The total surface area of the Great Lakes is over 94,250 miles 2 . Consisting of five large lakes, they contain over one fifth of the world's total surface fresh water, with depths of up to 400 m (EPA, 2020). The Great Lakes substantially influence the regional weather and climate via their effects on the atmospheric energy and water budget; open water typically has greater thermal conductance, lower albedo, and lower roughness compared to soil or vegetated surfaces (Notaro et al.,2013;Scott & Huff, 1996). The large thermal inertia of the lakes leads to a reduction in annual and diurnal temperature ranges across the Great Lakes Basin (Harris & Kotamarthi, 2005;Notaro et al., 2013). Mean minimum temperatures in the region are warmer during all seasons and over all five lakes, while maximum temperatures are cooler during spring and summer (Scott & Huff, 1996). Lake thermal impacts and associated evaporation have a strong influence on regional precipitation patterns. While many studies have investigated the impact of lake surface temperature (LST) on the cold-season precipitationwhich is primarily a direct product of warmth and moisture from the Great Lakes (e.g., lake-effect snow; Notaro et al., 2021; Shi & Xue, 2019)-the impact of LST on summer precipitation has only rarely been studied. During early summer, the lake surface is still relatively cool compared to the atmosphere, resulting in condensation on the lake surface and a stable boundary layer that deters over-lake convective processes (Miner & Fritsch, 1997;Workoff et al., 2012). Due to the temperature differences over lake and inland, lake breeze can cause air to rise inland and increases the likelihood of over-land precipitation (Schulkowski, 2020). During late summer, while the land cools and the lakes remain warm, the temperature differential between land and lake surface coupled with baroclinic waves (e.g., cold front and trough) and/or the Great Plains low-level jets can generate enhanced precipitation (Feng et al., 2016;Miner & Fritsch, 1997). Therefore, changes in summer LST could potentially affect its feedback to atmospheric stability and change the water and energy budget over the entire Great Lakes Region (GLR). The summer is an ideal time to evaluate the influence of LST on the lake surface-atmosphere
The Great Lakes are the largest freshwater lakes in the world, with a surface area of 244,000 km 2 (Notaro et al., 2013). These vast inland freshwater bodies provide water for many purposes, including drinking, irrigation, shipping, ecological habitats, hydroelectric power generation, and recreation. The Great Lakes Basin is home to 34 million people and is one of the largest economic units in the world; it supports 1.3 million jobs, and $82 billion in wages (Rau et al., 2018). Due to its massive size and the contrasting thermal characteristics (e.g., heat capacity, thermal inertia) between the lake and land, the Great Lakes profoundly influence their local and regional hydroclimate (Changnon & Jones, 1972). Locally, by supplying heat and moisture, the Great Lakes facilitate the formation of lake-effect snowstorms in winter and convective storms in summer (Notaro et al., 2015;Shi & Xue, 2019). Regionally, the lakes can modify atmospheric circulation and other mesoscale features, affecting precipitation and water cycle outside the GLR in nearby regions (
There are large uncertainties in our future projections of climate change at the regional scale, with spatial variabilities not resolved adequately by coarse-grained Earth System Models (ESMs). In this study, we use pseudo global warming simulations driven by end of the century upper end RCP (Representative Concentration Pathway) 8.5 projections from 11 state-of-the-art ESMs to examine changes in summer heat stress extremes using physiologically relevant heat stress metrics (heat index and wet bulb globe temperature) over the Great Lakes Region (GLR). These simulations, generated from a cloud-resolving model, are at a fine spatiotemporal resolution to detect heterogeneities relevant for human heat exposure. These downscaled climate projections are combined with gridded future population estimates to isolate population versus warming contributions to population-adjusted heat stress in this region. Our results show that a significant portion of summer will be dominated by critical outdoor heat stress levels within GLR for this scenario. Additionally, regions with higher heat stress generally have disproportionately higher population densities. Humidity change generates positive feedback on future heat stress, generally amplifying heat stress (by 24.2% to 79.5%) compared to changing air temperature alone, with the degree of control of humidity depending on the heat stress metric used. The uncertainty of the results for future heat stress are quantified based on multiple ESMs and heat stress metrics used in this study. Overall, our study shows the importance of dynamically resolving heat stress at population-relevant scales to get more accurate estimates of future heat risk in the region.
There is an increasing need for high-fidelity atmospheric data at or below kilometer-scale in Earth science (Lucas-Picher et al., 2021). These high-resolution data, oftentimes serving as meteorological forcings, are critical to a variety of regional studies, such as climate risk assessments (
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