 |
| Titel |
Water availability, demand and reliability of in situ water harvesting in smallholder rain-fed agriculture in the Thukela River Basin, South Africa |
| VerfasserIn |
J. C. M. Andersson, A. J. B. Zehnder, G. P. W. Jewitt, H. Yang |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1027-5606
|
| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 13, no. 12 ; Nr. 13, no. 12 (2009-12-09), S.2329-2347 |
| Datensatznummer |
250012068
|
| Publikation (Nr.) |
 copernicus.org/hess-13-2329-2009.pdf |
|
|
|
|
|
| Zusammenfassung |
Water productivity in smallholder rain-fed agriculture is of key interest
for improved food and livelihood security. A frequently advocated approach
to enhance water productivity is to adopt water harvesting and conservation
technologies (WH). This study estimates water availability for potential in situ
WH, and supplemental water demand (SWD) in smallholder agriculture in South
Africa's Thukela River Basin (29 000 km2, mean annual precipitation
550–2000 mm yr−1). The study includes process dynamics governing
runoff generation and crop water demands, quantification of prediction
uncertainty, and an analysis of the reliability of in situ WH.
The agro-hydrological model SWAT (Soil and Water Assessment Tool) was
calibrated and evaluated with the Sequential Uncertainty Fitting algorithm
against observed discharge (at ten stations) and maize yield (the dominant
crop type) for the period 1997–2006. The water availability was based on
the generated surface runoff in smallholder areas. The SWD was derived from
a scenario where crop water deficits were met from an unlimited external
water source. The reliability was calculated as the percentage of years in
which water availability ≥SWD. This reflects the risks of failure
induced by the temporal variability in the water availability and the SWD.
The calibration reduced the predictive uncertainty and resulted in a
satisfactory model performance. For smallholder maize yield, the Root Mean
Squared Error was 0.02 t ha−1 during both the calibration and the
evaluation periods. The width of the uncertainty band was reduced by
23% due to the calibration. For discharge during the calibration
(evaluation) period, the ten-station range in the weighted coefficient of
determination (Φ) was 0.16–0.85 (0.18–0.73), and in the coefficient
of determination (R2) 0.42–0.83 (0.28–0.72). The calibration reduced
the width of the uncertainty band by 25% on average.
The results show that the smallholder crop water productivity is currently
low in the basin (spatiotemporal median: 0.08–0.22 kg m−3, 95%
prediction uncertainty band (95PPU)). Water is available for in situ WH
(spatiotemporal median: 0–17 mm year−1, 95PPU) which may aid in
enhancing the crop water productivity by meeting some of the SWD
(spatiotemporal median: 0–113 mm year−1, 95PPU). However, the
reliability of in situ WH is highly location specific and overall rather
low. Of the 1850 km2 of smallholder lands, 20–28% display a
reliability ≥25%, 13–16% a reliability ≥50%, and
4–5% a reliability ≥75% (95PPU). This suggests that the risk of
failure of in situ WH is relatively high in many areas of the basin. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|