The Hieu River Basin in Vietnam experienced changes in rainfall and water flow over the years. By analyzing data from 1962 to 2014, researchers found that rainfall patterns shifted in 1982, while water discharge patterns changed in the late 1970s and late 1990s. Using a hydrological model, they discovered that a two-tank model with monthly data best represented the river's runoff. The comparison of observed and calculated runoff showed a significant decrease from 1999 to 2014, with lower basin discharge decreasing six times faster than the upper basin, likely due to reservoir construction and increased water usage for farming and homes.