A Glass of Water - Part 1

In examining the effect of changes to the hydrological cycles on human well being, it seems to make the most sense to start with perhaps the most obvious function that humans use water for - drinking. The human body can only survive for days without intake of water, so this is obviously a pretty important function. Let's run through some of the key ways climate change will affect the drinking water available to us.

Increased temperature

We've all heard of global warming, and there is certainly truth in that phrase - globally, temperatures are predicted to increase as a result of climate change. The hydrological cycle is one big set of physical, chemical and biological reactions, and temperature is the main factor influencing how these reactions work. 

Perhaps the most obvious example of the effect of increased global temperature is the melting of ice and glaciers - the melting polar icecaps (and associated images of forlorn looking polar bears) are regularly discussed in the media. While this is no doubt important, there is also plenty of ice away from the poles; in fact, you can find ice quite close to the equator, in tropical areas - take the northern end of the Andes mountains, for example. Here, climate models (computer models that run using maths) predict that temperatures will warm faster at higher altitudes (where the majority of ice is) than at lower altitudes. Bradley, et al. (2006) show that this could have serious implications for drinking water in the Andes - many large cities are located at high altitudes, and rely heavily on water released from these glaciers into rivers as they melt in the summer, and then re-freeze in the winter. However, more rapid summer melting caused by a rise in temperature means a lot of water will arrive all of a sudden, and then very little at all. The worst case scenario is that the glaciers could melt away completely, with communities losing a source of water. For cites such as Quito in Ecuador, and La Paz in Bolivia, this could have serious implications to the availability of drinking water.

The effect of temperature on biological reactions in water is also very important, as higher temperatures can encourage the growth of algae and phytoplankton in non-flowing bodies of water such as lakes and reservoirs, which are often important drinking water sources. This is evidenced by a drinking water crisis that took place during May 2007 in the city of Wuxi, Jiangsu Province, China. Here, unseasonably warm weather allowed a toxin producing cyanobacteria to bloom in Lake Taihu (China's third largest freshwater lake) and contaminate the water so as to make it unsafe to drink. This left nearly two million people without drinking water for a week - Lake Taihu was the only water supply to the city of Wuxi. Work by Qin, et al. (2010) suggests that this event was exacerbated by a multi-annual warming trend in the regions, which produced conditions that allowed this harmful organism to bloom, though it must be noted that poor water management also contributed to the crisis. As climate change trends are so long term, it can be hard to understand how much of an influence climate change has in individual events, a point worth bearing in mind!

Heavy rainfall

Extreme weather events are predicted to increase in their frequency and intensity - one of the key ways this will be expressed in the hydrological cycle is in events of very heavy rainfall. During such events, rivers can burst their banks, and water runs across the surface of the land. As such, heavy rainfall events are associated with a the transport of solid materials and pollution in the water, which can reduce the quality of drinking water and poses a risk to human health. Water treatment plants can become unable to cope with the increased amounts of water they are receiving, leading to either a water shortage, or untreated water being passed through the system. Further, cross-contamination between sewage and drinking water (a serious health hazard) is possible if poorly maintained infrastructure becomes overwhelmed by a surge of water - this is a particular problem in developing countries with weaker infrastructure.

Jean, et al. (2006), exhibited this relationship between heavy rainfall and the contamination of drinking water by examining an outbreak of enterovirus in a village in Taiwan. Enterovirus infection causes a polio-like illness that can lead to paralysis and death, for which there is currently no cure or treatment available. It is particularly topical given strains of the virus have recently been detected in the UK and the USA, which the tabloids have reported as a 'killer virus' (it is dangerous, but the number of cases are very low). In the Taiwanese village, a statistical relationship was shown to exist between rainfall rates and water contamination, as a result of heavy rainfall causing enterovirus to be flushed from soil (likely from burial graves in the area) into groundwater supplies used for drinking water, infecting people and causing fatalities. The probability of infection increased with increasing rainfall intensity (the amount of rain falling over a given time).

While the Taiwanese village is a specific case study in drinking water contamination from heavy rainfall, the broader trend is confirmed by Cann, et al. (2013), who reviewed four medical and meteorological databases to examine the relationship between waterbourne disease outbreaks and extreme weather events. For reports of outbreaks following extreme weather, 53% of these events were caused by contamination of drinking water supply, usually caused by increased runoff and inundation, both of which are mainly caused by heavy rainfall events. A changing climate in which these events become increasingly common comes with an increasing health risk.

As you can see , the hydrological effects of climate change have a great potential to impact drinking water - one of the most important things for human well being. In the next post, I'll consider some more factors of climate change that will influence drinking water.