Variability and Trends in Atmospheric Vapor Pressure Deficit with Heat Extremes across the United States

Heat extremes might soon be the new normal, considering the global temperature rise by 1.2°C in the recent decades, attributable to anthropogenic climate change. With temperature rise, it is also important to consider the change in humidity, as both play an important role in maintaining life, with significant implications in weather and ecosystem health.

In this context, our study investigates the evolution of Vapor Pressure Deficit (VPD), a measure of atmospheric dryness relative to saturation. This study utilizes the ERA5 reanalysis dataset in conjunction with the CESM 2 Large Ensemble (CESM-LE) historical and Greenhouse GAS (GHG) single forcing simulations spanning the years 1850 to 2014. VPD quantifies the difference between the moisture capacity of saturated air and the actual moisture content. This metric yields insights into atmospheric water vapor availability and its potential influence on various processes, such as evaporation, transpiration, and cloud formation.

Previous research has emphasized that changes in VPD impact energy partitioning towards latent heat (LH) to fulfill atmospheric moisture demand. We explore this phenomenon within large ensemble simulations, comparing historical runs to those with greenhouse gas forcing. Both increases and decreases in VPD carry significance, influencing various natural processes and systems, particularly in climate and ecosystem dynamics. Our composite analysis reveals a predominant increase in VPD, particularly evident during hot and humid seasons. By focusing on summer and spring, we observe a shift in the VPD pattern, with spring displaying a heightened VPD increase. This aligns with earlier findings of amplified spring temperatures. Furthermore, we scrutinize trends in heat extreme months within historical and greenhouse gas (GHG) forcing scenarios. It's important to highlight that the choice of the climatological period for calculating anomalies plays a crucial role in shaping the observed spatial patterns of VPD variability. These findings are useful for understanding the evolving climate and its implications for various sectors, including agriculture, public health, and infrastructure. However, it is important to acknowledge certain limitations in the data and simulations, such as potential model biases and methods.