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Rainwater harvesting to irrigate small-scale gardens enhances food self-sufficiency to overcome rural poverty. So far rainwater harvesting is not encouraged by the Namibian National Water Supply and Sanitation Policy nor supported financially by the Namibian government. This study proposes two rainwater harvesting facilities to irrigate gardens; one collects rain from household roofs with tank storage, the second collects rain on a pond roof with pond storage. The aim of this paper is to assess the benefits of rainwater harvesting-based gardening and to propose policy and financing implications for the Namibian government. We investigate the benefits of rainwater harvesting through a literature review, a cost-benefit analysis, monitoring of project pilot plants and a comparison with the existing irrigation and drinking water infrastructure. The results indicate that rainwater harvesting offers numerous benefits in technological, economic, environmental and social terms. The facilities have a positive net present value under favourable circumstances. However, material investment costs pose a financing problem. We recommend that government fund the rainwater harvesting infrastructure and finance privately garden and operation and maintenance costs. Integrating these aspects into a national rainwater harvesting policy would create the conditions to achieve the benefits of an up-scale of rainwater harvesting based gardening in Namibia.

Abstract:The design of rainwater harvesting based gardens requires considering current climate but also climate change during the lifespan of the facility. The goal of this study is to present an approach for designing garden variants that can be safely supplied with harvested rainwater, taking into account climate change and adaptation measures. In addition, the study presents a methodology to quantify the effects of climate change on rainwater harvesting based gardening. Results of the study may not be accurate due to the assumptions made for climate projections and may need to be further refined. We used a tank flow model and an irrigation water model. Then we established three simple climate scenarios and analyzed the impact of climate change on harvested rain and horticulture production for a semi-arid region in northern Namibia. In the two climate scenarios with decreased precipitation and medium/high temperature increase; adaptation measures are required to avoid substantial decreases in horticulture production. The study found that the most promising adaptation measures to sustain yields and revenues are a more water efficient garden variant and an enlargement of the roof size. The proposed measures can partly or completely compensate the negative impacts of climate change.

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While there has been significant progress regarding the research mode ''transdisciplinary research'' (TDR) on a theoretical level, case studies describing specific TDR processes and the applied methods are rare. The aim of this paper is to describe how the first phase (Phase A) of a TDR project can be carried out in practice and to evaluate its accomplishments and effectiveness. We describe and evaluate Phase A of a TDR project that is concerned with tipping points of riparian forests in Central Asia. We used a TDR framework with objectives for Phase A and selected a sequence of methods for transdisciplinary knowledge integration. Semi-structured expert interviews for eliciting problem perceptions prepared for two transdisciplinary workshops, in which perception graphs, interest-influence diagrams and stakeholder network analyses were applied in addition to discussions in the plenary and in break-out groups. Scientists and stakeholders achieved to jointly frame the real-world problem, formulate research objectives, design a framework for knowledge integration, build a TDR team and decide on specific research activities for the main project phase. TDR context, process and products were judged by workshop participants positively, with average ratings above 3 on a scale from 0 (worst) to 4 (best). Strengths of our particular TDR approach during Phase A were the direct contact (interviews and two workshops) with potential TDR participants and the ability to allocate sufficient time and money to Phase A due to the funded project pre-phase of 1 year. TDR in countries foreign to the scientists, as in our study, is hampered by language barriers as well as by a lack of familiarity with local conditions, in particular regarding stakeholder interrelations that cannot be simply overcome by a stakeholder analysis. We believe that the presented approach for setting up a TDR project can serve as a good basis for the design of other projects.