terrestrial areas.  This leads to more intense precipitation events over the ocean, and less rainfall over land areas, furthering the risks of drought in vulnerable regions. 
Relocation of precipitation also leads to risks in flooding, ironically.  In regions that are not affected by drought, rainfall and extreme events may actually increase dramatically.  Furthermore, more precipitation is likely to fall as rain rather than snow, and snowmelt in high altitude regions will occur earlier in the season.  This not only makes ineffectual the role of snow as a method of water “storage” for times of decreased precipitation, but also leads to increased runoff from heavier rainfall combined with snowmelt in the spring.  The combination leads to an increased likelihood of flooding in the spring and drought in the summer.  Floods can cause billions of dollars of damage and take thousands of lives, and droughts can have similar economic and ecological impacts, with the added risk of increased wildfires.  Effects of droughts and floods can both be mitigated by human intervention, such as improved drainage and irrigation, but there must be adequate plans in place to implement such changes.
            A final impact Trenberth discusses is the possibility of modest changes in winds, which may change patterns of precipitation and make wet areas wetter and dry areas drier.  A shift in the storm track may result in varied atmospheric circulation patterns, and as subtropical high-pressure systems move poleward, peak wind speeds in tropical storms and hurricanes will continue to increase.  The total number of storms worldwide appears to be decreasing, but the average intensities of the events are going up. 
            As suggested by Min et al. (2011), human influence in these recent changes is difficult to deny.  As humans add more carbon dioxide and particulates to the atmosphere, greenhouse gasses trap outgoing infrared radiation and warm the planet.  Water vapor increase in the atmosphere creates a positive feedback cycle for climate change, as increased vapor enhances the greenhouse effect.  Radiative forcing, changes in irradiance levels between levels of the atmosphere, also increases surface heating.  All of these effects are almost certainly direct or indirect results of human actions. 
            However, it is difficult to test exactly what the changes in precipitation will be in the future.  As Trenberth points out, there are many different conflicting models of future climate change and precipitation, some of which claim that there will be no changes whatsoever.  Hughes et al. (2011) experienced this difficulty in their study of the Okavango River Basin, where their seven models gave widely disparate accounts of future possibilities.  Another difficulty is that precipitation can be hard to measure.  Gauges used for data collection are affected by winds, especially when measuring light snow and rain.  Precipitation data are inherently messy because of the intermittency and variability of precipitation even under normal circumstances.  Furthermore, there are large variations on year-to-year and decadal scales, and between different geographies.  Local features like vegetation, soil, and topography play a large role in the effects of precipitation events, although generally regions in higher latitudes can be assumed to have increased overland precipitation.  In addition, vague definitions of terms make comparisons between studies difficult, as it is hard to know exactly what is meant by a “high impact” or “extreme” precipitation event without a universal definition for these terms.  Researchers have attempted to gain confidence in studies by using both remotely-sensed and gauge measured precipitation devices, and by looking at a range of variables including atmospheric moisture, soil moisture, and stream flow.  However, uncertainties still exist and past studies conflict strongly, ranging from claiming near zero global changes to significant predicted trends depending on the dataset and model used.   This report is inclined to emphasize those studies that claim the significant effects, but it is careful to mention that other viewpoints do exist.
            Even with disagreement among scientists about the precise effects of climate change on global precipitation, it seems evident from the body of studies that Trenberth has gathered that there will be significant impacts of some kind on the hydrological cycle in the future.  The most likely results are increased extremes in precipitation events, from flooding to droughts, which will make managing and using water resources more challenging and more essential in our uncertain future.
Works Cited
Hughes, D. A., Kingston, D. G., Todd, M. C., 2011.  Uncertainty in water resources availability in the Okavango River basin as a result of climate change.  Hydrology and Earth System Sciences 15, 931–941. 
Min, S., Zhang, X., Zwiers, F., Hegerl, G. C., 2011.  Human contribution to more intense precipitation extremes.  Nature 470, 378-381.  

