Visualization of Water Services in Africa: Data Applications for Nexus Governance - Governing the Nexus: Water, Soil and Waste Resources Considering Global Change - page 188

Fig. 3 Soil - water index of
South and Central Africa,
which shows the level of
soil - water in the root zone.
Source Melesse et al. ( 2007 )

pro le). The water colour of a sample can be a proxy of the pollution level or

sediment content, which then might be a proxy for soil erosion.
A second proxy type is often called index. Indices are mathematically derived
values that are calculated from several available data. Indices are single numbers
that represent a more complex reality, which makes them useful for decision-
makers. Another common feature of indices is that the data used for their calcu-
lation is generally easier to collect than the target data. Many indices that represent
this relationship are based on remote sensing. This is especially true for data-poor
environments as more satellites become available making satellite images more
affordable. Remote sensing indices are based on their spectral bands related to the
physical properties of the target value. An example is the vegetation index that is a
proxy for vegetation density and leaf area index, which is a proxy for biomass
production, photosynthesis, CO 2 uptake, water interception, plant height, root
development, plant health and others. A vegetation index is therefore useful for
agriculture management, hydrological analysis and climate change predictions.
Similarly, the wetness index and soil - water index are used as proxies for soil - water

content, which influences plant growth and in ltration capacity (flood protection)

and can be used for drought prediction (Melesse et al. 2007 ). The Food and
Agriculture Organization (FAO) applies the FAO-Agriculture Stress Index System
(ASIS) that facilitates the establishment of risk transfer tools such as crop insur-
ance. 2 Another example is water index (Fig. 3 ; Leblanc et al. 2011 ) or soil aridity
index (Costantini and L Abate 2009 ).

There are also socio-economic indices that integrate different data sources to
derive one single value representative of the social and economic conditions, which
can indicate where development or governmental support is required. The different
indicators are mathematically combined where different weights are allocated to
each data input variable. The level of allocated weights for each input parameter

'

2

For more information, see https://www.agriskmanagementforum.org .