The 1930s in North America, often called the Dust Bowl decade, were marked by an extraordinary climate anomaly characterized by severe drought and record-breaking heat waves. This period saw an unprecedented frequency and intensity of high temperatures, particularly across the Great Plains and Midwest regions of the United States. Many single-day high temperature records set during this era remain unbroken today. The simultaneous occurrence of multi-year drought and searing heat transformed the central U.S. into a parched landscape, setting the stage for one of the nation’s worst environmental disasters. This historic anomaly resulted from a complex interplay between distant oceanic influences, localized atmospheric patterns, and human-induced changes to the land surface.
Large-Scale Natural Climate Drivers
The foundational conditions for the 1930s heat and drought were initiated by large-scale, naturally occurring climate cycles, specifically anomalies in Sea Surface Temperatures (SSTs) across the Pacific and Atlantic Oceans. These oceanic temperature patterns act as teleconnections, influencing weather systems thousands of miles away. During the Dust Bowl era, the Pacific Decadal Oscillation (PDO) was in a negative phase, meaning the eastern tropical Pacific Ocean was cooler than average.
This cool Pacific anomaly, associated with La Niña-like conditions, shifted the jet stream’s path over North America. The altered jet stream favored the development of an atmospheric ridge of high pressure over the central and western United States, leading to reduced precipitation. Simultaneously, the Atlantic Multi-decadal Oscillation (AMO) was in a warm phase, characterized by warmer-than-average SSTs in the North Atlantic basin.
The combination of a cool Pacific and a warm Atlantic suppressed moisture transport into the Great Plains. The warm Atlantic Ocean diminished the strength of the Azores-Bermuda anticyclone, which pushes moist, subtropical air from the Gulf of Mexico northward into the central US. This reduction in moisture advection meant that air masses entering the Great Plains were already drier, pre-conditioning the region for drought. The confluence of these oceanic phases created a persistent, large-scale atmospheric setup that starved the central US of rainfall.
The Role of Atmospheric Blocking Patterns
The immediate meteorological cause of the sustained heat and lack of precipitation was the frequent presence of persistent, stationary high-pressure systems, known as atmospheric blocking. These upper-level ridges settled over the affected regions, acting like a “heat dome” that prevented the normal movement of weather systems. This blocking pattern steered rain-bearing low-pressure systems and cold fronts far north of the drought-stricken areas, resulting in significant precipitation deficits.
Within these blocking high-pressure zones, air slowly sinks, causing it to warm through adiabatic heating. As the air compresses and descends, its temperature rises, further intensifying the surface heat. The persistent high pressure also led to clear, cloudless skies, allowing maximum solar radiation to reach the surface, which superheated the already dry ground. This intense solar exposure, combined with the subsiding, warming air, ensured that heat waves were severe and long-lasting.
The mid-tropospheric blocking was a common feature during the late spring and early summer months, exacerbating the dry conditions established by the large-scale ocean drivers. This localized atmospheric stagnation prevented the advection of moist air from the Gulf of Mexico, maintaining the cycle of dryness and heat over the Plains. The sustained nature of this high-pressure setup locked in the pattern of intense heat, which was amplified by conditions on the ground.
Land Use and the Dust Bowl Feedback Loop
The most significant factor that amplified the natural drought into a catastrophic heat anomaly was the human alteration of the land surface. Prior to the drought, vast tracts of the Great Plains, covered by native prairie grasses, were plowed under to plant crops. This poor land management, coupled with the multi-year drought, led to massive crop failure and exposed the fine topsoil to the wind, creating the infamous dust storms.
The removal of the native grasses and the resulting bare soil initiated a powerful positive feedback loop that intensified surface temperatures—the evaporative cooling deficit. In a healthy ecosystem, a portion of the incoming solar energy is used to evaporate moisture from the soil and transpire water from plants (latent heat flux), which cools the air. When the soil dries out and vegetation dies, this cooling process ceases.
The solar energy used for evaporation is instead converted directly into heating the air near the surface (sensible heat flux). This shift in the surface energy balance caused air temperatures to soar far beyond what natural climate drivers alone would have produced. Computer models show that including human-induced land degradation, such as reduced vegetation and dust aerosols, is necessary to accurately reproduce the magnitude and location of the extreme heat experienced during the 1930s. The land use practices effectively turned the Great Plains into a furnace, amplifying a naturally occurring drought into one of the most severe heat events in North American history.