Effects of Rainfall Variability and Household Resource Endowment on Rooftop Rainwater Harvesting in Kathiani Sub-County, Machakos County, Kenya
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The global demand for fresh water exceeds supply leading to scarcity, especially in sub-Saharan African countries such as Kenya, the latter with 647 m3 of water per capita per annum against the recommended level of 1000 m3. Kenya therefore experiences water scarcity that is severe for the households in the semi-arid regions such as Machakos County. Rooftop-Rain-Water-Harvesting (RRWH) can improve domestic water supply but there is limited information on the effects of rainfall variability and household resource endowment hence the need for this study. The specific objectives of the study were (i) to establish the demographic attributes of households involved in RRWH; (ii) to evaluate the influence of rainfall variability on the feasibility of RRWH; and (iii) to assess the influence of household resource endowment on RRWH collection, delivery, storage and quality. To establish the household demographic attributes and status of RRWH, a sample of 92 households was selected using random sampling from a list of 1385 households. Questionnaires were therefore administered to the sampled households. To assess harvested water quality, rainwater samples were collected from a sub-sample of 27 households and data on attributes such as pH, temperature and turbidity collected. Long-term rainfall data (1980-2008) to assess effects of rainfall variability was obtained from the National Meteorological Station at Katumani. The collected data was processed and analyzed quantitatively and qualitatively using Statistical Package for Social Science Version 20. The study found out that there were three categories of households: rich, medium and poor based on farm size and income. The long-term mean annual rainfall for the area was 700 mm and in 16 out of the 28 years, the average annual rainfall was above the long-term average annual rainfall giving an estimated rainfall reliability of 55%. The rainfall pattern was bimodal with early rains experienced in March-April-May (MAM) and latter rains in October-November-December (OND). The seasonal rainfall was consistent with a regression coefficient of 0.996 and 0.997 for MAM and OND seasons respectively. The monthly standardized precipitation indices varied between 1.79 and -4.32 and the long-term rainfall pattern was moderately wet to extremely dry. Thirty-nine drought events were experienced between 1980-2008, with the magnitudes varying from -1.02 to -6.42, and lasting from one to ten months. At least 90% of the households studied harvested and stored water from their rooftops. The households in the rich and medium categories had houses with corrugated iron sheet roofs whereas 6% of the poor households had grass-thatched roofs. Only 6% of the poor households had gutters covering the whole roof area of their houses compared with 100% of the rich and 97% medium households. Poor households lacked resources to establish adequate water storage structures as opposed to the medium and rich households. The rainwater in the poor households did not meet the recommended standards for drinking water turbidity. The rainfall pattern in the study area had 55% reliability and high levels of consistency, making RWH feasible. In addition, the increased intensity and duration of drought events in the area made RRWH a viable option for increased domestic water supply. The households were heterogeneous and the RRWH collection, delivery and storage practices were dependent on the resource endowment. The study recommended that RRWH interventions and innovations should be matched to specific household resource endowment. Further studies on RRWH should focus on estimating the total roof-catchment area, assess impact of climate change on RRWH and establish corresponding adaptation strategies for the different categories of households.