TRODUCTIONThe Ibague watershed is situated in mid-western Colombia approximately 130 km west of the capital, Bogota.Maps for elevation, rain-gauge stations, headworks, and land use are shown in Figs. 1 and2.The Ibague watershed has an area of 1439 km 2 and its highest and lowest altitudes are 4955 m and 243 m, respectively.The monthly maximum and minimum temperatures in the central watershed are 27°C -29°C and 18°C -19°C, respectively.These values are stable throughout the year.The annual rainfall fluctuates significantly throughout the watershed, with an average of approximately 1700 mm.The area has a dry season and a wet season.The dry season is from January to April and from July to August.The wet season is from May to July and from September to November.An alluvial fan spreads out at the center of the watershed with a length of about 25 km and a ground surface gradient of 2°-3°.Rainfall runoff flows into the Magdalena River, which flows along the eastern edge of the watershed.The western part of the watershed is a mountainous area and has no rain-gauge stations.The primary land use in the central and eastern parts of the watershed is agriculture, predominantly rice and coffee, which are cultivated in the plain situated between the central and eastern parts of the watershed.A distributed long-term rainfall-runoff model was developed to quantify the watershed scale impacts of water-saving measures in the Ibague watershed, Colombia.The water-saving effects were evaluated by scenario analyses that incorporated the introduction of a water-saving irrigation method (early stopping) to improve irrigation efficiency with respect to redundant paddy irrigation water.In addition to water stopping, the impacts of a new water-saving rice genotype are analyzed.To calculate rainfall-runoff, the Sugawara tank model was utilized.The tank model quantified runoff discharges from forest, upland, paddy field, and urban areas by incorporating each land type into every mesh for a distributed rainfall-runoff model.This quantified the rainfall-runoff characteristics for each land use.Agricultural ponds and irrigation canals were allocated to each corresponding mesh to model irrigation management practices in the watershed.Agricultural ponds, which have a significant effect on the water balance at the watershed scale, were detected by performing cluster analysis on the seasonal transition of the backscatter coefficient obtained from multi-temporal Sentinel-1 SAR images.Quantitative analyses of the impacts of water-conservation under various scenarios indicated that the early-stopping irrigation method reduced water consumption by 9.4%, compared to the conventional methods.The scenarios, which assumed the introduction of a new water-saving rice genotype, assumed regular irrigation intervals of one or two days and indicated 24.1% and 48.2% reductions, for water consumption, respectively, compared to conventional irrigation methods.Scenarios that implemented a new water-saving rice genotype, as well as the early-stopping irrigation method showed reductions of 30.7% and 53.2% in water consumption compared to the conventional irrigation method, for the one and two day irrigation periods respectively.