Drought and Health Impacts in Arizona

Background Arizona Department of Health Services (ADHS) is a recipient of the Centers for Disease Control and Prevention (CDC) Climate-Ready States and Cities Initiatives Grant to help address and prepare for the health effects related to current and future climate hazards. In 2015, ADHS partnered with a local university to implement the first two steps of the CDC’s Building Resilience Against Climate Effects (BRACE) Framework to forecast climate impacts, assess vulnerabilities, and project disease burden in relation to drought. Arizona experiences extreme variability in precipitation due to its arid and semi-arid climate so a single dry year does not constitute a drought. Rather, drought in Arizona is characterized by a series of drier than normal years that may have occasional respites by a few wetter years. Based on this, Arizona has been in a state of drought for 21 years. Effects of drought extend beyond lack of water into environmental, economic, and social realms. One environmental consequence of drought is an increased risk of dust storms. The adverse health outcomes stemming from dust storm exposure include physical bodily harm in the form of vehicular accidents due to low visibility, exacerbation of chronic respiratory conditions such as asthma, exposure to anthropogenic materials such as pesticides and to biological materials such as the fungus that causes Valley fever. Drought has also been connected with wildfire risk due to decreased soil moisture, allowing for drier conditions that may lead to broadened fire expanse. Health effects related to wildfires include injury, loss of life, and smoke exposure. In alignment with the ADHS mission “to promote, protect, and improve the health and wellness of individuals and communities in Arizona”, ADHS and its partners operationalized the drought causal pathway and assessed Arizonans vulnerabilities for this hazard through the BRACE Framework to inform the Arizona Climate and Health Adaptation Plan. Methods A causal pathway tool was used to evaluate the relationship between drought and the potential health burden on Arizona residents. The pathway was broken down into three sequentially aligned components: exposure of interest, potential modifiers, and outcomes of interest. Potential modifiers were categorized into three categories: climate drivers, individual level activities, or societal level activities. To examine geographical variability in hazard vulnerability and exposure, an all-hazards social vulnerability index for Arizona was calculated in alignment with methodology detailed by the Hazards and Vulnerability Research Institute at the University of South Carolina. Annual precipitation totals was used as a proxy for drought exposure. The Standardized Precipitation Index (SPI) was used to determine future precipitation deviations. Arizona census tracts were assigned to one of five drought hazard risk categories: <5 inches, 5-10 inches, 10-15 inches, 15-20 inches, and >20 inches. Those in the <5, 5-10, and 10-15 inches categories represented high drought exposure. These were then linked with social vulnerability scores. Results We identified multi-scale drivers of health risks associated with drought. Climate drivers included atmospheric composition and changes driven by land use/cover and built environment. Individual level drivers included behavior and risk factors such as age, health status, time lived in Arizona, and pre-existing medical conditions. Societal level drivers included population size, population demographics, and interventions/policy efforts (e.g. early warning systems, public health education and outreach, modified construction and agricultural practices, and maintaining forest health). Social vulnerability analysis identified 6.8% of census tracts in the state associated with high vulnerability and another 21.8% of tracts associated with medium high vulnerability. Maricopa and Pima counties had the most people living in high and medium high vulnerability areas. Regarding county population percentage, Apache County saw the highest percent of residents living in high vulnerability areas (75.5%). The intersection of social vulnerability and hazard exposure revealed numerous locations across the state that are at highest risk of health effects from drought. Linking drought hazard risk to social vulnerability showed that Maricopa County contains the high or medium high socially vulnerable people (1,155,836; 28% of total population) that receive low rainfall (5-10 inches). Yuma County has a small population (108,939; 54% of total population) of high or medium high social vulnerability with <5 inches rainfall. La Paz County has the second highest percent of high to medium high social vulnerability associated with high drought exposure (38%, < 5 inches annually). For areas of low rainfall (10-15 inches), Graham and Greenlee counties have the greatest proportion of vulnerable populations (57% and 68%, respectively). Conclusions Applying the CDC BRACE framework to drought and its potential health effects in Arizona allowed ADHS and its partners to develop an all-hazards social vulnerability tool that is specific to Arizona. This tool was linked to precipitation estimates and projections to identify areas within Arizona that may be more vulnerable than others and thus require more resources in response to an extreme event. Identifying areas of higher risk is important not only for resource management but also to mitigate potential impacts of drought such as vector-borne disease, water-borne disease, mental health, and loss of income. Since conclusion of this project, both precipitation and drought data have been mapped and made publicly available through the ADHS Environmental Public Health Tracking program. The methods outlined have been applied to other potential health hazards associated with drought such as wildfire, dust storms, chronic respiratory conditions, and Valley fever. These results and potential adaptation activities to each hazard will be incorporated into the next version of the Arizona Climate and Health Adaptation Plan.