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500.0
Water Accounts (km 3 ) 300.0
400.0
200.0
100.0
0.0
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
Rainfall Utilizable flow Total ET Outflow
Figure 4: Inter- annual variability of water accounts-Volta basin (2003-2021).
3.6 Implementing the SIWA+ framework under future climate scenarios in the Volta River
Basin
The Scale Invariant Water Accounting Plus (WA+) framework was implemented in the Volta
River Basin under future climate scenarios following a request from stakeholders. The
methodology and data adopted for implementing the WA+ framework under future climate
scenarios is briefly described below.
3.7 Data and Methodology
Precipitation and temperature data from climate modelling are the basis for the input data
for future scenario WA+ water balance assessment. The primary WA+ input data required for
the future climate assessment are projected scenarios for precipitation (P), potential (PET)
and actual evapotranspiration (ET). The bias corrected climate data obtained for Socio
Economic Pathways: SSP585 consisted of two CMIP6 models: MPI-ESM1-2 and GFDL-ESM4.
Projections were analyzed for the time horizon:
2025–2050: Short-term (near future) climate
Daily time series data for precipitation (P), minimum and maximum temperature (Tmin,
Tmax), and downward shortwave radiation were downloaded from the NEX-GDDP dataset for
both models.
Daily potential evapotranspiration (PET) was calculated using the Modified Hargreaves
Equation for daily data [Farmer et al, 2011]:
