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Botswana International University of Science & Technology (BIUST) 2021

Characterization of drought over Botswana using multivariate statistics

Keitumetse, Onneile Nomsa

Titre : Characterization of drought over Botswana using multivariate statistics

Auteur : Keitumetse, Onneile Nomsa

Université de soutenance : Botswana International University of Science & Technology (BIUST)

Grade MSc Environmental science 2021

Résumé partiel
Droughts pose a significant challenge to water resources, causing several socio-economic consequences. The growing economy requires improved assessments of drought-related impacts in the water sector, particularly under semi-arid environments where its climate is getting drier and warmer. This study proposes a probabilistic model (copula approach) that is intended to contribute to the drought risk assessment by providing an essential information in drought prediction, decision making and management of the limited water resources available during drought events. The three key pillars (i. Drought monitoring and early warning systems, ii.vulnerability, and impact assessments, and iii. mitigation and response measures) are recommended as the basis of national drought policy and management plans, providing a practical way to organize multiple actions and activities that the country need to implement to better prepare and respond to drought. In the study, drought events are characterized by duration, severity and intensity, and the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI) were used to analyse hydrological drought based on gridded rain gauge and potential evapotranspiration data referred to as Climatic Research Unit (CRU) covering a period of 1901-2018 at a time scale of 12 months. Both SPI and SPEI were able to detect the spatial and temporal variation of drought. But SPEI was able to identify more droughts in the severe to moderate categories over wider areas in the country than SPI did. A set of seven homogeneous drought regimes based on spatial characteristics of SPEI were obtained. Region 1 and 7 are relatively wet regions, followed by region 2 and 6, while region 2 and 4 are relatively dry regions which borders the Kgalagadi Basin. The optimal marginal distribution for drought duration, severity and intensity were identified by employing the Akaike Information Criterion (AIC). The drought duration was best described by the Generalized Extreme Value distribution while the drought severity and intensity were both found to optimally fit with Weibull distribution. Nine copula distributions, namely-Normal, Student’s t, Gumbel-Hougaard, Rotated Gumbel, Clayton, Rotated Clayton, Joe Clayton, Frank, and Plackett copula distributions were applied to construct the bivariate and trivariate distributions. The most appropriate copula functions were determined also based on AIC.


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