Funding: NSF Paleoclimate Program, Paleo Perspectives on Climate Change (Arkansas = AGS-2201243, Columbia = AGS-2201653, Memphis = AGS-2201584, Missouri = AGS-2201498, Wisconsin-Platteville = AGS-2201352)

This collaborative research project involves the University of Arkansas, Lamont-Doherty Earth Observatory of Columbia University, the University of Memphis, the Univeristy of Missouri, and the University of Wisconsin-Platteville. The general goal of the research is to develop moisture sensitive tree-ring chronologies from old-growth populations of Juniperus, Pinus, and Taxodium trees from within or near the Great Plains for in situ reconstructions of seasonal precipitation and the long-term soil moisture balance that together will constitute the Great Plains Drought Atlas (GPDA). Five gridded reconstructions that span the Great Plains at 0.5 degree resolution will be developed, including the Standardized Precipitation Index (SPI) for the spring and summer seasons, precipitation totals for spring and summer, and the summer Palmer Drought Severity Index (PDSI). The reconstructions will be designed for maximum length, with the goal of extending the moisture estimates into the Medieval Period when the climate appears to have been much warmer and drier. The GPDA will be used to test hypotheses concerning the magnitude of Great Plains drought and pluvial, the anthropogenic imprint on recent moisture trends in the Great Plains, and the possible multi-decadal regimes in the frequency of rapid-onset spring to summer flash drought over the Great Plains during the past 500- to 1000-years.

The highest agricultural production in the United States occurs in the Great Plains, a region also subject to frequent drought, including the flash drought of 2012 that resulted in $30 billion in losses. Proxy tree ring and lake sediment data suggest that the instrumental record of precipitation and soil moisture may not be representative of the natural variability of severe droughts and prolonged wet intervals over the past millennium. Anthropogenic climate change may be contributing to wetter conditions in the Northern Plains and increasing dryness over the Southern Plains, a possible expression of the drying symptomatic of the expansion of the Hadley Cell and the weakening of the jet stream predicted by many climate models. These human-induced changes threaten to disrupt agriculture, energy production, and water use, and may be magnified by recurrent decadal moisture extremes witnessed in instrumental and paleoclimate records. Very few exactly dated, annual tree-ring chronologies are available from the mostly treeless Great Plains. The lack of data adds considerable uncertainty to the available reconstructions of moisture anomalies for this region. This project seeks to reduce the uncertainty by developing long tree-ring chronologies within and along the boundaries of the Great Plains to aid reconstruction of past drought and wetness in this critical agricultural region.

The potential Broader Impacts (B.I.) include improvement in understanding climate processes involving drought and extreme events in the Great Plains regions that impact the highest agricultural production in the United States. Importantly, the project includes researchers and students from a regional Primarily Undergraduate Institution (PUI) which has strong ties to affected agricultural and tribal communities.

Funding: Tennessee Department of Transportation (TDOT; RES 2020-23)

This project with lead PI Claudio Meier (Civil Engineering, University of Memphis) addressed the need for updating the existing peak flow equations for urban basins in Tennessee. After reviewing the current state of the art, the work focused on unraveling the complex, interacting effects that non-stationary precipitation, evolving urbanization levels, and spatial patterns in land development, rainfall, as well as antecedent conditions, all have on the hydrologic response in urbanizing basins. Potential uncertainties and biases in the estimation of extreme rainfall quantiles [intensity or depth-duration-frequency (IDF-DDF) values], due to the low density of weather stations and the use of totalized rainfall data, and in the frequency analysis of frequent floods, due to using annual maxima instead of partial duration (peaks over threshold) series, were also investigated. All urban basins in Tennessee have experienced growth in the amounts of developed areas in the past 20 years, and there is a significant increase in the frequency of extreme rainfall events in the region. Using rainfall data with the 15-minute resolution typically available in the U.S. introduces a negative bias that is highly variable across stations, while the low density of rain gauges increases the uncertainty in IDF-DDF values. We derived a novel urbanization index based on hydrologic connectivity that, in contrast with the traditional approach of using percentage of impervious area (IA), is able to reflect the hydrologic effects of different spatial distributions of urbanized patches within a watershed. This index outperforms IA when used as an explanatory variable in regression equations for predicting urban peak flows. A methodology to perform continuous hydrologic simulation with artificial neural networks was also proposed to investigate the effects of changing land cover, excluding concurrent effects of trends in precipitation.

This research produced eight national and international presentations by graduate students in Civil Engineering. One manuscript is in review.

Funding: University of Memphis, Research Investment Fund, Team Initiation Grant

This project with Claudio Meier (Civil Engineering, University of Memphis) and Laura Saija (City and Regional Planning, University of Memphis) obtained internal seed money from the University of Memphis to initiate a permanent, interdisciplinary research team to study and develop low-tech, highly applicable, community-based strategies for operationalizing concepts of urban resilience to extreme rainfall events and, more generally, issues surrounding the hydrological cycle in the city context.

