Exploring the Water Quantity-Quality Nexus under Climate and Landuse Change

Water quantity and quality are both critical to water security; however, they have been commonly considered as separate problems. There are clear connections between quantity and quality, e.g., the dilution effect of pollutants due to increased discharge, the rising pollutant flux during storm events, etc. Exploring the relationships between quantity and quality is not trivial due to the internal variability and complexity of each variable. Climate and change of landuse add to the complexity by increasing the frequency of extreme flow events, the addition of non-point source contaminants, and the interference of human activities. In this presentation, we combine a modeling approach and a statistical approach to examine the long-term variability of water quality by considering the uncertainties induced by daily and seasonal streamflow variation, sampling frequency, landuse, and climate change factors. Two sites were selected to represent different situations, a high-mountain Himalayan watershed in Nepal, and an agricultural watershed located in Indiana. Nitrate, Phosphorus, BOD, and DO are selected as representative water quality parameters of analysis. Our modeling and statistical results indicate the significance of major sources of the contaminants, the effects of discharge variability to water quality change, as well as the flow-normalized long-term trend of water quality.