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GIS-based hydrological modeling of global freshwater availability

English title GIS-based hydrological modeling of global freshwater availability
Applicant Abbaspour Karim
Number 109430
Funding scheme Project funding (Div. I-III)
Research institution Eawag
Institution of higher education Swiss Federal Institute of Aquatic Science and Technology - EAWAG
Main discipline Climatology. Atmospherical Chemistry, Aeronomy
Start/End 01.11.2005 - 31.10.2007
Approved amount 93'636.00
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Keywords (8)

global hydrology; GIS; country based freshwater availability; continental hydrologic modelling; Blue water; Green water; SWAT; SUFI-2

Lay Summary (English)

Lay summary
Africa has on a continental and on an annual basis abundant freshwater resources. However, there are great spatial and temporal disparities in water availability, both between and within African countries. Consistent high-resolution information on freshwater availability and water scarcity is still limited, while much sought-after. Existing global freshwater assessments focused largely on the traditional water resources definition, composed of the water yield and the deep aquifer recharge. This freshwater component is also termed “blue water flow”. The other, up-to-now often neglected freshwater component in large-scale studies, is green water, which itself can be subdivided into “green water flow” (i.e., actual evapotranspiration) and “green water storage” (i.e., soil moisture). (Semi-)distributed and GIS-coupled hydrological models are very useful tools for gaining deeper insight into the different components of the land-phase of the water cycle. But, as all hydrologic modeling results are subject to various sources of uncertainty it is essential to clearly quantify the prediction uncertainty. While various uncertainty analysis methodologies exist, to date these have not been consistently applied to global/continental freshwater assessments.

In this thesis a hydrological model for the whole African continent was developed, calibrated, and validated that allowes an assessment of the blue and green freshwater availability at sub-country (i.e., subbasin) level and at monthly resolution. The results are shown together with the inherent prediction uncertainty estimates and the consequences of considering them in advanced studies were analyzed.
The two main tools used in this study were the watershed simulation model “Soil and Water Assessment Tool” (SWAT) and the calibration and uncertainty analysis program “Sequential Uncertainty Fitting Algorithm ver. 2” (SUFI-2). SWAT was selected as it is a well-established, semi-physically-based continuous time model operating on a daily time step and has the ability to handle very large watersheds in a data efficient manner. SUFI-2 can easily be linked to SWAT and is very efficient in dealing with computationally intensive, large-scale models with many parameters and many calibration stations.
In conclusion, the SWAT model in combination with the SUFI-2 calibration and uncertainty analysis procedure was successfully applied to quantify the blue and green freshwater availability for the whole African continent at the subbasin level and at monthly intervals. The presented model and its results can be used in various advanced studies on climate change, water and food security, and virtual water trade, among others. Furthermore, this study is an important step for the development of hydrological models also for the other continents in order to ultimately obtain a global picture.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants


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Associated projects

Number Title Start Funding scheme
100076 GIS-based hydrological modeling of global freshwater availability 01.06.2003 Project funding (Div. I-III)