Prior to the creation of the global Aqueduct Water Risk Atlas, indicators (Table 1) were developed and tested in a number of river basins worldwide. The results of these Basin Studies helped inform and shape the global Aqueduct Water Risk Framework. Complete guidelines and processes for indicator selection, data collection, calculations, and mapping techniques are described in the Aqueduct Water Risk Framework.1 This study focuses on the specific characteristics of the indicator data and calculations in the Yangtze River Basin (YZB).
The data selection and validation process for the Yangtze River Basin Study involves three steps: (1) a literature review, (2) identification of data sources in the public domain, and (3) the compilation and expert review of selected data sources. Calculation of 6 of the 14 indicators required the creation of original datasets to estimate water availability and use at a sub-basin scale. The hydrological catchments used in the exercise were extracted from the Global Drainage Basin Database (GDBD) developed by Masutomi et al.2 Computation of the original datasets was completed by ISciences, L.L.C.
Two measures of water use were used in this study: total withdrawal, the total amount of water abstracted from freshwater sources for human use, and consumptive use, the portion of withdrawn water that evaporates or is incorporated into a product thus is no longer available for further use. Annual total water withdrawal by sector and province is reported in the 2010 Changjiang & Southwest Rivers Water Resources Bulletin. Consumptive water use is derived from the provincial consumptive use ratio from the 2010 Changjiang & Southwest Rivers Water Resources Bulletin. Both the withdrawals and consumptive use are coded at the hydrological catchment scale. Two metrics of water supply were computed: total blue water and available blue water. Total blue water approximates natural river discharge and does not attempt to account for withdrawals or consumptive use. Available blue water is an estimate of surface water availability minus upstream consumptive use. Modeled estimates of water supply are calculated using a catchment-to-catchment flow accumulation approach developed by ISciences, L.L.C., which aggregates water by catchment and transports it to the next downstream catchment. Water supply is computed from runoff (R), which is the water available to flow across the landscape from a particular location and is calculated as the remainder of precipitation (P) after evapotranspiration (ET) and change in soil moisture storage (ΔS) are accounted for (i.e., R = P – ET – ΔS). The runoff data is courtesy of National Oceanic and Atmospheric Administration (NOAA) and obtained from its Climate Forecast System Reanalysis (CFSR)3 for generating runoff values by GDBD for the years 1979–2009.
The remainder of this document contains the definitions, formulas, and data sources for Aqueduct’s Yangtze River Basin Study.