Nighttime temperatures the main cause of heat-related deaths in Barcelona 

High nighttime temperatures are found to be the main cause of heat-related deaths around Barcelona, according to two studies done at the Polytechnic University of Catalonia's Center for Land Policy and Valuations (CPSV). 

"People don't die in Barcelona from the heat wave during the day, they die at night because they can't recover," said Josep Roca, the CPSV professor and lecturer at the Barcelona School of Architecture. 

Roca said the nocturnal warmth is a "silent killer," and says the lack of cooling during the night prevents the body from recovering after episodes of extreme heat throughout the day. 

Data between 2007 and 2018 analyzed found that 721 deaths were linked to high nighttime conditions, and 571 were linked to daytime heat. 

Researchers question the high temperature warning protocols currently in place, as they do not give enough weight to the risk of high minimum values seen at night. 

The current nighttime heat warning sits at 27°C.

Roca, however, described this figure as "real madness" since he considered the health risk to be "much earlier."

Specifically, Roca and the CPSV, places significant risk of mortality at 30°C maximum temperatures during the day and 24°C minimums for night. 

The CPSV has also warned that the elderly "are most vulnerable to this threat."

The research centre has begun installing sensors inside homes of elderly people to monitor temperatures and humidity during the night. 

They hope to create a database on indoor thermal comfort.