Modeling of Current and Future Low Flow Characteristics Under Climate Variability and Water Abstraction: Case of Likhubula River Catchment in Malawi

Abstract Water resources are essential in sustaining ecosystems, agriculture and the ever-growing water demands of human population. However, the delicate balance of water availability for these sectors is increasingly facing unprecedented present and future challenges due to climate change and anthropogenic pressures. This study was aimed at characterizing the current and future low flows under climate variability and water abstraction in the Likhubula River Catchment, key a sub-catchment of the major Shire River Basin in Malawi. The study employs a multi-faceted approach, where trend analysis is conducted using the Mann-Kendall test and the Sens Slope Estimator at α = 0.05 significance level. The SWAT hydrological model was set up for simulating future streamflow conditions and forced with RCP and SSP scenarios. Flow duration curves (FDCs) and low flow frequency curves (LFFCs) were employed to compute low flow indices, including the Q90, Q95, 7Q2 and 7Q10. The SWAT model exhibited a satisfactory performance with an R 2 , PBIAS, NSE and RMSE of 0.98, 3.6, 0.94 and 0.29 respectively during calibration and R 2 , PBIAS, NSE and RMSE of 0.96, -2.4, 0.84 and 0.42 respectively, during calibration and validation. Examination of low flow indices indicated substantial increases in low flow frequencies after 2007 with anticipated further increases in low flow duration, magnitude and frequencies after 2027. The RCP4.5 and RCP8.5 indicate less severe low flows as compared to historical periods. The combinations of RCP and SSP scenarios has shown varying results, RCP4.5 & SSP2 indicating significant improvements, while others (e.g., RCP4.5 & SSP4, RCP8.5 & SSP4) showing potential for highly severe low flows; an indication that climate change and intensification of water abstraction activities have a significant impact on the magnitude, duration and frequency of low flows in the Likhubula catchment. Despite the non-significant increasing trend in rainfall being observed, both significant positive trend in temperature and significant declining trend in streamflow imply radical environmental decision-making calls to deal with uncertain future using the 3-H approach. These findings provide crucial insights for sustainable water resource management as these low flow characteristics are critical for managing water quality and quantity.