Agricultural production in dry areas, which is usually delivered by subsistence farmers, depends on unreliable rainfall. Rainwater harvesting is as an effective opportunity to substantially improve productivity of small-scale farming and enhance food security and economic development. The natural environment and the instability of environmental conditions in dry area in times of climate change is a permanent threat to the livelihood of these rural people. Practical experience has shown an increase in agricultural production when adapted to local environmental, social and economic framework conditions. As part of integrated agricultural water management, rainwater harvesting systems could be used as an adaptation mechanism for climate change and to improve the livelihood of these small-scale farmers.
Background
Rainwater harvesting refers to a wide range of different techniques for accumulation, storage and provision of rainwater. Uses of collected water include provision of drinking water, water for livestock and irrigation, diversion of run-off water for infiltration in water scarce cropping areas, and refill of aquifers (groundwater recharge).[1] Rainwater harvesting is an ancient practice, and has been developed in areas where rainfall is not sufficient to support crop production or is too variable to guarantee a harvest, or where drinking water sources are scarce. Around 80% of crop land worldwide is rainfed. Nowadays, water resources in dry areas are under even more pressure due to population growth, environmental degradation and climate change.[2]
Climate change refers to the increased occurrence of droughts and varying rainfall patterns. Rainwater harvesting can be used as a low cost adaptation mechanism at the farm level for increasing soil moisture, reducing soil temperature, and recharging groundwater and other water resources. Around a third of the African continent has the potential for rainwater harvesting; in the past few years, many programmes have been launched for promoting such measures throughout Africa.
Rainwater harvesting technologies
Many different kinds of rainwater harvesting-technologies, both indigenous and introduced, exist, and most of them are for irrigation purposes or human and animal consumption. Thus, different names exist in different areas, as well as different classification systems. UNEP (2009) breaks the rainwater harvesting systems down into two main areas of in situ and ex situ technologies, as well as manmade/impermeable surfaces (Figure 1). The storage mediums range from soil profile over small ponds, tanks and cisterns to big reservoirs. ICARDA classifies water harvesting methods, as shown in Figure 2.
In situ rainwater harvesting
In situ rainwater harvesting systems are based on changing soil and water management techniques, with the aim to improve infiltration, water holding capacity and fertility of the soil, and to counter soil erosion. Via various types of barriers, rainwater runoff in sloping fields can be captured in the field and stored in the soil for immediate use by the crop. Capture and storage areas are within a small distance. Rainwater harvesting is basically about enhancing the water intake at
• the soil surface (infiltration through diverting surface runoff)
• the rooting zone (water uptake by plants)
• the groundwater (groundwater recharge).
It can also be used as a water source for livestock or domestic purposes if it recharges shallow groundwater aquifers or other water flows or small ponds.12 In addition, flooding and peak flows can be reduced through slowing down runoff and storage of water in the soil. These systems can achieve even higher outcomes if supplemented by measures of conservation agriculture, such as no-tillage, mulching, and crop rotation for increasing organic matter content in the soil. Figure 3 shows an example of an in situ rainwater harvesting system.
Ex situ rainwater harvesting
In ex situ systems, water is not collected in the same area as the storage medium. The water is stored in natural or artificial reservoirs with different dimensions, i.e. wells, ponds (Figure 4) or cisterns, for irrigation purposes or for domestic use. The capture surface has little or no infiltration capacity. A common method is the collection of rainwater in small scale basins or on rooftops; the latter is mainly collected for domestic purposes but can also be used for small kitchen gardens. Ex situ rainwater harvesting can reduce pressure on surrounding surface water and groundwater resources, as well as peak flows and flow durations.[3]
Overview of rainwater harvsting technologies
Table 1 and 2 give some in situ and ex situ rainwater harvesting systems with technological descriptions, requirements, potentials for climate change adaptation, agro-ecological and socio-economic effects, success and sustainability factors and costs.
Table 1: Examples of rainwater harvesting systems implemented in countries of sub-Saharan Africa, with overview on technique, climate change adaptation potential, effects, success factors and costs.
Table 2: Small-scale basins as an example of an ex situ rainwater harvesting system, with overview on technique, climate change adaptation potential, effects, success factors and costs.
Benefits of rainwater harvesting systems
It is commonly agreed that water harvesting systems are beneficial. Experiences of development projects suggest that sustainable and locally adapted rainwater harvesting systems can contribute to food security and adaptation to climate change, and improve the livelihood of farmers (Table 1 and 2). Rainwater harvesting can be an alternative and/or complementary method to large-scale water withdrawals and reduce negative impacts on ecosystems services, such as erosion. In addition, small-scale rainwater harvesting systems can yield a higher amount of collected water than large dams, as evaporation and water losses are reduced.[4]
An overview of possible benefits through rainwater harvesting in marginal rural areas is given in Table 3.
