Chapters 5.66

5.66 -Rooftop Rainwater Harvesting In sub-Saharan Africa

Noah Graham, University of Guelph, Canada

Suggested citation for this chapter.

Noah,G. (2022) Rooftop Rainwater Harvesting In sub-Saharan Africa, In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Shortcomings in African Agricultural Irrigation

According to The World Bank, during the period from 1990 to 2007, Africa stood out as the sole developing region where the increase in land area surpassed the growth in crop yield percentages (World Bank, 2013). One of the direct factors responsible for this is illustrated by a quote from Unlocking Africa’s Agricultural Potential, “Of the 183 million Ha of cultivated land in sub-Saharan Africa (SSA), 95 percent is rain-fed and less than 5 percent benefits from some sort of agricultural water management practice… the lowest irrigation development rate of any region in the world” (World Bank, 2013). This paper will focus on effective strategies to utilize the available rainfall for irrigation purposes.

Current Sub-Saharan Irrigational Methods

Africans in the sub-Saharan region do have irrigation techniques in operation, but not in a wide-scale. Only 6 million Ha or 4% of the cultivated land in sub-Saharan Africa is irrigated, with the remaining nearly 200 million Ha being rain-fed (Kadigi et al, 2013). However, among the limited range of current manufactured irrigation methods, it is pertinent to highlight the existing costs. Traditional community-based irrigation methods such as swamp irrigation can range from 600 - 1000 USD per Ha on average. Individual methods utilizing small lift systems and pumps can cost 1500 - 3000 USD per Ha on average. Finally, Inter-community systems using dams, tube wells, and river diversions can cost anywhere from 3000 - 8000 USD per Ha to develop (Kadigi et al, 2013).

Benefits of Rooftop Rainwater Harvesting (RRWH)

Rooftop Rainwater Harvesting (RRWH) has the potential to alleviate stresses for people across rural sub-Saharan Africa facing issues of water scarcity. 60-70% of people in sub-Saharan Africa live in rural environments, and rely on the agricultural sector for their livelihoods (Pachpute et al, 2009). “Most of the agriculture in [sub-Saharan Africa] is located in semi-arid areas where rain falls irregularly and much of it is carried away in the form of surface runoff” (Pachpute et al, 2009). Several researchers and developmental organizations propose RRWH systems as viable solutions to enhance crop productivity in smallholder farming communities, offering potential supplementary moisture/water resources (Pachpute et al, 2009). “Studies conducted by Botha et al. (2003), Gicheru et al. (2003), Biamah and Nhlabathi (2003) and Chilimba and Kabambe (2003) have demonstrated in-situ RWH systems increasing crop yields by 30% to 50%” (Pachpute et al, 2009).

Rooftop Rainwater Harvest Methodology

Figure 1. RRWH basic flow model (Mun & Han, 2012).

All RRWH systems are quite simple. They consist (in order) of a catchment area (i.e. the roof) that collects the rain, a filter to remove particulates, and a storage tank (Mun & Han, 2012).

Figure 2. The flow model above demonstrates the methodology of a RRWH system (Mun & Han, 2012).

Figure 3. An active RRWH system in Rwanda

(Rwanda Green Fund, 2018) https://www.flickr.com/photos/127716409@N05/42858825782/in/album-72157698171605835/.

Visual Breakdown

Figure 3 provides a better understanding of a RRWH system. The sheet roof on the building acts as the catchment area, with gutters and pipes leading to the black storage container seen on the right. Attached to the container is a red handle used to pump out the water without the use of, or access to electricity. This system can be replicated cheaply with various materials and can be set up virtually anywhere with moderate rainfall, as seen in sub-Saharan Africa (Kadigi et al, 2013).

Figure 4. An alternate storage method using buried concrete tanks to store the collected rainwater (Rwanda Green Fund, 2018) https://www.flickr.com/photos/127716409@N05/42007081835/in/album-72157698171605835/.

RRWH Potential in Small-scale Agriculture

In RRWH systems with storage containers ranging from 2 to 10 m3 in volume, the sheet roof catchment areas often vary from 15 to 40 m2 in size, according to a survey conducted by J.S. Pachpute of current RRWH systems in sub-Saharan Africa. The capacity for roof runoff during dry years in these systems varied from 13.2 to 35.2 m3 annually in highland regions, and 4.8 to 12.8 m3 annually in lowland areas (Pachpute et al, 2009). It should be noted that in years with typical rainfall patterns, the irrigation potential of the systems rose by 39%, showcasing the significant impact of rainfall variability (Pachpute et al, 2009).

