Dry Events Research Articles

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.

Loess accumulation in Harbin with implications for late Quaternary aridification in the Songnen Plain, Northeast China

The Harbin loess in Northeast China, located in the easternmost part of the Eurasian loess belt, has great potential to reconstruct the aridity history of the Songnen Plain and to reveal its dynamic process. However, the relationship between coupled tectonic-climate-drainage evolution and the aridification in the Songnen Plain is currently poorly understood. In this study, we present a high-resolution magnetic susceptibility, grain-size, trace element, SrNd isotope, total organic carbon (TOC), and organic carbon isotope composition (δ13C) record retrieved from the Harbin loess-paleosol sequences to reveal the aridification history in the Songnen Plain. These results reveal a long-term drying trend in the Songnen Plain since 0.46 Ma, indicating the birth of the Songnen Sandy Land at that time. Superimposed on the major aridification trend, two significant abrupt drying events were found at ~300 ka and ~ 380 ka. However, the climate in the Songnen Plain became wetter and warmer under the background of the long-term drought since 180 ka. The global ice/temperature changes, regional tectonics (i.e., uplift of the Songliao divide) and drainage change (i.e., river pattern shift in the Songnen Plain from endorheic to exorheic drainage, and termination of the Songnen paleolake) were collectively responsible for the aridification in the Songnen Plain. This study has further improved knowledge of the process of the aridification in Northeast China, which is of great significance to control land desertification and ecological imbalance.

Diagnosis of wet and dry events and its associated atmospheric circulation anomaly over Malawi, Southeast Africa

This paper presents an analysis of December to February (DJF) season wet and dry events and their associated circulation anomalies during the period of 1978–2010 over Malawi. The study was conducted using meteorological daily observed rainfall datasets during the entire study period. A set of regional wet and dry indices with a scheme of classifying their severity was employed to classify the wet and dry into seven different grades using the Z-Index. The results reveal severe wet during 1997 and 2007 rainfall season, while extreme dry events were observed in 1992 and 2000 season. The wind components (u;v) and velocity potential/divergence analysis revealed that dry years were characterized by divergence at low level and convergence at upper troposphere, especially over region of study, Mozambique, Madagascar as well as North Madagascar. It was observed that there is a pattern of enhancement for vertical velocity (Omega) and Relative humidity during wet years and reduction during dry years. The SST uncovers dry years were manifested with negative anomalies over equatorial western Indian ocean and the eastern equatorial Pacific Ocean. Wet years were characterized by a pool of positive anomaly over the south west and equatorial of Indian Ocean, and a negative anomaly in the equatorial Pacific Ocean.

A 14000 year multi-proxy alluvial record of ecotone changes in a Fynbos-Succulent Karoo transition in South Africa

To address long-standing questions concerning Southern Hemisphere climate dynamics and palaeoecological change in southern Africa, a Late Glacial-Holocene alluvial sediment sequence from the relatively dry interior year-round rainfall zone in South Africa was investigated. The study site borders the Fynbos biome and Succulent Karoo biome ecotone, and comprises a rare stratified sequence of sandy and organic-rich silt deposits, shown to span the last 14,000 years. A high resolution multi-proxy record of ecological change was derived using pollen, phytoliths and organic geochemical analyses. For the period 14–11 ka, significant valley aggradation occurred under relatively drier conditions, followed, during the early and middle Holocene, by alternating phases of humid and dry events with higher stream energy, slower accumulation or subtle seasonality changes. A transition from relatively humid to more arid conditions at 4–3 ka is identified and is consistent in timing with several interior year-round rainfall zone records. Results revealed alternations of fynbos and karroid elements and C3/C4 grasses throughout the last fourteen thousand years, but did not suggest large-scale biome shifts. The record joins a growing number of sites contributing to debate over the complex atmospheric-oceanic drivers of palaeoclimate in this region. These data broadly fit to the regional pattern for the southernmost interior of South Africa in showing alternating influences from the westerly winter rain systems in the early Holocene, with a greater contribution from subtropical summer rain system during the middle and later Holocene.

