Extreme Wet Events Research Articles

Contrasting urban greenness across cities with varying trends in above-normal weather events

Effective urban management demands global empirical research findings. The work aims to determine whether green areas are more significant in cities where above-normal wet events have plateaued. This work compares the green surface cover characteristics of the entire city and identified zones of 54 cities representing cities worldwide. These cities experience varying amounts of above-normal weather conditions. This article classifies the cities in the data set into two groups: Group 1 – frequency of extreme wet weather events has plateaued, and Group 2 – frequency of extreme weather events are increasing or decreasing at higher rates. Next, the work uses structural features of co-located spatial networks, roads and terrain, to identify zones. Finally, high-resolution satellite imagery quantified urban green spaces in the city and identified zones of the two city groups using geospatial and machine learning methods for 2000 and 2020. The data is compared for two groups to understand the pattern of green spaces in cities. Empirical analysis results recognise a higher greenness index in the zones and the entire city amongst the cities of Group1. The pattern in the temporal change in the greenness index of the zones is helpful to formulate a priority plan for locating inter-linked green spaces in urban areas paving the way for Nature-based Solutions. The findings can guide planners and policy-makers to identify and prioritise locations to incorporate a robust green infrastructure network to build resilient cities by 'nature bringing a solution’, the essential concept of Nature-based Solutions.

Response of grassland net primary productivity to dry and wet climatic events in four grassland types in Inner Mongolia.

Increasing frequency and intensity of climate extremes have profound impacts on grassland biodiversity functioning and stability. Using Moderate Resolution Imaging Spectroradiometer (MODIS) net primary productivity (NPP) data and standardized precipitation evapotranspiration index, we assessed the response of NPP to growing-season and annual climate extremes and time-lag of climatic conditions across four grassland types (meadow steppe, typical steppe, steppe desert, and desert steppe) in Inner Mongolia, China from the period 2000 to 2019. Results showed that annual NPP varied significantly across four grassland types, with the highest NPP in meadow steppe and the lowest in desert steppe. Annual NPP of all grassland types increased over the past 20years, but NPP in meadow steppe and typical steppe decreased for the period 2012-2019. Irrespective of grassland type, the 1- and 2-month time-lag of climatic conditions showed significant effects on annual NPP. Growing-season climate was found the better predictor of annual NPP in all grassland types than the annual climate. Compared with growing-season normal climates, annual NPP was lowest in extreme dry events in all grasslands, while highest in extreme wet events in meadow steppe and typical steppe, and in moderate wet events in steppe desert and desert steppe. Typical steppe and steppe desert are highly vulnerable to the increasing intensity of climate extremes, as we found that the losses of NPP in these grasslands in extreme dry were almost double than that of moderate dry events. Surprisingly, for meadow steppe and desert steppe, the losses of NPP for both moderate and extreme dry events were almost the same, which highlights that a low-intensity drought may have profound impacts on the annual NPP of these grasslands. The study provides the key insight in scientific basis to improve our understanding of the effects of climate extremes on grassland NPP, which is critical to sustainable management of grassland and maintain ecosystem stability.

NDVI-based vegetation dynamics and its resistance and resilience to different intensities of climatic events

