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Rainfall Variability Analysis of rainfall variability and drought in the 1961-2002 period
Rainfall variability and drought in the 1961-2002 period

Global analysis  Annual rainfall | National rainfall index | Global rainfall pattern
Case studies  Burkina Faso | Cambodia | Nepal | Tanzania
Downloads  Images (IDA) | Images (GeoTiff) | Movies (AVI) | Windisp | Quantum GIS

In 1994, a volume on the Rainfall Variability and Drought in Sub-Saharan Africa was published as No.9 in the FAO Agrometeorology Working Paper Series. The document defines a national rainfall index (NRI) for areas where water is limiting for agricultural production. Actually, the previous work is updated to cover the period 1961 to 2002 and improved on the methodology by using rainfall grids that become available since 1994. Furthermore, the analyses is expanded to global scale. Global annual rainfall maps in an equal-area projection (Hammer-Aitoff projection) are created for each year. They illustrate the rainfall pattern in the observation period and serve after applying appropriate corrections to acount for N-S hemisphere differences as basis for the global maps of the national rainfall index (NRI). Comparison of the rainfall maps with the maps of NRI demonstrates that drought is not necessarily associated with low precipitation totals.




Figure 1: Spatial distribution of 12 rainfall classes as a result of a combined EOF and cluster analysis.

To get an overview of global rainfall variability, a pixel-by-pixel classification has been performed (see Figure 1). Each of the marked 4 countries, as can be better seen in the zoomed cut-outs of Figure 1, incorporate several different rainfall classes. Methodology applied on the global scale is refined and applied with higher spatial and temporal resolution in these countries in the period 1983 to 2002. The countries chosen are Burkina Faso, Cambodia, Nepal and Tanzania.

 

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