Chiang Mai Journal of Science

     Land use change is a crucial issue when considering global dynamics and their interactions with the hydrologic properties of the soil and water management in catchment areas. Between 2017 to 2018, research was conducted on the effects of land use changes on water quality and flooding in the upper Nan River Basin. In Nan Province, land use is distributed as follows: natural forest protection covers 61.77 percent, agricultural purposes account for 35.23 percent, residential areas constitute 1.95 percent, and water usage represents 0.7 percent. The results indicate that the expansion of urban and agricultural regions has impacted the water quality of the river basin. A significant positive correlation was observed between agricultural land use and total phosphate content, while a strong negative correlation was found between forest land and total phosphate content. Residential occupancy and water quality demonstrated a strong correlation with total coliform contents. There were significant differences in water quality between the wet and dry seasons, particularly temperature, turbidity, total solids, total dissolved solids, and conductivity. Moreover, increases in annual and seasonal stream flow amounts were noted in relation to water levels and residential and construction projects.