Table 3: Some potential benefits on different aspects of rainwater harvesting systems in rural areas.2,8,9,11,12
Limitations and challenges of rainwater harvesting systems
A collaborative analysis of ADB , FAO , IFAD , IWMI and World Bank indicate for sub-Saharan Africa little involvement of international donors in rainwater harvesting technologies. The report shows that many in situ rainwater harvesting systems, such as pits, trenches and contour ridges, have been abandoned by farmers. Their minimal impact is due to agricultural advisory approaches that are supply driven, rather than demand driven. Many systems lack the adequately heavy machinery necessary for feasibility; also, many of these machines are not affordable for subsistence farmers. Also, some rainwater harvesting measures are not profitable, and farmers lack the ability to expand them. In addition, the study concluded that conservation agriculture provides higher positive impacts than rainwater harvesting measures.[5] More detailed examples of limitations and challenges of rainwater harvesting systems are shown in Table 4.
An enabling environment and governmental support are essential for spreading the concept and implementation of rainwater harvesting systems on a large scale. Mainstreaming in policy agendas, awareness raising, capacity building and technical exchange are all important for enhancing the use of rainwater harvesting systems.
For sustainable impacts of rainwater harvesting systems, experiences of German development projects reveal that a good community organization and moblisation of labour input are essential for the implementation and maintenance of the systems (see Table 1 and 2). The GIZ regional program for implanting UNCCD strategies in Central America and the Carribean benefited from a positive involvement of civil society networks in the implementation and promotion of rainwater harvesting techniques.[6]
It is essential to identify and assess potential obstacles before implementing a system. The most appropriate solution, adapted to local circumstances, has to be identified in each situation. This should include assessment of the watershed and its ecological conditions: i.e. rainfall, evaporation, topography, soil properties, soil degradation, and vegetation cover. Remote Sensing and Geographical Information Systems can be used for locating suitable areas. Furthermore, land use and land ownership have to be taken into account, as well as suitable technology and storage medium. To be successful, sustainable and replicable, measures must be technically and physically feasible, of low cost, and have economic benefit for farmers. Especially as some systems are high-maintenance, it is important that rainwater harvesting options are made attractive for farmers themselves to invest in these technologies.
Table 4: Limiting factors to be taken into account when implementing rainwater harvesting systems through development projects.2,8,9,11,12
Examples of rainwater harvesting measures
Atajados in Bolivia
In the rural areas of Bolivia’s semi-arid Andes, many households face food insecurity because of the harsh climatic and geographical conditions, as well as the effects of climatic change. Even in the high altitudes, farmers use the land for agricultural production. The steep slopes risk erosion and landslides, and limit agriculture production. The increase of heavy rains results in rapid surface water runoff without sufficient infiltration of fields located on the slopes, as well as erosion. In addition, due to higher average temperatures, evaporation and thus the water requirement of crops increase. The available water for irrigation from precipitation is insufficient to secure harvests; farmers need additional water to adequately irrigate rainfed land.
For this reason, farmers use water storages, as well as rain water harvesting measures with specific water reservoirs (atajados) to improve the water availability in small-scale irrigation systems (Figure 5, see also Table 2).
Including video in Spanish on atajados in Bolivia:
http://www.youtube.com/watch?v=VJ_XabXdZwE
For further information on Atajados see:
• http://proagro-bolivia.org/
• GIZ/Goetter, J. (2010a): Adaptación al Cambio Climático: Cosecha de Agua de Lluvia con “Atajados” en Bolivia, Lima, Peru. http://www.riesgoycambioclimatico.org/documentos/ACC_con_CA.pdf [Access 2012-10-08]
• GIZ/Goetter, J. (2010b): El Cambio Climático en el areá rural del Sur de Cochabamba y Norte de Potosí (Bolivia); La Paz, Bolivia. http://www.riesgoycambioclimatico.org/biblioteca/archivos/DC1115.pdf [Access 2012-10-08]
• GIZ/Goetter, J. (2010c): Water harvesting: A promising climate change adaptation option for traditional Andean agriculture in Bolivia, -in: Rural Development News 2/2010. http://www.agridea-international.ch/fileadmin/10_International/PDF/RDN/RDN_2010/9_Water_harvesting.pdf [Access 2012-10-08]
Small earth dams in Zambia
In the southern part of Zambia, the climate is semi-arid / sub-humid with an average rainfall of 700 mm/a. The medium fertile soils are cultivated mainly by poor small-scale farmers with an average land size per household of 2 ha. In order to collect runoff from upstream areas, small earthen dams are constructed (Figure 6). The wall of the dam is compacted for stabilization, the embankment is planted with Kikuyu grass (Pennisetum clandestinum) to prevent erosion, and a fence is built around the dam to stop livestock from entering. Typically, the dam is 50-100 m (length) by 4-8 m (depth) in size, holds a capacity of 50,000 to 100,000 m³, and has a spillway for excess water. The collected water is used for livestock, domestic consumption and irrigation.
