The thickness of the blue lines in this chart correspond to the quantity of water that flows through the Willamette Basin, from left to right. The units shown are in of cm3/cm2/year (abbreviated as cm; 1 cm = 235,000 acre-feet). Use the drop down menu to look at the water balance for different modeling scenarios, and the slider to look at how fluxes change during different times of the year. The Year position on the slider summarizes average fluxes for a water year, October-September. Winter and Summer positions on the slider summarize fluxes for two six month periods, November-April, and May-October.
The scenarios on the drop down menu allow you to switch between depictions of the water budget for the past (1950-2010) and for the future (2070-2100). The Simulated Historical scenario estimates the water budget with simulated climate data representing conditions we have experienced in recent decades. The three futures scenarios represent what the water budget might be like in the late 21st century (2070-2100), given different assumptions about climate change and water use. The Reference Case scenario (2070-2100 Reference) adopts mid-range assumptions about climate warming and population growth, the High Climate Change scenario (2070-2100 HighClim) assumes greater climate warming than in the Reference Case, and the Extreme Scenario (2070-2100 Extreme) adopts the warmer climate assumptions of the High Climate Change scenario along with rapid population growth and policies that maximize resource use.
Annual Storage Cycle - Set the drop down box to “simulated historical” and move the slider to trace changes in water flux over the water year, from October through September. Focus your attention on the storage boxes – snow, reservoirs, and soil and groundwater as you read this narrative. During October, fall rains begin and there is a net inflow of water into storage as rainfall saturates previously dry soils. During Fall, there is also a net flux of water out of the reservoir storage box – this reflects flow releases from the 13 reservoirs that are part of the USACE Willamette Project. The USACE’s goal is to empty reservoirs by December, to create capacity to capture water during flood season. By December and January, snowfall begins and that leads to net storage of water in snowpack. By early Spring, the largest influx to storage is to the reservoirs. This reflects the end of flood season and the time period when the USACE begins to fill the reservoirs for the summer irrigation and recreation season. During the summer months, there is very little precipitation, and most of the water in the river comes out of storage, either from melting snowpack, releases from reservoirs, or fluxes out of soil and groundwater.
Annual Water Use Cycle - As in exercise 1, set the drop down box to “simulated historical” and move the slider to trace changes in water flux over the water year, from October through September. Focus on the water use boxes in the middle of the diagram. Human uses (municipal and agricultural) are a very small proportion of the total amount of water flowing through the basin. They are so small that they have been enlarged in the detail box by 20x so that they can be compared. Move the slider to compare how these uses changes with the seasons. During fall and winter, there are diversions for municipal and industrial uses, but very little for agriculture. By spring and summer months, water demand for irrigation overtakes the demand for cities. Most water used for municipal and industrial sectors ultimately returns to the river as wastewater. But in the case of irrigation, much of the water applied to fields eventually leaves the system as evapotranspiration. The diagram also represents environmental flow requirements at Salem. The thickness of this line (top of diagram) shows the proportion of total streamflow that is needed to meet these requirement, which are in effect during summer months from April-October.
Scenario Comparison - You can also use the diagram to compare changes in fluxes and storage between different WW2100 modeling scenarios. First, set the slider to August and use the drop down menu to compare the Simulated Historical and the Reference Case. The climate is warmer and there are more people, so there is more evapotranspiration and greater water demand for municipal sectors. Next, set the slider to January and notice how the snow reservoir is smaller in the Reference Case than in the Simulated Historical scenario – the climate is warmer so less precipitation falls as snow and builds up in that reservoir during winter. This change is even more apparent in the HighClim and Extreme scenarios – the snow reservoir is much smaller and is completely melted by June.
[Figure developed by Haggerty, Preppernau, Wright; data from WW2100 3.0, last updated: 12/28/16. Read more about the development of this diagram at: http://inr.oregonstate.edu/ww2100/analysis-topic/hydrology]