94 options to increase water productivity the

9.4 Options to increase water productivity: the modelling approach
The simulation models as described in previous Chapters serve two purposes: (i)
understanding the current situation and processes and (ii) explore options for the future.
Understanding the current situation and processes includes also a detailed analysis of
performance assessment for the different crops, farms, regions, etc., which is helpful in
defining possible options or scenarios for the future. Strictly speaking there is a difference
between scenarios and options, where a scenario is somewhat more a projection of the future
which cannot be easily altered (climate change, population growth, economic growth), while
options are seen as responses to these changes (water allocation, cropping patterns). We will
use here a mixture of scenarios and options for the future, and concentrate on four factors that
might change in the future or that can be used as measures to improve water productivity:
changes in groundwater level (field and regional)
changes in salinity level of irrigation water (field and regional)
changes in irrigation applications (field)
climate change (regional)
Obviously more scenarios and options can be defined, but these four factors should be
considered as the most relevant ones as outlined in Chapters 1 and 2. These four scenarios
function also as an example on how others can be analysed as well.

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Ideally, these scenarios should be analysed with the full regional model as presented in
Chapter 7. However, since one model run takes about 10 hours, only three scenarios were
analysed at the regional level: (i) an overall increase in groundwater level of 2 meters, (ii)
wetter conditions by taking climatic data of 1995, and (iii) a doubling of salinity levels of
irrigation water. The second scenario does not reflect only the conditions as in 1995, but
reflects more what could happen if climate change will occur and climate will become wetter.
These three scenarios were implemented in the regional modelling set-up by the following
approaches:
Climate change. The year 1/11/1994 – 1/11/1995 was simulated (a precipitation of
441 mm, in stead of 188 mm).
Rising groundwater tables. In the reference situation 36 of the 324 villages, or 10 %
(36856 ha) of the whole area, has an average water table within 4 m below the soil
surface. The average groundwater table at village level was raised by 2 meter, which
implied that 101 of the 324 villages, or 25 % (98746 ha) of the area, have an average
water table within 4 m.
Increasing salinity. Salinity of groundwater was doubled with a maximum of 10 dS
m
-1
, by changing the concentration of the groundwater at village level.
Figure 9.9 Water Productivity, expressed as gross return ($) per amount of water consumed (m
3
) for four
spatial scales: field (top-left), calculation unit (top-right), village (bottom-left), and irrigation district (bottom-
right). Period included is rabi and kharif 2001-02 and are based on measurements and SEBAL analysis.

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