Publication: Identifying metrics for understanding and monitoring drought: The Eastern Nile Basin in Sudan
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Year: 2014 ISBN:
Language: Inglés External Link: ...
Type: Abstract
Taking the Eastern Nile Basin in Sudan as a case study, this study updates the Standardized Precipitation Index (SPI) until 2012 and identifies additional indicators for understanding and monitoring in the region. Although the decades following the 1980s – the decade which witnessed the peak of the drought – have recorded several years with higher rainfall amounts, this recovery is limited by serious changes in other rainfall indicators. A threshold of significant drought (regional SPI 1 mm) has declined in the arid areas. On the other hand, rainfall concentration indicated by increased probability of raindays with rainfall of > 10 mm or > 20 mm has been noticed in semi-arid areas. These results indicate less rainfall reliability. Despite the occurrence of ~50% of the rain days in the moderate rainfall class (1.1-10.0 mm), the total annual fall is highly dependent upon very few heavy falls (stronger than 20.0 or 30.0 mm). During the period of peak drought, the regional temperature observations present positive standardized anomaly indices (SAIs) during both the daytime and nighttime. A mounting evidence of increased climate warming is found thereafter using the SAIs. A combination of the dryness ratio (rainfall to potential evapotranspiration) and the Normalized Difference Vegetation Index (NDVI) enables setting a threshold of drought severity of vegetation greening. At least 10% of the growing season evapotranspiration must be received as rainfall in order that the vegetation starts greening or a crop to be productive. The maximum NDVI (NDVIx) that is reached during the wet/growing season can also constitute an indicator of the degree of drought. A low peak is likely to reveal in dry conditions as reflected from the direct relationship between NDVIx and overall annual dryness ratio. Different drought behaviours are exhibited by the Standardized Riverflow Index (SRI) of minimum, maximum and annual flows. In conclusion, although the SPI is a useful and widely accepted drought indicator, it should be complemented by other rainfall, meteorological, hydrological and vegetation indices in order to make drought assessment, understanding and monitoring completely satisfactory.
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