Water Availability and Heat-Related Mortality: Evidence from South Africa Kelly Hyde University of Pittsburgh1 Rising global surface temperatures threaten to reduce precipitation and evaporate surface freshwa- ter in areas already experiencing water stress. In this paper, I demonstrate that higher upstream water availability significantly reduces the slope of the temperature-mortality relationship dur- ing the summer. This suggests investment in water infrastructure is an effective community-level adaptation to climate change, especially where the status quo of water access is relatively poor. As an example of such investment, I show a transnational water transfer project both increased water availability and reduced hot-season mortality in receiving districts. 1 Introduction As global surface temperatures rise, adaptations to heat become more important to survival and quality of life. Excess heat has been shown to decrease cognitive performance (Zivin et al. 2018), increase cardiovascular and respiratory mortality risk (Basagan˜a et al. 2011, Curriero et al. 2002), increase incidence and severity of injury during physical exertion (Nelson et al. 2011), increase in- cidence of low birth weight (Deschˆenes et al. 2009) and infant mortality (Banerjee and Bhowmick 2016), and ultimately, increase overall mortality (Hajat and Kosatky 2010). Higher tempera- tures have also been associated with reduced economic production through effects on time use (Graff Zivin and Neidell 2014), crop yields (Schlenker and Roberts 2009), and aggregate economic activity (Burke and Emerick 2016). In this paper, I demonstrate that higher potable water availability significantly reduces the slope of the heat-mortality relationship. At the status quo median of water availability, I find a statistically significant, positive relationship between heat and mortality, with effect sizes in line with prior literature (Burgess et al. 2017, Hajat et al. 2005). However, at one standard deviation above the mean of water availability, the heat-mortality relationship is not statistically significant, with a substantially smaller point estimate. For example, a back-of-the-envelope calculation sug- 14530 Wesley W. Posvar Hall, 230 S Bouquet St, Pittsburgh, PA 15260; email [email protected]. Acknowledgements: I thank Osea Giuntella, Karen Clay, Yogita Shamdasani, Randall Walsh, Andrea La Nauze, Evan Plous Kresch, Seema Jayachandran, anonymous referees, and conference session attendees at the Population Association of America (PAA) 2019 annual meeting, the American Society of Health Economists (ASHEcon) 2019 annual meeting, NCSU CEnREP Camp Resources 2019, and the Population Health Sciences Research Workshop 2019 for helpful comments and guidance. I also thank Vusi Nzimakwe, Kelebogile Olifant, and Thabo Molebatsi with Statistics South Africa for their assistance with the mortality data used in this paper. 1 gests the December 2018 heat wave in Pretoria2, despite only lasting a few days, would on average increase the monthly mortality rate by about 3.2 per million people (p < 0.01). Increasing potable water availability by one standard deviation from the mean reduces this point estimate to about 0.8 per million (p 0.29). ≈ I employ two causal identification strategies. First, I create measures of upstream, down- stream, and within-district potable water availability for each of the 52 districts of South Africa, and I isolate the effect of upstream water availability by controlling for within-district and down- stream measures in panel fixed-effects regressions. This strategy has been used in prior literature (e.g. Jerch (2018), Chakraborti (2016), Garg et al. (2018)) to address confounders such as local precipitation, which affects a broad range of local outcomes that may be correlated with the heat- mortality relationship (e.g. areal flooding, land suitability for agriculture). To confirm that the estimated effect is specific to heat-related mortality, I use colder months as a comparison group in a difference-in-difference specification, finding that upstream water availability differentially reduces mortality in the summer. Finally, I introduce local precipitation controls and estimate conditional moderating effects of water availability at varying levels of precipitation. I only find a significant moderating effect when local precipitation is relatively scarce, suggesting that upstream water availability moderates heat-related mortality by insuring against local drought. Second, I use a transnational water transfer project as a natural experiment that increased potable water availability in receiving districts. The Lesotho Highlands Water Project, formally inaugurated in 2004, diverted water from the mountains of Lesotho to Gauteng Province, the densely populated industrial center