Recent increasing frequency of compound summer drought and heatwaves in Southeast Brazil

An increase in the frequency of extremely hot and dry events has been experienced over the past few decades in South America, and particularly in Brazil. Regional climate change projections indicate a future aggravation of this trend. However, a comprehensive characterization of drought and heatwave compound events, as well as of the main land–atmosphere mechanisms involved, is still lacking for most of South America. This study aims to fill this gap, assessing for the first time the historical evolution of compound summer drought and heatwave events for the heavily populated region of Southeast Brazil and for the period of 1980–2018. The main goal is to undertake a detailed analysis of the surface and synoptic conditions, as well as of the land–atmosphere coupling processes that led to the occurrence of individual and compound dry and hot extremes. Our results confirm that the São Paulo, Rio de Janeiro and Minas Gerais states have recorded pronounced and statistically significant increases in the number of compound summer drought and heatwave episodes. In particular, the last decade was characterized by two austral summer seasons (2013/14 and 2014/15) with outstanding concurrent drought and heatwave conditions stemmed by severe precipitation deficits and a higher-than-average occurrence of blocking patterns. As result of these land and atmosphere conditions, a high coupling (water-limited) regime was imposed, promoting the re-amplification of hot spells that resulted in mega heatwave episodes. Our findings reveal a substantial contribution of persistent dry conditions to heatwave episodes, highlighting the vulnerability of the region to climate change.

Climatic aridity increases temporal nestedness of invertebrate communities in naturally drying rivers

Climate change is altering the water cycle globally, increasing the frequency and magnitude of floods and droughts. An outstanding question is whether biodiversity responses to hydrological disturbance depend on background climatic context – and if so, which contexts increase vulnerability to disturbance. Answering this question requires comparison of organismal responses across environmental gradients. However, opportunities to track disturbed communities against an undisturbed baseline remain rare. Here we gathered a global dataset capturing responses of aquatic invertebrate communities to river drying, which includes 112 sites spanning a gradient of climatic aridity. We measured the effects of river drying on taxonomic richness and temporal β‐diversity (turnover and nestedness components). We also measured the relative abundance of aquatic invertebrates with strategies that confer resilience (or resistance) to drying. Contrary to our expectations, we found that taxonomic richness recovered from drying similarly across the aridity gradient. The turnover component of β‐diversity (i.e. species replacements over time) largely accounted for differences in community composition before versus after drying. However, increasing aridity was associated with greater nestedness‐driven compositional changes at intermittent sites – that is, after drying communities became subsets of those before drying. These results show that climatic context can explain variation in community responses to the same hydrological disturbance (drying), and suggest that increased aridity will constrain biodiversity responses at regional scales. Further consideration of the climatic context in hydroecological research may help improve predictions of the local impacts of hydrological disturbance by identifying climate regions where communities are more (or less) sensitive to extremes, including river drying events.

Multi-centennial reconstruction of drought events in South-Western Iran using tree rings of Mediterranean cypress (Cupressus sempervirens L.)

Semi-arid regions are among the most vulnerable areas prone to the negative impacts of climate change. Long-term high-resolution proxy climate data will enable us to put the recent climate trends into a long-term context of natural climate variability. We developed the hitherto first regional ring-width chronology (1450–2015C.E.) from Cupressus sempervirens L. in the Zagros Mountains, western Iran and reconstructed precipitation variability for the semi-arid region during the period 1560–2015C.E. Climate-growth relationships revealed that precipitation and minimum temperatures are positively correlated with radial growth, whereas maximum temperatures reveal negative impacts. Spatial correlations with gridded precipitation data, Palmer drought severity index (PDSI), and standardized precipitation-evapotranspiration index (SPEI 01) further indicate that the climate signals contained in tree-ring width variations capture the precipitation variability in the Near East and other eastern Mediterranean regions. The southern Zagros Mts. experienced multiple megadroughts during the reconstructed period. The longest dry period occurred from 1956 to 1971 and the highest frequency of dry events occurred in the 20th century. In addition, documented famines in Iran occurred within prolonged droughts. The southern Zagros Mts. has experienced high frequency of extreme/severe dry events and long dry phases during the Little Ice Age (1560–1850C.E.). The reconstructed dry and wet events occurred irregularly, and one-year and two-year drought/wet events showed the highest frequency during the reconstructed period, highlighting the importance of sustainable water management strategies for the semi-arid southern Zagros region.

