Rare Climatic Events Research Articles

Impacts of Tropical Cyclone Seroja on the Phytoplankton Chlorophyll-a and Sea Surface Temperature in the Savu Sea, Indonesia

The tropical cyclone (TC) Seroja is one of the rare climatic events in the Indonesian Seas, particularly in the Savu Sea. This unprecedented event, which matured on April 4, 2021, caused fatalities and severe damage to the region’s infrastructure and economy. High spatio-temporal resolution satellite measurements of surface winds, chlorophyll-a, and sea surface temperature (SST) are used to disentangle the impact of extreme wind speed (> 10 m∙s-1) on chlorophyll-a and SST. High wind speed associated with TC Seroja induced strong upwelling and vertical mixing in the Savu Sea, which led to phytoplankton blooms and SST depression. An abrupt change of daily variability and positive anomaly in phytoplankton chlorophyll-a concentrations reaches 13 mg∙m-3 and 0.3 mg∙m-3, respectively. At the same time, the SST shows significant cooling up to 3°C. Our results provide novel insights on the exceptional occurrence of a TC within the Indonesian Seas and highlight its impact on the surface ocean.

Smaller brained cliff swallows are more likely to die during harsh weather.

The cognitive-buffer hypothesis proposes that more harsh and unpredictable environments favour animals with larger brains and resulting greater cognitive skills. Comparisons across taxa have supported the hypothesis, but it has rarely been tested within a species. We measured brain size, as inferred from head dimensions, for 1141 cliff swallow specimens collected in western Nebraska, 1982-2018. Cliff swallows starving to death during unusual late-spring cold snaps had significantly smaller brains than those dying from other causes, suggesting that brain size in this species can affect foraging success and that greater cognitive ability may confer advantages when conditions exceed normal environmental extremes. Brain size declined significantly with the size of the breeding colony from which a specimen came. Larger brains may be favoured in smaller colonies that represent more unpredictable and more challenging social environments where there is less public information on food sources and less collective vigilance against predators, even in relatively normal conditions. Our results provide intraspecific support for the cognitive-buffer hypothesis and emphasize the potential evolutionary impact of rare climatic events.

Path Properties of Atmospheric Transitions: Illustration with a Low-Order Sudden Stratospheric Warming Model

AbstractMany rare weather events, including hurricanes, droughts, and floods, dramatically impact human life. To accurately forecast these events and characterize their climatology requires specialized mathematical techniques to fully leverage the limited data that are available. Here we describe transition path theory (TPT), a framework originally developed for molecular simulation, and argue that it is a useful paradigm for developing mechanistic understanding of rare climate events. TPT provides a method to calculate statistical properties of the paths into the event. As an initial demonstration of the utility of TPT, we analyze a low-order model of sudden stratospheric warming (SSW), a dramatic disturbance to the polar vortex that can induce extreme cold spells at the surface in the midlatitudes. SSW events pose a major challenge for seasonal weather prediction because of their rapid, complex onset and development. Climate models struggle to capture the long-term statistics of SSW, owing to their diversity and intermittent nature. We use a stochastically forced Holton–Mass-type model with two stable states, corresponding to radiative equilibrium and a vacillating SSW-like regime. In this stochastic bistable setting, from certain probabilistic forecasts TPT facilitates estimation of dominant transition pathways and return times of transitions. These “dynamical statistics” are obtained by solving partial differential equations in the model’s phase space. With future application to more complex models, TPT and its constituent quantities promise to improve the predictability of extreme weather events through both generation and principled evaluation of forecasts.

Adaptation or ecological trap? Altered nest-site selection by Reed Parrotbills after an extreme flood

BackgroundFloods and other extreme events have disastrous effects on wetland breeding birds. However, such events and their consequences are difficult to study due to their rarity and unpredictable occurrence.MethodsHere we compared nest-sites chosen by Reed Parrotbills (Paradoxornis heudei) during June‒August 2016 in Yongnianwa Wetlands, Hebei Province, China, before and after an extreme flooding event.ResultsTwenty-three nests were identified before and 13 new nests after the flood. There was no significant difference in most nest-site characteristics, such as distance from the road, height of the reeds in which nests were built, or nest volume before or after the flood. However, nests after the flood were located significantly higher in the vegetation compared to before the flood (mean ± SE: 1.17 ± 0.13 m vs. 0.75 ± 0.26 m, p < 0.01). However, predation rate also increased significantly after the flood (67% vs. 25%, p = 0.030).ConclusionsOur results suggested that Reed Parrotbills demonstrated behavioral plasticity in their nest-site selection. Thus, they appeared to increase the height of their nests in response to the drastically changing water levels in reed wetlands, to reduce the likelihood that their nests would be submerged again by flooding. However, predation rate also increased significantly after the flood, suggesting that the change in nest height to combat the threat of flooding made the nests more susceptible to other threats, such as predation. Animals’ response to rare climatic events, such as flooding, may produce ecological traps if they make the animals more susceptible to other kinds of threats they are more likely to continue to encounter.