The growing season normalized difference vegetation index (NDVIGS) of vegetation and their responses to climate extremes are critical in assessing the resistance and resilience of the terrestrial ecosystem. Using satellite-derived NDVIGS and widely used Standardized Precipitation and Evapotranspiration Index (SPEI) datasets of 18 sites in cold steppe, humid temperate and temperate dry steppe ecoregions for the period of 1982–2012, the NDVIGS response, resistance, and resilience to climate extreme intensity were assessed. The results showed that the mean NDVIGS varied significantly across ecoregions, where higher mean NDVIGS was observed in humid temperate and lower was in temperate dry steppe. The NDVIGS at most sites in three ecoregions showed significantly positive correlations with increasing SPEI. The responses of NDVIGS to climate extreme intensity revealed that moderate and extreme dry events decreased NDVIGS, while moderate and extreme wet events increased NDVIGS in all ecoregions. The results showed that vegetation resistance and resilience were highly dependent on climate extreme intensity. Resistance and resilience to moderate wet, extreme wet, moderate dry and extreme dry events in all ecoregions varied significantly, where vegetation in cold steppe and humid temperate ecoregions showed lower resistance but higher resilience to moderate and extreme dry events, and higher resistance but lower resilience to moderate and extreme wet events. Vegetation in temperate dry steppe showed higher resistance to moderate dry and higher resilience to moderate wet events. The study results suggest that more productive ecosystems (i.e. higher NDVIGS in cold steppe and humid temperate ecoregions) generally provide a lower (higher) resistance but higher (lower) resilience to dry (wet) events. Knowledge from this study also implies that less productive ecosystem (i.e. lower NDVIGS in temperate dry steppe) provides higher resistance to moderate dry and higher resilience after moderate wet events. This study highlights the impacts of climate extremes on NDVIGS, and improves our understanding of the resistance and resilience of vegetation to climate extreme intensity, which is of importance in the face of climate change.

Extreme wet events as important as extreme dry events in controlling spatial patterns of vegetation greenness anomalies

Understanding plant responses to hydrological extremes is critical for projections of the future terrestrial carbon uptake, but much more is known about the impacts of drought than of extreme wet conditions. However, the latter may control ecosystem-scale photosynthesis more strongly than the former in certain regions. Here we take a data-driven, location-based approach to evaluate where wet and dry extremes most affect photosynthesis. By comparing the sensitivity of vegetation greenness during extreme wetness to that during extreme dryness over a 34 year record, we find that regions where the impact of wet extremes dominates are nearly as common as regions where drought impacts dominate. We also demonstrate that the responses of wet-sensitive regions are not uniform and are instead controlled by multiple, often interacting, mechanisms. Given predicted increases in the frequency and intensity of extreme hydrological events with climate change, the consequences of extreme wet conditions on local and global carbon cycling will likely be amplified in future decades.

Impacts of hydroclimatic variability on surface water and porewater dissolved organic matter in a semi-arid estuary

Hydroclimatic disturbances, like flooding, may greatly impact dissolved organic matter (DOM) composition in coastal waters by altering hydraulic gradients, groundwater residence times, and seafloor recirculation. This study provides new evidence regarding seasonal molecular DOM changes, in a submarine groundwater discharge influenced semi-arid estuary, across different hydroclimatic conditions: from flood peak (summer) to flood recession (fall), to typical dry (winter) to semi-wet (spring) conditions. DOM molecular characterization of seasonal surface- and pore- water samples was conducted using PPL solid phase extraction and UPLC-Orbitrap Fusion mass spectrometry, in positive mode. The proportion of CHO compounds present was lowest during flooding (34%), increased during fall flood recession (39%), and was highest under semi-wet baseflow (spring) conditions (42%). While CHON compounds increased from the flood and flood recession events (27% and 22%, respectively) to dry and semi-wet conditions (35% and 34%, respectively), sulfur and phosphorous containing compounds decreased (flood ~34% and flood recession ~6%; dry <25% and semi-wet <3%, respectively). During the flood recession, DOM was considerably different from all other events, with over 1000 compounds significantly specific to this period. These significant changes were likely driven by submarine groundwater discharge, particularly as the compounds identified in surface- and pore- water were very similar, and surface water DOC and DON showed porewater influence. Baseflow characteristics were highly similar, with low saturation and high likelihood of rings or double bonds. It was evident that the influence of riverine inputs decreased within six months from the flood peak, which also showed the limited fresh riverine inputs outside extreme wet precipitation events when benthic fluxes became one of the major drivers of DOM characteristics. Thus, surface water DOM molecular characteristics showed significant responses to hydrologic changes, due to surface runoff inputs and benthic fluxes, which reflect changes in source and processing of OM within the estuary.

