WATER estuary 2014 2009 2004 1999 1994 1989 1984 1979 1974 1969 1964 1959 1954 1949 1944 The San Francisco Estuary receives 90% of its freshwater inflow from the Sacramento-San Joaquin watershed, whose rivers and streams drain nearly one third of the state. Freshwater flows from this watershed are affected by both natural and man-made factors. California’s Mediterranean climate and unpredictable cycles of wet and dry years pro- duces large year-to-year and seasonal variations in rain and snow precipitation and runoff; freshwater inflows to the Estuary during a wet, flood year can be nearly ten times greater than inflows during a drought year. Flows are also affected by humans. Dams capture and store runoff from the moun- tains for release into the rivers flowing to the Estuary at different times of the year and even in different years. Water diversions on rivers and in the Delta, the upstream region of the San Francisco Estuary, remove water for local agricultural or urban use or export to other regions in California, reducing the amount of water that flows to the Estuary. And increas- Poor Folsom Dam spillway. Photo: Bureau of Reclamation 4.0 3.5 3.0 2.5 INDEX 2.0 1.5 1.0 0.5 Fair terns of freshwater flow into the San Francisco Estuary from its tributary rivers and streams are critical drivers for the Estuary’s ecological health. Freshwater inflows control the quality and quantity of estuarine habitat, drive key ecological processes, and significantly affect the abundance and survival of estuarine biota, from tiny planktonic plants and animals to shrimp and fish. The mixing of inflowing fresh water and saltwater from the ocean creates low salin- ity, or “brackish,” water habitat for estuary-de- pendent species. Seasonal and inter-annual changes in inflow amounts trigger biological responses like reproduction and migration, and high flows transport nutrients, sediments and organisms to and through the Bay, promote mixing and circulation, and flush contaminants out to sea. 1939 CONTEXT The amounts, timing and pat- F R E S H WAT E R I N F L O W Good FLOWS 21 FRESHWATER FLOWS ESTUARY . . S TAT U S . . Poor . . . .T R E N D . . . . Variable but declining .....BENCHMARK..... Flows needed to protect ecological integrity ingly, climate change and resultant warmer temperatures and shifts in precipitation from snow to rain have altered the amounts, timing and duration of seasonal flows in the Estuary’s tributary rivers. INDICATOR The Freshwater Inflow Index uses ten indicators to measure and evaluate the amounts, timing, and variability of freshwa- ter inflow from the Sacramento-San Joaquin watershed into the Delta and the Bay, and