Previously Recorded Outcomes

Figure 5. Average Monthly Rooftop Runoff potential during dry years in various regions of Tanzania with a roof size of 15 m2 (Pachpute et al, 2009).

As displayed in Figure 5 above, there were two seasons when rainfall was high, and two when it was quite low. October to December, as well as February to April, showed the highest rainfall in all demographics. Most of the annual rooftop runoff was collected in these date ranges, as shown in Figure 6.

Figure 6. Average runoff potentials, irrigation volumes, and storage tank balances of RRWH systems with a roof size of 15 m2 during surveyed dry years, derived from samples collected across High, Middle, and Lowland regions (Pachpute et al, 2009).

Analysis of Surveyed Outcomes

Continuing from above, Fig. 5 and 6 give insight into the potential of RRWH. Fig. 6 shows that the rainwater storage tanks were at their fullest during the drier parts of the year, maintaining levels until the next rain period came. This is important, as it means farmers with these systems have the ability to keep their crops such as in home gardens irrigated year-round, even when there is very little rain (Pachpute et al, 2009). During the rainy seasons, farmers can save the collected water, leaving their crops to be rainfed. However, once the dry seasons are reached, the farmer has a reserve of water to last them until the upcoming rainy season arrives.

Costs of Implementation

Retailers such as Alibaba and Indiamart offer affordable options in terms of RRWH products, that are accessible to most countries in sub-Saharan Africa. Alibaba provides temporary options for collection tanks, including inflatable and light plastic materials. While many of the tanks sold are not durable, they allow farmers the opportunity to trial RRWH at an affordable price, often under $50 USD. Indiamart offers a wide variety of filters to be fitted to RRWH systems, available in many configurations for under $100 USD. With proper tank maintenance, and when combined with a rainwater filter, RRWH can reduce shortages of clean drinking water (Pachpute et al, 2009). As many people living in sub-Saharan Africa do not have close access to clean drinking water, RRWH, when combined with proper sanitary measures, can eliminate the time and potential costs required to collect potable water (Pachpute et al, 2009).

Critical Analysis

While rainwater harvesting has been implemented in the sub-Saharan region, it has faced challenges for wide scale implementation. Inadequate policy support, lack of knowledge and skills by facilitating institutions and communities to implement RWH, and limited scientific and socioeconomic knowledge of RWH, are all constraints that have been met in past attempts to create wide-scale change with the infrastructure (Pachpute et al, 2009).

With an estimated irrigation potential of 15 to 32 m2 based on surveyed rooftop rainwater harvesting systems in SSA, the practice is only practical for small-scale applications such as vegetable gardens and for use as a potable water source (Pachpute et al, 2009). Compared to methods such as subsurface rain runoff harvesting that showed irrigation potentials of 304 m2 under similar circumstances, it is obvious that the RRWH system is not the most efficient option (Pachpute et al, 2009). However, the method is quite practical and potentially beneficial for domestic/small-scale implementation (Ojwang et al, 2017).

However, the RRWH startup costs can be high, often requiring the purchase and potential installation costs of storage tank(s), plumbing, filters, and pumps (Ojwang et al, 2017). In a survey conducted by J.S. Pachpute, the installation cost of these systems was near US $ 59.90 per cubic meter of stored water (Pachpute et al, 2009).

A large majority of these costs are for the purchase and installation of the collection tank. Long term storage tanks are the most expensive aspect of the system, and therefore one of the greatest hinderances to adopting RRWH. Roofing material should be noted as another, as the system is only possible with steel, tin, or other forms of solid roofing material; straw and thatched roofs are not ideal for efficient water collection. Farmers must also account for construction costs, unless self-trained in the process. As stated, retailers such as Alibaba sell cheaper tank models, using inexpensive and light-weight materials like rubber and nylon. Low-cost, quality options for durable tanks are needed to make RRWH an attainable practice for broader adoption across sub-Saharan Africa.

Conclusion

In conclusion, the adoption of Rooftop Rainwater Harvesting (RRWH) systems presents an avenue for addressing water scarcity challenges faced by smallholder farmers across sub-Saharan Africa. By addressing rainwater runoff potential from rooftops, RRWH offers solutions to enhance crop productivity and mitigate the impacts of irregular rainfall patterns in semi-arid regions. However, despite its potential benefits, the widespread implementation of RRWH faces challenges.

