Documentation for the Water Security Indicator Model - Global Land Data Assimilation System (WSIM-GLDAS) Monthly Grids, Version 1

This document outlines the basic methodology and data sets used to construct the Water Security Indicator Model using Global Land Data Assimilation System (WSIM-GLDAS) data product, along with use cases, limitations, and use constraints. The WSIM-GLDAS data set characterizes surpluses and deficits of fresh water, and parameters determining them, across the global terrestrial surface. Driven by outputs of NASA’s Global Land Data Assimilation V2.0 monthly Noah Land Surface Model (Beaudoing, Rodell, NASA/GSFC/HSL, 2015), WSIM generates anomaly values of temperature, precipitation, soil moisture, potential minus actual evapotranspiration (PETME), runoff, total blue water (flow-accumulated runoff), composite index of water surpluses, and composite index of water deficits in terms of their return periods with respect to a fitted generalized extreme value (GEV) probability distribution function over a historical baseline period of January 1950 to December 2009 at a global spatial resolution of 0.25 degrees over 1-month, 3-month, 6-month, and 12-month periods of integration. The data cover January 1948 through December 2014, inclusive, with a spatial extent of -180.0, -60.0, 180.0, 90.0 (minimum longitude, minimum latitude, maximum longitude, maximum latitude, respectively).