DEPICTION OF CLIMATE ZONES IN THE CONTERMINOUS UNITED STATES USING REMOTE SENSING: APPLICATION TO VULNERABILITY ASSESSMENT AND PUBLIC HEALTH

摘要

Identification of areas with comparable weather patterns has the potential to substantially improve forecasting of adverse health outcomes, disturbances in ecosystems, and infrastructure damages caused by extreme meteorological events. We aimed to design informative climate classification for assessing vulnerability and health risks. We proposed to define climate zones for the Conterminous United States using remote sensing and to compare it with the Koppen-Geiger divisions. Using the nationwide database of hospitalizations, maintained by the Centers of Medicare and Medicaid Services, we examined the utility of the unsupervised classification based on a time series of Normalized Difference Vegetation Index (NDVI) to assess vulnerability to extreme weather, defined by the likelihood of extreme cold weather, the number of residents prone to adverse effects, and the rate of severe health outcomes relevant to exposure to cold among older adults. Individual biweekly MODIS NDVI image composites from July 2002 to July 2012 were aggregated, masked, and compiled into a 229-dimensional dataset. Longitudinal and temporal data redundancies were reduced by extracting the first 12 principal components. A "majority" 15×15 convolution was applied to the classification output. Locations of climate zones were determined by k-means unsupervised classification. NDVI-based zones exhibited a high degree of similarity with KSppen-Geiger divisions and a well-defined separation by the annual and seasonal temperature and precipitation values. We determined that relatively warm and humid south eastern region had the largest population at risk (10.9 million) and the highest rate of hospitalizations due to exposure to cold (28.3 cases per 10,000 persons-at-risk). The dry south-western region had the lowest rate of hypothermia hospitalizations (14.6 cases per 10,000 persons-at-risk). Although vulnerability assessment and public health study was limited to a relatively short period 1991-2006 and exposures to cold weather among adults aged 65 and older, the proposed method demonstrates strong potentials for public health applications.