PRE2018 3 Group16

Group members

Edwin Steenkamer	1006712
Sjir Schielen	1024154
Thijs Conner	1011148
Tobin van den Hurk	1009573
Tom Verberk	1016472

Subject

The environmental challenges in Africa, which are only increasing in difficulty due to, among other factors, the consequences of global warming, are a real concern for the food production in this area. As a consequence, independent and poor small-scale farmers and small villages living of agriculture across Africa may struggle to sustain themselves. The agricultural sector in Sub-Saharan Africa is dealt a bad hand, considering the suboptimal conditions they have to deal with in this arid and drought-prone land. Since the agricultral sector makes up a large part of the Sub-Saharan labor market, every improvement made in this area will benefit a substantial part of the African population. However, the lack of proper education and the misuse of technology in these agricultural areas hinders the development of efficient food production. This problem knows many sides and solving all of these in one solution is virtually impossible.

While researching the exact problems, it has become apparent that the lack of water is a clear limiting factor in agriculture. Even though this does not come completely out of the blue, only after some research it became apparent that there is still a lot of room for improvement regarding water usage. Therefore, we want to make a system that collects, stores and distributes water in a smart and efficient way. Since the climate varies heavily across the enormous continent which is Africa, the solution presented on this wiki focuses primarily on Southern Africa, where both the dry season and rainy season are lengthy and significant. This allows for collecting water when rain is abundant, and storing it untill it is needed in the more dry parts of the year. This in turn would decrease the amount of failed harvest caused by drought, allow for a greater variety in crops, and shift the farmers' focus from trying to survive even if a harvest fails to maximizing harvest all year long instead.

Objectives

The objective is to find a solution that improves the situation with respect to water in Africa's arid and drought-prone areas. This can be done by designing a system that collects, stores and distributes water, while closely paying attention to what the users really require. To do this, the first objective is a literature study, which is needed to provide the required knowledge. Then, the objective is to design the system based on the knowledge.

Milestones

• Summarize at least 7 scientific articles each
• Current situation sketch
• Determine & discuss possibilities for improvement of current situation
• Cost analysis
• (Low-level) System design
• Example scenarios

Approach

For this project, an initial literature study is required. By exploring the subject in a top-down fashion, the main focus of the project can be adjusted. In other words, gathering information on the broad topic of farming in sub-optimal conditions in general, allows for the project to delve deeper into the aspects of farming deemed most important. Using this method instead of starting with a focus on a specific problem regarding farming, eliminates the threat of discovering this specific problem is not as interesting or important as expected. Another benefit of starting with an extensive research on the state-of-the-art, is that the amount of assumptions is expected to be limited. This allows for more grounded arguments and reasoning as to why certain aspects are deemed more important.

This led to the opinion that the most effective way of improving agricultural gains is by conquering extended periods of drought. Transporting water from more humid areas is a possibility, but unfavorable due to transportation costs and limited availlability of water even in those more humid parts. Therefore, a means to improve the usage of the already availlable water during the rain seasons is more desirable.

The process of increasing water efficiency has 3 distinctive steps, which all need to be looked at individually first: collection, storage and distribution. Then, these parts need to be combined into one construction, centered around the user.

Deliverables

This project will ultimately consist of

• A literature study on automated farming
• In-depth analysis on yet to be specified topics, exploring their possibilities
• A design for automated farming in Sub-Saharan conditions, which solves at least 1 of the problems discovered during the research, albeit partially.

Planning

The planning can be viewed by following this link.

Role division

The role division, or 'who will do what' section, is likely to change over time, because newly obtained knowledge can steer the project in a (slightly) different direction. As of now, the following role division is made:

Edwin focuses on the state-of-the-art and the users requirements that the design should satisfy.

Sjir does research on water management and livestock and specifies the requirements the design should satisfy with respect to water management and livestock.

Thijs and Tobin do research on what measurements should be performed and how they should be performed. They also specify the requirements with respect to measurements and perform a cost analysis.

Tom does research on and specifies design requirements on water management and irrigation. He also does a cost analysis.

A completer role division is listed in the planning. There is some overlap in the tasks that are carried out, which is done on purpose to create room for discussion on the requirements.

Users

The users of the technology can be divided into primary, secondary and tertiary users. The primary users are small based farmers that live in conditions which are suboptimal for agriculture. These conditions are mainly found in drought-prone areas of Africa, such as the areas in or around deserts. As primary users, the artifact or technology is directly aimed to be of use to this group.