Trees Likely to Suffer from Water Stress with Climate Change

As global climate change increases water stress in many regions of the world, humans are not the only organisms that will be severely affected.  Trees have adapted for thousands of years to maximize their ability to gather sunlight, growing taller and taller to reach energy from the sun.  However, this also means that water must travel further from their roots to reach the extremities.  This has lead to a range of physiological functions that are highly dependant on a consistent supply of water.  Many climate change scientists predict that severe drought events may increase worldwide by 30% or more, significantly reducing the amount of moisture in the soil available for root uptake.  Extreme weather events are also likely to become more prevalent, leading to increased runoff and thus less water availability in the soil in regions affected.  Hartman (2011) predicts that droughts will lead to reduced functioning, growth and yield and in extreme cases, plant death.  He presents several hypotheses about potential reasons for water stress leading to tree mortality including carbon starvation because of stomatal closure, rupture and dysfunction of the cells of the water transport system, reduced electron availability for photosynthesis, and constrained cell metabolism.  Furthermore, water stress may cause indirect mortality increases in trees as well, sometimes many years after the actual drought event.  Trees that are irreversibly weakened may be more susceptible to death by parasites, insects, fires, and further natural disasters.  If these predictions are true, increases in temperature will likely change ecosystem composition, as some will be able to adjust better than others.  It remains to be seen if an evolutionary selection for taller plants may now be a deadly disadvantage in this era of change.
Hartman, H., 2011.  Will a 385-million year struggle for light become a struggle for water and carbon? — How trees may cope with more frequent climate change drought events.  Global Change Biology 17, 642-655. 

At first, it may seem surprising that water stress could impact such a hardy and diverse group of organisms.  Trees survive in some of the most adverse climates in the world, from the freezing northern regions to the driest deserts.  However, in order to adapt to these inhospitable regions, species have had to evolve for thousands of years.  The rapid shifts in climate that have been occurring since industrialization and are predicted to continue exponentially will not give trees time to adapt adequately to the changing environment, and many species that cannot find coping methods may face extinction.  Compounding the severity of the issue is the fact that trees, in order to attain maximum height and gather the most possible sunlight, tend to live at the edge of hydraulic dysfunction.  Taller trees are clearly more prone to drought susceptibility than species that have evolved to have lower canopies, and although they also tend to have deeper root systems this is often not enough to offset the difficulty of obtaining sufficient water for survival.  Individual trees can adapt to drought to some extent by shedding leaves and devoting more carbon and energy to growing longer roots, and in the long run can even develop thicker leaves with increased storage ability.  However, tall trees may respire hundreds of liters of water every day, making these adaptations inadequate in the long-term drought scenarios that are likely to become prevalent in future climate change.
In the case of increased droughts, predicted mortality from water stress may be direct or indirect.  The most widely circulated theory in the scientific community is that water stress leads to carbon starvation in trees.  Leaves have stomata (small openings on the underside of their leaves) that allow for the diffusion of carbon dioxide into the plant and the evaporation of water out, meaning that water loss from the leaves must continuously be replaced with moisture from the soil.  In times of water stress, stomata close off so that less water can escape from the plant.  While may be an effective measure to increase survival in short extreme events, during a prolonged drought this adaptation may be fatal, as no carbon dioxide can enter the plant with the stomata closed and the tree effectively “starves” to death. 
