In the summer of 2023, southwestern North America endured a climatic phenomenon of unprecedented severity: a hot drought that fused the devastating elements of both drought and extreme heat into a relentless and compounded crisis. This event, manifesting across Arizona, New Mexico, and Texas, was not simply a matter of high temperatures colliding with arid conditions; rather, it illustrated a complex interplay of atmospheric and soil moisture dynamics that researchers have only recently begun to unravel. A new study published in Geophysical Research Letters presents compelling evidence that the origins of this scorching drought extend beyond U.S. borders, pointing to dry soil conditions in northern Mexico as a key driver in the propagation of extreme heat and drought hundreds of miles downstream.
Traditionally, drought and heatwaves have been treated as separate threats, each with distinct meteorological signatures and impacts. However, “hot droughts,” as defined by the research team led by Enrique Vivoni and Somnath Mondal, occur when these phenomena simultaneously overlap — specifically when at least two weeks of unusually low precipitation coincide with three or more consecutive days of anomalously high temperatures. Unlike isolated heatwaves or droughts, hot droughts create a feedback loop that intensifies both heat and soil moisture deficits, yielding far-reaching consequences for ecology, agriculture, public health, and infrastructure resilience.
A critical insight from the 2023 hot drought analysis is the discovery that dry soils in northern Mexico play a disproportionately influential role in exacerbating heat and drought conditions in the southwestern United States. Through extensive data analysis—including satellite and ground-based soil moisture readings, rain gauge data, and high-resolution temperature records—Mondal and Vivoni demonstrated that the traditional understanding, which places local soil dryness as the primary factor for heatwaves in the U.S. Southwest, may underestimate the transboundary nature of this phenomenon. The weak North American Monsoon in 2023 led to diminished moisture transfer from the Pacific Ocean over Mexico; this stifled the typical evaporation and subsequent atmospheric moisture recycling that fuels regional rainfall, leaving Mexican soils critically desiccated, and triggering a cascade of dry air masses moving northward into the American Southwest.
This moist-to-dry atmospheric transit underscores a broader lesson in climate science: weather and climate do not heed geopolitical boundaries. The researchers stressed that dry winds know no borders, meaning that environmental conditions in Mexico can precipitate direct and severe effects on neighboring U.S. regions, compounding heat and drought stress. This cross-border drought propagation challenges current forecasting methodologies that often focus on localized precursors and opens a new pathway for early warning systems that could mitigate impacts through transnational cooperation.
Additionally, the study brought to light an overlooked dimension of hot drought: the abnormal persistence of elevated temperatures during night-time hours. Ordinarily, desert regions experience considerable cooling after sunset, as the ground loses accumulated solar heat rapidly. However, in the extreme case of 2023, researchers found a deviation from this natural cycle. The heat amassed during daytime did not dissipate fully overnight, maintaining warmer conditions and thereby reducing the respite typically afforded to ecosystems and humans alike. This phenomenon creates a thermal carryover effect that accumulates over consecutive days and weeks, enhancing the severity and persistence of heat stress. Importantly, the study observed this effect not only in urban heat islands—where anthropogenic structures retain heat—but also across rural landscapes traditionally characterized by cooler nocturnal temperatures.
The mechanisms underpinning this nocturnal heat retention involve complex thermodynamic interactions between dry soils, air temperature, and atmospheric stability. Dry soils absorb and re-radiate heat more efficiently than moist soils, given that less energy is expended on evaporative cooling. Coupled with diminished cloud cover and weakened monsoonal moisture fluxes, the arid soil surfaces acted as persistent heat sources well into the night. This multifaceted climate feedback inherently exacerbates risks to human health, particularly for vulnerable populations, outdoor workers, and recreationists who may underestimate the ongoing exposure to hazardous heat after sunset.
Quantitatively, the hot drought of summer 2023 was startling in its intensity. The heat anomaly incremented regional temperatures by as much as 8 degrees Celsius above typical summer highs, elevating the thermal baseline from already scorching ranges near 35 to 40 degrees Celsius to new extremes. This elevation translated into stresses on regional water resources, widespread agricultural failures, and heightened wildfire likelihood. The event’s magnitude was nearly quintuple the average severity of hot drought conditions observed over the prior forty years, emphasizing an accelerative trend likely exacerbated by anthropogenic climate change.
From a climatological perspective, this heat escalation was interlinked with atmospheric circulation anomalies that suppressed moisture inflow from the Pacific Ocean, disrupting the North American Monsoon’s usual rhythm. The monsoon, responsible for a significant fraction of annual precipitation (up to 80% in some areas), faltered due to persistent high-pressure ridges and altered wind patterns. These atmospheric stunts curtailed the moisture recycling process—typically sustained by soil evaporation in Mexico fueling downstream thunderstorms—leading to a vicious cycle of aridity spreading northward into the U.S. Southwest.
This discovery holds profound implications for climate forecasting and preparedness strategies. Currently, heatwave warnings and drought prognostications prioritize localized environmental indicators. However, Vivoni and Mondal’s results advocate for a paradigm shift toward integrated, cross-regional monitoring frameworks. Alert systems capturing upstream soil moisture deficits in Mexico could provide critical lead time for southwestern U.S. communities to activate health protections, adjust agricultural practices, and deploy emergency cooling resources. This interconnectedness necessitates bi-national collaboration in climate risk management, transcending conventional boundaries to ensure comprehensive resilience against hot drought hazards.
Moreover, the study reveals a troubling consequence that hot droughts amplify health risks beyond those associated with classical heatwaves alone. Persistent nocturnal heat leaves vulnerable populations with no “cooling window” to recover, heightening incidences of heat-related illnesses and mortality. This lack of overnight respite challenges existing public health advisories that often promote early morning activity as a mitigation measure. Thus, enhanced public awareness campaigns explicitly tailored to the unique dangers of hot droughts are vital for safeguarding communities exposed to these evolving climate extremes.
Looking forward, the researchers emphasize the need to deepen mechanistic understanding through advanced climate models that can simulate the downwind transfer of hot drought more precisely. Observational data has laid the groundwork, but capturing the nuanced atmospheric and soil interactions responsible for these phenomena demands sophisticated computational approaches. Furthermore, exploratory studies are proposed to investigate if similar cross-boundary hot drought propagation dynamics exist in other monsoonal arid regions worldwide, such as the India-Pakistan border area. This broader comparative analysis could illuminate universal principles governing hot drought behavior in semi-arid climates subject to seasonal moisture fluxes.
In conclusion, the summer 2023 hot drought in southwestern North America signifies a clarion call in climate science and environmental management. The event not only exemplifies the intensifying threats posed by climate change but also reveals previously underappreciated transboundary processes that magnify risks in interconnected regions. As Vivoni succinctly articulated, “Climate doesn’t respect national borders. We’re more interconnected than we thought.” Recognizing and adapting to this interconnectedness enables targeted, effective responses to protect lives, livelihoods, and ecosystems amid a warming world where hot droughts become an increasingly frequent and persistent hazard.
Subject of Research: Not applicable
Article Title: Hot Drought of Summer 2023 in Southwestern North America
News Publication Date: 17-Sep-2025
Web References:
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GL118308
- https://www.nature.com/articles/s41597-025-04610-y
References:
Mondal, S., & Vivoni, E. R. (2025). Hot Drought of Summer 2023 in Southwestern North America. Geophysical Research Letters. https://doi.org/10.1029/2025GL118308
Keywords: hot drought, southwestern United States, soil moisture, North American Monsoon, climate change, heatwaves, drought propagation, nocturnal heat retention, transboundary climate impacts, public health, atmospheric moisture cycling
