A shift to further aridification of dry portions of the world is underway. This is especially the case in the world’s most biodiverse desert, the Sonoran Desert of the southwest United States and northern Mexico. In addition to an ongoing more than two-decade drought this region is experiencing, anomalous heat and drought events are rapidly becoming frequent events, such as what occurred in 2020 through 2021, which are altering the climatic underpinnings of the region.

What is the impact of these recent extreme drought events on the vegetation across the region and what plant thresholds are being past?

Myself and colleagues from across the Sonoran Desert conducted a study, “Plant Responses to Anomalous Heat and Drought Events in the Sonoran Desert” to evaluate the impacts of the 2020–2021 region-wide heat and drought event at three scales:

1. A landscape level assessment of ecosystem stress across the entirety of the Sonoran Desert based on precipitation and temperature data from meteorological stations and a satellite-derived vegetation health index (VHI),
2. Assessments of stress on iconic columnar cacti and succulent trees, and
3. Mechanistic plant responses to extreme heat and drought, and secondary biotic stressors from insect attacks.

2020 was the hottest and driest year since 1980 across the Sonoran Desert region, and vegetation health, determined from VHI, was also near its lowest point. Field-based assessments of columnar cacti across the Sonoran Desert revealed high levels of acute plant stress, including cactus scorching, defined by rapid onset of discolored photosynthetic tissue that leads to permanent photosynthetic dysfunction and increased plant mortality. Tissue scorching corresponded with a three-fold increase in mortality of giant cactus species across the region relative to background levels following 2020–2021. Likewise, repeated plant health surveys show a persistent legacy of the 2020–2021 anomaly, resulting in a marked reduction in the current health and survival of the iconic giant saguaro (Carnegiea gigantea) in the northern Sonoran Desert.

We have also created an iNaturalist project to help collect data across the desert.

To help understand the impact of heat and drought events on the vegetation of the Sonoran Desert, we created this video of weekly Vegetation Health Index values derived from NOAA satellite data between 1980–2022. Read more in the research paper, Plant Responses to Anomalous Heat and Drought Events in the Sonoran Desert, https://onlinelibrary.wiley.com/doi/10.1111/gcb.70217