Another common hypothesis states that the cells of a tree’s vascular system, called xylem, may not be able to physically withstand the pressures of water stress.  Because trees need  a constant supply of water, they have a complex transport system that draws water from the roots up through a water column and into the vascular system of the plant.  As water evaporates from the leaves and diffuses into the atmosphere, water potential is increased in the tree compared with the surrounding atmosphere.  Water uptake by the roots passes into the water column, where capillary and adhesive forces draw water molecules upward into the low-potential leaves.   However, when the roots draw water out of the soil they temporarily reduce the moisture content surrounding them, and if this moisture is not replaced through precipitation the soil dries out and air replaces water in the soil pores.  There is thus a harder “pull” on the vascular water column to overcome the increase in adhesive force created between water and soil particles.  This in turn creates negative pressure in xylem, which can cause embolisms and water column ruptures and result in partial or complete loss of water conductance through the tree over time.  Fortunately, if the tree manages to survive the drought, xylem can be repaired once water is available and the vessels can be refilled.  The consequences of this mechanism also tend to be less fatal for the tree as a whole, as it can sacrifice twigs and leaves and maintain its core if only a part of its water system is ruptured.
            Photosynthesis, which is essential for growth and survival of an individual tree, relies on the electrons supplied by water intake for its reactions to function.  In the case of impeded movement of water up to the crown of the tree where photosynthesis has the most energy from sunlight, this process can be disrupted and a tree may “starve.”  Finally, some scientists believe that low water potentials in tissues may constrain cell metabolism, resulting in a reduction of carbon assimilation.  As of this writing, no empirical studies have been conducted regarding the latter two hypotheses, but they are certainly probable enough to merit future study. 
            On a more optimistic note, it is possible that an increase in carbon dioxide in the atmosphere could in fact help trees as they take it up through their stomata.  In a perfect scenario, this could lead to higher growth rates and increasing water-use efficiency even in times of drought.  However, if the elevated atmospheric carbon dioxide concentration makes leaves grow larger and the water efficiency does not compensate adequately, trees could be even more severely exposed to drought stress.  In addition, different species have varied stomatal responses to higher carbon dioxide, so it is difficult to generalize this theory.
            Diverse species may also have differing responses in regards to the other hypotheses as well.  Isohydric tree varieties close their stomata well in advance of any danger to the xylem, which can be helpful in the case of short, extreme events but deadly in a prolonged drought because of carbon starvation.  Anisohydric species, on the other hand, close their stomata only when in immediate risk of hydraulic failure, making them less prone to carbon starvation but vulnerable to water transport issues and xylem rupture.  Gymnosperms and angiosperms also differ in their vulnerability to water stress.  Angiosperms have more conductive xylem, but their vessels require more carbon input to function as compared with gymnosperms.  Angiosperms, therefore, are more at risk of carbon starvation, while gymnosperms are more likely to suffer from transportation challenges during droughts.  Although the specific challenges differ between species, all types will likely be negatively impacted in some way by global climate change and increased water stress. 
If increased water stress does lead to a decline in trees in some regions of the word, this will in turn affect humans powerfully.  Trees are worth trillions of dollars a year, and there cannot be a price placed on the quality of life that they provide.  In addition, trees are a major component of earth’s carbon cycle, making up about 90% of earth’s terrestrial biomass and cycling 8% of atmospheric carbon dioxide annually.  If the health of trees suffers from climate change, there are few organisms on earth that will not be affected.
            Clearly, an issue that will affect so many people and organisms so powerfully is a topic that deserves further research.  Unfortunately, tree mortality studies are particularly difficult to conduct because it can take years (and sometimes even decades) to gather enough data to draw any sort of viable conclusions.  This is something that scientists will have to work with, either through developing sophisticated modeling or obtaining support that will allow for such time consuming studies to be undertaken.  One important avenue of research is to determine which of the above hypotheses is most likely to be the cause of tree mortality in water stress events.  Future studies must also look at different regions, environments, and species in order to determine how various trees might be affected differently by climate changes.   A diversified study will also be essential to facilitate a full understanding because as patterns of precipitation change, different regions of the world will experience climate change differently.   What will likely be universal is a strong impact from global climate change on tree species around the world, and scientists must be prepared for the results of such a possibility. 

