Constructing vulnerability curves considering mitigation capacity to enhance the predictive ability of disaster losses

Changes in the frequency and severity of drought events associated with climate change could affect plant growth, development, and adaptability. Hydraulic failure caused by xylem embo-lism is the main physiological consequences of drought stress. How to accurately quantify xylem embolism is particularly important for understanding plant responses to drought stress. The vulnerability of xylem to embolism is usually evaluated by constructing vulnerability curves (VCs). Several methods have been developed to construct VCs, but be inconsistent in their results. A deep understanding of the design principles of xylem embolism measurement methods and comparison of the similarities and differences of various methods in actual research are particularly important for the rational interpretation of literature results, and properly using VCs in models for predicting plant responses to water deficits. Here, we compared seven methods for constructing xylem vulnerability curves to embolism: bench dehydration, centrifugation, air injection, acoustic measurements, synchrotron and X-ray microtomography (Micro-CT), optical visualization method, and pneumatron method. We summarized current achievements and controversial viewpoints of the application of these methods in specific research. Finally, we provided prospects for measuring the vulnerability of xylem embolism and the selection of relevant methods for practical application in future studies.

The formation of air emboli in the xylem during drought is one of the key processes leading to plant mortality due to loss in hydraulic conductivity, and strongly fuels the interest in quantifying vulnerability to cavitation. The acoustic emission (AE) technique can be used to measure hydraulic conductivity losses and construct vulnerability curves. For years, it has been believed that all the AE signals are produced by the formation of gas emboli in the xylem sap under tension. More recent experiments, however, demonstrate that gas emboli formation cannot explain all the signals detected during drought, suggesting that different sources of AE exist. This complicates the use of the AE technique to measure emboli formation in plants. We therefore analysed AE waveforms measured on branches of grapevine (Vitis vinifera L. 'Chardonnay') during bench dehydration with broadband sensors, and applied an automated clustering algorithm in order to find natural clusters of AE signals. We used AE features and AE activity patterns during consecutive dehydration phases to identify the different AE sources. Based on the frequency spectrum of the signals, we distinguished three different types of AE signals, of which the frequency cluster with high 100-200 kHz frequency content was strongly correlated with cavitation. Our results indicate that cavitation-related AE signals can be filtered from other AE sources, which presents a promising avenue into quantifying xylem embolism in plants in laboratory and field conditions.

The pneumatic method is a novel method determining vulnerability to embolism in plants, yet it remains unclear whether this method is suitable for all species with different xylem anatomy. In this study, using six tree species with contrasting xylem anatomy, including four vessel-bearing species (diffuse-porous wood and ring-porous wood) and two tracheid-bearing species (non-porous wood), we test the reliability of the pneumatic method by comparing to hydraulic methods and also considering turgor loss point and native embolism. Vessel length distribution and cut-open vessel volume were also evaluated using the silicone injection technique. Additionally, we also synthesized published data to find out the consistency between the pneumatic method and hydraulic methods. Results showed that there was a maximum 10-folds difference in mean vessel length and mean vessel diameter varying from 30 to 56 μm among species. The estimated open vessel volume ranges from 0.064 to 0.397 mL, with a maximum of 14% of the tube vacuum reservoir. For four vessel-bearing species, the pneumatic method showed good consistency with hydraulic methods, and this consistency was evidenced by turgor loss point and native embolism. For two tracheid-bearing species, the pneumatic method significantly overestimated vulnerability because of the bad consistencies with hydraulic methods and plant water relations. Data synthesis of 56 species also suggested that the pneumatic method can accurately measure the embolism vulnerability of vessel-bearing species but not for tracheid-bearing species. Our study provided further evidence that the pneumatic method is accurate for most vessel-bearing species and thus has the potential to be widely used in the plant hydraulics field. However, we proposed that the precise calculation of air discharge volume should take into account the volume of open vessels for species with wide and long vessels.

A vulnerability curve (VC) describes the extent of xylem cavitation resistance. Centrifuges have been used to generate VCs for decades via static- and flow-centrifuge methods. Recently, the validity of the centrifuge techniques has been questioned. Researchers have hypothesized that the centrifuge techniques might yield unreliable VCs due to the open-vessel artifact. However, other researchers reject this hypothesis. The focus of the dispute is centered on whether exponential VCs are more reliable when the static-centrifuge method is used rather than the flow-centrifuge method. To further test the reliability of the centrifuge technique, two centrifuges were manufactured to simulate the static- and flow-centrifuge methods. VCs of three species with open vessels of known lengths were constructed using the two centrifuges. The results showed that both centrifuge techniques produced invalid VCs for Robinia because the water flow through stems under mild tension in centrifuges led to an increasing loss of water conductivity. In addition, the injection of water in the flow-centrifuge exacerbated the loss of water conductivity. However, both centrifuge techniques yielded reliable VCs for Prunus, regardless of the presence of open vessels in the tested samples. We conclude that centrifuge techniques can be used in species with open vessels only when the centrifuge produces a VC that matches the bench-dehydration VC.

