DOI: 10.5061/dryad.k6djh9wjn
title: Plant responses to anomalous heat and drought events in the Sonoran Desert

description: A shift to greater aridification in dry regions of the world is ongoing
 and rapidly increasing in intensity, including in the biodiverse Sonoran
 Desert of the Southwest United States and northern Mexico. In addition to
 experiencing over two decades of drought, the Sonoran Desert is facing
 anomalous heat events that are increasing in frequency, evidenced in a
 record hot and dry period in 2020 through 2021. This paper evaluates 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 cactus 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
 cacti 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. This multi-scale assessment of
 previously anomalous heat and drought events on succulent desert plants
 shows landscape-wide impacts that could fundamentally reshape populations
 of these keystone species and the communities that depend on them.
description: # Plant responses to anomalous heat and drought events in the Sonoran
 Desert Dataset DOI: [10.5061/dryad.k6djh9wjn](10.5061/dryad.k6djh9wjn) ##
 Description of the data and file structure **General information on
 precipitation and temperature data**. Meteorological records from Mexico
 were obtained from 10 stations ranging from latitude 24° to the US border
 and for five specific Sonoran Desert locations in the U.S., ranging from
 the Mexican border to latitude 36.1°. We only used data from 1980 onwards,
 before that date significant gaps were found in some of the stations in
 Mexico. A small number of missing data points in some stations were
 gap-filled with the data from the nearest station within the same
 ecological region (missing data points were less than 1% of the monthly
 series in all stations). All data, both for Mexico and the US, was
 recorded in SI units: mm for rainfall and °C (degrees Celsius) for
 temperature. **Data from Mexican weather stations**. Between 2016 and 2018
 the Mexican  weather stations transitioned from manual to automated
 operation. Data from before the transition (i.e., from manual readings)
 were downloaded from CONAGUA's "Información Estadística
 Climatológica"
 ([https://smn.conagua.gob.mx/es/climatologia/informacion-climatologica/informacion-estadistica-climatologica](https://smn.conagua.gob.mx/es/climatologia/informacion-climatologica/informacion-estadistica-climatologica)). Data from the transition onwards (i.e., from the automated weather stations database) were downloaded from CONAGUA's "Resúmenes Mensuales de Temperatura y Lluvias" ([https://smn.conagua.gob.mx/es/climatologia/temperaturas-y-lluvias/resumenes-mensual](https://smn.conagua.gob.mx/es/climatologia/temperaturas-y-lluvias/resumenes-mensual) es-de-temperaturas-y-lluvias). **Data from US weather stations**. Meteorological records from the US were obtained using the PRISM online database, using the Time Series Values for Individual Locations (PRISM Climate Group, Oregon State University, [https://www.prism.oregonstate.edu/explorer/](https://www.prism.oregonstate.edu/explorer/)). **The "ecological year" for the calculation of annual cumulative precipitation**: Taking into account the predictable arid fore-summer throughout the Sonoran Desert (April-May, see main text), we calculated the yearly cumulative precipitation for each of the 15 locations between May and April in the following year, summarizing the precipitation data into “ecological years.” Thus, the cumulative precipitation data for each location was reduced to a series of 44 ecological years. **The "ecological year" for annual maximum temperature**: Taking into account the predictable arid fore-summer throughout the Sonoran Desert (April-May, see main text), we selected the annual maximum monthly temperature for each of the 15 locations between May and April in the following year, summarizing the maximum temperature data for each “ecological year” as a proxy for periods where heat waves might have occurred. ### Files and variables #### File: SonoranDesert\_VegZones\_MajorCropAreasRemoved.zip **Description:** A zip-folder containing the ARC-GIS shapefile (.SHP) describing in vector format the boundary of the Sonoran Desert as used in this study, plus all the other auxiliary files that are necessary to open the shp file. The external perimeter of the Sonoran Desert has the major agricultural areas under irrigation removed (e.g., the Imperial Valley, the Lower Colorado River irrigation districts, the Gila River irrigated plains, and the Mexicali Valley), as these areas might underestimate the severeness of droughts because of the input of allochthonous sources of water. ##### Variables * Vectorized shapefile readable in any desktop GIS Software such as ARC-GIS, ILWIS, MapWindow GIS, QGIS, and many more. #### File: BCS\_plant\_stress\_data.xlsx **Description:** Data on drought damage for 99 species surveys on 20 sites from Loreto to Los Planes, in Baja California Sur. ##### Variables * Column A indicates the location where the survey was done and column B the species that was surveyed in that particular location. Columns C to G indicate the number of individuals found in each health condition (H), with levels I, II, and III of damage, or standing dead (D). The rest of the columns show the data collectors that did the survey, the latitude and longitude of the location, the larger region where the location is found, and the date of the survey. * Drought stress categories were: I (little impact), II (clear impact, with some new growth), III (severe impact, no new growth, unlikely to survive), and D (dead). In the case of *Bursera microphylla*, impact was evaluated by the amount of green foliage, the proportion of dead branches, and the presence of entrance holes to tunnels from wood borers, often exuding a mixture of resin and frass. In the case of cacti, damage was assessed by the amount of epidermal browning in the stem, the presence of stem constrictions close to the apex, and signs of damage by cactus borers (*Moneilema* spp., Cerambicidae). #### File: Pooled\_precipitation\_dataset.xlsx **Description:** Cumulative annual precipitation between 1980 and 2023 for 15 meteorological stations in the larger Sonoran Desert, both in Mexico and the US. ##### Variables * Row labels indicate the year of observation, and the column labels show the location where the weather records were collected. #### File: Pooled\_temperature\_dataset.xlsx **Description:** Maximum mean monthly temperature (hottest month of the year) for 15 meteorological stations in the larger Sonoran Desert, both in Mexico and the US, between 1980 and 2023. ##### Variables * Row labels indicate the year of observation, and the column labels show the location where the weather records were collected. ## Code/software * [Microsoft Excel](https://zapier.com/blog/best-spreadsheet-excel-alternative/#Excel) * [Google Sheets](https://zapier.com/blog/best-spreadsheet-excel-alternative/#google-sheets) * [Zoho Sheet](https://zapier.com/blog/best-spreadsheet-excel-alternative/#zoho-sheet) * [LibreOffice Calc](https://zapier.com/blog/best-spreadsheet-excel-alternative/#LibreOffice) * ARC-GIS * QGIS * ILWIS ## Access information Other publicly accessible locations of the data: * None Data was derived from the following sources: * Our own research