Extreme group sizes in a colonial bird favored during a rare climatic event

AbstractWhat maintains stasis in animal group‐size distributions is an unresolved problem in behavioral ecology. One potential driver could be rare climatic events that favor certain group sizes in ways that do not occur in normal conditions. We investigated mortality among colonially nesting cliff swallows (Petrochelidon pyrrhonota) during a rare climatic event in western Nebraska in 1996 that led to the starvation of thousands of adult birds. Colonies at the extreme end of the size distribution exhibited less size reduction (higher adult survival) than those of intermediate size. That this event resulted in disruptive selection on colony size was suggested by an underrepresentation of locally produced yearling birds that recruited into colonies of intermediate size the following year. There was no evidence that the colony‐size‐related mortality could be explained by differential sorting of birds among colonies based on body size or differing patterns of selection on morphology. The selection on colony size was likely driven by lower competition for food in the smallest colonies and better quality foraging habitat associated with the largest colonies, with these advantages enhanced in severe weather. Selection on colony size during rare climatic events can reinforce or oppose selection occurring during other times of the annual cycle. Whether such selection results in long‐term change in the colony‐size distribution may depend on the frequency and severity of these climatic events.

Fluctuating viability selection on morphology of cliff swallows is driven by climate

The extent to which fluctuating selection can maintain evolutionary stasis in most populations remains an unresolved question in evolutionary biology. Climate has been hypothesized to drive reversals in the direction of selection among different time periods and may also be responsible for intense episodic selection caused by rare weather events. We measured viability selection associated with morphological traits in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska, USA, over a 14-year period following a rare climatic event. We used mark-recapture to estimate the annual apparent survival of over 26000 individuals whose wing, tail, tarsus and bill had been measured. The fitness functions associated with tarsus length and bill dimensions fluctuated depending on annual climate conditions on the birds' breeding grounds. The oscillating yearly patterns may have slowed and occasionally reversed directional change in trait trajectories, although there was a trend over time for all traits except tarsus to increase in size. The net positive directional selection on some traits, despite periodic climate-associated fluctuations, suggests that cliff swallow morphology in the population is likely to keep changing and supports recent work contending that selection in general does not fluctuate enough to be an effective driver of stasis.

Population Response of Giant Galápagos Tortoises to Feral Goat Removal

AbstractEfforts to eradicate nonnative mammals to restore oceanic island ecosystems have become increasingly successful but parallel tracking of response by native species for which control efforts are intended to benefit has been rare. A major campaign to eradicate nonnative goats and burros was initiated in 1995 on Alcedo Volcano in the Galápagos Archipelago that ultimately removed 62,868 goats and eliminated them by 2006. Planners of the eradication program had the foresight to invest in intensive monitoring of the status of the volcano's giant tortoise (Chelonoidis nigra) population whose welfare was a primary motivation for the eradication effort. Monitoring revealed an increase in the proportion of juveniles among all tortoises as well as increased growth rates of individual tortoises on Alcedo Volcano from earlier to later phases of the eradication campaign. Over the same time frame in a control population on nearby Santa Cruz Island (where goats and donkeys were not removed) juvenile fraction and individual growth rates remained unchanged. Although goat removal coincided with occurrence of a rare climatic event that simultaneously boosted forage availability for tortoises, failure to observe a comparable improvement in the control population implies that removal of goats and burros was the primary causative factor of improving population status of tortoises on Alcedo Volcano.

Population Dynamics of Marsilea villosa (Marsiliaceae) on O'ahu, Hawai'i

Marsilea villosa Kaulfuss is an endemic Hawaiian fern with a very small, fragmented natural range and an ephemeral habit that makes it difficult to assess population health. Its sporocarps are presumed to remain viable for many years, allowing it to survive periods of drought and then sexually reproduce when there is sufficient precipitation to cause them to be submerged in standing water. Surveys of plant cover at 'Ihi'ihilauākea Crater, where the largest and best-protected stand was located, have shown that vigorous growth of the species occurs after the crater floor is flooded. This study documents dramatic decline over the last 8 yr, during which growth has been largely vegetative. Analyses of rainfall records suggest that events producing long-duration floods occur on average every 6.5 yr, yet 13 yr have elapsed since the last one. Although this may in part explain the poor condition of the population, other ecological changes have occurred including decline of the dominant trees and invasion of alien grasses that may influence flooding frequency. Marsilea villosa may be able to avoid extinction because flooding caused by rare climatic events will kill off the competitors that have encroached on its former ecological space. However, it is predicted to be a less-conspicuous part of the ecosystem most of the time unless management can effectively suppress invaders.