Secondary users are the people in nearby villages that benefit from a more consistent food supply. They benefit from the available food through the farmer's use of the artifact. Bigger farmer organizations (or collectives/unions) are also considered secondary users, as they benefit from higher production caused by the farmer's use of the artifact. Larger scale farmers may also use the technology, although it was intended for small scale farmers. Larger scale farmers are therefore considered secondary users.

The tertiary user is society as a whole. If food production increases it will benefit society. Society as a whole is not using the artifact, but it benefits from a more efficient use in water for agriculture through the increased production. As the artifact is aimed to increase the efficiency in the use of water, it is projected that more food becomes available. This is likely to cause economic growth in these developing areas, which makes it attractive to investors. Therefore, investors can also be seen as a tertiary user.

User Requirements

The technology requires a source of energy. As the energy infrastructure in Africa is underdeveloped to non-existent in certain areas, this forms a problem. In, for example, Sub-Saharan Africa, only an estimated 31% of all inhabitants have access to electricity [15]. Access to electricity is usually in towns or cities, which is not where the farmer has his piece of land. This means that the users require the technology to generate its own needed energy or to work on fuel.

The scarcity of water is the main reason behind this artifact. Water is very valuable in areas prone to drought and the sad reality is that it literally is a matter of life and death. Therefore the artifact must be efficient with water. This means that it should catch as much water as possible and store it while keeping losses at a minimum.

Although the technology is primarily aimed to be used for crops, it is unlikely that it will be the only use. If drought strikes and there is water available in the storage tank, people will use it for consumption. Even if it is explicitly clarified that it is no drinking water, to the people it is still better than no water at all. Therefore it is required that the storage tank keeps the water clean to a certain degree. This induces more difficulty in the design of the artifact which was not projected at first, but it does make the artifact more user oriented.

Former automation solutions have failed due to the weak state of the economy in these developing countries. Farmers live off the harvest rather than the profit they receive from selling their crops. This means that no jobs should be replaced by the artifact, which is vital for it to be adopted in the first place. The farmers will not use technology that replaces their jobs, therefore it is important that the artifact performs a task that no farmer can do. The system collects, stores and irrigates water, which are tasks that farmers cannot do themselves.

The artifact is aimed to help the farmer with water management. It is projected to perform this task autonomously, but in the end the farmer should have full control. In the case of a severe drought, if the water is required for drinking, the farmer should have access to the storage tank. Therefore the farmer should be able to intervene with the autonomous way of operation on request. The farmer should be able to understand how to interact with the artifact in the desired way. Therefore, it should be understandable. When specifying the system requirements, it should be taken into account that illiteracy rates are globally the highest in the underdeveloped parts of Africa, which is the same area in which the artifact is projected to operate.

A requirement that is applicable to all users and non-users of the artifact, is that the artifact’s greenhouse gas emissions should be as low as possible. This requirement becomes more and more important as the effects of climate change begin to show. It is especially important for the farmers in drought-prone areas as they live in areas which are expected to be heavily affected by climate change.

General design concepts

There are multiple possible way to gather water, some of these are better suited for the situation than others. Below the possible solutions are listed, the solutions are graded based on:

• Feasibility
  
• costs
  
• Revenue
  
• Space needed
  
• weather dependency

Below are the different criteria explained.

Feasibility
When looking at the feasibility of a solution we look at the practical and technical feasibility, in this technology invented yet and how do you transport all the needed material with bad infrastructure are questions asked when looking at the feasibility.

Cost
The costs can be seperated into two mayor categories short term costs and long term cost. Short time costs are the cost needed to buy the required materials to build the artifact, long term costs are the fixed costs that comes with the artifact.

Revenue
Revenue is measured by how much water the artifact will collect on average.

Space needed
Small based farmers often don’t have a lot of free space which is not used for farming or living. Our artifact therefore has to be space effective.

weather dependency
As the weather is not something that can be regulated some artifacts might not work with negative weather.

Criteria assessment

Solutions Dig a well

• Feasibility
  

As has been shown before a dig can be dug in Africa and is a good way to get some water, Wells are however highly greographicly dependent. Meaning that a well cannot be build at any place.

