Hi Sharmin,
I don't have any technical proof to that but i have noticed that hot weather causes dehydration (as zainab sweats a lot)and dehydration causes hb drop,so i always urge my daughter to drink more and more water in hot weather,some juices,and try my best not to send her out much,other then the school.Try to keep her clothing light and make her take shower at least twice a day.
Love,
ZAINI.