The New York-based nonprofit group said hundreds of workers are dying every year and has urged authorities in the Gulf state to "enforce adequate restrictions on outdoor work" while also calling for regular investigations and information on worker deaths.
It said migrant workers in other Gulf Cooperation Council (GCC) countries -- Bahrain, Oman, Kuwait, Saudi Arabia and the United Arab Emirates -- were also vulnerable as statutory summer work breaks were not linked to actual weather conditions.
Generally, government regulations prohibit workers in Qatar from working outdoors between 11:30am and 3pm from June 15 to August 31.
But, in a statement, HRW said weather conditions in Qatar outside those times frequently reach levels that can result in "potentially fatal heat-related illnesses in the absence of appropriate rest."
"Limiting work hours to safe temperatures -- not set by a clock or calendar -- is well within the capacity of the Qatari government and will help protect hundreds of thousands of workers," said Sarah Leah Whitson, Middle East director at Human Rights Watch.
Sheik Saif Al Thani, director of the Government Communications Office, told CNN in a statement that Qatar was committed to is labor reform program and was constantly reviewing its policies to ensure that "migrant workers receive the necessary on-site protections."
He said Qatar was the first Gulf country to implement restrictions on summer working hours and that these daily restrictions "exceeded those of Saudi Arabia and the UAE."
"In addition to issuing harsh financial penalties," he continued. "Qatar is also the only country in the Gulf that shuts down companies that are found to be operating in violation of the ban."
'Unexplained causes of death'
Migrant labor accounts for 95% of Qatar's total labor workforce, with 40% or 800,000 of these workers employed in construction, according to the HRW report.
Qatar was announced as the host city for the 2022 World Cup in December 2010 and has since embarked on a huge infrastructure campaign in preparation for football's biggest tournament, spending nearly $500m a week on World Cup projects according to Qatari authorities.
In 2013, the Qatari government revealed that 520 workers from Bangladesh, India and Nepal died in 2012 -- 385 of them from unexplained causes.
Last year, authorities told HRW that 35 workers had died, mostly from falls.
HRW recommended that the government of Qatar release data on migrant worker deaths for the past five years, including cause of death which would "allow an assessment to the extent to which heat stress is a factor."
Sheik Thani said the government submitted statistics on all work-related deaths in Qatar for 2016 to the International Labour Organization (ILO), which is publicly available on their website.
"We continue to co-ordinate closely with the ILO and international NGOs to implement reforms that will improve the health, safety and rights of migrant workers," he said
'Authorities need to scale up transparency'
Qatar's World Cup organizers, the "Supreme Committee for Delivery and Legacy," says it's attempting to enact higher welfare standards than are generally applied to migrant workers in Qatar, last year introducing work-to-rest ratios which were in proportion with the risk posed by heat and humidity.
But HRW said that applied to only about 1.5% of the country's construction workforce and did not take into account the effect of sunlight which, according to the statement, significantly increased the risk of heat stress.
"As Qatar scales up its FIFA World Cup construction projects, authorities need to scale up transparency about worker deaths that could be heat related, and take urgent steps to end risks to workers from heat," Whitson said.
Of a total of 10 worker deaths on World Cup projects between October 2015 and July 2017, the Supreme Committee classified eight deaths as "non-work related" with seven of the deaths resulting from "cardiac arrest" and "acute respiratory failure."
HRW said such terms made it "impossible to determine" whether those deaths were related to working conditions, such as heat stress.
In a statement issued on its website, the Supreme Committee said it acknowledged the concerns raised by HRW and had discussed those concerns "at length" with HRW representatives over the last few weeks.
The statement read: "However, we whole-heartedly refute the suggestion the SC has "abdicated responsibility" or that the SC has failed to protect the lives of workers on our projects.
"To date there have been two work-related fatalities and nine non-work related deaths of workers engaged on our projects. The SC profoundly regrets the death of any worker, and we treat every incident with the utmost seriousness.
"However, the SC does not have the authority or mandate to determine cause of death, which is reflected in death certificates issued by the medical authorities in Qatar... The SC investigates all fatalities on SC sites to establish whether they could have been prevented and, if so, to identify improvements for the future.
"The SC has provided HRW with the information requested concerning the circumstances surrounding non-work related deaths on our projects."
The HRW statement also criticized the Qatari government's failure to implement two key recommendations of a 2014 report by the international law firm DLA Piper, which the government itself had commissioned.
DLA Piper had reported that the number of deaths in Qatar attributed to cardiac arrest was "seemingly high" and had called for legal reform in the country to allow postmortem examinations in cases of unexpected or sudden deaths, and an independent study into the deaths "vaguely attributed to cardiac arrest."
"Qatar sought the spotlight by bidding for the 2022 World Cup, brought in hundreds of thousands of migrant workers to build roads, stadiums, and hotels, and then shelved key recommendations from their own consultants to investigate migrant worker deaths," added Whitson.
"FIFA and national football associations should make clear they expect life-saving changes to law and practice that could set a Gulf-wide example of how to save construction worker lives now -- and in the future."
FIFA 'Fully committed'
FIFA told CNN it was "fully committed" to protecting the rights of construction workers involved in building infrastructure for the World Cup in Qatar.
A FIFA spokesperson said it was working closely with the Supreme Committee, adding that health and safety and workers' protection measures put in place by the committee met the "highest international standards."
"Contrary to the implications made by Human Rights Watch in its statement, the vast majority of construction work currently undertaken in Qatar is not linked to the 2022 FIFA World Cup," the spokesperson continued.
"As part of their National Vision 2030, Qatar started a wide-ranging and ambitious (program) to develop its national infrastructure well before and independent of the awarding of the 2022 FIFA World Cup.
"Nevertheless, FIFA will continue to engage with the Qatari authorities to build on the initiatives put in place for the 2022 FIFA World Cup and help raise the bar in regards to (labor) standards across the country, and in accordance with relevant International Labour Oorganization (ILO) Conventions, to the benefit of all workers employed in Qatar."