Investigating the effects of aridity and its impacts on water resources availability in the Luvuvhu River Catchment

Abstract

The study investigated aridity and its impacts on water resource availability in the Luvuvhu River Catchment (LRC). Hydrological information indicates gradual changes towards more arid conditions in the LRC. The shift towards aridity has impacted negatively on water resources availability. Aridity indices for the LRC were determined using both meteorological and hydrological data. The 5-year or 10-year rainfall or streamflow averages were used to detect drought thresholds, except during flood events. A significant study was done on drought conditions using Standardised Precipitation Index (SPI), Standardised Precipitation-Evapotranspiration (SPEI) and Standardised Streamflow Index (SDI). The study hypothesised increased inter-station variations (spatial and temporal) observable from 5-year or 10-year rainfall or streamflow averages over a historical hydrological period. The study used rainfall and temperature data from the Agricultural Research Council (ARC) and South African Weather Service (SAWS) spanning 58 years (1961 - 2018). National Centers for Environmental Prediction (NCEP) data with a resolution of 10 km was used to determine historical and future aridity in the LRC. The spatiotemporal variations and trends of aridity are reflected in the availability and distribution of water resources. The study developed the aridity indices using United Nations Environment Programme (UNEP) Aridity Index (AI) to determine the spatiotemporal variability of water resources in the LRC. The variations and trends of aridity indices were determined using the coefficient of variation and Mann Kendall test, respectively. Due to a limited number of weather stations in the study area, the Kriging method was used to interpolate aridity indices for areas with no stations. The temporal changes of the 5-year or 10-year cycles of hydrological data analyses show progressive, gradual increases linked to global environmental changes such as global warming. The Hierarchical clustering (HC) analysis revealed the presence of two factors that account for 59.7% and 39.3% of the variability in rainfall within the LRC. The results show that upstream of the catchment experiences more rainfall and lower temperatures than downstream. The increase in temperature and decrease in rainfall might negatively impact the availability of water resources for downstream users. Thus, more arid conditions are experienced downstream of the catchment than upstream. Flood events have become rare and more intense, a characteristic associated with areas prone to droughts. The results of the study reveal significant year-to-year variability in floods and drought events. The increase in aridity should be considered when allocating water resources and implementing sustainable water resources management in the LRC. Thus, the study provides a baseline for monitoring and modelling hydrological processes in arid environments.