• costs
  

The cost of digging a well are only short term, the only costs is building the well, besides the material for the well the digging of the hole has to be financed as well. digging a hole will have a cost ranging from 2.000 to 500.000 usd. http://nora.nerc.ac.uk/id/eprint/9185/1/CEB%20Danert%20Draft%204%20UNESCO%2022%20April09.pdf

• Revenue
  

The revenue of the well in depth dependent. With an average bucket of 10 liter and after installing a system which gets the water up at a speed of 1 m/s. The well will get at max capacity a yield of 36.000 liters / meter per hour. However one must be careful not to dry the well.

• Space needed
  

The well itself doesn’t take up a lot of space, only problem is that there has to be a suited space to dig the well.

• Weather dependency
  

The well is only weather dependent if there are long droughts which will make the well empty.

• Automated pump
  

Instead of building a well we can also dig an automated pump.

• Feasibility
  

As stated by the well, an automated pump will be geographically dependent. The main disadvantage is that a automated well needs more sophisticated equipments, which means that getting the right machines there might be a problem.

• Cost
  

The average cost of building a automated well will lie around 8000 usd. Which is way less than the average well costs.

https://waterwellsforafrica.org/whats-the-cost/

• Revenue
  

The average revenue is about 5 gallons per minute for 2 hours. This to make sure the well doesn’t dry

https://www.des.nh.gov/organization/commissioner/pip/factsheets/dwgb/documents/dwgb-1-8.pdf

• Space Needed
  

A pump doesn’t need any space, but the position the pump will be places must depend on the terrain.

• Weather Dependency
  

The pump is only weather dependent during long droughts.

Rooftop water harvesting systems.
The general idea of an rooftop water harvesting system is that all the water that falls on your rooftop will be collected.

• Feasability
  

This method is reasonably feasable, the farmers already have houses and there are no technical solutions needed only problem would be the material of the houses and wether it is a good material to transport water.

• Costs
  

The only things that would cost money with this idea is a huge tank, pipes to transport the water to the tank and some sort of material to improve the roof if needed. The overal cost would therefore highly depend on the amount of water that can fit into the tank. Prices can vary from 100 euro (100 liter) till 360 euro (1000 liter).

• Revenue
  

The revenue of the system is primarily based on the surface of the roof. Therefore we don’t expect this solution to have the revenue to support an entire farm, given the small amount of rainfall.

• Space needed
  

For this artifact is only space needed for the watering tank.

• Weather dependency
  

This artifact is highly weather dependent, if the weather is bad, this artifact will have a lower revenue than expected, when the weather is good the revenue will increase.

Government?

Robot who gets water?

PVC Sheet (afdekzeil)

• Feasibility
  

A construction to keep the sheet in place is required. This is easily achieved by connecting the sheet to wooden poles, where the height of these poles is variable

• Cost
  

A 10m x 12m sheet costs between 60 and 80 euros, depending on the thickness of the sheet chosen. If the sheet is placed over the crops as described in the ‘space needed’ section, a mechanism should be created to roll the sheet in and out. When decided that the farmer can make use of a semi-automatic, manual mechanism, costs are expected to remain low when using a pulley system. An automated sheet, however, can become rather expensive. As an example, fully automatic pool covers for small pools cost around 2500USD. A benefit of the fully automatic method is the option to add a rain sensor for opening and closing based on weather conditions.

• Revenue
  

The revenue of this method depends heavily on precipitation. If the construction of the sheet is sufficiently stable, it would be able to collect most if not all rainfall in the area covered by the sheet. No water should remain on the sheet, as this water would evaporate and go to waste.

• Space needed
  

2 different methods of placing the sheet are possible. The first method is placing the sheet on unused areas, allowing for the sheet to be close to the ground. The second, more efficient method would be to place the sail over the crops, and create a mechanism that can roll out the sheet when it rains and roll it back in as it clears up.

• Weather dependency
  

The sheet collects water only when it precipitates, which varies heavily across Africa
> Northern Africa remains dry for most of the year, except for the coastal areas which see the most rain between November and March.
Southern Africa has half a year of drought, from April to October, and half a year of rain, November to March. In particular, Botswana seems to have these clear distinctions.

State-of-the-art

Agriculture is one of the biggest sectors we have in this world. Without food, we would not be able to live on this planet. Since this project focuses on small-scale farmers, the research is divided into different subjects deemed most important in getting a better picture of how small-scale farmers could be assisted. The first section will briefly touch on some of the core aspects of Sub-Saharan agriculture, after which a more in-depth state of the art for things like water collection, irrigation, and water storage.

