Examining Water Use Regimes of Suburban Watersheds at Annual and Subannual Timescales

Human water use can place considerable stress on hydrologic systems. Humans directly affect the water cycle through water withdrawals and return flows. Aside from climate change, humans indirectly impact hydrologic systems through dam building, land use change, and urbanization. Given the increasing incidence of water overdraft and water scarcity globally, there is a growing need to understand and quantify these effects so that appropriate water management and policy decisions can be made both in the United States and abroad. Massachusetts, in the northeastern United States, is located in a “water-rich” region, and yet issues of water overdraft and exceptional low flows have been documented throughout the state. This study demonstrates the application of water use regimes for characterizing the water balance in two suburbanized basins in eastern Massachusetts: The Charles River watershed (CRW) and the Ipswich River watershed (IRW). Water use regimes categorize river basins based on the magnitude of human water withdrawals and return flows relative to streamflow. Water use regimes for the upper/middle portions of the CRW and the IRW were examined at annual and subannual timescales for the period 2000–2004, which was the only time during which detailed water use data were available. Although the water use regimes of these watersheds displayed only minor alterations on an average annual scale, increased regime indicator values were noticeable at the annual scale of a low-flow (drought) year. At the subannual scale, water use intensity was low in high-flow months (e.g., April), but increased by more than an order of magnitude during low-flow months (e.g., August). A shift in water regime, from natural flow–dominated toward withdrawal-dominated, was observed at the average monthly timescale and during the low-flow months of a single low-flow year. Despite the fact that the CRW and IRW are similar in their suburban characteristics and experience a similar climate, the two displayed different water use characteristics and variability in regime change. Therefore, water use characteristics and subannual variability in water regime shifts should be emphasized when examining the relationship between water use and water resource availability.