Assessing Runoff Changes in Major Catchments in Swaziland Due to Climate Change

Abstract

It has been reported that 2016 was the hottest year in the history of instrumentation (since 1850) and the global surface temperature rise is attributed to the rise in greenhouse gases. The combined global land and ocean surface temperature for July 2010 was the second warmest on record—behind 1998—and the warmest average January–July period on record. The effects of global warming will bring changes in annual average precipitation values in the order of ±20%. The southern African region has been projected to receive less precipitation and Swaziland is no exception. The average results (precipitation, potential evapotranspiration) of 12 general circulation models (GCMs) in the future (2021–2060) and in the observed streamflows (1961–2000) were input to a calibrated rainfall–runoff model (WatBal model) in order to determine the water resources in four catchments in Swaziland under the anticipated climate change conditions. Simulation results show that the present streamflows lie within the 95% confidence interval of the projected flows in all the catchments. This implies that there is no significance difference between the observed and projected streamflow at the 5% confidence level. However, the runoff change between the 2.5 and 97.5% quantile ranges from −17.4% to 26.6%; −31.2% to 18.1%; −40.3% to 27.7%; and −40.8% to 34.9% in the Komati, Mbuluzi, Usutu and Ngwavuma catchments, respectively, and the median of the runoff change is negative for most months in three catchments (Usutu, Mbuluzi and Ngwavuma) excluding the Komati catchment. Thus, there will be less runoff in the three catchments under the projections for expected climate change. Therefore, proposed adaptation options to climate change for Swaziland are: efficient water use (at domestic and farm level), wastewater recycling, rainwater harvesting, ground water utilization, implementation of integrated water resources management (IWRM), water resources development and inter-basin transfers.