Sub-Saharan African agriculture

The best ways to provide energy to systems implemented on a farm.

Energy production is vital to the development of Africa. Currently only an estimated 31% of the whole population in Sub-Saharan Africa has access to electricity, whereas about 80% of the energy consumption is still accounted for by traditional biomass energy. An increase in energy consumption is needed for Sub-Saharan Africa to develop. Climate changes poses a threat to the already vulnerable agricultural sector of Sub-Saharan Africa. Energy sources other than biomass with low carbon emissions are needed to improve the agriculture in these fragile environments. The lack of funding is the major problem and as the globe warms, time is of the essence [15]. Sub-Saharan Africa offers conditions that may be beneficial for energy production. The area receives solar radiation with an intensity that is among the highest on the planet. The now commercially available technology concentrating solar power (CSP) is a candidate technology which, with the right investments, can generate a lot of power in North Africa [32]. There are possibilities for large scale energy production in this area, which may benefit other parts of the world as well, but the main problem remains funding.

How does livestock and vegetation affect (and benefit) each other.

There are theoretical benefits to the interaction between crops and livestock. Livestock can be used for physical labour on the land and manure can fertilize the soil. In Sub-Saharan Africa, however, this concept is not well integrated. The concept is not applied through the availability of information, but through environmental differences [25]. Another theory suggests that households in Sub-Saharan Africa use livestock as a buffer stock to insulate their consumption from income fluctuations. As the problems of engaging in rainfed agriculture are inevitable in a drought-prone area, it is often assumed that livestock form a buffer for the dry season. Results indicate that livestock transactions play less of a consumption smoothing role than often assumed. One can conclude that there are better ways to manage agriculture [13]. Another problem is that most livestock was introduced to Africa through trade with Europe and the Middle-East, hence the animals are less adapted to the extreme conditions [19]. The use of different animals as livestock may benefit the harsh areas. It is, however, important to analyze how effective species are with water. A way to do this is by the concept of livestock water productivity (LWP) [10]. LWP is defined as the ratio between the sum of all net livestock products and services and the sum of all depleted/ degraded water. It assigns a numerical value with the unit dollar per cubic meter of water. By using this concept a numerical problem can be formulated that allows optimization. This approach does, however, rely on available information and it is estimate based.

Methods of Soil sampling and analysis.

Soil consists of many different kind of elements which can have an effect on the crop growth. To measure these elements soil sampling and analysis has to be done. Different analysis methods are needed for different elements such as chemical, biological, organic matter, physical and water analyses [6] [17] [24]. The effectiveness of these tests, for a low budget and uneducated farmer, are dependant on the ease of use and low-cost equipment. Investigating new and improved ideas of how to measure specific elements may help in choosing the right tests [33] [35] [20]. In case of putting these sensors on a robot an assessment also has to be made about the effectiveness of different kind of agricultural robots [26].

Soil analysis and degradation.

Not just the drought, but rather soil degradation combined with the rapid increase in population in developing areas such as Sub-Saharan Africa, will pose a major threat for food production in the near future[31]. To combat this degradation, adequate measures should be applied. Measuring the soil composition at different locations in a single field, will give more insight in the so-called micro-variabilities[5]. These measurements can be used to more efficiently water, manure, and weed crops, which has proven to be more effective than simply introducing new techniques or machinery[4].

Obstacles for small scale farmers in poor countries.

The demand for food products for export markets is increasing severely in developing countries . But most of the small-scale farmers in those countries have difficulties profiting from this increasing demand. This article[12] gives a few problems small-scale farmers are having including pesticide use and poor storage facilities. To improve these farmers need technology, but to choose which technology is needed and then actually integrate this technology is easier said than done[14]. The conclusion is that a combination of lack of knowledge, resources, and technology is the reason small-scale farmers are having trouble to increase their production and make their farm more efficient[9].

Technology that is used in agriculture in industrialized countries.

Nowadays technology is having a massive impact on agriculture, especially in industrialized countries. A great example of this is precision farming. This type of farming uses wireless network systems (WNSs) to make sure every plant or animal gets a very precise treatment[7]. Other examples of smart farming is given in these articles[16][18]. The first article describes a system that can measure physical parameters of the soil that play a vital role in farming activities and the second article describes a system that can reduce the amount of water used by implementing a soil moisture sensor to automate the water sprinkler.

