Beating the heat: water or electricity?

When temperatures increase, how does demand for water and electricity change? A recent study conducted by NUS Economics Associate Professor Alberto Salvo has revealed that different socioeconomic groups of Singapore households display significant variance in the way they use water and electricity for heat relief. Results from the study showed that when ambient temperatures rise, demand for water increases in lower-income households while demand for electricity increases among higher-income households. This suggests that lower-income households use water to cool down while higher-income households are more likely to turn to air-conditioning to beat the heat.

The study examined the water and electricity bills of over 130,000 households — a 1-in-10 random sample of Singapore households — from 2012 to 2015. Unseasonably warm or cool months were identified and each household’s use of resources in these months was compared against its usage at the same point in surrounding years.

Analysis of the data showed that with a one degree Celsius increase in temperature, the average lower-income household, such as those living in a 2-room apartment of about 50sqm, increased its water use by nine litres per day, which amounts to an additional daily shower for every 2.3 households. At the time of the study, less than 20 per cent of 2-room apartments had an air-conditioner.

However, when the data turned to higher-income households, such as those staying in 5 or 6-room apartments (110sqm or more) where air-conditioners are more prevalent, no significant change in water consumption was observed; instead there were large shifts in electricity demand. Demand for electricity in higher-income households increased by an average of two kilowatt hours per day per additional one degree Celsius, which is equivalent to operating an air-conditioning unit for two more hours each day.

The rise in global temperatures affects demand for the vital and scarce resources of water and energy, said Assoc Prof Salvo. “Examining the demand for such resources among Singapore households across the socioeconomic distribution can provide insights on how other urban populations in tropical Asian cities will respond as incomes rise and the climate warms. This will enable policymakers to introduce cooling strategies that better balance the use of natural resources with local availability, such as water,” he added.

To complement the observational evidence from the study, Assoc Prof Salvo did a 300-person survey that looked at the heat relief behaviours by Singapore households. The results of the survey showed that 39 per cent of respondents stated that they would shower more often and longer on a very hot day, and 36 per cent indicated that they would turn on the air-conditioner. The survey also revealed that more showers, washing of one’s face and washing of one’s clothes are the more common water-based cooling behaviours adopted by Singapore households.

“As we face shifting temperature extremes and rainfall variability, the study can contribute towards improving demand forecasting for water and electricity in water-stressed cities in tropical Asia...This can facilitate better design and allocation of water and electricity grids,” said Assoc Prof Salvo. Looking specifically to Singapore, he suggested that the study could help in adjusting the supply of residential water and electricity as temperatures continue rising over the next decades, and during periods of draught, which may be more frequent. 

Additionally, this research could help the region in understanding and adapting to climate change. “Since electricity generation emits carbon dioxide, the study can also help predict the nation’s emissions relative to its international commitments,” he said.

Looking to the future, Assoc Prof Salvo aims to conduct further studies to explore if the findings for Singapore can be extended to urban populations in other cities in tropical Asia such as Mumbai and Jakarta, which have different climates or levels of economic development.

The findings were published in scientific journal Nature Communications on 20 December.