Seesaw Terrestrial Wetting and Drying Between Eastern and Western Australia

AbstractAustralia, the driest inhabited continent, is prone to natural disasters, such as droughts, floods, bushfires, and heatwaves. Strong climate variability causes recurring threats to water supply, agriculture, and the environment. Improving our insight into changes in hydroclimatic patterns is required to provide useful information for society. Previous studies mainly focused on the causes of extreme wet or dry events in specific periods and their impacts on agriculture and ecosystems. An understanding of long‐term spatio‐temporal patterns of wetting and drying in Australia is still lacking. Here we show, based on analyses of Gravity Recovery and Climate Experiment satellite derived terrestrial water storage and extended datasets, that there are four consecutive periods of seesaw wetting and drying between eastern and western Australia in the past five decades. The seesaw phenomenon is characterized by eastern Australia gaining water, while western Australia is losing water, and vice versa. Strong La Niña induced continent‐wide wetting, resets this pattern, leaving each seesaw to last for 11 ± 5 years. We provide one possible mechanism related to vegetation response to climate variability and its feedback on hydrological processes to explain the seesaw pattern. The identified recurring seesaw pattern indicates that society would need to become more adaptive in managing forest, water, and disaster risks in the wake of a next strong La Niña induced continent‐wide wetting in Australia.

Trends in Extreme Wet Events during Summer Monsoon Season over India

India is a predominantly agrarian country with most of the agriculture in India being rainfed. Summer monsoon means life-giving rains for the entire Indian subcontinent. In India, the success or failure of the harvest and water scarcity in any year is always considered with the greatest concern. Extreme wet and dry events play a vital role in the intra-seasonal variability of monsoon rainfall. Particularly, in recent times, the occurrences of wet spells over India have led to widespread floods in the country. With changing climatic conditions, the occurrence and prediction of these extreme events have become a major stabilizing factor for the millions inhabiting the country. In this study, using 117 years (1901-2017) of high resolution daily gridded rainfall data, trends in extreme high rainfall events over six regions of India have been examined. The temporal change in extreme rainfall events during the time period 1901-1950 and 1951-2017 in summer monsoon months (June, July, August and September) has also been examined, in order to understand the increasing effect of anthropogenic factors after 1950. Using standardized scores (z-scores), each grid cell is analyzed to identify the number of extreme wet spells experienced during the study period. The analysis reveals that the number of extreme wet events showed an increasing trend in the month of June, as against a decreasing trend in July, after 1950, in most of the regions. In the recent period, the number of wet extreme events also show a decreasing trend in the northeastern region, which is considered as one of the rainiest zones of the world. As the present study tries to evaluate the changing trend of extreme wet events, it will help in formulation of hazard management strategies and policies by government planners.

Spatiotemporal meteorological drought assessment in a humid Mediterranean region: case study of the Oued Sebaou basin (northern central Algeria)

In this research, the spatiotemporal meteorological drought pattern was assessed in the Oued Sebaou basin (northern central Algeria) based on data from 23 rain gauges from 1972 to 2010 analyzed at seasonal and annual scales using the standardized precipitation index (SPI). A geographic information system was used to determine the cartographic precipitation concentration index and modified Fourier index (MFI) as well as the drought and rainfall characteristics of the stations. The analysis revealed moderate precipitation concentrations for all stations in the basin, for which longitude explains approximately 60% of the variance. The MFI results show three main aggressiveness distributions: weak, moderate and strong, which are similar to the spatial distribution of rainfall. The results show a prolonged drought that began in the late 1980s. In addition, more than 50% of the stations were affected by moderate and severe dry events during the period from 1986 to 2001. The comparison of the SPI values among the decades indicates that more than 20% of the cases were dominated by wet conditions from 1972 to 1981 and from 2002 to 2010, with near-normal and -normal events exceeding 70%. During the 2002–2010 decade, extreme wet events occurred in 7% of the cases, while in the 1972–1981 decade, only 1.75% of the cases were of this type. These results can provide watershed managers with more information to understand past drought and improve future water resource management.