Critical analysis reveals that while RRWH systems can strengthen irrigation potential and provide supplementary water resources, their effectiveness is reliant upon factors such as roof size and material, rainfall variability, and storage capacity of the tanks. Moreover, compared to alternative irrigation methods, RRWH is best suited for small-scale applications due to its practicality and affordability.

Although RRWH startup costs can be high, the long-term benefits in terms of water security and agricultural resilience may outweigh the initial investment. A RRWH system gives farmers the ability to store water during dry seasons for vegetable gardens, providing a valuable food source, especially for micronutrients (Pachpute et al, 2009). Efforts are needed to address existing constraints, thereby empowering smallholder farmers to improve their livelihoods and enhance food security in the face of mounting water challenges including droughts associated with climate change.

Practical Resources to Get Started

Video Training Manual for RRWH https://youtu.be/DhEaKdmHeCk?si=Pyg11UedbQTGoB0p

Further Reading and Information

Sustainability of Rainwater Harvesting Systems in Sub-Saharan Africa

https://doi.org/10.1007/s11269-009-9411-8

RRWH Design Parameters https://doi.org/10.3390/w7041402

Ugandan RRWH Infomercial https://youtu.be/z_n6etqUu_Y?si=uRCf75ZgH8uIdXBm

Links to RRWH Products RRWH Tank Products https://www.homeinsulations.co.za/water-tanks/

SSA RRWH Product Company https://afritank.co.zm/

Modern Water Solutions Company in SSA https://www.jojo.co.za/

Alibaba Steel Gutters for RRWH Systems https://www.alibaba.com/product-detail/Multi-Span-Greenhouse-Connection-Kits-Galvanized_1600847548230.html?spm=a2700.galleryofferlist.p_offer.d_title.3ce44503tp9U0r&s=p

Indiamart RRWH Filters https://dir.indiamart.com/search.mp?ss=rooftop+rainwater+harvesting+filters&mcatid=36839&catid=94&prdsrc=1&stype=attr=1%7CattrS&res=RC3&com-cf=nl&ktp=N0&mtp=S&qry_typ=P&lang=en

Beneficial Initiatives Funding Irrigation Continental Africa Water Investment Programme (AIP). https://aipwater.org/ The Comprehensive African Agricultural Development Programme (CAADP). https://caadp.org/ AGRA. https://agra.org/ Feed the Future Initiative.

https://www.feedthefuture.gov/

References

1.Nash, J., Halewood, N., & Melhem, S. (2013). Unlocking Africa's agricultural potential: an action agenda for transformation (No. 76990, pp. 1-70). The World Bank. https://documents1.worldbank.org/curated/en/795321468191670202/pdf/769900WP0SDS0A00Box374393B00PUBLIC0.pdf

2.Kadigi, R. M., Tesfay, G., Bizoza, A., & Zinabou, G. (2013). Irrigation and water use efficiency in Sub-Saharan Africa. No. 63 Working Paper. https://doi.org/10.21955/gatesopenres.1115251.1

3.Pachpute, J. S., Tumbo, S. D., Sally, H., & Mul, M. L. (2009). Sustainability of rainwater harvesting systems in rural catchment of Sub-Saharan Africa. Water Resources Management, 23, 2815-2839. https://doi.org/10.1007/s11269-009-9411-8

4.Mun, J. S., & Han, M. Y. (2012). Design and operational parameters of a rooftop rainwater harvesting system: definition, sensitivity and verification. Journal of Environmental Management, 93(1), 147-153. https://doi.org/10.1016/j.jenvman.2011.08.024

5.Ojwang, R. O., Dietrich, J., Kasargodu Anebagilu, P., Beyer, M., & Rottensteiner, F. (2017). Rooftop rainwater harvesting for Mombasa: Scenario development with image classification and water resources simulation. Water, 9(5), 359. https://doi.org/10.3390/w9050359

6.Woltersdorf, L., Liehr, S., & Döll, P. (2015). Rainwater Harvesting for Small-Holder Horticulture in Namibia: Design of garden variants and assessment of climate change impacts and adaptation. Water, 7(4), 1402-1421. https://doi.org/10.3390/w7041402