The figure shown is a stream hydrograph. In this figure, streamflow is plotted with respect to time in a year. Streamflow is the rate at which a volume of water moves downstream and is often presented in units of volume per unit of time (i.e. here in units of cubic feet per second =cfs). Streamflow (stream discharge) is a combination of surface-water, snowmelt, and baseflow runoff.
Many modern waterways are not in their natural state. Flows are altered by dam and reservoirs projects, as well as by diversions for irrigation, industrial, and municipal water supply. The flows in this study are intended to represent natural flows. Modeled flows may be biased (flows too high, too low, too variable) and bias correction is used to map the modeled flows into the reference frame of physical observations. When physical observations of stream flow are available for an adequate time period, and the impacts of regulation/diversions removed, then bias-correction is possible. Changes in the hydrograph (magnitude, timing) provide an important window into assessing alterations in streamflows that may arise from climate change and which have repercussions for water availability.