An improved typhoon risk model coupled with mitigation capacity and its relationship to disaster losses

Vulnerability to cavitation curves describe the decrease in xylem hydraulic conductivity as xylem pressure declines. Several techniques for constructing vulnerability curves use centrifugal force to induce negative xylem pressure in stem or root segments. Centrifuge vulnerability curves constructed for long-vesselled species have been hypothesised to overestimate xylem vulnerability to cavitation due to increased vulnerability of vessels cut open at stem ends that extend to the middle or entirely through segments. We tested two key predictions of this hypothesis: (i) centrifugation induces greater embolism than dehydration in long-vesselled species, and (ii) the proportion of open vessels changes centrifuge vulnerability curves. Centrifuge and dehydration vulnerability curves were compared for a long- and short-vesselled species. The effect of open vessels was tested in four species by comparing centrifuge vulnerability curves for stems of two lengths. Centrifuge and dehydration vulnerability curves agreed well for the long- and short-vesselled species. Centrifuge vulnerability curves constructed using two stem lengths were similar. Also, the distribution of embolism along the length of centrifuged stems matched the theoretical pressure profile induced by centrifugation. We conclude that vulnerability to cavitation can be accurately characterised with vulnerability curves constructed using a centrifuge technique, even in long-vesselled species.

Development of vulnerability curves of buildings to windstorms using insurance data: An empirical study in South Korea

ContextUnderstanding plant resilience and adaptation to drought is a major challenge in crop and forest sciences. Several methods have been developed to assess the vulnerability to xylem embolism. The in situ flow centrifuge (or cavitron) is the fastest technique allowing to characterise this trait for plants having vessel lengths shorter than the rotor size.AimsWe present (i) a series of changes to the earlier cavitron design, aimed at improving the accuracy and speed of measurement through automated operations, and (ii) a new development through the design of a large diameter rotor expanding the range of species that can be measured.MethodsBoth hardware and software modifications to the original design have been developed. In order to avoid artefacts caused by cut open vessels, a centrifuge with a large rotor (1 m) has been developed, and vulnerability curves obtained with this new device were compared with those obtained using reference methods.ResultsThe new set-up expands the range of conductance measurable with a cavitron and enables it to accurately determine the absolute value of conductivity even for species having very low hydraulic conductivity. The large rotor cavitron shows good agreement with the reference techniques for conifers and diffuse-porous species but also for ring-porous species having long vessels.ConclusionThe set-up described in this manuscript provides a faster, safer and more accurate method to construct vulnerability curves, compared to the original cavitron design, and extends the measurement capabilities to new species that are difficult to measure to date.Key messageRecent improvements to cavitron setup enable to measure xylem vulnerability curves for an expanded number of plant species, with longer vessels or lower hydraulic conductivity.

The cohesion-tension (CT) theory requires stability of liquid water in conducting elements under high tensions. This stability has been measured using different methods, some of which yielded contradictory results. In this study a method is presented to establish known tensions in the water inside conifer tracheids, to detect cavitation events under these conditions and to construct vulnerability curves. Tangential sapwood sections of Juniperus virginiana L. were placed closely over the surface of NaCl solutions with water potentials ranging from -0.91 to -7.57 MPa. Water potentials were measured with a thermocouple hygrometer in contact with the section, and ultrasound acoustic emissions (UAE) from the sections were registered with an ultrasound transducer. The emission rate of signals increased with the concentration of the solution. Exposure of 100 microm sections in the airspace over a solution provided optimal conditions for the rupture of the water column: many tracheid walls bordered on air, and water in the lumen came under high tension. Nevertheless, the water remained in the metastable liquid state for periods of many hours. The vulnerability obtained from simultaneous measurements of water potentials and ultrasound acoustic emissions on sapwood sections was substantially higher than from conventionally measured curves of detached branches. It is argued that the isolation of tracheids in a massive organ as well as the rate of potential decline will influence the probability of cavitations at a given water potential and thus the parameters of the vulnerability curve.

Data on tsunami damaged houses, collected and compiled by the Department of Census and Statistics, Sri Lanka, was used to construct vulnerability curves with tsunami height as the demand parameter. A common curve could be used for all administrative divisions where a majority of houses had permanent walling materials, whether these divisions were on the southwest coast or the north and east coast. A Monte Carlo simulation was carried out for a typical building using varying tsunami inundation depths, and the resulting vulnerability curve was found to be similar, but lie just below, the survey-based curve, because all the buildings used for the simulated curve had permanent walling materials. This paper focuses only on the ‘complete damage’ state for vulnerability.

