What is Terrestrial Water Storage?

Terrestrial water storage (TWS) refers to the total amount of water stored over a certain time period (e.g. one month) in a river basin. Water in a river basin can be stored in several ways: snow, river channels, lakes and reservoirs, soils, groundwater aquifers, and even in vegetation. Direct determination of TWS is difficult due to insufficient in situ data on space-time variability of hydrologic stores (snow, soil moisture, groundwater) and fluxes (precipitation, evapotranspiration). However, alternative methods using new data sets show great potential to improve the estimation of intra-annual and interannual TWS changes.


 

Why are changes in TWS important?

The total amount of water stored in a river basin affects streamflow at various timescales and defines the river basins response to atmospheric forcing. For example, spring runoff in mountainous midlatitude catchments depends on winter snowpack, and groundwater storage sustains flow during dry periods. An accurate estimation of TWS is thus paramount for improved water management. Increases in TWS will reduce the risk of prolonged drought, but too much TWS increase can increase the potential for flooding.


How do we estimate TWS changes?

Estimating TWS changes in time at the river basin scale is still a challenge. However, there are several methods and data sets available (see Troch et al., 2007 for details). This website provides near real-time estimates of TWS changes for the Colorado River basin and sub-basins within. For details about methods and data used, click Data & Methods.


What are the seasonal changes in TWS?

In the Colorado River basin there is a strong seasonal cycle in the TWS changes (see Climatology). During winter months, the basin receives and stores snow in the Upper Colorado's Rocky Mountains. During spring, this snow pack melts and leaves the catchment as runoff. Summer monsoon in the Lower Colorado brings additional rain, but due to high evaporation rates in the semi-arid climate not much of that water is stored in the basin. See also TWS Maps for more details on spatial patterns of TWS changes.