Conjoining Rainfall and Irrigation Seasonality to Enhance Productivity of Water in Large Rice Irrigated Farms in the Upper Ruaha River Basin, Tanzania.
Improving productivity of water in agriculture (more crop per drop) has been identified as an urgent global priority. However, there is lack of knowledge to inform the necessary strategies and actions for achieving this goal. A study was conducted to assess water utilization and productivity in one of the largest rice irrigation schemes in the Upper Ruaha River Basin. The water balance approach was applied to determine the components of water use and rice yield. Rainfall analysis was done for trends and variability in relation to the on-set, cessation and their likely contribution during the rice-growing season using data of ten years from the meteorological station in the study area. The gross water use was 2300mm per ha, of which 28% was used for wetting up the fields during land preparation. With an average effective rainfall of 500mm, irrigation requirement was estimated to be 1800mm and productivity of irrigation water was less than 0.3kg/m3. The findings from this study show that productivity of water can be improved relatively easily up to nine percent from the current levels if the transplanting season coincides with rainfall between the last decads of December and January, the period with sufficient and uniformly distributed rainfall. This conjunctive use of water leads to shorter season lengths and savings of water that can then be considered for allocation to other intra or intersectoral uses.
WaterNET/WARFSA Symposium Proceedings, 15-17 October 2003, Gaborone, Botswana, Paper 87: pp 97-101