<p>Humid heat extremes are expected to intensify in conjunction with rising global temperatures, leading to prolonged and elevated exposure to hazardous levels of heat stress (HS). Even moderate levels of HS have been observed to trigger a range of health and socioeconomic impacts, underscoring the need for regional climate information. Therefore, we examine the present and future conditions of two different HS indices, wet bulb temperature (WBT) and environmental stress index (ESI), for the first time at such high resolution over northwestern Türkiye using a non-hydrostatic regional climate model, COSMO-CLM. The study is also pioneering in its effort to assess population exposure to these indices at the provincial scale. The findings indicate that the most substantial shifts in the probability density function of both HS indices from the middle of the 21^st century onward are expected to occur in June relative to the reference period. However, WBT intensity with ~ 4&#xa0;°C increase is projected to undergo the most significant change in September, while ESI has the largest increase in July. According to ESI projections, almost all areas (&gt; 95%) in cities such as Istanbul, Tekirdağ, Edirne and Çanakkale will experience severe HS at least once in July after 2071, while based on WBT projections, the same cities will face similar conditions after 2091. The 2091–2100 period will be subject to the longest exposure duration, the greatest areal expansion, and the highest population exposure levels. Conversely, Kütahya, Bilecik, and Kırklareli are expected to have the least substantial increase in exposure among 12 cities.</p>