Rainfall data is part of the main components in the hydrological cycle and firmly associated with almost all aspect of climate. Previous research indicated that Macro rainwater harvesting techniques (RWH) can be implemented successfully in Sinjar area northwest Iraq. Recently, prediction of rainfall trends in the Middle East and Iraq in particular suggest a decrease in rainfall due to climate change. This raises the question about the future validity of RWH in the area. In this research, the validity of RWH was investigated using predicted rainfall data in Sinjar area. Eight seasons were selected representing different decades that start 2020 to 2099. The results showed that the maximum, minimum and average harvested future runoff volumes reached about 28.5, 7.61, and 13.9 million cubic meters, that may occurred during the seasons 2055-2056, 2046-2047, and 2065-2066 respectively. The resultant harvested runoff volumes produced by four selected basins at Eastern Sinjar as a catchment area with total area of 435.15 km2.In the second part, an attempt had been made to provide the study area by a set of charts that can help in estimating daily runoff under dry, wet and normal conditions for rainfall depths that ranged between 15 to 55 mm.