Dry and Wet Events in Andean Populations of Northern Peru: A Case Study of Chachapoyas, Peru

Climate change and population growth have heavily impacted the ecosystem’s water resources, essential for anthropogenic activities. These also apply to the Andean city of Chachapoyas, located in the north of Peru, which has gone through a substantial population increase in recent years, therefore increasing its water demand. This research aimed to assess dry and wet events from 1981 to 2019 that have taken place in Chachapoyas, by applying the Standardized Precipitation Index (SPI), and the Standardized Precipitation Evapotranspiration Index (SPEI). These events were periodically characterized, and the index relationship was determined at different timescales. The SPI and SPEI indices were calculated at the city’s only weather station for timescales of 3, 6, 12, and 24 months using climatic data. The indices showed a remarkably consistent behavior for timescales of 12 and 24 months detecting an extreme drought event in 1993, while for timescales of 3 and 6 months a severe drought event was detected in the same year. Contrastingly, there has been an increase in extreme wet events in the last decade, hence Chachapoyas is categorized between "moderate drought" and “moderate wet”. It should be noted that the indices have a high correlation between them when calculated for the same timescale. The results were statistically significant (p &amp;lt; 0.05). Considering the results obtained related to dry and wet events and their relation with economic activities such as environmental management, we can conclude that the SPI and SPEI indices are useful and valuable tools for local and regional governments.

Rankings of extreme and widespread dry and wet events in the Iberian Peninsula between 1901 and 2016

Abstract. Extensive, long-standing dry and wet episodes are two of the most frequent climatic extreme events in the Iberian Peninsula. Here, a method for ranking regional extremes of persistent, widespread drought and wet events is presented, considering different timescales. The method is based on the multi-scalar Standardized Precipitation Evapotranspiration Index (SPEI) gridded dataset for the Iberian Peninsula. Climatic Research Unit (CRU) data are used to compute the SPEI between 1901 and 2016 by means of a log-logistic probability distribution function. The potential evapotranspiration (PET) is computed using the Penman–Monteith equation. The ranking classification method is based on the assessment of the magnitude of an event, which is obtained after considering both the area affected by the respective dryness or wetness – defined by SPEI values over a certain threshold – and its intensity in each grid point. A sensitivity analysis of the impact of different thresholds used to define dry and wet events is also performed. For both the dry and wet periods, this simple yet robust tool allows for the identification and ranking of well-known regional extremes of persistent, extensive dry and wet periods at different timescales. A comprehensive dataset of rankings of the most extreme, prolonged, widespread dry and wet periods in the Iberian Peninsula is presented for aggregated timescales of 6, 12, 18, and 24 months. Results show that no region in the Iberian Peninsula is more prone to the occurrence of any of these long-term (dry and/or wet) extreme events. Finally, it is highlighted that the application of this methodology to other domains and periods represents an important tool for extensive, long-standing, extreme event assessment worldwide.

An assessment of gully pot sediment scour behaviour under current and potential future rainfall conditions

Gully pots actively trap sediments transported by urban runoff to prevent in-pipe blockages and surface flooding. However, due to poor maintenance (resulting in sediment build-up) and increasingly extreme wet weather events, the scour of previously-deposited sediments from gully pots is identified as a potential contributor to EU Water Framework Directive failure. While basal sediment scour deterministic models have been developed and validated using laboratory and field gully pot data sets, the ability of these models to predict behaviour at sites other than those for which they were established has not been addressed. Nor has the impact of future rainfall predictions on the role of gully pots as sediment sources been systematically examined. As a contribution to addressing these knowledge gaps, the performance of two gully pot basal sediment scour models of distinct complexity levels are evaluated under current and future rainfall conditions. The output from Model One suggests that the scour-induced total suspended solids in gully pot discharge can be kept well below 25 mg/L if the gully pot fullness level is maintained at under 60%. Results identify the opportunity to incorporate the actual/targeted ecological status of recipients in scheduling gully pot maintenance operations and that proactive gully pots maintenance will reduce the impacts of increased rainfall intensity/duration on the magnitude of sediment scour. Results from Model Two suggest that fine sediments are particularly susceptible to in-pot scour. For example, sediment with a specific gravity of 1.1 and diameter of >63 μm accounts for 50% of scour-induced total suspended solids in gully pot discharge. The effluent suspended solids concentrations predicted by the two models differ by up to two orders of magnitude. However, without further empirical field data pertaining to their respective competences/applications, neither model could be discounted at this stage. For example, the use of Model One is more appropriate in the establishment of gully pot maintenance schedules, with Model Two more suited to the dimensioning of gully pots based on performance requirements. This application, however, relies on the development and adoption of a more stringent regulation on gully pots discharge.