Human Impact on Growing Precipitation Extremes

Observed increases in intense precipitation events have been a focus of much research in recent years.  One matter of significant debate is to what extent humans have contributed to these precipitation events. Greenhouse gases and aerosols can affect the atmosphere in ways that cause increased temperatures globally.  The amount of water the atmosphere can hold in clouds increases on an exponential scale with temperature increase, leading to potential for dramatic dry spells in certain areas and equally violent release of precipitation in others.  Atmospheric circulation is also affected by global warming, altering the patterns of precipitation on a global scale.  Both of these systems can have dramatic impacts on global water resources, whether in the form of severe drought, flooding, or shifts in seasonality for agriculturalists.  However, because natural disasters and severe precipitation have always occurred, it is difficult to determine to what extent humans have impacted these events.  This study marks the first formal claim that humans have significantly contributed to the intensification of extreme precipitation events.
Min, S., Zhang, X., Zwiers, F., Hegerl, G. C., 2011.  Human contribution to more intense precipitation extremes.  Nature 470, 378-381.  [GSSS: human contribution precipitation]

            Min et al. (2011) compared observed and simulated changes in maximum precipitation to see how accurate the models were and determine if they would be useful for prediction in the future.  Three models incorporating historic data of natural events and anthropogenic factors like aerosols and greenhouse gases were generated.  Both single-day and five-day-consecutive precipitation maxima were used in order to see broad trends, and because these time periods tend to be characteristic of the types of dramatic precipitation events that heavily impact human society.  From the data and regressions, the models seemed to underestimate the level of intensity in precipitation, but were otherwise generally accurate. 
            When analyzing the results of the simulations, it is important to keep in mind that precipitation varies geographically.  Because of data scarcity, this study could only focus on regions in the Northern Hemisphere, capturing North America, Eurasia, and India in its direct studies.  In order to improve comparability of results and reduce uncertainty from this confined sample, Min et al. (2011) created a weighted index to standardize their measurements between geographical regions.  The indexed results showed increasing trends in heavy precipitation events in 61–65% of the total area studied.  When the regressions were run with just natural events, human impact and natural events, and human impact alone, it was very clear that humans are making a large difference in precipitation in these affected areas. 
            The global impact of increased dramatic precipitation events may be extreme, and this study shows compelling evidence that humans are playing a role in the frequency and magnitude of these disasters.  However, as always in a scientific study, the researchers were careful to mention that there was some uncertainty due to the sample size and potential omitted data.  Fortunately for those researchers looking for work in a tough economy, there is much room for further study on this topic. 

Mountain Water Resources: An Endangered Necessity

From river basins like the Okavango Basin (Hughes et al., 2011)  to mountain ranges all over the world, water resources in all types of ecologies will likely be dramatically affected by global climate change.  Mountain water sources are particularly important because they also have huge impacts on the lowlands below them.  Much of the demand for water by farmers and households in  lowland areas is met by a supply from mountain ranges, and 53% of mountainous areas worldwide are considered essential components of downstream water supply.  High altitude regions redistribute winter precipitation in the form of runoff in the spring and summer, reducing variability of water flows and contributing to the level of water available in resevoirs.  Stream-flow variability is also positively correlated with basin elevation, making mountain basins among the most vulnerable environments in terms of climate change.  Although several past studies have indirectly pointed to the vital role of mountains for global water resources, no studies had yet been focused exclusively on this topic. Viveroli et al. (2011) discuss the impacts of climate change on mountain resources and give suggestions for future research, management, and policy.  By studying eleven different case studies and attempting to integrate information from each, the researchers were able to conclude that global generalizations about the impact of climate change on mountain water supply cannot be drawn.  Instead, research and management must work on a regional scale because of the many interactions between topography, vegetation, and soil composition with water supply.  The authors suggest that the most important conclusion to be drawn is that further monitoring, research, and policy implementation is essential to helping mountain regions and their lowland dependants cope with the challenges that future climate change will pose to water resources.
Viviroli, D., Archer, D. R., Buytaert, W., Fowler, H. J., Greenwood, G. B., Hamlet, A. F., Huang, Y., Koboltsching, G., Litaor, M. I., Lopez-Moreno, J. I., Lorentz, S., Schadler, B., Schreider, H., Schwaiger, K., Vuille, M., and Woods, R., 2011.  Climate change and mountain water resources: overview and recommendations for research, management, and policy.  Hydrology and Earth System Sciences 15, 471-504.  GSSS: mountain water (2011)



