Number Of Extreme Events Research Articles

Climate Variability and Trends in Bolivia

AbstractClimate-related disasters in Bolivia are frequent, severe, and manifold and affect large parts of the population, economy, and ecosystems. Potentially amplified through climate change, natural hazards are of growing concern. To better understand these events, homogenized daily observations of temperature (29 stations) and precipitation (68 stations) from 1960 to 2009 were analyzed in this study. The impact of the positive (+) and negative (−) phases of the three climate modes (i) Pacific decadal oscillation (PDO), (ii) El Niño–Southern Oscillation (ENSO) with El Niño (EN) and La Niña (LN) events, and (iii) Antarctic Oscillation (AAO) were assessed. Temperatures were found to be higher during PDO(+), EN, and AAO(+) in the Andes. Total amounts of rainfall, as well as the number of extreme events, were higher during PDO(+), EN, and LN in the lowlands. During austral summer [December–February (DJF)], EN led to drier conditions in the Andes with more variable precipitation. Temperatures increased at a rate of 0.1°C per decade, with stronger increases in the Andes and in the dry season. Rainfall totals increased from 1965 to 1984 [12% in DJF and 18% in June–August (JJA)] and decreased afterward (−4% in DJF and −10% in JJA), following roughly the pattern of PDO. Trends of climate extremes generally corresponded to trends of climate means. Findings suggest that Bolivia’s climate will be warmer and drier than average in the near-term future. Having entered PDO(−) in 2007, droughts and LN-related floods can be expected in the lowlands, while increasing temperatures suggest higher risks of drought in the Andes.

Hydrologic Characterization of the Koshi Basin and the Impact of Climate Change

Assessment of surface and groundwater resources and water availability for different sectors is a great challenge in Nepal mainly due to data limitations. In this study, the Soil Water Assessment Tool (SWAT) was used to simulate the hydrology and to calculate sub-basin wise water balances in the Koshi Basin, Nepal. The impacts of Climate Change (CC) projections from four GCMs (CNRM-CM3, CSIRO-Mk3.0,ECHam5 and MIROC 3.2) on the hydrology of the basin were also calculated. This paper summarizes some of the key results. The full report of the study is in preparation.The basin can be divided into the trans-mountain, central mountain, eastern mountain, eastern hill and central hill regions. Results show that current precipitation is highest in the central mountain and eastern mountain regions during both the dry and wet seasons. Water balance results showed that Actual ET as well as Runoff is also highest in the central and eastern mountain regions followed by the mid-hills. Results from climate change projections showed that average temperature will increase in the 2030’s by 0.7-0.9° Celsius. Results for 2030s projections also show that during the dry season, precipitation increases in the trans-mountain but decreases in the other regions for both A2 and B1 scenarios. During the wet season, the MarkSim projections show a decrease in precipitation in all the regions. Net water yields also increased for the trans-mountain zone during the dry season but show varying results during the monsoon. Assessment of projected future flow time series showed that there will be an increase in the number of extreme events; i.e., both low flows and large floods. There is however; a high degree of uncertainty in the projected climate data as the relative standard deviation was quite high.DOI: http://dx.doi.org/10.3126/hn.v11i1.7198 Hydro Nepal Special Issue: Conference Proceedings 2012 pp.18-22

Climate variability in Andalusia (southern Spain) during the period 1701–1850 based on documentary sources: evaluation and comparison with climate model simulations

Abstract. In this work, a reconstruction of climatic conditions in Andalusia (southern Iberian Peninsula) during the period 1701–1850, as well as an evaluation of its associated uncertainties, is presented. This period is interesting because it is characterized by a minimum in solar irradiance (Dalton Minimum, around 1800), as well as intense volcanic activity (for instance, the eruption of Tambora in 1815), at a time when any increase in atmospheric CO2 concentrations was of minor importance. The reconstruction is based on the analysis of a wide variety of documentary data. The reconstruction methodology is based on counting the number of extreme events in the past, and inferring mean value and standard deviation using the assumption of normal distribution for the seasonal means of climate variables. This reconstruction methodology is tested within the pseudoreality of a high-resolution paleoclimate simulation performed with the regional climate model MM5 coupled to the global model ECHO-G. The results show that the reconstructions are influenced by the reference period chosen and the threshold values used to define extreme values. This creates uncertainties which are assessed within the context of climate simulation. An ensemble of reconstructions was obtained using two different reference periods (1885–1915 and 1960–1990) and two pairs of percentiles as threshold values (10–90 and 25–75). The results correspond to winter temperature, and winter, spring and autumn rainfall, and they are compared with simulations of the climate model for the considered period. The mean value of winter temperature for the period 1781–1850 was 10.6 ± 0.1 °C (11.0 °C for the reference period 1960–1990). The mean value of winter rainfall for the period 1701–1850 was 267 ± 18 mm (224 mm for 1960–1990). The mean values of spring and autumn rainfall were 164 ± 11 and 194 ± 16 mm (129 and 162 mm for 1960–1990, respectively). Comparison of the distribution functions corresponding to 1790–1820 and 1960–1990 indicates that during the Dalton Minimum the frequency of dry and warm (wet and cold) winters was lower (higher) than during the reference period: temperatures were up to 0.5 °C lower than the 1960–1990 value, and rainfall was 4% higher.

