A watershed approach to upgrade rainfed agriculture in water scarce regions through Water System Innovations: an integrated research initiative on water for food and rural livelihoods in balance with ecosystem functions J. Rockstro ¨m a,b, * , C. Folke b , L. Gordon b , N. Hatibu c , G. Jewitt d , F. Penning de Vries e , F. Rwehumbiza c , H. Sally e , H. Savenije f , R. Schulze d a WaterNet, University of Zimbabwe, P.O. Box MP 600, Mount Pleasant, Harare, Zimbabwe b Department of Systems Ecology, Stockholm University, Sweden c Soil and Water Research Management Group, Sokoine University of Agriculture, Tanzania d School of Bioresource Engineering and Environmental Hydrology, University of Natal, South Africa e IWMI, Pretoria, South Africa f Unesco-IHE, Delft, The Netherlands Abstract The challenge of producing food for a rapidly increasing population in semi-arid agro-ecosystems in Southern Africa is daunting. More food necessarily means more consumptive use of so-called green water flow (vapour flow sustaining crop growth). Every increase in food production upstream in a watershed will impact on water user and using systems downstream. Intensifying agriculture has in the past often been carried out with negative side effects in terms of land and water degradation. Water legislation is increasingly incorporating the requirement to safeguard a water reserve to sustain instream ecology. To address the challenges of increasing food production, improving rural livelihoods, while safeguarding critical ecological func- tions, a research programme has recently been launched on ‘‘Smallholder System Innovations in Integrated Watershed Manage- ment’’ (SSI). The programme takes an integrated approach to agricultural water management, analysing the interactions between the adoption and participatory adaptation of water system innovations (such as water harvesting, drip irrigation, conser- vation farming, etc.), increased water use in agriculture and water flows to sustain ecological functions that deliver critical ecosystem services to humans. The research is carried out in the Pangani Basin in Tanzania and the Thukela Basin in South Africa. A nested scale approach is adopted, which will enable the analysis of scale interactions between water management at the farm level, and cascading hydrological impacts at watershed and basin scale. This paper describes the integrated research approach of the SSI programme, and indicates areas of potential to upgrade rainfed agriculture in water scarcity-prone agro-ecosystems while securing water for downstream use. Ó 2004 Published by Elsevier Ltd. Keywords: Rainfed agriculture; Water productivity; Watershed; Catchment hydrology; Semi-arid 1. Introduction The dominant water resources management challenge over the coming generations is how to secure water to cover food demands of a rapidly expanding world 1474-7065/$ - see front matter Ó 2004 Published by Elsevier Ltd. doi:10.1016/j.pce.2004.09.016 * Corresponding author. Tel.: +46 (0) 8 412 1400; fax: +46 (0) 8 723 03 48. E-mail address: johan.rockstrom@sei.se (J. Rockstro ¨m). www.elsevier.com/locate/pce Physics and Chemistry of the Earth 29 (2004) 1109–1118