For the purposes of simplification,  this paper focuses on surface water while largely ignoring groundwater, even though groundwater will likely play a large role in future water resources as well.  Instead of going into great depth of detail about all the various factors that might affect water resources in mountain regions, therefore, this study seeks to see what we already know and what we need to find out in order to suggest management and policy as well as further research and monitoring.  One of the most important pieces of information that the study gleaned was that different mountain regions are at differing risk for climate change impact.   Climate change is a challenge everywhere, but regional variance in the type of difficulty that a warming climate will present makes it so that regional, not global, plans must be made to cope with these changes.  In each region, researchers look at what they refer to as “water stress,” or how much of the available water is used up by the demand in that region.  A level of 0.4 or higher indicates a large amount of water stress.  Water stress computations also take into account land use change, economic development, population growth, and the ability of water management to adapt to climate change.  For instance, dry areas are likely to continue getting even drier in a warming scenario, but may be better equipped to deal with this change because their infrastructure is already set up to cope with high water stress.   On the other hand, subtropical climate zones have both vulnerability to water scarcity and high dependence on mountain water resources, making them face a very high level of water stress.  In general, areas with low GDP, high growth rates, and a high dependence on mountain runoff in the lowlands face the highest projected water stress from climate change.
            One aspect of mountain water resources that is common among many regions is the importance of snow and glacial melt.  The study projects that in a warming climate there will likely be less ice and therefore less runoff, meaning a lower water yield as a whole in high altitude areas.  Expected seasonal shifts will also greatly impact the runoff patterns and water supply from snow.  This is a particularly disturbing trend, as one-sixth of the world’s population currently lives within a snowmelt-dominated region where 75% of summer runoff is generated by glacial or ice melting.  Glaciers and snow also act as “storage,” creating a way for water resources to be saved up during cold and wet years and later released during dry, hot years.  Less snowmelt, therefore, means more variability in water availability with climate change.  In order to see if other storage mechanisms could combat this change, the authors compare simulated annual runoff from snowmelt in the regions studied to the capacity of existing reservoirs to see if the storage capacity was available to buffer seasonal shifts in runoff.  Their findings suggest that these reservoirs are helpful in reducing variability, but cannot act on the same scale as glacial water storage.  In addition, the models project an increase in precipitation falling as rain rather than snow in the winter, and earlier timing for snowmelt in the spring.  These issues compound the problem with disappearing glacial and ice-bound sources of water in the mountains.
            In order to combat these challenges, the authors devote a large part of the paper to suggesting mechanisms for future change.  Firstly, future research and monitoring must be increased and undertaken on a much larger scale.  Currently, there is little monitoring of mountain areas, as they are often inconvenient to run labs in because of their isolation and often freezing temperatures.  The data gleaned from these monitoring bases must then be shared between scientists and water resource managers or policymakers in the region to ensure that conclusions from scientific studies can have a practical application in preparing for climate change.  One way to ensure increased communication, according to the authors, is to put some of the monitoring responsibilities in the hands of those who are most invested: the farmers and people living in these mountain and lowland communities whose lives will be directly impacted by future climate changes. This will also help studies remain at a regional scale where they can be most effectively utilized.  It is important to remember, however, that ecological regions can and often do cross national borders, and it is therefore essential for different countries to work together to combat future climate change challenges in water resource management.  Finally, the authors point out that solutions to these challenges in mountainous regions must be interdisciplinary in scope, and attempts to integrate climate change with other challenges such as economic growth will be essential to helping save the world’s mountain water resources.
Works Cited
Hughes, D. A., Kingston, D. G., Todd, M. C., 2011.  Uncertainty in water resources availability in the Okavango River basin as a result of climate change.  Hydrology and Earth System Sciences 15, 931–941.  

Potential Climate Change Effects on the Okavango River Basin

The Okavango River basin of Southern Africa is the second largest inland wetland region on earth, and as such supports a huge diversity of ecological habitats. It is also an important source of water for the people of Angola, Namibia, and Botswana, providing invaluable resources for agricultural and household use. There are currently plans in place for pipelines and irrigation from the river to better utilize the basin’s resources. However, as this study suggests, global climate change will almost certainly impact the available water from the basin, perhaps jeopardizing these future plans. Because the magnitude of future temperature change cannot be divined, the researchers in this study used a total of 6 possible estimates for warming scenarios: increases of 1, 2, 3, 4, 5, and 6°C. Each of these scenarios showed a different effect on the monthly flow and rainfall in the Okavango River, but to differing degrees and with differing signs. What seems certain is that some change will occur in the Okavango basin, and the degree of this transformation will result from the magnitude of climate change. In order to prepare for this change, it will be essential for the three nations directly affected by the Okavango river to make an integrated water management plan, and to quantify the impacts of development intervention in the basin. Tensions over water resources could cause not only famine, but also political unrest and even violent conflict in the region. Soil and water conservation (SWC) technologies may play a large role in the development of the basin as farmers attempt to maximize the supply of water they get from the area (Ringler et al. 2011) . At the same time, these plans must take into account the fragile ecological systems that the basin supports. The only thing that the people who rely on the water resources of the basin can rely on is uncertainty and transformation, and further studies should be undertaken to better plan for a changing future in this essential region.

Hughes, D. A., Kingston, D. G., Todd, M. C., 2011. Uncertainty in water resources availability in the Okavango River basin as a result of climate change. Hydrology and Earth System Sciences 15, 931–941. [GSSS: uncertainty Okavango (2011)]

Although scientists cannot be sure what the precise effect of climate change will be on the Okavango River basin, predictive models have allowed some striking possibilities to be outlined. In three of the scenarios, very substantial changes to the magnitude of river flows on the order of 30% result from temperature increase. Additionally, in at least two of the models there is a change in the timing of the season of discharge, the “wet season.” In fact, at temperature increases over 4° C, there is an almost complete loss of the wet season in the basin, due to increased evaporation and decreased rainfall and flow. Even using a relatively conservative estimate of a 2°C increase in temperature by the year 2065, significant changes in flow and discharge are predicted. These impacts are probably underestimations, a fact that makes it even more apparent how essential it will be for the region to prepare itself for change in under a drying climate change scenario.

