7. Conclusion

The Okavango Delta is an inland delta in northern Botswana which in mainly fed by the Okavango River. Hydrological droughts in the delta have caused problems for both wildlife and people in the region. One of the cases is hippos getting stuck in the mud, because there is not enough water to fill up the lakes. This study suggested that inflow of the Okavango River is an indicator for the hydrological droughts.

First, the total yearly volume flowing through the river was connected to known cases of droughts in the delta. This study claimed that when the yearly volume falls below the 15th percentile of historical observed data, it is likely that that Okavango Delta experiences a hydrological drought. After determining this threshold, three drought categories were made: moderate (15th percentile), severe (10th percentile) and extreme (5th percentile). The threshold values for these categories were 6,591 Mm3/y, 6,135 Mm3/y and 5,937 Mm3/y respectively. For reverence, on average the Okavango River supplies the delta with 10,000 Mm3/y.

After the determination of threshold values, the HBV model was used to model the discharge of the Okavango River. The nine parameters were calibrated using a combination of the KGE and log-NSE method. These calibrated parameters were then used with historical CMIP6 data. The results did not represent the observed data well, so quantile mapping was used for bias correction. This same bias correction was used to model the discharge of the river in the period from 2030 to 2100 using the SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5 climate scenarios.

The central research question was:

“What is the impact of climate change on the future discharge patterns of the Okavango River and how will it impact the frequency of hydrological droughts in the Okavango Delta?”

The results indicate that the total volume flowing from the river into the delta will decrease in the future, particularly in the SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios, resulting in a higher frequency of hydrological droughts. This will have a negative effect on wildlife and people in the Okavango Delta. For scenario SSP1-2.6, the situation in the Okavango River actually improves slightly in period 2065 – 2099 compared to the observations between 1986 – 2020.