Observed Climate Extreme in Nepal

The climate-induced disasters are causing more than half of the total economic and human losses annually due to natural disasters and that hampers the socioeconomic development of the country. In recent decades, these climate extreme induced disasters are increasingly becoming more pronounced and devastating, is further known to be intensified due to anthropogenic warming. In this context, this study endeavors to address the research gap on the spatial and temporal variability of temperature and precipitation extremes in Nepal. Here, 26 climate extreme indices of temperature (13) and precipitation (13) as recommended by the World Meteorological Organization (WMO) were calculated using RClimDex software for 90 meteorological stations. Then the statistical significance of the long-term trend of the indices was tested using the Mann-Kendall method, and true magnitude of the trend was identified utilizing Sens’ slope method for each index at each station. Overall, the hot (warm days, warm nights, summer days, tropical nights, and warm spells) and cold (cold days, cold nights, cold spells) extreme indices show significant positive and negative trends respectively. However, extreme precipitation indices also show an increasing trend, but the statistical significance and spatial coherence is low. Extreme temperatures increased more in the Mountain and Himalayan regions than the other regions. Extreme wet day precipitation events are significantly increasing in far western region, adjoining areas of mid-western and western Siwalik though Mountain regions and then again in the central and eastern Mountains and Himalayan regions.

Anthropogenic influence has increased climate extreme occurrence over China

The changes in occurring probability of exceeding historically observed climate extreme events under the future warming scenario of SSP5-8.5. The probability ratios are estimated relative to the current state of 1995–2014. Maps in the left column show the probability changes for the period 2046–2065 and the mid column displays the results for the period 2081–2100. The projected changes in regional frequencies of climate extreme events are also displayed in the right panels for the future years. The shaded areas show the interquartile model spread, i.e., the range between the 25th and 75th percentiles of model ensemble, representing the confidence level. Climate change has exerted substantial influence on climate extreme events. To what degree anthropogenic influence has increased the risks of climate extreme events is of high public concern and still heavily debated. We find that the observed trends have exerted substantial influences on the severity and probability of the unprecedented hot, cold, wet, and dry events during the past decades across China. Attribution analyses based on different forcing simulations of CMIP6 indicate that humans have increased probabilities of historical hot and wet extremes, including in more than 75% and 56% of the areas in China, respectively. Particularly for the hottest day, the probability has increased by more than two times in over 20% of the area, while the probability of historical clod events decreases over most of China. Increasing emissions in the future are likely to cause substantial and widespread additional increases, including more than tenfold for the hottest day and twofold for the extreme wet events by the end of this century. For example, the observed hottest day would occur for each year over 80% of China from 2080, while the observed coldest night would never occur, and the driest events would markedly decrease by the end of this century. Therefore, it is now urgent for governments and the public to properly adopt effective strategies to mitigate anthropogenic influence on climate change in the future.

Analysis of dry and wet climate characteristics at Uttarakhand (India) using effective drought index

Drought is a complex natural disaster that adversely affects human life and the ecosystem. A variety of drought indexes are available for monitoring meteorological drought events. In the present study, Effective Drought Index (EDI) was utilized to quantify the drought and wet conditions with their probability at 13 districts of Uttarakhand State (India). The EDI was calculated for all study locations by using monthly rainfall data. The drought and wet incidents (i.e., moderate, severe, extreme) were categorized by setting a truncation level to the respective EDI value by using the runs theory concept. The results of the EDI examination explore that the probability of occurrence (PO) of normal events (conditions) was found to be 68% at Almora and Dehradun; 72% at Bageshwar; 71% at Chamoli and Pauri Garhwal; 69% at Champawat; Haridwar, Nainital, and Rudraprayag; 77% at Pithoragarh; 74% at Tehri Garhwal; and 44% at Pantnagar. Similarly, the PO of moderate drought and wet (MD and MW) events was found to be relatively more than the severe and extreme drought and wet events, except the Pantnagar station (extreme wet = 0.54). Thus, the outcomes of this study can be utilized to formulate the mitigation strategy in that way to store the surplus water in wet eras and utilized the same during drought for domestic and agricultural drives in the study districts.