Different areas of the Okavango River basin have physical characteristics such as geology, vegetation, and soil composition that affect rainfall-runoff response. Thus not every specific area in the region will feel the effects of climate change to the same degree, or even experience the same “symptoms.” The numerous deltas of the main river will also be affected in a trickle-down (no pun intended) effect. These climate models must therefore be understood in terms of interactive physical processes that make up the projected changes. In the same manner, further studies should be conducted in order to determine critical thresholds in rainfall and river flow to sustain ecological environments. Previous research had collected some data on water resource estimations, such as monthly rainfall and runoff, but there is still a dearth of data regarding evaporation, stream flow, and discharge. Particularly in light of the significant changes that are inevitably approaching with global climate change, data collection and further analysis will be invaluable in maintaining the physical, ecological, and anthropological stability of the Okavango River basin.

Combating Global Climate Change with Soil and Water Conservation Technologies

Global climate change has increased the uncertainties and risks that have always been inherent in agriculture, especially in regards to the availability of water resources for crops. In response to this heightened jeopardy, some experts have advised the promotion of soil and water conservation (SWC) technologies for farmers. SWC technologies include bunds (structures to control runoff and reduce erosion), grass strips, tree planting, irrigation, and water harvesting structures such as dams and ponds. Farmers must weigh the risks of adopting a new technology with the potential gains in crop yield in order to decide if implementing a particular SWC technology will be beneficial. This study creates a mathematical model to assess the impact of SWC techniques in 5 ecologically different regions of the Nile Basin in Ethiopia. After running statistical analysis, the model suggests that all of the SWC options studied have large positive impacts on crop output in low-rainfall areas, while only waterways and tree planting have an impact in high-rainfall areas. In addition, irrigation alone has no effect or results in lower yields in both high- and low-rainfall areas of the country, but when it is combined with other SWC technologies, large positive impacts can be seen in all regions. This finding should lead us to consider that the answer to water management in the face of climate change will not be a “silver bullet” solution, but rather the result of interactions between many different technologies. The results from this statistical model may be used to give advice to farmers in Ethiopia, improve targeting of SWC techniques to certain areas, and provide insight for policymakers, NGOs, and other development agencies in order to help farmers adapt to changing water resources in the face of global climate change.–Nora Studholme

Kato, E., Ringler, C., Yesui, M., Bryan, E., 2011. Soil and water conservation technologies: a buffer against production risk in the face of climate change? Insights from the Nile basin in Ethiopia. Agricultural Economics 42, 593–604.

In order to build an accurate statistical model, researchers used diverse data from 50 households across 5 regions of Ethiopia, resulting in a total sample size of 6,000 plots. Researchers then separated the regions based on historical rainfall patterns, so that the impact of different technologies could be observed in disparate ecological environments.

The model assumes that farmers are risk-averse and want to maximize their profits. The equation is set up to show how farmers might maximize utility using different levels of SWC inputs. In order to account for the fact that different crops might be produced in larger or smaller quantities, the success of the inputs is based on the value of the crops produced per hectare of land on a plot. In addition, the statistical model controls for soil type, plot size, human capital, and fertilizer. After running the numbers, a positive coefficient from the equation means that the inputs have risk-increasing effects, while a negative coefficient implies risk-decreasing effects.

Each region was affected differently by SWC technologies, and the degree to which the innovations helped them was also variable. Grass strips and soil bunds have more risk-reducing results in low-rainfall areas, while some techniques, such as rainwater harvesting and irrigation, require a certain amount of rainfall to be viable. Even within the same rainfall area, some SWC technologies produced different results. This could be because of differing chemical properties of the soil, availability of nutrients, the needs of a specific crop, or other physical characteristics. What is clear is that it is important to investigate effects of SWC technologies with a specific region in mind in order to determine the best way to reduce risk in the face of climate change.

This statistical model and the results it has already produced will be valuable resources for farmers and policymakers as water resources become more jeopardized and droughts, floods, and other climate-driven events continue to plague the world. SWC technologies have great potential to mitigate the effects of climate change on water resources, and thus improve agricultural yields and food production worldwide even in these unstable ecological times.