Testis size increases with colony size in cliff swallows

By using a sample of over 800 male cliff swallows (Petrochelidon pyrrhonota) that died during a rare climatic event in our Nebraska study area in 1996, we investigated how testis size was related to body size, age, parasite load, a bird's past colony-size history, and spleen size. Testis volume increased with body size. After correcting for body size, testis volume was lowest for birds age 1 and 2 years but did not vary with age for males 3 years old or more. Birds occupying parasite-free (fumigated) colonies had significantly larger testes than did birds at nonfumigated sites. Testis volume increased significantly with the size of the breeding colonies a bird had used in the past. Testis volume had no relationship with spleen volume after correcting for body size. The results show within a species that larger testes are favored in more social environments, probably reflecting a response to increased rates of extrapair copulation (and thus sperm competition) among cliff swallows in large colonies. The presence of ectoparasites, by inflating levels of plasma corticosterone, may in turn reduce testis mass. These data provide no support for the hypothesis that large testes, perhaps by producing more testosterone, are immunosuppressive and thus costly for that reason. Copyright 2003.

Evolution of Darwin’s finches caused by a rare climatic event

Populations of animals and plants often undergo conspicuous ecological changes when subjected to climatic extremes. Evolutionary changes may accompany them but are less easily detected. We show that Darwin9s finches on a Galapagos island underwent two evolutionary changes after a severe El Nino event caused changes in their food supply. Small beak sizes were selectively favoured in one granivorous species when large seeds became scarce. The effects of selection were transmitted to the next generation as a result of high trait heritabilities. Hybridization between this species and two others resulted in gene exchange, but only after the El Nino when hybrid fitness was much enhanced under the altered feeding conditions. These observations imply that if global warming increases the frequency or severity of El Nino events on the Galapagos, microevolutionary changes in animal and plant populations are to be anticipated.

North Carolina Climate Changes Reconstructed from Tree Rings: A.D. 372 to 1985

Millennium-old bald cypres trees (Taxodium distichum [(L.) Rich.] have ben used to develop a 1614-year reconstruction of the June Palmer drought severity index for North Carolina. This proxy paleoclimatic record indicates that the growing season climate of North Carolina has undergone many changes between significantly different regimes of drought and wetness that persist for approximately 30 years. Alternating wet and dry regimes were particularly well developed during the Medieval Warm Epoch (A.D. 1000 to 1300). The record June droughts in 1985 and 1986 and the preceding three decades of much wetter than average conditions both appear to have been rare climatic events, equaled only five times each since A.D. 372.

The Calculation and Interpretation of Climatic Predictabilities

Descriptors of predictability for temperature and precipita- tion were calculated as sums of constancy (C) and contingency (M) components. These indices were compared with the proportions of vari- ability accounted for by models developed using Fourier and ARMA methods of time series analysis. Data from six sites in North America at latitudes ranging from arctic to sub-tropical were analysed. The predict- ability indices for both temperature and precipitation were similar across all sites, although climatic regimes differed widely. Similarity in predict- ability indices of temperature among these sites resulted from opposing latitudinal gradients in constancy and contingency; constancy decreased and contingency increased with increasing latitude. A model constructed using the single peak of Fourier spectra, a 52-week periodicity, indicated both a greater predictability for temperatures and greater differences among sites than did the indices. Patterns in the constancies or contingencies of precipitation were more complex. Predictability indices were lower than those for temperatures at each site, and latitudinal gradients were not evident in either component. Proportions of variation accounted for using models derived from Fourier and ARMA analyses were similar, but both indicated much lower predict- ability for precipitation than did the sum of constancy and contingency. Two factors affected the results and interpretation of indices of climate pattern: (1) the impact of rare climatic events when differing timespans are compared, and (2) effects of global versus local ranges in calculations of predictability and its components. The similarity in indices of the predict- ability of climates, while components of predictability differ widely, sug- gest that the influence of climate on life history characteristics of species may be due to differences in the impacts of constancy and contingency on life histories and predictability.