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\hypersetup{pdftitle={Potential Impacts of Water Harvesting and Ecological Sanitation on Crop Yield, Evaporation and River Flow Regimes in the Thukela River Basin, South Africa},pdfauthor={Jafet Andersson, Hong Yang, Alexander J.B. Zehnder, Johan Rockström},pdfsubject={Tropentag 2010: Abstract},pdfkeywords={Evapotranspiration, natural flow regime, sub-Saharan Africa, water system innovation},pdfpagemode=None,colorlinks=true}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 14-16, 2010, Zurich}}\\[1ex] \Large{``World Food System  ---\\A Contribution from Europe''\\[2ex]}}
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\Large{\textbf{Potential Impacts of Water Harvesting and Ecological Sanitation on Crop Yield, Evaporation and River Flow Regimes in the Thukela River Basin, South Africa\footnote{\textbf{Contact Address:} Jafet Andersson, Eawag,  Swiss Federal Institute of Aquatic Science and Technology, 8600~Dübendorf, Switzerland, \mbox{e-mail}: \email{jafet.andersson@eawag.ch}}\\[0.8ex]}}
\normalsize{\textsc{Jafet Andersson$^{1}$, Hong Yang$^{1}$, Alexander J.B. Zehnder$^{2}$, Johan Rockström$^{3}$}}
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\begin{itemize*}
\item[]{\small{\textit{$^{1}$Eawag,  Swiss Federal Institute of Aquatic Science and Technology, Switzerland}}}
\item[]{\small{\textit{$^{2}$Alberta Water Research Institute (AWRI), Canada}}}
\item[]{\small{\textit{$^{3}$Stockholm Environment Institute (SEI), Sweden}}}
\end{itemize*}
\index[author]{Andersson, Jafet}
\index[author]{Yang, Hong}
\index[author]{Zehnder, Alexander J.B.}
\index[author]{Rockström, Johan}
\begin{center}
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\textbf{Abstract}
\begin{abstract}
\normalsize{
Water harvesting and ecological sanitation are two widely promoted strategies to enhance food security through increased crop yield and crop water productivity in smallholder rain"=fed agriculture. Field"=scale studies are numerous but river basin"=scale research is lacking. In this research we estimate the potential basin"=scale impacts of \textit{in~situ} water harvesting and conservation technologies (in situ WH), and fertilisation with stored human urine (Ecosan). Our case study is the Thukela river basin (29 000 km$^{2}$) in South Africa.







The agro"=hydrological model SWAT (Soil and Water Assessment Tool) was used to simulate potential effects on smallholder maize yields (the dominant crop type), river flow regimes, plant transpiration, and soil and canopy evaporation. Smallholder management was adjusted to represent a set of water and fertility management approaches in smallholder agriculture.







On the basin scale, our results suggest potential maize yield impacts are likely to be small with \textit{in~situ} WH, but significant with Ecosan. High nitrogen stress on maize yields, and low or untimed soil moisture enhancement with \textit{in~situ} WH were the primary causes. Impacts varied significantly in time and space. The variability mapping can be used to target policies toward areas of highest potential impact. Soil fertility improvements primarily raised yield levels, whereas soil moisture enhancements reduced spatial yield variability. Both increased the temporal yield stability. Yield enhancements also improved the productivity of the green water flux by significantly increasing transpiration and reducing soil and canopy evaporation. River flow regimes are not likely to be significantly impacted by \textit{in~situ} WH. The likely effect on aquatic ecosystems and reservoir management is therefore small. However, significant changes did occur occasionally: higher risk of flooding in some areas but also enhanced low flows, which could increase habitat availability for fish and other aquatic organisms.



}

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\noindent \textbf{Keywords:} Evapotranspiration, natural flow regime, sub-Saharan Africa, water system innovation
\index[key]{Evapotranspiration}
\index[key]{Natural!flow regime}
\index[key]{Sub-Saharan Africa}
\index[key]{Water!system innovation}
\end{document}