How do you define and track a heat wave? Like many other extreme
weather phenomena, there is no single way to define or track
heat waves, but common definitions take into account their
potential impacts. The heat index, for example, is an aggregate
measure that combines temperature and humidity — two primary
weather factors that determine human perception of heat. On the
other hand, human mortality, in the devastating heat waves of
Chicago or Paris, for example, is often caused not just by high
daytime temperatures but by consecutive nighttime temperatures
exceeding certain thresholds. One other measure for heat waves
is cooling degree days, which attempts to relate temperatures to
energy demand for air conditioning. For agriculture and food
security, heat waves and temperature extremes may be defined
through specific thresholds beyond which certain crops cannot
survive. Occasionally while studying climate variability or
change, we track temperatures that set new records, which would
in turn vary depending on