While the signature of anthropogenic climatic change is associated with observed and ongoing increases in temperature, it is concomitant changes in precipitation and the frequency and duration of drought that will have the most direct and immediate consequences for human populations. Changes in regional hydroclimate will exacerbate threats to sustainable water supplies from growing populations, pollution, declining infrastructure, and resource conflicts. One robust prediction of the most recent Intergovernmental Panel on Climate Change (IPCC) climate model ensemble is that precipitation rates will decrease over Guatemala and most parts of Central America in both the summer and winter under future increased greenhouse gas scenarios. Critical to mitigating the consequences of changes in water availability is a long-term perspective on the potential range of variability in precipitation and the integration of this knowledge within water planning and natural resources policy. However, long-term instrumental records of drought are sparse in Guatemala and throughout the Central American tropics. This is particularly true for high elevation regions, which are likely to demonstrate the earliest and more severe local consequences of global climate change. In the absence of long instrumental records, scientists investigating the causes and consequences of climate variability and change depend on proxy records that can be used to reconstruct past ocean-atmosphere conditions. Tree-ring chronologies form the bulk of the available, high-resolution terrestrial proxy records. However, they are almost entirely absent from the tropical Americas south of Mexico. The lack of a high resolution, long-term perspective on drought from this region also limits opportunities to validate climate model predictions. The development of long, annually resolved records of climate from this region is therefore necessary for understanding the local response to broad-scale forcing, detecting and attributing long-term trends related to anthropogenic climate change, and verifying the fidelity of the climate models used as the primary forecasting tool for predicting future change.
The investigators will expand the geographic frontier of dendroclimatology into the mountains of Guatemala, identifying species and sites which show sensitivity to precipitation, and developing estimates of drought variability over the last several centuries. They will investigate and utilize a combination of high elevation tropical conifer species in this study. All candidate taxa will be carefully and systematically examined to establish annual ring formation and chronology development. Once dating and chronology development has been completed and verified, the tree-ring time series will be compared against the available local and gridded meteorological data in order to detect physiologically reasonable climate/growth relationships. Models will be developed to estimate past climate anomalies from the absolutely dated ring width series. Reconstructions of past precipitation and drought will be objectively compared against independently developed climate fields as well as estimates of past forcing. The drought reconstructions will also be used to interpret the possible role of climate in important historical events of the last several hundred years. This research will provide a long-term context for drought variability that is critical for efforts to mitigate the consequences for vulnerable human populations from climatic change. Active outreach and participatory education in Maya communities in the regions are integrated in the proposed research.
The continued expansion of dendroclimatology into Mesoamerica requires the identification and evaluation of species whose rings can be precisely dated and then statistically compared with precipitation and temperature variability in order to make inferences about past climate. We established the basis for using Abies guatemalensis Rehder (Pinaceae) for climate reconstruction in Central America. Annual crossdating in this montane species is demonstrated at high elevation sites in the Sierra los Cuchumatanes in western Guatemala. We find that ring width is most strongly influenced by early growing season moisture conditions, controlled by late dry season rainfall, and negatively correlated with growing season temperature. Our chronology is also significantly negatively correlated with eastern tropical Pacific sea surface temperature anomalies. Our confirmation of annual chronology and the identification of a climatic signal in this species now allows its use in local and regional paleoclimate reconstructions, as well as ecological studies. Abies guatemalensis in the high elevations of the Cuchumatanes of Guatemala forms annual rings that can be crossdated. Interannual variability in ring widths is most strongly controlled by early growing season moisture, as determined by the late boreal winter precipitation and spring-summer temperatures. The climate signal can be detected using both the limited local observation and the longer but regional-scale gridded data. We have shown robust crossdating within and between trees, as well as across several sites over an elevation difference of ~400m. Collectively, our findings here demonstrate that this species can be used to characterize broad-scale hydroclimate variability and used for paleoclimate reconstruction in the region. One remaining challenge is to identify, collect, and date older individual trees that can be used to extend climate reconstructions further back in time. Relatively little is known about the ecophysiology of this species, and so additional research is also required to understand the timing of growth initiation and senescence and the association between monthly climate and intra-annual growth patterns. We anticipate that information about the climate response, growth rates, and age structure of this species will also aid in protection, conservation, and restoration efforts. We have trained community members from the Cuchumatan community of La Ventosa to be independent field technicians. We also provided them with a broader understanding of climate change and how tree rings can be used to help interpret climate change. We have also spread this knowledge and skills to the Environmental Research Lab at the University del Valle, Guatemala. We installed a complete dendrochronology lab at the Universidad del Valle Guatemala. We also provided university employees there with initial training on that equipment.