Assessment of drought and wet projections in the humid climatic regions for Pakistan

Investigation of extreme hydrological events are necessary for planning and designing hydrological structures. In this study, we examine and project two hydrological extremes of drought and wet conditions over the north and eastern regions of the country. A statistical procedure of the Reconnaissance Drought Index at the annual time scale was used to combine the monthly rainfall and temperature data for the assessment of extreme drought and wet events. These hydrological extreme events were combined with Index-Drought Procedure using L-moments to obtain study results. Homogenous regions were satisfied for both the extremes based on statistical measures. Two statistical tools were used to select suitable probability distributions in the form of Generalized Pareto and Pearson Type-III distributions to discuss drought risk and wet conditions in the regions. Secondly, regional projections of drought risk and wet conditions were performed based on regional quantiles at different interarrival periods which show greater chances of the wet condition in region one while drought risk in region two. Lastly, at-site projections were carried out for all the included sites for both extremes at various interarrival periods using the suitable probability distributions. Both at-site and regional projections show greater similarity at lower while uncertainty at higher interarrival periods. As droughts and wets cover, a large area, therefore, regional results are more functional and better for regional planning and development programs. These statistical projections will help planners of water resources management and hydrological extremes in the study area.

Hydroclimate extremes in a north Australian drought reconstruction asymmetrically linked with Central Pacific Sea surface temperatures

An understanding of tropical hydroclimate variability, the associated drivers and how it is likely to change is a major scientific and societal challenge that is acutely hampered by short instrumental records. We present a 246-year tree-ring drought reconstruction of the Standardised Precipitation Evaporation Index (SPEI) for monsoonal northern Australia for the end of the wet season (March–May; MAM). This reconstruction extends the instrumental record back by 150 years. Around one third of total annual rainfall falls during MAM, making it a crucial component of the monsoonal cycle. MAM is also the season most impacted by the differential decay process of Central Pacific (as opposed to Western Pacific) El Nino events that are linked with dry conditions over northern and northwestern Australia more generally. Our reconstruction therefore provides an opportunity to consider how central Pacific variability has modulated MAM hydroclimate in Australia's monsoonal north over the past two and a half centuries. We found that MAM hydroclimate extremes in the region have a strong, but asymmetric relationship with central Pacific sea surface temperatures (SSTs) and ENSO indices. Extremely wet MAMs in monsoonal north Australia were associated with cooler SSTs, above average rainfall across much of Australia, and often coincided with La Nina events. The spatial relationship between dry extremes and Pacific SSTs during dry events was generally, but weakly, consistent with the SST signature of central Pacific El Nino events. The association between reconstructed dry extremes in the monsoonal north and dry conditions across the rest of Australia is also less extensive and weaker than for wet events. Results suggest that more extreme wet events in the Australian monsoonal north likely reflect cool central Pacific SSTs and later termination of the Australian monsoon. Consecutive years with extremely dry MAMs became more frequent over the latter part of the 20th Century while the probability of an extreme dry MAM followed by an extreme wet MAM the next year peaked in the mid 20th Century and has since declined.

Hydroclimatic variability in Santiago (Chile) since the 16th century

AbstractThe long‐term hydroclimatic variability in Santiago (Chile) was analysed by means of a new 481‐year (1536–2016 CE) tree‐ring reconstruction of the Standardized Precipitation Evapotranspiration Index (SPEI) of August, integrating the hydroclimatic conditions during the preceding 14 months. Results show a high frequency of extreme drought events in the late 20th and early 21st centuries, while the frequency of extreme wet events was higher in the 17th–18th centuries. The mid‐20th century represents a breaking point for the hydroclimatic history in the region, including some significant changes: (a) the interannual variability increased; (b) the wet events became less intense; (c) the extreme dry events became more frequent; and (d) the most intense dry event of the entire period was identified, coinciding with the so‐called Megadrought (2006–2016). A correlation analysis between the reconstructed SPEI and three climate indices (PDO, SOI and Niño3.4) was performed at monthly scale, considering different multi‐annual aggregations. The analysis shows diverse impacts on the hydroclimatic variability, with positive correlations between SPEI and PDO as well as Niño3.4, and negative correlations between SPEI and SOI. The most significant correlations were, overall, found at multi‐annual time scales (&gt;7 years). Results help to better understand the current hydroclimatic changes (Megadrought) in a long‐term context.