Sources SotA

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[16] Ivanov, S., Bhargava, K., & Donnelly, W. (2015, July 14). Precision Farming: Sensor Analytics - [Journal]. Retrieved February 13, 2019, from https://ieeexplore.ieee.org/abstract/document/7156034

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[25] Okoruwa, V., Jabbar, M. A., & Akinwumi, J. A. (2016, April 19). Crop-Livestock Competition in the West African Derived Savanna: Application of a Multi-objective Programming Model. Retrieved February 13, 2019, from https://vtechworks.lib.vt.edu/handle/10919/65734
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[29] Springer International Publishing AG 2018. W. Leal Filho and J. de Trincheria Gomez (eds.). (2017). Rainwater-Smart Agriculture in Arid and Semi-Arid Areas. Retrieved February 13, 2019, from https://doi.org/10.1007/978-3-319-66239-8_2
[30] Strauch, A. M., Kapust, A. R., & Jost, C. C. (2009, September). Impact of livestock management on water quality and streambank structure in a semi-arid, African ecosystem [Book, pages 795-803]. Retrieved February 13, 2019, from https://www.sciencedirect.com/science/article/pii/S0140196309000962
[31] THE WORLD BANK. (2017, December 2). Agriculture in Africa: Telling Facts from Myths. Retrieved February 13, 2019, from http://www.worldbank.org/en/programs/africa-myths-and-facts
[32] Ummel, K., & Wheeler, D. (2008, December). Desert Power: The Economics of Solar Thermal Electricity for Europe, North Africa, and the Middle East. Retrieved February 13, 2019, from https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1321842

[33] Viscarra Rossel, R. A., Cattle, S. R., Ortega, A., & Fouad, Y. (2009, May 15). In situ measurements of soil colour, mineral composition and clay content by vis-NIR spectroscopy. Retrieved February 13, 2019, from https://www.sciencedirect.com/science/article/pii/S0016706109000408

[34] Wang, H., Wang, T., Zhang, B., Li, F., Toure, B., Omosa, I., . . . Pradhan, M. (2013, September 30). Water and Wastewater Treatment in AFrica- Current Practices and Challenges. Retrieved February 13, 2019, from https://onlinelibrary.wiley.com/doi/full/10.1002/clen.201300208

[35] Widmer, F., Fliessbach, A., Laczkó, E., Schulze-Aurich, J., & Zeyer, J. (2001, June). Assessing soil biological characteristics: a comparison of bulk soil community DNA-, PFLA-, and Biologtm_analyses [Book, pages 1029-1036]. Retrieved February 13, 2019, from https://www.sciencedirect.com/science/article/pii/S0038071701000062

SotA focussed on water collection, usage and storage in Botswana

Drought

Drought is considered to be one of the most complex natural hazards, as it affects more people than any other natural hazard, yet for all the damage it causes it receives relatively little attention. Of all natural hazards, it is the most difficult to predict and it can last longer than any other. Currently, there are many factors that cause a lack in preparedness by people living in drought-prone areas. One of these factors is the lack of a universally accepted definition of the word drought. Various scientific disciplines, such as meteorology, agriculture, hydrology and socio-economy, have different definitions. Here, the focus lies on the agricultural definition and the meteorological definition. The agricultural definition refers to a period of time in which the amount of water in the soil no longer meets the requirements of the crop. Meteorological drought is defined as the amount of precipitation being a certain percentage lower than usual for a prolonged period of time[9].

The Botswanan situation

Rainfal, PET and day length in Gaborone[7]

Botswana is a typical semi-arid country: average annual evapotranspiration (sum of evaporation and transpiration by vegetation) exceeds the annual rainfall by a factor 3-4 in the north-east to 8-10 in the south-west. Seasonal rainfall and its distribution are very irregular and dry periods of more than one month are common. The country’s agricultural sector is built around the rainy season. The figure below shows the average rainfall from recorded data between 1925 and 1984, the average Penman potential evapotranspiration (PET) and theoretical day length for Gaborone[7].

What stands out is that rainfall is less than PET all year round. This means that the shortage of water is a problem not only in the dry season but also in the wet season. Keep in mind that the figure shows average data. The fluctuations in precipitation are unpredictable and it is not uncommon for a dry month to appear in the rainy season.