Two interdisciplinary, graduate-level classes were taught in the Fall 2017 and Spring 2018 semesters (Urban Resilience to Flooding I and II). Graduate students gave presentations to community partners at the end of the Fall 2017 semester, and in the Spring 2018 students proposed low-cost, low-tech solutions to BLDG Memphis. We are currently seeking funding to expand this project nationally and internationally.

Funding: NSF Paleoclimate Program, Paleo Perspectives on Climate Change (Arkansas = AGS-1266014, Columbia = AGS-1301587, Memphis = AGS-1266015)

This collaborative research project involved the University of Arkansas, Lamont-Doherty Earth Observatory of Columbia University, the University of Memphis, and NASA's Goddard Institute for Space Studies. This project used 439 selected tree-ring chronologies that are significantly correlated with December-April precipitation totals and 547 different chronologies correlated with May-July totals to develop the first gridded reconstructions of both cool and warm season precipitation totals across North America. The December-April and May-July seasons were used because they are most representative of the monthly precipitation signals found in the largest number of discretely correlated chronologies. The discrete subsets of tree-ring chronologies were then statistically calibrated with December-April or May-July precipitation totals at 6,812 North American grid points (at 0.5 degree grid spacing) using a localized principal components regression procedure during the period 1928-1978 in common to all tree-ring chronologies and instrumental precipitation data. The gridded reconstructions of cool and warm season precipitation were validated upon comparison with independent precipitation data from 1901-1927 and extend back for 500- to 2,000-years for most of the continent, depending on the length of the tree-ring chronologies located near each grid point.

This research produced 12 publications: Cook et al. (2016, WIREs Climate Change), Cook et al. (2018, Journal of Geophysical Research: Atmospheres), Howard et al. (2018, Climate Dynamics), Stahle et al. (2016, Quaternary Science Reviews), Stahle et al. (2015, Tree-Ring Research), Torbenson et al. (2016, Tree-Ring Research), Torbenson and Stahle (2018, Journal of Climate), Torbenson et al. (2019, Paleooceanography and Paleoclimatology), Burnette et al. (2020, Recovering Ancient Spiro: Native American Art, Ritual, and Cosmic Renewal), Stahle et al. (2020, Journal of Climate), Burnette (2021, Bulletin of the American Meteorological Society), and Burnette et al. (2022, Following the Mississippian Spread: Climate Change and Migration in the Eastern U.S. (ca. AD 1000-1600)).

Note Burnette (2021) describes a new portal of webtools for all tree-ring reconstructed drought atlases, the Tree-Ring Drought Atlas Portal

Funding: NOAA Climate Change and Detection, Paleoclimatology (NA08OAR4310727)

Part of my postdoctoral funding with Dave Stahle at the University of Arkansas came from this project. This research project reanalyzed existing tree-ring collections from the Southeast and Southwest to build new earlywood, latewood, total ring width, and adjusted latewood width chronologies. These new chronologies were then used to derive separate millennium-long reconstructions of cool and warm season precipitation. A review of the paleoclimate applications of long tree-ring chronologies derived from living and subfossil baldcypress trees in the U.S., Mexico, and Guatemala has been published using these new chronologies (Stahle et al. 2012, Quaternary Science Reviews). A second manuscript improved on the chronological "gap" from AD 1250 to 1400 at Mesa Verde, Colorado (Stahle et al. 2015, Tree-Ring Research).

Funding: NSF Paleoclimate Program (ATM-0753399)

Part of my postdoctoral funding with Dave Stahle at the University of Arkansas came from this project. The project developed the first exactly dated millennium-long chronology of tree growth and climate history in central Mexico (Stahle et al. 2011, Geophysical Research Letters), and investigated the ocean-atmospheric dynamics responsible for drought and wetness over the region (Stahle et al. 2012, Climate Dynamics). A review of the paleoclimate applications of long tree-ring chronologies derived from living and subfossil baldcypress trees in the U.S., Mexico, and Guatemala has also been published (Stahle et al. 2012, Quaternary Science Reviews).

Funding: NSF Doctoral Dissertation Research Improvement Grant (BCS-0622894)

This was my Ph.D. project that recovered daily temperature and precipitation data from selected 19th century stations in Kansas, Missouri, and Oklahoma to extend the temperature and precipitation history of northeastern Kansas backward into the 19th century (Burnette et al. 2010, Journal of Climate; Burnette and Stahle 2013a, Climatic Change). Helpful methods and computer code were also developed to facilitate additional development of historical climate data across the United States (Burnette and Stahle 2013b, Computers and Geosciences).

Project Website