Quantification of temperature and precipitation changes in northern China during the “5000-year” Chinese History

High-quality paleoclimate reconstructions can provide crucial climate context to test the hypothesis of climatic impact on historical culture changes. Here we report high-resolution and quantitative temperature and precipitation records covering the entire “5000-year” Chinese history in northern China. Our temperature record shows a slight decrease before 1800 cal yr BP and a ∼4 °C rapid cooling afterwards, superimposed with four major ∼2–3 °C centennial-scale cold events, potentially corresponding to the widespread North Atlantic ice-rafted debris Bond events. While precipitation record shows high value before 3000 cal yr BP, and a gradual decrease of ∼250 mm with two distinct ∼100 mm centennial-scale dry intervals after 1100 cal yr BP. Our data not only provide a more complete climate background for Chinese dynasties, but show the coincidence in the timing between abrupt cold and/or dry events and large-scale social unrests and southern migration of nomads. This finding reveals climate fluctuations, in particular variations in temperature, played an important role in affecting Chinese historical cultural changes.

Evaluation of PBL parameterization schemes against direct observations during a land depression over Central India

Detailed observations from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase III integrated observational campaign 2014 are used to validate six different planetary boundary layer (PBL) schemes in Weather Research and Forecasting (WRF) model during a land depression over central India in summer monsoon season. This work is a continuation of our previous study on a dry event associated with a heatwave over the same region (Sathyanadh et al. 2017). Four local and two nonlocal PBL schemes are evaluated with hourly observations of air temperature, eddy covariance fluxes, friction velocity, wind, and radiation components for the model performance of the complete energy budget and weather parameters. The models simulated a slightly warmer and drier surface layer with strong winds and overestimated sensible heat flux and ground heat flux during the wet event. The errors in the surface layer temperature are closely associated with errors in the sensible heat flux and incoming radiation, while the errors associated with moisture are linked to the excessive surface layer mixing. The interrelationships between various surface layer parameters and PBL heights are investigated to identify the key controlling factors of PBL evolution in the context of land depression.

Environmental conditions and the emergence of ceramics in the Late Pleistocene-Early Holocene at the Krasnaya Gorka site in the Transbaikal region, Southern Siberia

New investigations of the Krasnaya Gorka site suggest the emergence of pottery in the Late Pleistocene-Early Holocene in the Transbaikal region. Several new AMS dates obtained for the early ceramic cultural layer 2 indicate an age between 13900-10500 cal BP. The results of palynological studies of the Krasnaya Gorka deposits are given in the paper for the first time, and the Late Pleistocene-Holocene environmental changes were reconstructed. Pollen data obtained from the Krasnaya Gorka profile showed cold and dry Late Pleistocene environmental conditions. The regional climate became milder and more humid around 13900–12700 cal BP, which corresponds to the Allerød interstadial thus corroborating the radiocarbon age results. The warmest interval of the Late Pleistocene occurred around 13500 cal BP. Between 12700 and 11800 cal BP, cooling probably corresponds to the cold and dry event of the Younger Dryas. There is some stratigraphical in deposits of the Krasnaya Gorka archeological site. The deposits forming in the early Holocene and beginning of the middle Holocene most likely were removed by erosion. Warming and increased humidity occurred in middle of the late Holocene (2700-1800 cal BP). During the late Holocene, the climate was unstable. Beginning 400 cal BP, the vegetation of the region acquired its modern appearance. Some published materials concerning reconstructions of paleoclimate in the region of Ust’-Karenga XII, Studenoe I, and Ust’-Menza I are considered in the context of general characteristics of the region. Therefore, both palynological reconstructions and radiocarbon dates place the earliest ceramics from Krasnaya Gorka within the final stage of the Late Pleistocene – Early Holocene between 13900-10500 cal BP.

