The main objective of this study is to identify how climate variability influences human comfort levels in tropical-coastal urban environments. San Juan Metro Metropolitan Area (SJMA) of the island of Puerto Rico was chosen as a reference point. Temperature and relative humidity are identified as key environmental variables to maintain human comfort level. A new Human Discomfort Index (HDI) using the key environmental variables based on environmental enthalpy is defined. This index is expanded to determine the energy required to maintain indoor human comfort levels and is compared to total electric energy consumption for the island of Puerto Rico. Regression analysis shows that both temperature and HDI are good indicators to predict total electrical energy consumption. Results showed that over the past 35 years the average environmental enthalpy have increased, resulting in the increase of average HDI for SJMA. Surface weather station data further shows clear indication of urbanization biases ramping up the HDI. Long-term local scale (weather station; 30-years record) data shows a decreasing rate of maximum cooling per capita at −11.41 kW-h/years, and increasing of minimum cooling per capita of 10.64 kW-h/years. This contrasts with regional scale data for the whole Caribbean where increasing trends are observed for both minimum and maximum energy per capita. To estimate human comfort levels under extreme heat wave events conditions, an event of 2014 in the San Juan area was identified. The analysis is complemented by data from the National Center for Environmental Prediction (NCEP) at 250km spatial resolution, North American Regional Reanalysis (NARR) at 32 km spatial resolution, and simulations of the Weather Research and Forecasting model (WRF) at a resolution of 1 km, and by weather station data for San Juan. Model results were evaluated against observations showing good agreement for both temperature and relative humidity and improvements from the NCEP input. It also shows that Energy Per Capita (EPC), required to maintain indoor space at human comfort level, in urban areas during a heat wave event can increase to 21% as compared to normal day.

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