Page 107 - CIWA Water Data Revolution Overview Report

consequences of these changes and the need to adjust current water allocations, water

management processes, and investment decisions accordingly.

1.2. Water Accounting Plus (WA+)

A water accounting system is implemented using a standardized methodology and

1
nomenclature. The approach developed by the International Water Management Institute ,
“Water Accounting +” (WA+), is one such approach. In contrast to other approaches that rely

heavily on national-level hydro-meteorological data and statistics, WA+ is a framework that

recognizes the limited availability of these data in many countries and relies instead on

remote sensing derived data, hydrological models, and open source global data sets to i)

calculate consistent water accounts for a particular location; ii) avoid data discrepancy
between adjacent regions/across national borders; iii) provide estimates where local data is

insufficient. The information provided through this approach gives a solid understanding of

the state of the resource and how competing sectors use water. However, it is to be noted
that, to ensure the reliability of the WA+ framework, it is essential to validate remote sensing

and model-derived data with ground-based observations wherever possible.

With recent advances in earth observation sensors, it has been demonstrated and widely
accepted that accurate measurements of key water balance parameters (e.g.

evapotranspiration and precipitation) can be derived from satellite data. Remote sensing

offers consistent and continuous (gridded) field-to-basin scale information on hydrological

fluxes. Because of the improvements in the technological and computing capabilities, the
application and reliability of remote sensing datasets in hydrological studies is constantly

increasing and becoming more and more common. Over the past few years, the increasing

availability of data from earth observation satellites has dramatically changed our ability to

quantify water resources at different scales, as demonstrated by IWMI and its partners
through the WA+ approach (Batchelor et al., 2016; www.wateraccounting.org).

The major advantage of a water accounting approach which is based on actual ET

measurements, such as WA+, is that water withdrawals and return flows do not need to be

1 In collaboration with its partners UNESCO IHE and FAO