Evaluation of drought indices using the 40-percentile threshold for the north-central regions of Namibia.

Abstract

Drought is not uncommon to the Southern African climate and it has become a matter of serious concern in Namibia. For that reason, almost all parts of Namibia have become vulnerable to drought occurrence. Whilst recognising agriculture as a pertinent component of the Namibian economy, it is imperative to underscore the importance of drought early warning products for short- and long-term decision making in various sectors of the country’s economy. Following the 1991/92 drought, which ravaged more than 80% of Southern Africa, Namibia now realise the value of meteorological information in weathersensitive decisions. This severe drought has been described as the worst in living memory. Five stations (Ombalantu, Oshakati, Rundu, Katima Mulilo and Tsumkwe) in the northern part of Namibia were assessed. The researcher used the rainfall decile method to assess drought conditions by evaluating whether the widely used 40-percentile threshold is appropriate for triggering a drought warning in Namibia. Results showed that the threshold might have been set too high to be of use in warning farmers of coming droughts. In order to determine the percentile that would be best serve as trigger for drought warnings, there is need for further examination at 30, 25 and 20 percentile mark thresholds. Based on the 40-percentile threshold, much of the drought and a decrease in rainfall accumulation in Ombalantu and Oshakati in the Omusati and Oshana regions respectively, occurred towards the end of the 20th century.