An integrated modelling framework to aid smallholder farming system management in the Olifants River Basin, South Africa M.S. Magombeyi ⇑ , A.E. Taigbenu School of Civil and Environmental Engineering, Witwatersrand University, Private Bag X3, Wits 2050, South Africa article info Article history: Available online 16 August 2011 Keywords: Crop management practices Family balance Integrated model Smallholder farmer Socio-economic abstract Computerised integrated models from science contribute to better informed and holistic assessments of multifaceted policies and technologies than individual models. This view has led to considerable effort being devoted to developing integrated models to support decision-making under integrated water resources management (IWRM). Nevertheless, an appraisal of previous and ongoing efforts to develop such decision support systems shows considerable deficiencies in attempts to address the hydro-socio- economic effects on livelihoods. To date, no universal standard integration method or framework is in use. For the existing integrated models, their application failures have pointed to the lack of stakeholder participation. In an endeavour to close this gap, development and application of a seasonal time-step integrated model with prediction capability is presented in this paper. This model couples existing hydrology, agronomy and socio-economic models with feedbacks to link livelihoods of resource-con- strained smallholder farmers to water resources at catchment level in the semi-arid Olifants subbasin in South Africa. These three models, prior to coupling, were calibrated and validated using observed data and participation of local stakeholders. All the models gave good representation of the study conditions, as indicated by the statistical indicators. The integrated model is of general applicability, hence can be extended to other catchments. The impacts of untied ridges, planting basins and supplemental irrigation were compared to conventional rainfed tillage under maize crop production and for different farm typol- ogies. Over the 20 years of simulation, the predicted benefit of untied ridges and planting basins versus conventional rainfed tillage on surface runoff (Mm 3 /year) reduction was 14.3% and 19.8%, respectively, and about 41–46% sediment yield (t/year) reduction in the catchment. Under supplemental irrigation, maize yield improved by up to 500% from the long-term average yield of 0.5 t/ha. At 90% confidence inter- val, family savings improved from between US$ 4 and US$ 270 under conventional rainfed to between US$ 233 and US$ 1140 under supplemental irrigation. These results highlight the economic and environ- mental benefits that could be achieved by adopting these improved crop management practices. How- ever, the application of various crop management practices is site-specific and depends on both physical and socio-economic characteristics of the farmers. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Agricultural development in the Olifants subbasin of the Limp- opo River Basin, South Africa is severely constrained by low and er- ratic rainfall, high temperature, decreasing soil fertility and limited farmer access to increased productivity options. Availability of new and technically feasible farm production systems, supported by appropriate policies, is generally considered to enhance food secu- rity, especially in smallholder rainfed agriculture. However, local farmers, water management institutions including agricultural institutions have been slow in building both technical and policy related capacity to adapt to new crop management practices under both climate and market variability. Climate change, likely to increase the occurrence and intensity of water-related natural disasters (IPCC, 2001, 2007), compounded by political and socio- economic changes, has called to question the viability of traditional decision-making norms that are typically guided by experience and rules of thumb in achieving sustainable rural livelihoods. In the design and selection of decisions related to effective agri- cultural policy and technological interventions over a range of practices from rainfed, field conservation to full irrigation (CAWMA, 2007), integrated systems modelling has proved to be a useful tool (RNAAS, 2005; Loevinsohn et al., 2002; Parker et al., 2002; Sibbald et al., 2000). In addition, a comprehensive approach to coordinated policy-making continues to be recognised interna- tionally through major UN Conferences (Abaza and Hamwey, 2001). It is on this basis that a study was carried out to develop an integrated model, ICHSEA (innovative coupling of hydrological 1474-7065/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2011.07.079 ⇑ Corresponding author. Tel.: +27 117177155; fax: +27 117177042. E-mail address: manumagomb@yahoo.com (M.S. Magombeyi). Physics and Chemistry of the Earth 36 (2011) 1012–1024 Contents lists available at SciVerse ScienceDirect Physics and Chemistry of the Earth journal homepage: www.elsevier.com/locate/pce