To manage agriculture, the rainy season is divided in three periods which roughly coincide the farming cycle. The early rainy season spans from October to December and is meant for soil preparation, planting and the first stages of crop development. The mid rainy season lasts from January to February. This period contains fast vegetative growth and has the highest water requirements. The late rainy season concludes the rainy season in the months March and April. In the late rainy season, the final stages of crop development occur and the water requirement declines[7] [8].

In practice, the farmers face challenges. First of all, the PET is higher than the amount of rainfall all year round. This means that even in the rainy season there is not enough water to support all biomass. Second, the fluctuations in arbitrary dry periods in the rainy season cause unpredictable risks in the cycle. The farmer needs enough time for his crops to grow while there is water available. Yet, if a dry month occurs it can cause the harvest to fail without enough time left in the rainy season for the farmer to replant. Even if the crops survive, the lack of water will cause less biomass to be produced.

A system that collects, stores and smartly irrigates water can be a solution. Since annual evapotranspiration exceeds annual rainfall, a smart way of collecting, storing and using the water is necessary. By collecting more water, a part of the water that would otherwise evaporate can be used. By improved storage, the farmer has a water supply that can act as a buffer in potential arbitrary dry months. If the water is used in a more effective way, which is aimed to be optimized by the use of technology, less water is lost in watering crops.

Farmer's current efforts of dealing with drought

Stagnant or moving water storage?

It has been shown that mismanagement of irrigation resulting in the formation of stagnant pools lead to the transmission of water-related diseases such as schistosomiasis, malaria and typhoid fever [1]. Moreover, under the condition of stagnant water, cyanotoxins can reach high concentrations in water and might represent health and ecological risks [2]. Furthermore, stagnant water has a decreased oxygen content which is disadvantageous for crop growth. It has been found that aeration of crops can increase the yield by up to 96% [3] [4] [5]

Best type of irrigation?

(Subsurface) drip irrigation can reliably provide an increased yield and water use efficiency. Some difficulties in adopting this technology have been expressed by the few farmers who adopted it. The main recommendations for being able to have a successful adoption of this technology is. (1) Redesign drip system to help prevent common problems (2) Invest in clear education for adopter, focusing on maintenance and repairs. (3) Encourage the adoption of complementary technologies to support the function of drip systems, such as water storage, purification and delivery systems[6].

How to measure soil moisture levels?

There are many different techniques to measure the soil moisture levels. To make a better choice which one to pick, the different techniques will be compared to each other with regard to the user requirements. This is listed in this table.

Water collection, storage and usage in Botswana SotA Sources

[1]: Doorenbos, J., & Kassam, A. H. (1979). Yield response to water. Irrigation and drainage paper, 33, 257.

[2]: Bláha, L., Babica, P., & Maršálek, B. (2009). Toxins produced in cyanobacterial water blooms-toxicity and risks. Interdisciplinary toxicology, 2(2), 36-41.

[3]:Bhattarai, S. P., Huber, S., & Midmore, D. J. (2004). Aerated subsurface irrigation water gives growth and yield benefits to zucchini, vegetable soybean and cotton in heavy clay soils. Annals of applied biology, 144(3), 285-298.

[4]:Armstrong, W., & Boatman, D. J. (1967). Some field observations relating the growth of bog plants to conditions of soil aeration. The Journal of Ecology, 101-110.

[5]:Hook, D. D., Langdon, O. G., Stubbs, J., & Brown, C. L. (1970). Effect of Water Regimes on the Survival, Growth, and Morphology of Tupelo Seedlings1. Forest Science, 16(3), 304-311.

[6]: Friedlander, L., Tal, A., & Lazarovitch, N. (2013). Technical considerations affecting adoption of drip irrigation in sub-Saharan Africa. Agricultural water management, 126, 125-132.

[7]: Vossen, P. (1988). Agricultural and Forest Meteorology (4th ed.). [Pages 369-382]. Retrieved from https://www.sciencedirect.com/science/article/pii/0168192388900445

[8]: Valentine, T. (1993). World Development. [Pages 109-126] Retrieved from https://www.sciencedirect.com/science/article/pii/0305750X93901405

[9]: Keshavarz, M., Karami, E., & Kamgare-Haghighi, A. (2010). A Typology of Farmers Drought Management. Retrieved February 23, 2019, from https://www.researchgate.net/profile/Marzieh_Keshavarz2/publication/267997549_A_Typology_of_Farmers'_Drought_Management/links/54b6356f0cf28ebe92e7b889.pdf

Scientific papers

The summaries of the scientific papers which have been read can be found here