North Atlantic Oscillation influence and weather types associated with winter total and extreme precipitation events in Spain

An analysis of winter intensity and frequency of precipitation is presented, based on 102 daily precipitation stations over Spain and the Balearic Islands for the 1997–2006 decade. Precipitation stations have been merged in the eight different regions which compose the analyzed area by the use of an EOF analysis. NAO influence on the intensity and frequency of precipitation of each region is described in terms of mean precipitation, mean rain frequency, the number of extreme events, changes in the precipitation distribution and the prevalent synoptic configuration. Results indicate a non-stationary response; NAO signal being more evident in mid–late winter. Strong regional differences in the response to NAO are also found, which vary according to the specific character of the precipitation under analysis. Thus, NAO exerts a clear effect on the intensity of total and extreme precipitation rates in northern and westernmost Spanish regions, whereas the frequency of precipitation is clearly affected by NAO in central and southwestern areas. While the correlation between NAO and precipitation is negative for most of the analyzed area, two regions reveal positive responses to NAO in total precipitation occurrence and intensity for specific months. Further analyses reveal asymmetric responses to opposite phases of NAO in the precipitation distributions of some regions. The complex regional relationship between NAO and precipitation is also revealed through the modulation of the former in the preferred Circulation Weather Types associated to precipitation in each region. This spatially non-homogeneous NAO signal stresses the need of caution when employing Iberian precipitation as a proxy for NAO.

Are extreme rainfall intensities more frequent? Analysis of trends in rainfall patterns relevant to urban drainage systems

The fact that climate change is affecting the intensity and frequency of rainfall is well accepted in the scientific community. This is backed by a multitude of reports on the basis of daily rainfall series analysis; however, little research is available for short duration intensities. Due to its significant influence on the behaviour of urban drainage, it is critical to investigate the changes in short duration rainfall intensities. In this study different intensities relevant for the urban drainage and the total rainfall per rain event are analysed. The trend is investigated using the Mann-Kendall test. The rainfall series analysed are from the alpine region Tyrol. The results present differences depending on the duration of the intensity and the series considered, however an increase in the number of extreme events is detectable for short durations for the most series.

A new method to reconstruct low-frequency climatic variability from documentary sources: application to winter rainfall series in Andalusia (Southern Spain) from 1501 to 2000

In this work a simple approach to reconstruct climatic variables from documentary data is proposed. This approach may be especially useful when an overlapping period between documentary and instrumental data is not available. On the other hand, the method avoids use artificial statistical procedures to rescale the reconstructed series and overcome the problem of the loss of variance. The methodology allows reconstruct changes in the mean value and standard deviation of the climate variables. It is based on accounting the number of extreme events in past, and inferring mean value and standard deviation using the assumption of normal distribution for the climatic variables. The application of the method is only possible if a sufficient number of events is recorded in the data base. It is useful to reconstruct changes in the long-time scale, using at least decadal periods as time units. The method is applied to winter rainfall series corresponding to 30-year periods in Andalusia (southern Spain), obtaining results comparable with those of previous analysis.

Tropical Atmospheric Variability Forced by Oceanic Internal Variability

Abstract Atmospheric general circulation model experiments are conducted to quantify the contribution of internal oceanic variability in the form of tropical instability waves (TIWs) to interannual wind and rainfall variability in the tropical Pacific. It is found that in the tropical Pacific, along the equator, and near 25°N and 25°S, TIWs force a significant increase in wind and rainfall variability from interseasonal to interannual time scales. Because of the stochastic nature of TIWs, this means that climate models that do not take them into account will underestimate the strength and number of extreme events and may overestimate forecast capability.

Future winter extreme temperature and precipitation events in the Arctic

This study investigates the possible changes in future winter temperature and precipitation extremes in the Arctic using the regional climate model HIRHAM4. Under the B2 emission scenario conditions, frequency and intensity of future (2037–2051) extremes have changed significantly compared to the present‐day (1981–1995) extremes. Extreme precipitations have intensified and the number of extreme events has changed significantly over East Siberia and Barents Sea. Extreme warm and extreme cold temperatures have become warmer with maxima over Barents Sea and Central Eurasia. Changes in the mean climate and its variability are modulating the future winter extreme events.