The local community is involved in the planning and construction process, and is supported technically and financially by a government agency for the planning, construction and management of the dam. The maintenance of the dam, e.g. (re-)planting of grass on the dam, is conducted by the community, as well as soil and water conservation management of the catchment area. High labour input and well trained technical advisors are required for the construction of the dam, followed by low to medium maintenance requirements.
Figure 6: Construction of a small earth dam in Zambia with communal action.3
Due to these dams and the increased water availability, the small-scale farmers obtain an increased crop yield and animal production, resulting in improved income and food security. In addition, the shallow aquifer can be recharged, and the impact of extreme flooding events can be reduced. The communities are strengthened in their institutional capacities through communal action in planning, construction and maintenance.[7]
For further information see: FAO/Liniger, H., Studer, R. M., Hauert, C. & Gurtner, M. (2011): Sustainable Land Management in practice. Prepared by WOCAT. A TerrAfrica Partnership Publication. http://www.fao.org/docrep/014/i1861e/i1861e00.htm [Access 2012-11-10]
References
- ↑ Prinz, D., (1996). Water Harvesting: Past and Future. In: Pereira, L. S. (ed.), Sustainability of Irrigated Agriculture. Proceedings, NATO Advanced Research Workshop, Vimeiro, 21- 26.03.1994, Balkema, Rotterdam.
- ↑ Prinz, D., (1996). Water Harvesting: Past and Future. In: Pereira, L. S. (ed.), Sustainability of Irrigated Agriculture. Proceedings, NATO Advanced Research Workshop, Vimeiro, 21- 26.03.1994, Balkema, Rotterdam.
- ↑ UNEP (2009): Rainwater harvesting: a lifeline for human well-being http://www.unep.org/publications/search/pub_details_s.asp?ID=4024 [Access 2012-11-18]
- ↑ UNEP (2009): Rainwater harvesting: a lifeline for human well-being http://www.unep.org/publications/search/pub_details_s.asp?ID=4024 [Access 2012-11-18]
- ↑ World Bank (2008): Investment in Agricultural Water for Poverty Reduction and Economic Growth in Sub-Saharan Africa, Washington, DC. http://www.fanrpan.org/documents/d00508/ [Access 2012-10-08]
- ↑ GIZ (2011a): Bringing the UNCCD down to earth. Bonn. http://www.desertifikation.de/fileadmin/user_upload/downloads/2011/giz2011-en-Lessons-learned-Bringing-the-UNCCD-down-to-earth.pdf [Access 2012-10-08].
- ↑ FAO/Liniger, H., Studer, R. M., Hauert, C. & Gurtner, M. (2011): Sustainable Land Management in practice. Prepared by WOCAT. A TerrAfrica Partnership Publication. http://www.fao.org/docrep/014/i1861e/i1861e00.htm [Access 2012-11-10]
1 AfDB (2012): African Water Facility Grant Helps Kenyan Pastoralists Build Resilience to Droughts, Climate Change. Press release 09/08/2012. http://www.afdb.org/en/news-and-events/article/african-water-facility-grant-helps-kenyan-pastoralists-build-resilience-to-droughts-climate-change-9597/ [Access 2012-10-08]
2 FAO/Critchley, W., Siegert, K. & Chapman, C. (1991): Water Harvesting. http://www.fao.org/docrep/U3160E/u3160e00.htm#Contents [Access 2012-10-08]
3 FAO/Liniger, H., Studer, R. M., Hauert, C. & Gurtner, M. (2011): Sustainable Land Management in practice. Prepared by WOCAT. A TerrAfrica Partnership Publication. http://www.fao.org/docrep/014/i1861e/i1861e00.htm [Access 2012-11-10]
4 GIZ (2006): Zanjas de infiltración, La Paz, Boliva. http://proagro-bolivia.org/files/CARTILLA_4_ZANJAS_inflitracion.pdf [Access 2012-10-08]
5 GIZ/Goetter, J. (2010a): Adaptación al Cambio Climático: Cosecha de Agua de Lluvia con “Atajados” en Bolivia, Lima, Peru. http://www.riesgoycambioclimatico.org/documentos/ACC_con_CA.pdf [Access 2012-10-08]
6 GIZ/Goetter, J. (2010b): El Cambio Climático en el areá rural del Sur de Cochabamba y Norte de Potosí (Bolivia); La Paz, Bolivia. http://www.riesgoycambioclimatico.org/biblioteca/archivos/DC1115.pdf [Access 2012-10-08]
7 GIZ/Goetter, J. (2010c): Water harvesting: A promising climate change adaptation option for traditional Andean agriculture in Bolivia, -in: Rural Development News 2/2010. http://www.agridea-international.ch/fileadmin/10_International/PDF/RDN/RDN_2010/9_Water_harvesting.pdf [Access 2012-10-08]
8 GIZ (2011a): Bringing the UNCCD down to earth. Bonn. http://www.desertifikation.de/fileadmin/user_upload/downloads/2011/giz2011-en-Lessons-learned-Bringing-the-UNCCD-down-to-earth.pdf [Access 2012-10-08].
