Search for: All records

We describe the utility of false rings inTaxodium distichum(i.e. baldcypress) as a proxy for hydroclimatic extreme events in three different river basins (Pascagoula, Mobile, and Choctawhatchee) that discharge into the northern Gulf of Mexico. False rings occur as a result of a change in the environmental limiting resource for tree stem growth, and inT. distichum, false ring production is usually a result of increases in mid-growing season water availability. Our results show that false ring occurrence (from 1931 to 2018) is similar across sites but occur in different years, suggesting that false ring production is indicative of tree response to its local environment. False ring production inT. distichumhas previously been correlated with summer streamflow, the season when tropical cyclone precipitation (TCP) is highest. To assess a stand-wide response, we define high false ring (HFR) years as all years when$⩾$20% of trees produced a false ring. We show total TCP in July is the best predictor for HFR years inT. distichum, and false ring production in smaller river basins captures local TCP better than larger river basins. Additionally, HFR years coincide with summers of anomalously high precipitation, anomalously low temperatures, and a positive phase of the North Atlantic Oscillation. 77% of HFR years occur in seasons when there is heavy tropical cyclone activity near sample sites, building a foundation to use false ring records as robust TCP proxies with hydroclimate reconstruction potential.

 

Understanding the response of tropical cyclone precipitation to ongoing climate change is essential to determine associated flood risk. However, instrumental records are short-term and fail to capture the full range of variability in seasonal totals of precipitation from tropical cyclones. Here we present a 473-year-long tree-ring proxy record comprised of longleaf pine from excavated coffins, a historical house, remnant stumps, and living trees in southern Mississippi, USA. We use cross-dating dendrochronological analyses calibrated with instrumental records to reconstruct tropical cyclone precipitation stretching back to 1540 CE. We compare this record to potential climatic controls of interannual and multidecadal tropical cyclone precipitation variability along the Gulf Coast. We find that tropical cyclone precipitation declined significantly in the two years following large Northern Hemisphere volcanic eruptions and is influenced by the behavior of the North Atlantic subtropical high-pressure system. Additionally, we suggest that tropical cyclone precipitation variability is significantly, albeit weakly, related to Atlantic multidecadal variability. Finally, we suggest that we need to establish a network for reconstructing precipitation from tropical cyclones in the Southeast USA if we want to capture regional tropical cyclone behavior and associated flood risks.

 

Despite growing in wet lowland and riparian settings, Taxodium distichum (L.) Rich. (bald cypress) has a strong response to hydroclimate variability, and tree ring chronologies derived from bald cypress have been used extensively to reconstruct drought, precipitation and streamflow. Previous studies have also demonstrated that false rings in bald cypress appear to be the result of variations in water availability during the growing season. In this study 28 trees from two sites located adjacent to the Choctawhatchee River in Northwestern Florida, USA were used to develop a false ring record extending from 1881 to 2014. Twenty false ring events were recorded during the available instrumental era (1931–2014). This record was compared with daily and monthly streamflow data from a nearby gage. All 20 of the false-ring events recorded during the instrumental period occurred during years in which greatly increased streamflow occurred late in the growing season. Many of these wet events appear to be the result of rainfall resulting from landfalling tropical cyclones. We also found that the intra-annual position of false rings within growth rings reflects streamflow variability and combining the false-ring record with tree ring width chronologies improves the estimation of overall summer streamflow by 14%. Future work using these and other quantitative approaches for the identification and measurement of false ring variables in tree rings may improve tree-ring reconstructions of streamflow and potentially the record of tropical cyclone rainfall events. 

Since 2013, extreme floods within the Santee River basin (North/South Carolina, USA) caused $1.5B in damage. The instrumental period, however, is too short to determine if recent extreme events are anomalous within a long‐term context. Here, we present reconstructions of storm‐, base‐, and total streamflow for the Santee River using a multi‐species tree‐ring network calibrated to flow data during the period 1923–2018. Tree‐ring data explained higher variance (r = 0.59;p < 0.01; 900–2018) of instrumental baseflow than total streamflow (r = 0.41;p < 0.01; 1500–2018) or stormflow (r = 0.26;p < 0.05; 1690–2018). Our reconstruction reveals a long‐term increase in baseflow over the past millennium. The North Atlantic subtropical high regulates baseflow in the Santee River (r = 0.45;p < 0.01). Recent high levels of baseflow may be connected to the position of the subtropical high, increasing the likelihood of flooding.