22 ENVIRONMENT AND ENERGY
storm events , when wastewater is allowed to bypass the treatment plant . Thus , much of the wastewater is not treated ( or inadequately treated ) and discharged in water bodies , and subsequently affects the water quality ( and its availability ) for users downstream .
GLOBAL WATER AVAILABILITY – SCARCITY GROWING MORE SEVERE BY THE YEAR Water resources ( surface water and groundwater ) are renewed through the continuous cycle of evaporation , precipitation , and run-off . The water cycle is driven by global and climatic forces that introduce variability in precipitation and evaporation , which in turn define run-off patterns and water availability over space and time ( modulated by natural and artificial storage ).
Observations over the past decades and projections from climate change scenarios point towards an exacerbation of the spatial and temporal variations of water cycle dynamics . As a result , discrepancies in water supply and demand are becoming increasingly aggravated . Recent research has demonstrated that two-thirds of the world ’ s population currently live in areas that experience water scarcity for at least one month a year . Noteworthy is that about 50 % of the people facing this level of water scarcity live in China and India . Such a month-by-month assessment of water scarcity is essential , as the water stress that results from dry periods can be masked by annual averages of water availability .
Areas where non-renewable resources ( that is , fossil groundwater ; never a sustainable source ) continue to decrease , have become highly vulnerable and dependent on water transfers from areas with abundant water . Even though floods and droughts are a natural phenomenon and part of the spatio-temporal variable water cycle dynamics , the frequency and severity of floods and droughts have changed in many river basins worldwide , often due to a combination of climate change and human activities . Land use changes , including urbanisation , river channelization , and other human activities , modify the storage capacity of catchments and impact high flows as well as groundwater recharge and low flows .
Changed storage capacity and run-off generation processes can increase the occurrence of water-related disasters . The frequencies of floods and droughts are likely to change with increasing temperatures . The results of an ensemble of projections show a large increase in flood frequency where events that are now considered 100-year floods would increase in frequency in many areas . Having too much ( floods ) or too little ( drought ) water , which is often accompanied by too dirty water ( higher pollution concentrations in both extremes ), make the necessity for wastewater use even greater .
The economic costs arising from river flooding worldwide could increase twentyfold by the end of the twenty-first century , if no
October 2017 Volume 23 I Number 8 www . plumbingafrica . co . za