A quantitative hydroclimatic context for the European Great Famine of 1315\u20131317

The European Great Famine of 1315–1317 triggered one of the worst population collapses in European history and ranks as the single worst European famine in mortality as a proportion of population. Historical records point to torrential rainfall, land saturation, crop failure, and prolonged flooding as important causes of the famine. Here we use the tree-ring based Old World Drought Atlas (OWDA) to show that the average of each growing season preceding the Great Famine years (1314–1316) was the fifth wettest over Europe from 1300 to 2012 C.E. The spatial and temporal characteristics of our OWDA-estimated anomalies are in excellent agreement with available historical accounts. We also characterize a mode of European hydroclimate variability that is associated with the Great Famine, which we term the “Great Famine mode.” This mode emerges as the leading mode of European hydroclimate variability from 1300–2012 and is strongly associated with extreme wet and dry events in Europe over the last millennium.

Projected changes in hot, dry and wet extreme events’ clusters in CMIP6 multi-model ensemble

Concurrent extreme events, i.e. multi-variate extremes, can be associated with strong impacts. Hence, an understanding of how such events are changing in a warming climate is helpful to avoid some associated climate change impacts and better prepare for them. In this article, we analyse the projected occurrence of hot, dry, and wet extreme events’ clusters in the multi-model ensemble of the 6th phase of the Coupled Model Intercomparison Project (CMIP6). Changes in ‘extreme extremes’, i.e. events with only 1% probability of occurrence in the current climate are analysed, first as univariate extremes, and then when co-occurring with other types of extremes (i.e. events clusters) within the same week, month or year. The projections are analysed for present-day climate (+1 °C) and different levels of additional global warming (+1.5 °C, +2 °C, +3 °C). The results reveal substantial risk of occurrence of extreme events’ clusters of different types across the globe at higher global warming levels. Hotspot regions for hot and dry clusters are mainly found in Brazil, i.e. in the Northeast and the Amazon rain forest, the Mediterranean region, and Southern Africa. Hotspot regions for wet and hot clusters are found in tropical Africa but also in the Sahel region, Indonesia, and in mountainous regions such as the Andes and the Himalaya.

Projected Changes in Precipitation Extremes over Shaanxi Province, China, in the 21st Century

Extreme precipitation events, which have intensified with global warming, will have a pernicious influence on society. It would be desirable to understand how they will evolve in the future as global warming becomes more serious with time. Thus, the primary objective of this study is to provide a comprehensive understanding of the changing characteristics of the precipitation extremes in the 21st century over Shaanxi Province, a climate-sensitive and environmentally fragile area located in the east of northwestern China, based on a consecutive simulation of the 21st century conducted by the regional climate model RegCM4 forced by the global climate model HadGEM2-ES at high resolution under middle emission scenario of the Representative Concentration Pathway 4.5 (RCP4.5). Basic validation of the model performance was carried out, and six extreme precipitation indices (EPIs) were used to assess the intensity and frequency of the extreme precipitation events over Shaanxi Province. The results show that RegCM4 reproduces the observed characteristics of extreme precipitation events over Shaanxi Province well. Overall for the domain, the EPIs excluding consecutive dry days (CDD) have a growing tendency during 1980–2098 although they exhibit spatial variability over Shaanxi Province. Some areas in the arid northern Shaanxi may have more heavy rainfalls by the middle of the 21st century but less wet extreme events by the end of the 21st century. And the humid central and southern regions would suffer more precipitation-related natural hazards in the future.