when conventional methods/products show their limits

When conventional methods/Products show their

limitsAlkhalil AdoumFEWS NET Regional Scientist for the Sahel/West AfricaAGRHYMET Regional Center, B.P. 11011, Niamey, Nigera.alkhalil@agrhymet.ne

Content• The 2009 growing season – bad rainfall

distribution in Eastern Sahel (Niger)• NDVI anomaly - analysis on large areas in

West Africa• Indices/derivatives to address the

problem• Conclusion

• Addressing the bad rainfall distribution issue– Two field visits were sent by AGRHYMET– Information collected during field visits indicated:

• bad rainfall distribution seriously affected crop and pasture development conditions over most of the country

• The result was a very heterogeneous crop condition situation

• Necessity for a method that takes into account pixel history such as temporal profiles

• MODIS NDVI good candidate due to its good resolution and stability of the signal

• Percent of average images for each dekad & values extracted at points of field observations

• Profiles plotted grouped/similarities• Profiles groups/Mapping of the 2009 rainfed

crop productivity in Niger

Characterizing the 2009 growing season in Niger using MODIS NDVI profiles

Corresponding photographs: points # 12

At Point # 12 : very green but too late into the season.

Corresponding photographs: points # 22

At Point # 22 : very green but too late into the season. These heads were still baring flowers and given dryness due to the end of the season fertilization will abort.

Characterizing the 2009 growing season in Niger using MODIS NDVI

Characterization the 2009 growing season in Niger using MODIS NDVI

Concluding remarks• The product very well reflected field

conditions• It does not miss the bad and the good but it is

hard to make a good judgment around the mean

• The process is too lengthy for operational purposes

• A tool might exist to get the profile based classification performed more quickly

VCI vs Anomaly

The classic anomaly very good and useful for many applications

VCI is better to reflect local ecosystem productivity

Number of dekads out of 10 (1st dekad of June to first dekad of September) when VCI <=20%

1. Good only for the Sahel because of cloud contamination further south

2. Experimental but very consistent with areas where dryness problems are being or have been reported at one point in the season