Behaviour of Multi-Layered Corrugated Paperboard Cushioning Systems under Impact Loads

This paper presents some of the latest results of a research project aimed at using composite corrugated paperboard structures for protection of products against mechanical shocks and vibration during transportation and handling. Specifically, the behaviour of multi-layered corrugated paperboard (MCPB) under shock loading is investigated. Conventionally, packaging cushion design requires the determination of the maximum expected shock levels or equivalent drop which are usually determined from statistical analysis of original field measurements. With this approach, it is generally acknowledged that the cushioning element is engineered to provide adequate protection for statistically likely events but not for extreme events with low statistical likelihood. It is reluctantly accepted that, should it occur, the latter will result in damage to the product. MCPB can be formed with a broad range of compressive characteristics and with various proportions of elastic and plastic behaviour. The objective of this experimental investigation was to determine the optimum elastic/plastic proportion to extend the protective range to include large shock levels. The experimental results obtained include the effects of compression history on the stress-strain properties of MCPB as well as the behaviour of the material in both virgin and pre-compressed form under impulsive loads. The mechanism of deformation of the corrugations (flutes) was studied using high-speed video equipment. The complex acceleration signals produced during deformation of the composite corrugated paperboard cushions under shock loading were analysed by means of the shock response spectrum. Experiments have shown that inserting a sacrificial crumple element of virgin corrugated paperboard at the optimum contact area ratio dramatically lowers the overall level of the resulting shock response spectrum. This has the effect of increasing the allowable drop height for a limited number of extreme events. The main conclusion of the research is that MCPB in both virgin and pre-compressed forms can be combined to provide significantly enhanced protection to products against mechanical hazards during distribution.

LONG–TERM PRECIPITATION ANALYSES FOR THE CENTRAL TEXAS BLACKLAND PRAIRIE

Continuous records of intensively monitored precipitation data are rare, but where available they provide valuable regional information on hydrologic structure design and on other water supply and water quality management and modeling issues. One such long–term precipitation record exists for the Texas Blackland Prairie region. Beginning in 1937 and continuing to the present, hydrologic data have been collected at the USDA–ARS Grassland Soil and Water Research Laboratory watershed facility near Riesel, Texas. The objectives of this article are to present long–term analyses and to publicize the availability of that precipitation database. Long–term analyses included examination of general precipitation properties, depth–duration–frequency relationships, and trends in rainfall amount and occurrence. Annual rainfall for the region averages about 890 mm, with relatively wet springs and falls and drier summer and winter months. Depth–duration–frequency results emphasize the need for engineers to use the most current and extensive data sets and/or proven relationships in the design of hydrologic structures. Several significant temporal trends that can affect water resource management were also determined. These trends include increases in October rainfall, non–spring rainfall, and the number of summer, fall, and annual rainy days. These increases, however, are offset to some degree by decreases in April rainfall, in the number of extreme events in the spring, and in the magnitude of extreme fall rain events.

A Climatology of Northwest Missouri Snowfall Events: Long-Term Trends and Interannual Variability

The goal of this study was to develop a 50-yr. statistical climatology of snowfall occurrences using data from a dense network of cooperative station observations covering northwest and central Missouri, and these records were provided by the Missouri Climate Center. This included a study of the long-term trends and interannual variability in snowfall occurrence as related to sea surface temperature variations in the Pacific Ocean basin associated with the El Niño and Southern Oscillation (ENSO) and the North Pacific Oscillation (NPO). These trends and variations were then related to four synoptic-scale flow regimes that produce these snowfalls in the Midwest. The results demonstrate that during the snowfall season (Oct-April) the northwest Missouri region can expect about eight snowfall events which produce ≥3 in. (>7.5 cm) of accumulation. While no significant long-term trend in overall snowfall occurrence was found, a decrease in the number of extreme events (≥10 in., >25 cm) was noted. Also, fewer snowfall events were found during El Niño years, while more heavy snowfall events occurred during "neutral" years, and these results could be related to synoptic-scale variability. A closer examination of the results demonstrated that El Niño/La Niña related variability in snowfall occurrence was superimposed on longer-term NPO-related variability.

