Michael A. Crimmins

Both topography and climate affected forest and woodland burn severity in two regions of the western US, 1984 to 2006

Fire is a keystone process in many ecosystems of western North America. Severe fires kill and consume large amounts of above- and belowground biomass and affect soils, resulting in long-lasting consequences for vegetation, aquatic ecosystem productivity and diversity, and other ecosystem properties. We analyzed the occurrence of, and trends in, satellite-derived burn severity across six ecoregions in the Southwest and Northwest regions of the United States from 1984 to 2006 using data from the Monitoring Trends in Burn Severity project. Using 1,024 fires from the Northwest (4,311,871 ha) and 497 fires from the Southwest (1,434,670 ha), we examined the relative influence of fine-scale topography and coarse-scale weather and climate on burn severity (the degree of change from before the fire to one year after) using the Random Forest machine learning algorithm. Together, topography, climate, and weather explained severe fire occurrence with classification accuracies ranging from 68% to 84%. Topographic variables were relatively more important predictors of severe fire occurrence than either climate or weather variables. Predictability of severe fire was consistently lower during years with widespread fires, suggesting that local control exerted by topography may be overwhelmed by regional climatic controls when fires burn in dry conditions. Annually, area burned severely was strongly correlated with area burned in all ecoregions (Pearsons correlation 0.86–0.97; p < 0.001), while the proportion of area burned severely was significantly correlated with area burned only in two ecoregions (p ≤ 0.037). During our short time series, only ecoregions in the Southwest showed evidence of a significant increase (p ≤ 0.036) in annual area burned and area burned severely, and annual proportion burned severely increased in just one of the three Southwest ecoregions. We suggest that predictive mapping of the potential for severe fire is possible, and will be improved with climate data at the scale of the topographic and Landsat-derived burn severity data. Although severity is a value-laden term implying negative ecosystem effects, we stress that severity can be objectively measured and recognize that high severity fire is an important ecological process within the historical range of variability in some ecosystems.

Monitoring Plant Phenology Using Digital Repeat Photography

Repeated observations of plant phenology have been shown to be important indicators of global change. However, capturing the exact date of key events requires daily observations during the growing season, making phenologic observations relatively labor intensive and costly to collect. One alternative to daily observations for capturing the dates of key phenologic events is repeat photography. In this study, we explored the utility of repeat digital photography for monitoring phenologic events in plants. We provide an illustration of this approach and its utility by placing observations made using repeat digital imagery in context with local meteorologic and edaphic variables. We found that repeat photography provides a reliable, consistent measurement of phenophase. In addition, digital photography offers advantages in that it can be mathematically manipulated to detect and enhance patterns; it can classify objects; and digital photographs can be archived for future analysis. In this study, an estimate of greenness and counts of individual flowers were extracted by way of mathematic algorithms from the photo time series. These metrics were interpreted using meteorologic measurements collected at the study site. We conclude that repeat photography, coupled with site-specific meteorologic measurements, could greatly enhance our understanding environmental triggers of phenologic events. In addition, the methods described could easily be adopted by citizen scientists and the general public as well as professionals in the field.

Interactions between antecedent climate and wildfire variability across south-eastern Arizona

Long-term antecedent climate conditions are often overlooked as important drivers of wildfire variability. Fuel moisture levels and fine-fuel productivity are controlled by variability in precipitation and temperature at long timescales (months to years) before wildfire events. This study examines relationships between wildfire statistics (total area burned and total number of fires) aggregated for south-eastern Arizona and antecedent climate conditions relative to 29 fire seasons (April-May-June) between 1973 and 2001. High and low elevation fires were examined separately to determine the influence of climate variability on dominant fuel types (low elevation grasslands with fine fuels v. high elevation forests with heavy fuels). Positive correlations between lagged precipitation and total area burned highlight the importance of climate in regulating fine fuel production for both high and low elevation fires. Surprisingly, no significant negative correlations between precipitation and seasonal wildfire statistics were found at any seasonal lag. Drought conditions were not associated with higher area burned or a greater number of fires. Larger low elevation fires were actually associated with wet antecedent conditions until just before the fire season. Larger high elevation fires were associated with wet conditions during seasons up to 3 years before the fire season.

Correlations between components of the water balance and burned area reveal new insights for predicting forest fire area in the southwest United States

We related measurements of annual burned area in the southwest United States during 1984-2013 to records of climate variability. Within forests, annual burned area correlated at least as strongly with spring-summer vapour pressure deficit (VPD) as with 14 other drought-related metrics, including more complex metrics that explicitly represent fuel moisture. Particularly strong correlations with VPD arise partly because this term dictates the atmospheric moisture demand. Additionally, VPD responds to moisture supply, which is difficult to measure and model regionally due to complex micrometeorology, land cover and terrain. Thus, VPD appears to be a simple and holistic indicator of regional water balance. Coupled with the well-known positive influence of prior-year cold season precipitation on fuel availability and connectivity, VPD may be utilised for burned area forecasts and also to infer future trends, though these are subject to othercomplicatingfactorssuchaslandcoverchangeandmanagement.Assuminganaggressivegreenhousegasemissions scenario, climate models predict mean spring-summer VPD will exceed the highest recorded values in the southwest in nearly40%ofyearsbythemiddleofthiscentury.Theseresultsforewarnofcontinuedincreasesinburnedforestareainthe southwest United States, and likely elsewhere, when fuels are not limiting. Additional keywords: fire danger, tree mortality, warming.

