Analysing droughts in the Magdalena-Cauca macro-basin in Colombia

Abstract

Droughts can have detrimental consequences for agriculture, hydropower generation and ecology. It is important to increase our understanding of this phenomenon to be able to assist in water management and to be able to take preventive measures. The Magdalena-Cauca macro-basin (MCMB) is located in the northwest of Colombia. The climate is mainly influenced by shifting of the Inter Tropical Convergence Zone, the north-easterly trade winds and the Chocó-jet. Droughts are known to occur in the MCMB during El Niño events. Four large scale hydrological models (ORCHIDEE, HTESSEL, WaterGAP3 and PCR-GLOBWB) were evaluated for the MCMB, followed by a quantification of droughts using five different drought indices (SPI, SPEI, ETDI, SMDI and SDI) and the determination of the correlation between droughts and the El Niño Southern Oscillation (ENSO). The MSWEP precipitation data exhibited good performance. Therefore, this forcing dataset was used as forcing for the MCMB. Not all model products had a good performance, nevertheless, they were still valuable for the drought analysis because the absolute error is longer relevant for drought indices due to their computation procedure. Droughts were found to occur most often in the southeast of the catchment, likely because this region is less affected by the westerly Chocó-jet, which supplies moist air. During El Niño events, the drought-affected area starts in the northeast of the MCMB and moves from there to the southwest. This finding agrees well with the fact that the Chocó-jet decreases in intensity during El Niño events, enabling the drier easterly trade winds to reach further to the west. The correlation with ENSO is strongest in the west of the catchment, and is strongest for the 6-month model ensemble mean SPEI index. The correlation between drought indices and the Multivariate ENSO index (MEI) is weaker for a strongly positive MEI values. This drought analysis of the MCMB can assist in future research using use drought indices, and their correlation to ENSO, to predict droughts in the MCMB and assist in water management.