9 GIZ (2012a): Good Practices in Soil and Water Conservation, Eschborn. http://www.giz.de/Themen/en/SID-F89EB9ED-AC839C2B/36546.htm [Access 2012-10-08]
10 ICARDA/Oweis, T., Prinz, D. & Hachum, A. (2001): Water Harvesting Indigenous Knowledge for the Future of the Drier Environments, ICARDA, Aleppo, Syria. http://temp.icarda.org/wli/pdfs/Books/Water_harvest_En.pdf [Access 2012-11-18]
11 Prinz, D., (1996). Water Harvesting: Past and Future. In: Pereira, L. S. (ed.), Sustainability of Irrigated Agriculture. Proceedings, NATO Advanced Research Workshop, Vimeiro, 21- 26.03.1994, Balkema, Rotterdam.
12 UNEP (2009): Rainwater harvesting: a lifeline for human well-being http://www.unep.org/publications/search/pub_details_s.asp?ID=4024 [Access 2012-11-18]
13 World Bank (2008): Investment in Agricultural Water for Poverty Reduction and Economic Growth in Sub-Saharan Africa, Washington, DC. http://www.fanrpan.org/documents/d00508/ [Access 2012-10-08]
Additional Literature
Agarwal, A. & Narain, S. (2005): Dying wisdom: Rise, fall and potential of India’s traditional water harvesting systems 4th edition. Eds., State of Indias Environment, a citizens’ report 4, Centre for Science and Environment. New Delhi.
Hasse, R. (1989): Rainwater reservoirs above ground structure for roof catchment. Deutsches Zentrum für Entwicklungstechnologien-GATE. In: Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH. http://www.itacanet.org/doc-archive-eng/water/Rainwater_reservoirs_GTZ.pdf [Access 2012-11-18].
ICARDA/ Theib, O., Prinz, D. & Hachum, A. (2012): Rainwater harvesting for Agriculture in the Dry Areas. International Center for Agricultural Research in the Dry Areas. CRC Press, The Netherlands.
Malesu, M, Oduor, A.R., Odhiambo, O.J. eds. (2008): Green water management handbook: rainwater harvesting for agricultural production and ecological sustainability Nairobi, Kenya. World Agroforestry Centre ICRAF.
PASP (2003): Référentiel des mesures techniques de récupération, de protection et d’exploitation durable des terres. Niamey.
PATECORE (2005): Développement et diffusion de techniques de lutte contre la désertification au Sahel. Capitalisation des expériences du PATECORE / PLT, Tomé 1 Approche et méthodologie de la section fertilité des sols. Kongoussi.
Prinz, D. (2002): The role of water harvesting in alleviating water scarcity in arid areas. In: Water resources development and management. Proceedings. International Conference on Water Resources Management in Arid Regions, WaRMAR. Kuwait. Ed.: Al-Rashed. Vol. 3. Rotterdam. S. 107-122. http://www.ipcp.org.br/References/Agua/aguaCapta/WaterHarvesting.pdf [Access 2012-10-08]
The World Bank (1988): Sub-Saharan Africa Water Harvesting Study.
ZEF/Nasr, M. (1999): Assessing Desertification and Water Harvesting in the Middle East and North Africa: Policy Implications: ZEF Discussion Papers on Development Policy Number. Bonn http://www.zef.de/fileadmin/webfiles/downloads/zef_dp/zef_dp10-99.pdf [Access 2012-10-08]