Causes and Implications of Extreme Atmospheric Moisture Demand during the Record-Breaking 2011 Wildfire Season in the Southwestern United States

AbstractIn 2011, exceptionally low atmospheric moisture content combined with moderately high temperatures to produce a record-high vapor pressure deficit (VPD) in the southwestern United States (SW). These conditions combined with record-low cold-season precipitation to cause widespread drought and extreme wildfires. Although interannual VPD variability is generally dominated by temperature, high VPD in 2011 was also driven by a lack of atmospheric moisture. The May–July 2011 dewpoint in the SW was 4.5 standard deviations below the long-term mean. Lack of atmospheric moisture was promoted by already very dry soils and amplified by a strong ocean-to-continent sea level pressure gradient and upper-level convergence that drove dry northerly winds and subsidence upwind of and over the SW. Subsidence drove divergence of rapid and dry surface winds over the SW, suppressing southerly moisture imports and removing moisture from already dry soils. Model projections developed for the fifth phase of the Coupled Mod...

Spring and summer patterns in flowering onset, duration, and constancy across a water-limited gradient.

UNLABELLED PREMISE OF THE STUDY Community-level flowering patterns can be characterized by onset, duration, and end as well as constancy, the degree to which species commence, cease, and reinitiate flowering within a season. In the mountainous Sky Islands region of the southwestern United States, flowering onset is clearly influenced by elevation in the spring, but much less so in the summer season. We evaluated whether these flowering metrics reflect these dissimilar patterns between distinct spring and summer seasons regarding the influence of the elevation and moisture gradient. • METHODS We characterized flowering onset, end, duration, and constancy by plant functional type and their relationships to climate variables in spring and summer. We also evaluated the influence of climate on seasonal flowering patterns. • KEY RESULTS Gaps in seasonal flowering occur frequently in this system in both seasons and among all plant functional types. In both seasons, annual plants exhibit the shortest flowering durations and highest constancies, and plants at low elevations, inhabiting environments with variable moisture conditions, show a greater tendency for longer flowering durations and lower constancy than high-elevation plants. Spring flowering characteristics are most influenced by the total amount of October-March precipitation as well as temperatures in these months, whereas summer flowering characteristics are influenced by the timing of summer-season precipitation, and next by the total amount of summer precipitation. • CONCLUSIONS Flowering metrics, especially constancy and duration, show similar patterns in spring and summer and vary across elevation and moisture gradients. These patterns have substantial implications for plant and animal communities.

Informing Decisions with a Climate Synthesis Product: Implications for Regional Climate Services

AbstractThe demand for regional climate information is increasing and spurring efforts to provide a broad slate of climate services that inform policy and resource management and elevate general knowledge. Routine syntheses of existing climate-related information may be an effective strategy for connecting climate information to decision making, but few studies have formally assessed their contribution to informing decisions. During the 2010–11 winter, drought conditions expanded and intensified in Arizona and New Mexico, creating an opportunity to develop and evaluate a monthly regional climate communication product—La Nina Drought Tracker—that synthesized and interpreted drought and climate information. Six issues were published and subsequently evaluated through an online survey. On average, 417 people consulted the publication each month. Many of the survey respondents indicated that they made at least one drought-related decision, and the product at least moderately influenced the majority of those d...

Designing Institutions to Support Local-Level Climate Change Adaptation: Insights from a Case Study of the U.S. Cooperative Extension System

AbstractIn light of global climate change, adaptation will be necessary at all levels of social organization. However, the adaptation literature emphasizes that because the impacts of climate change and vulnerability are locally specific, adaptation is inevitably local. In this paper, in order to inform the design of institutions that can encourage and support effective local-level adaptation, the authors derive principles for their design theoretically and use a case study to explore how these principles could be practically implemented. Ten design principles are synthesized from principles derived from reviews of the literatures on local-level adaptation, usable science, and boundary organizations. Bringing these three literatures together highlights the characteristics of boundary organizations that make them particularly valuable for addressing the challenges of local-level adaptation. The case study then illustrates how an existing boundary organization, The University of Arizona Cooperative Extensio...

Drought, Climate Variability and Implications for Water Supply and Management

Arizona has burgeoning urban areas, large agricultural regions, water-dependent habitats for endangered fish and wildlife, and a growing demand for water-based recreation. As one of the seven states in the Colorado River Basin, Arizona must cooperate, and sometimes compete, with other state, tribal, and federal governments in securing its water needs—a process that is complicated by a multi-year drought and climate-related variability in water supply. Arizona Water Policy addresses these issues from academic and policy perspectives that include economics, climatology, law, and hydrology. The book explores Arizona’s water management and extracts lessons that are important worldwide.

Rain Gauges to Range Conditions: Collaborative Development of a Drought Information System to Support Local Decision-Making

AbstractDrought monitoring and drought planning are complex endeavors. Measures of precipitation or streamflow provide little context for understanding how social and environmental systems impacted by drought are responding. Here the authors report on collaborative work with the Hopi Tribe—a Native American community in the U.S. Southwest—to develop a drought information system that is responsive to local needs. A strategy is presented for developing a system that is based on an assessment of how drought is experienced by Hopi citizens and resource managers, that can incorporate local observations of drought impacts as well as conventional indicators, and that brings together local expertise with conventional science-based observations. The system described here is meant to harness as much available information as possible to inform tribal resource managers, political leaders, and citizens about drought conditions and to also engage these local drought stakeholders in observing, thinking about, and helpin...