Agriculture Reference
In-Depth Information
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pastures and could be used for vulnerability assessment as well. Figure 19.4
shows the index based on the average of the three indices.
The analysis generally shows that good growing conditions prevailed
over the Sahelian zone, with the exception of few limited areas distributed
over all the countries. The largest of these areas is in eastern Chad (north-
eastern Biltine and southeastern Ennedi). At the western end of the Sahel,
such areas are also seen in western Mali and in the border region of north-
ern Senegal-southern Mauritania. The rest of the Sahelian zone looks very
good.
The results for the Sahelian zone are in good agreement with statistical
analysis. The analysis shows that 2001 growing season conditions were
slightly worse than average over most of the Sudanian zone. However,
the magnitude of the departures shows that the deficits are mild when
compared to average conditions. The lowest negative values are around
−
[261
1.0. However, over most of the Sudanian zone the index is between -0.4
and -0.1, which suggests milder departures from average conditions when
considering that the highest positive value is about 3.2.
Agricultural statistics indicate that the 2001 rain-fed production was
very good even in the Sudanian zone. The RNCD results are, therefore,
only in partial agreement with the agricultural statistics data. Further in-
vestigation has shown that there are good reasons for this disagreement.
The RNCD index represents departures of NDVI and RFE from their re-
spective averages. Although in the Sahelian zone any deficit in rainfall, and
consequently in biomass, can have serious repercussions on production,
this is not always the case in the Sudanian zone. In the Sudanian zone,
where cumulative rainfall varies from 800 to 1000 mm, a 200-mm deficit
may not have any ill effect on crop growth and development if rainfall is
well distributed. In fact, in some cases, reasonable-length dry periods may
contribute to increased yield, due to increased facility for weeding when
soil moisture decreases for a period of time.
The negative departures of the RNCD index are small, since the low-
est values are less than -1.0, whereas positive departures go above 3.0.
Furthermore, most of the area within the Sudanian zone depicting nega-
tive departures has values ranging from -0.4 to -0.1. The area of values
ranging from
Line
——
0.0
——
Norm
PgEn
[261
0.4 is relatively small. The RNCD method is good
for detecting anomalies in rainfall and biomass pattern. For this reason
a comparison with recorded rainfall was made. Comparison of rainfall
departures with respect to average was performed and good agreement
was found between the spatial distribution of RNCD results and rainfall
departures. Mali and Burkina Faso (figure 19.4) were chosen for this com-
parison because of the relatively high density of rain gauge distribution. In
Mali, both RNCD and actual rainfall show some deficit in the south, espe-
cially the southeast. RNCD shows the northern part of the agricultural area
of this country as above average in rainfall and rainfall records show the
same area as average and slightly above average. In Burkina Faso the same
is observed. RNCD shows that western and central parts of the country
−
1.0 to
−
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