Occurrence of Extreme Precipitation Events in California and Relationships with the Madden–Julian Oscillation

California receives most of the annual precipitation during the boreal winter season. Additionally, large spatial and temporal variations in the total rainfall amounts are observed. This study investigates the occurrence of extreme precipitation events in California and the modulation by the Madden–Julian oscillation (MJO). Three questions are investigated. 1) Are extreme precipitation events in California more likely to occur during active MJO than inactive periods? 2) In what phase of the MJO life cycle are extreme events more likely? 3) Are interannual variations in the frequency of extreme events in California related to interannual variations of the MJO? Daily totals derived from gridded hourly station data are used to define extreme precipitation events from January 1958 to December 1996. Outgoing longwave radiation from polar orbiting satellites (1979–96) and zonal component of the wind at 200 hPa and 850 hPa from the National Centers for Environmental Prediction–National Center for Atmospheric Research reanalysis (1958–96) are used to describe the life cycle of the oscillation and its interannual variability. The results indicate that the frequency of extreme events are more common when tropical activity associated with the MJO is high, as opposed to periods of quiescent phases of the oscillation. Second, a slight preference for a higher number of events is observed when convective anomalies are located in the Indian Ocean. In this situation, low-level westerly and easterly wind anomalies are observed over the Indian and western Pacific Oceans, respectively. The analysis of the interannual variability in the amplitude of the MJO and the occurrence of extreme events over California indicates no direct and systematic relationships with the number of extreme events.

Forecasting Summertime Surface-Level Ozone Concentrations in the Lower Fraser Valley of British Columbia: An Ensemble Neural Network Approach

ABSTRACT Empirical models for predicting daily maximum hourly average ozone concentrations were developed for 10 monitoring stations in the Lower Fraser Valley (LFV) of British Columbia. According to data from 1991 to 1996, ensemble neural network models increased explained variance an average of 7% over multiple linear regression models using the same input variables. Without modification, all models performed poorly on days when the observed peak ozone concentration exceeded 82 parts per billion, the National Ambient Air Quality Objective. When numbers of extreme events in training data were increased using a histogram equalization process, models were able to forecast exceedances with improved accuracy. Modified generalized additive model (GAM) plots and associated measures of input variable importance and interaction were generated for a subset of the trained models and used to investigate relationships between input variables and ozone levels. The neural network models displayed a high degree of interaction among inputs, and it is likely the ability of these model types to account for interactions, rather than the nonlinearity of individual input variables, that explains their improved forecast skill. Inspection of GAM-style plots indicated that the relative importance of input variables in the ensemble neural network models varied with geographic location within the LFV. Four distinct groups of stations were identified, and rankings of inputs within the groups were generally consistent with physical intuition and results of prior studies.

Estimation of regional intensity-duration-frequency curves for extreme precipitation

Regional estimation of extreme precipitation from a high resolution rain gauge network in Denmark is considered. The applied extreme value model is based on the partial duration series (PDS) approach in which all events above a certain threshold level are modelled. For a preliminary assessment of regional homogeneity and identification of a proper regional distribution L-moment analysis is applied. To analyse the regional variability in more detail, a generalised least squares regression analysis is carried out that relates the PDS model parameters to climatic and physiographic characteristics. The analysis reveals that the mean annual number of extreme events varies significantly within the region, and a large part of this variability can be explained by the mean annual rainfall. The mean value of the exceedance magnitudes can be assumed constant for intensities with durations less than one hour. For larger durations a pronounced metropolitan effect is evident, the mean intensities in the Copenhagen area being significantly larger than found in the rest of the country. With respect to second and higher order moments the region can be considered homogeneous for intensities with durations less than 24 hours. A regional parent distribution is identified as the generalised Pareto distribution.

Scenarios of extreme temperature events

Based on the principles of the probability theory a statistical model has been developed assessing the likelihood of occurrence of extreme temperature events from the knowledge of the statistical characteristics of the daily temperature extremes. It is demonstrated that the probability of such events is more sensitive to changes in the variability of climate than to changes in its average. Further, this sensitivity increases at a nonlinear rate the more extreme the event. The applicability of the model has been verified by comparing the simulated frequencies of a large spectrum of temperature events with the observed numbers derived from a long time series of daily temperature extremes at Potsdam. Accordingly, the relative simulation errors increase significantly as the events become more extreme. A correction is possible, because most of these errors are systematic rather than random. Moreover, in accordance with the climate observations the simulations reveal statistically significant linear trends in the number of extreme events since the end of the last century. Local scenarios of extreme temperature events have been derived for the city of Berlin by considering both hypothetical new climate states and climate changes simulated by a General Circulation Model (GCM). As a consequence of an increase in the atmospheric concentration of greenhouse gases up to the end of the next century according to the IPCC Scenario A the repetition rate of extreme events in summer (e.g., hot days) is expected to rise considerably relative to the current climate. Moreover, in the winter season cold days will become extremely rare.