WATER SECURITY INDICATOR MODEL
The ISciences Water Security Indicator Model (WSIM) monitors and forecasts water anomalies on a near global basis. Each month, WSIM documents current anomalies and provides forecasts with lead times from 1-9 months. WSIM products include data, visualizations, and reports. WSIM has been run continuously since April 2011 and has been validated. WSIM includes algorithms to assess the impacts of water anomalies on people, agriculture, and electricity generation.
WSIM identifies regions with significant water anomalies -- either deficits or surpluses relative to historically expected quantities using a 1950-2009 baseline period. WSIM expresses anomalies in terms of return period. This describes how rare the surpluses (increasing intensity of blue) or deficits (increasing intensity of red) are relative to expectations. For example an anomaly with a return period of 10 years would be expected to occur once every 10 years on average based on historical distributions. WSIM calculates composite deficits based on soil moisture anomalies, evapotranspiration deficit anomalies, and total blue water anomalies. Surplus anomalies are based on runoff and total blue water anomalies. Purple regions exhibit aspects of both water deficits and surpluses. A good example is a river that runs through a region with below normal soil moisture, but where levels are high due to a larger than normal spring snow melt in the headwaters.
WSIM historical data starts in January 1950. This allows us to assess current and forecast anomalies in historical context. For example, Brazil is not typically considered drought prone. However, the past 15 years are a clear departure from past trends with frequent large exceptional droughts. Notable examples include 2002, 2005, 2007, 2010, 2012, 2013, and 2014. The 2014 drought forced water rationing in Sao Paulo, required extensive use of imported natural gas to generated electricity that would normally have been provided by hydropower, and significantly reduced production of several agricultural products.
WSIM makes use of:
- Past, current, and forecast temperature and precipitation. Forecasts are derived from an ensemble of 28 NOAA CFSv2 forecasts issued the last week of each month. This ensemble is carried all of the way through the processing chain and allows us to characterize uncertainty in the forecasts.
- Physical geography including soil properties, elevation, and routing networks.
- Human geography including water withdrawals by sector and the fraction of withdrawals that is consumptive by sector.
WSIM is a reduced form hydrological model that produces a suite of physical quantities for soil moisture, runoff, evapotranspiration, evapotranspiration deficit, snow water equivalent and total blue water (flow accumulated runoff). These values are computed on monthly basis from January 1950 through present, and into the future with lead times of 1-9 months. These quantities are combined with estimates of total withdrawals and consumptive use to produce estimates of the water withdrawal ratio (withdrawals relative to renewable supplies with upstream consumptive use removed) and the water reuse index (fraction of available water previously used and discharged upstream). Coverage is near global (only excluding Antarctica and most of Greenland) at 0.5° x 0.5° resolution (approximately 55 km x 55 km at the equator). This deep history allows us to characterize historical distributions and estimate the return periods for past, present, and forecast conditions. Return periods are calculated using 1, 3, 6, 12, 24, 36 and 60 month integration periods to characterize short and long term anomalies.
The WSIM agricultural assessment evaluates the degree to which water anomalies restrict agricultural production. It uses data about cultivation areas, crop calendars, and reservoir capacity to provide geographically explicit loss risk maps. This capability has been validated against USDA yield and insurance data for the coterminous United States.
The WSIM electricity assessment evaluates the degree to which water deficits restrict electricity production from hydropower and thermal plants (including nuclear). It considers upstream reservoir capacity and consumptive use, fuel stock and cooling technology, and downstream water stress.
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