Adequate leaf hydraulic conductance (Kleaf) is critical for preventing transpiration-induced desiccation and subsequent stomatal closure that would restrict carbon gain. A few studies have reported midday depression of Kleaf (or petiole conductivity) and its subsequent recovery in situ, but the extent to which this phenomenon is universal is not known. The objectives of this study were to measure Kleaf, using a rehydration kinetics method, (1) in the laboratory (under controlled conditions) across a range of water potentials to construct vulnerability curves (VC) and (2) over the course of the day in the field along with leaf water potential and stomatal conductance (gs). Two broadleaf (one evergreen, Arbutus menziesii Pursh., and one deciduous, Quercus garryana Dougl.) and two coniferous species (Pinus ponderosa Dougl. and Pseudotsuga menziesii [Mirbel]) were chosen as representative of different plant types. In addition, Kleaf in the laboratory and leaf water potential in the field were measured for three tropical evergreen species (Protium panamense (Rose), Tachigalia versicolor Standley and L.O. Williams and Vochysia ferruginea Mart) to predict their daily changes in field Kleaf in situ. It was hypothesized that in the field, leaves would close their stomata at water potential thresholds at which Kleaf begins to decline sharply in laboratory-generated VC, thus preventing substantial losses of Kleaf. The temperate species showed a 15-66% decline in Kleaf by midday, before stomatal closure. Although there were substantial midday declines in Kleaf, recovery was nearly complete by late afternoon. Stomatal conductance began to decrease in Pseudotsuga, Pinus and Quercus once Kleaf began to decline; however, there was no detectable reduction in gs in Arbutus. Predicted Kleaf in the tropical species, based on laboratory-generated VC, decreased by 74% of maximum Kleaf in Tachigalia, but only 22-32% in Vochysia and Protium. The results presented here, from the previous work of the authors and from other published studies, were consistent with two different strategies regarding daily maintenance of Kleaf: (1) substantial loss and subsequent recovery or (2) a more conservative strategy of loss avoidance.

Environmental risk assessment and comprehensive index model of disaster loss for COVID-19 transmission

On the basis of daily observations data from 1984 to 2020, the spatiotemporal characteristics of extreme precipitation events in the Poyang Lake Basin (China) were analyzed using the intensity–area–duration method. With consideration of spatially distributed data on gross domestic product (GDP), population, and disaster losses related to historical extreme precipitation events, the exposure and vulnerability of the population and GDP of the study area to extreme precipitation events were systematically assessed. The results revealed the following. 1) The intensity and frequency of extreme precipitation, as well as the area affected, showed trends of increase, especially in the northeast of the basin. 2) Population exposure in the basin showed a trend of increase of 2.43 million/a. Change in population exposure was greatest in the most recent 10 years, with an average increase of 6.64 million/a. Change in extreme precipitation was the primary driver of the rapid increase in population exposure. 3) The average annual GDP exposure of the basin was ¥5.43 billion, and economic exposure has increased substantially at an average rate of ¥0.56 billion/a. Unlike population exposure, the increase in economic exposure was driven mainly by rapid economic growth. 4) By constructing vulnerability curves of economic losses in different decades, the trend of economic vulnerability was found to have clearly declined, i.e., economic vulnerability in 2010 was 13.3 (4.1) times lower than that in the 1990s (2000s). Effective disaster prevention and reduction measures should urgently be adopted in the study area to mitigate the effects of increase in extreme precipitation events.

Drought is one of the most serious natural disasters in the world and causes great economic losses in China every year, especially in its southwest region. Yet, few studies have reported the quantitative comprehensive risk of drought in the Yunnan, Guizhou, and Guangxi provinces of China. Taking these three provinces as the study area, we obtained annual precipitation, disaster loss, and agricultural planting data during 1964–2013. Following an optimal estimation of annual precipitation by the Bayesian maximum entropy method, we mapped the annual Standardized Precipitation Index. Based on the theory of information diffusion and exceeding probability, the hazard of drought was evaluated. We also fit the vulnerability curves using the drought loss data. As a basis, we constructed a multiplicative formula to calculate the comprehensive risk of drought, which integrates the hazard and the vulnerability and produces drought loss rate (DLR) maps. We found that the DLR caused by mild drought was about 3%, moderate drought 10%, severe drought 25%, and extreme drought 50%. We also created a risk zoning map to provide practical information, such as a scientific basis for optimization of regional allocation of resources for drought preparedness and response.

Vulnerability of xylem to embolism is an important trait related to drought resistance of plants. Methods continue to be developed and debated for measuring embolism. We tested three methods (benchtop dehydration/hydraulic, micro-computed tomography (microCT) and optical) for assessing the vulnerability to embolism of a native California oak species (Quercus douglasii Hook. & Arn.), including an analysis of three different stem ages. All three methods were found to significantly differ in their estimates, with a greater resistance to embolism as follows: microCT > optical > hydraulic. Careful testing was conducted for the hydraulic method to evaluate multiple known potential artifacts, and none was found. One-year-old stems were more resistant than older stems using microCT and optical methods, but not hydraulic methods. Divergence between the microCT and optical methods from the standard hydraulic method was consistent with predictions based on known errors when estimating theoretical losses in hydraulic function in both microCT and optical methods. When the goal of a study is to describe or predict losses in hydraulic conductivity, neither the microCT nor optical methods are reliable for accurately constructing vulnerability curves of stems; nevertheless, these methods may be useful if the goal of a study is to identify embolism events irrespective of hydraulic conductivity or hydraulic function.