Climate Change and rain water harvesting
Water is the primary medium through which the effects of Climate Change are felt
In the face of Climate Change the United Nations World Water Development Report of 2015 suggests that population growth, pollution and Climate Change are likely to produce a drastic decline in the amount of water available in many parts of the world.
By Felicity Nyamakupe
Water is the primary medium through which the effects of Climate Change are felt.
The variations in water availability from water sources like lakes, rivers and dams has led to water stress (Worm, 2006).
Rain water harvesting can serve as a solution to the water crisis.
Harvesting rain water is a technology used to collect, convey and store water for future use from relatively clean surfaces such as roofs, land or rock catchments. (Khoury-Nolde, 2016).
Rain water can be harvested into big containers directly from the sky.
It is done to provide water for drinking, sanitation and agricultural purposes (Lasage et al., 2015).
Rain water harvesting is a practice that is very simple and can provide tremendous environmental, social and economic benefits.
The practice of collecting rain water can be classified into two broad categories which are Land-based and roof-based.
Land-based rain water harvesting
Occurs when run off from land surfaces is collected in furrow dikes, ponds, tanks and reservoirs.
Macro-catchment rainwater harvesting system involves the harvesting of runoff water from a larger non cultivated catchment area to a smaller cultivated area.
The runoff that is directly conveyed to the cropping area and stored in the soil profile for uptake by the crops (Recha et al., 2015). Examples include bunds and contour ridges.
In-situ rainwater harvesting is a technique of keeping rainwater in the field by increasing filtration, runoff and evaporation.
This improves soil moisture directly in the crop rooting zone by trapping and holding the rain where it falls (Gebreegziabher et al., 2009).
They are referred to as soil and water conservation techniques such as mulching, conservation tillage and furrowing.
Roof-based rain water harvesting
This is the collection of rain water runoff from roof surfaces which usually provides a much cleaner source of water that can be also used for drinking (Khoury-Nolde, 2016).
For the Domestic Rain Water Harvesting System (DRWHS) the water is harvested from the roof top gutters.
The roofs provide an ideal catchment surface for harvesting rain water provided they are clean.
The roof tops consist of different materiel that include galvanized corrugated iron sheets, corrugated plastic and tiles that all make good roof catchment surfaces.
Advantages of Rain Water Harvesting
The merits of rain water harvesting are that the structures are simple to construct.
It is not affected by local geology or topography and has low environmental impact and is easy to maintain especially at house level (Worm, 2006).
Rain water harvesting has a potential of addressing spatial and temporal water scarcity for domestic, crop production, livestock development, environmental management and overall water resources management (Ngigi, 2003).
Rain water harvesting saves high-quality drinking water sources and relieves the pressure on sewers and the environment by mitigating floods, soil erosion and replenishing groundwater levels (Khoury-Nolde, 2016).
It plays an important role in increasing water security for individuals and government (Christian Amos et al., 2016).
The harvested water can be collected on the surface or subsurface and this is the biggest capital investment.
A tank is referred to as an above storage reservoir and a cistern as a below ground storage reservoir.
The material used for surface tanks include metal, wood, plastic, fibreglass, bricks, soil, ferro cement and reinforced concrete (Worm, 2006).
The choice of material depends on availability and affordability. Surface tanks are more expensive and durable than sub-surface tanks.
The sub-surface reservoirs include the round and square cisterns.
Rain water might be polluted by bacteria and hazardous chemicals requiring treatment before usage (Helmreich et al., 2009).
The treatment of stored water makes sense when it is done properly.
The methods of treatment include sand filtering, chlorination, boiling and exposure to the sunlight.
The different roof types lead to the pollution of water in some cases such as zinc concentrations higher in galvanised iron roof catchments, while pH, conductivity and turbidity levels are higher in concrete tile roof catchments (Thomas et al., 1993).
The maintenance of the rain water harvesting system is very important because this will lead to the efficiency of the system.
Maintenance is generally limited to the annual cleaning of the tank, regular inspection, cleaning of gutters and down-pipes.
Maintenance typically consists of the removal of dirt, leaves and other accumulated material (Khoury-Nolde, 2016).
Cleaning should take place before the start of the rain season and regularly as the season progresses. Cracks create major problems and should be repaired immediately.
In conclusion, rain water harvesting is one of the most promising alternatives for the supply of water as a result of the increased water scarcity and demand caused by Climate Change.
It presents an opportunity for the augmentation of water supplies. Its adoption is greatly encouraged.
However a feasibility assessment should be done before the technology is introduced to ensure its suitability to the intended users and its successful adoption.
The feasibility assessment should take into consideration local circumstances such as climatic conditions, water demand, socio- economic conditions, environmental factors and availability of alternative water sources.
- Christian Amos, C., Rahman, A., & Mwangi Gathenya, J. (2016). Economic analysis and feasibility of rainwater harvesting systems in urban and peri-urban environments: A review of the global situation with a special focus on Australia and Kenya. Water, 8(4), 149.
- Gebreegziabher, T., Nyssen, J., Govaerts, B., Getnet, F., Behailu, M., Haile, M., & Deckers, J. (2009). Contour furrows for in situ soil and water conservation, Tigray, Northern Ethiopia. Soil and tillage research, 103(2), 257-264.
- Helmreich, B., & Horn, H. (2009). Opportunities in rainwater harvesting. Desalination, 248(1-3), 118-124.
- Khoury-Nolde, N. (2016). Rainwater harvesting. Zero M. Germany.
- Lasage, R., & Verburg, P. H. (2015). Evaluation of small scale water harvesting techniques for semi-arid environments. Journal of Arid Environments, 118, 48-57.
- Ngigi, S. N. (2003). What is the limit of up-scaling rainwater harvesting in a river basin? Physics and Chemistry of the Earth, parts A/B/C, 28(20-27), 943-956.
- Programme, U. N. W. W. A. (2015). The United Nations World Water Development Report 2015: Water for a Sustainable World: UNESCO Paris.
- Recha, C., Mukopi, M., & Otieno, J. (2015). Socio‐economic determinants of adoption of rainwater harvesting and conservation techniques in semi‐arid Tharaka sub‐county, Kenya. Land Degradation & Development, 26(7), 765-773.
- Thomas, P., & Greene, G. (1993). Rainwater quality from different roof catchments. Water science and technology, 28(3-5), 291-299.
- Worm, J. (2006). AD43E Rainwater harvesting for domestic use: Agromisa Foundation.
Further editing by Tapiwa Makosa