Heat index is the apparent temperature human body feels when the actual air temperature and relative humidity both are on the higher side. Increased exposure to high heat index can cause extreme exhaustion and heat stroke.
Taking the summer season from May to September, when the effects of Heat index are much more conspicuous, Pakistan can be defined into following major climatic zones based on his index.
Low Index Climatic Zone
It is the climatic zone of Pakistan where index lies between 80 to 90 F from May to September each year. The effects on human body are mild and fatigue is possible with prolonged exposure or physical activity done. This zone includes the hilly areas of KPK, Baluchistan, Punjab and Kashmir. Typical stations in this category are Abbotabad, Murree, Parachinar, Rawalakot, and Quetta. This is the most comfortable zone during the summer seson.
Moderate Index Climatic Zone
In this climatic zone the index remains between 91 F to 106 F. This zone includes places closer to hill stations but are not themselves hill stations like Islambad/ Rawalpindi, Haripur, Muzaffarabad and the piedmont plains of Punjab. The effects of this moderate index are that heat cramps and heat exhaustion possible with prolonged exposure to heat and by performing any sort of Physical activity.
High Index Climatic Zone
This contains almost whole of Punjab (minus the hill stations and lower Punjab adjoining Sindh), all the Plain areas of KPK, almost whole of Baluchistan minus Quetta, Kallat and Ziarat etc., and complete coastal belt of Pakistan. Here index ranges from 107 F to 130 F. In this zone, in addition to heat exhaustion and heat exhaustion, heat stroke is likely with prolonged exposure.
Very High Index Climatic Zone
This comprises of Interior Sindh, lower Punjab and the area around Sibbi in Baluchistan. Here the heat index remains above 130 F from May to September each year and Heat Stroke is highly likely with continued exposure. It is this zone where most of the sunstroke cases are reported each year. Therefore the hottest part of the day must be avoided as much as possible for any outdoor activity.
Thus, Pakistan has a variety of Heat index but the point to note is that except a few hill stations in the North of the country, where the temperatures are comfortable enough, there is clear risk of exhaustion and heatstroke during the Months of May to October.