of South Africa. In doing so, the transfer created a new way for upstream water sources to reach targeted districts as well as those positioned downstream. In a difference-in-difference specification, I find the slope of the heat-mortality relationship differentially declined in receiving districts after 2004, and this difference cannot be explained by a decline in overall mortality. In addition to corroborating the preceding findings of the paper, this suggests investment in water infrastructure is an effective community-level adaptation to climate change, especially where the status quo of water access is relatively poor. This finding contributes to the growing literature on the efficacy of adaptations. Adaptations to avoid heat damages can be placed in two broad categories: household-level and community- level (Deschenes 2014). Household-level adaptations are predominantly based on heat avoidance, including spending more time indoors; investing in fans, better insulation, or air conditioning; and migrating away from the heat. Households engaged in agricultural production can also adapt through crop choice and irrigation (Burke and Emerick 2016, Di Falco et al. 2011). Community- level adaptations include early-warning systems for extreme weather, building climate-controlled shelters, and increased access to quality water (Deschenes 2014). This paper provides evidence that 2Coverage: https://www.thesouthafrican.com/weathersa/gauteng-weather-heatwave-expected/. The heat wave resulted in 5 cooling degree days (CDD) in Pretoria in December 2018 at a base temperature of 90◦F (used throughout this paper as a measure of heat incidence). 2 Figure 1: Temperature-Mortality Relationship for South Africa, 2000-2016 200 150 100 Daily death rate per million Daily death rate 50 0 40 50 60 70 80 Daily average temperature (degrees Fahrenheit) increased potable water availability, which has already been shown to have several other positive effects (e.g. Ao (2016), Devoto et al. (2012)), is an effective adaptation to heat. The paper proceeds as follows. Section 2 describes the data and context. Section 3 describes the empirical strategy used to identify the causal effect of water availability on the heat-mortality relationship. Section 4 presents results. Section 5 uses a water transfer project as a natural experiment increasing water availability in receiving districts. Section 6 concludes. 2 Data To identify the effect of water availability on the heat-mortality relationship, I have constructed a panel of mortality, temperature, hydrological, and geographic data. I describe each component of this panel below. Mortality data. I obtained counts of deaths by district and month from 1997 to 2015 from Statistics South Africa. Since there are many ways excess heat can increase mortality, including unnatural causes (see Dell et al. (2014) for a review), my dependent variable includes all deaths, regardless of cause. For a robustness check, I also obtained counts of deaths attributed to infectious gastroenteritis and diarrhea, a leading waterborne cause of death in sub-Saharan Africa, to verify that the results hold for causes of mortality more directly associated with lack of quality water. 3 Temperature data. I use cooling degree days (CDD) at a base temperature of 90◦F (with other base temperatures as robustness checks) as a measure of heat. Degree days are primarily a measure of the energy required to cool or heat a building’s interior to the base temperature3, but prior literature in environmental economics has used them as a measure of heat exposure (e.g. Deschˆenes and Greenstone (2007)). I use CDD in this paper for two reasons. One, it is a continuous monthly measure of both duration and intensity of heat, which may have independent or cumulative effects on mortality. Two, as depicted in Figure 1, the marginal effect of heat on the mortality rate is increasing as the temperature rises above 70◦F, and there is a wide range of temperatures for which the marginal effect is zero or negative. Because CDD truncates temperatures below the selected threshold, the estimated coefficient regressing CDD on mortality rates is the average marginal effect of temperature above the threshold (i.e., the effect of excess heat), which is the effect of interest to this paper. I construct monthly CDD measures from the Global Historical Climatology Network Daily (GHCN-Daily) dataset provided by the National Oceanic and Atmospheric Association (NOAA). The spatial distribution of weather stations included in this dataset are described in Section 3.1. The base temperature was selected in line with prior literature, which typically defines “ex- cess heat” as temperatures above the 90th or 95th percentile in a region (Burgess et al. 2017, Curriero et al. 2002, Hajat and Kosatky