Socioeconomic Drought in a Mexican Semi-arid City: Monterrey Metropolitan Area, a Case Study

The Monterrey Metropolitan Area (MMA) is located in northeastern Mexico in a semi-arid region. As in other areas of the world, prolonged and severe meteorological droughts are recurrent. Meteorological droughts affect the level of dam reservoirs, rivers, and groundwater (aquifers) in the region to the extent they become hydrological droughts which in turn may contribute to socioeconomic droughts. The recent dry event (2011–2013) in northern Mexico severely affected various socioeconomic sectors and may serve as an example of future climatic and hydrologic conditions in this region. Meteorological droughts in northeastern Mexico, mostly induced by anomalously intense subsidence, frequently result in hydrological droughts and intense pressure in the water resources services of the Monterrey Metropolitan Area (MMA), one of the largest cities in Mexico. Landfalling tropical cyclones entering northeastern Mexico historically have alleviated water crises during prolonged droughts. In 2013, the rains from tropical cyclone Ingrid helped to recover water levels in the system of dam reservoirs that provides water to the MMA. However, water management is only one part of a complex socioeconomic system that must respond to the growing demands for water in a region where aquifers are already overexploited. Trends in the atmospheric circulation indicate that droughts in the region may become more severe in the coming decades. Improved water management programs and protocols should be considered in addition to closer reviews of the hydraulic infrastructure. Water transfers from one region to another should be carefully planned because solving a problem in one place may adversely affect another. The use of climate information may be critical to avoidance of water conflicts in the future.

Dry and Wet Climate Periods over Eastern South America: Identification and Characterization through the SPEI Index

A large part of the population and the economic activities of South America are located in eastern regions of the continent, where extreme climate events are a recurrent phenomenon. This study identifies and characterizes the dry and wet climate periods at domain-scale occurring over the eastern South America (ESA) during 1980–2018 through the multi-scalar Standardized Precipitation–Evapotranspiration Index (SPEI). For this study, the spatial extent of ESA was defined according to a Lagrangian approach for moisture analysis. It consists of the major continental sink of the moisture transported from the South Atlantic Ocean throughout the year, comprising the Amazonia, central Brazil, and the southeastern continental areas. The SPEI for 1, 3, 6, and 12 months of accumulation was calculated using monthly precipitation and potential evapotranspiration time series averaged on ESA. The analysis of the climate periods followed two different approaches: classification of the monthly SPEI values as mild, moderate, severe, and extreme; the computation of the events and their respective parameters (duration, severity, intensity, and peak). The results indicate that wet periods prevailed in the 1990s and 2000s, while dry conditions predominated in the 2010s, when the longest and more severe dry events have been identified at the four scales.

Evaluación de eventos secos y húmedos en el contexto del cambio climático: El caso del sur de la Región Pampeana (Argentina)

El objetivo de este estudio fue analizar la duración, intensidad, periodicidad y frecuencia de los eventos secos y húmedos durante i) pasado reciente (1977-1997), ii) presente (1998-2018), iii) futuro cercano (2019-2039) y iv) futuro lejano (2079-2099) en el sur de la Región Pampeana (Argentina). Se aplicó el Índice Estandarizado de Precipitación a escala anual, estacional, semestral y mensual, utilizando datos de doce estaciones meteorológicas. Los resultados fueron interpolados con el método Kriging en un Sistema de Información Geográfica y de esta manera se obtuvo la distribución espacial de los eventos analizados. El área de estudio evidenció una prolongación de los períodos secos, alcanzando 12 meses de duración en el futuro lejano. Los períodos húmedos presentaron un comportamiento similar entre las épocas estudiadas. Teniendo en cuenta su distribución espacial, el sur del área de estudio fue la que registró cambios significativos, dado que presentará mayor frecuencia de eventos secos y húmedos en el futuro. Esta situación podría afectar las actividades económicas que actualmente se desarrollan en el área. La información resultante es esencial para que la población conozca las situaciones a las que podrían estar expuestos ante las fluctuaciones que tendrá la precipitación en situaciones meteorológicas futuras. This study aims to analyze the duration, intensity, periodicity, and frequency of dry and wet events in the south of Pampas (Argentina), considering i) recent past (1977-1997), ii) present (1998-2018), iii) near future (2019-2039), and iv) far future (2079-2099). In this sense, monthly rainfall data were assessed from twelve weather stations using the Standardized Precipitation Index with 1-month, 3-months,6-months and 12-months timescales. Kriging interpolation method was applied to analyze information spatially. The results showed an extension of dry events with a duration up to 12 months in the far future, while wet events showed a similar behavior among the considered periods. It is worth noting that the south part of the study area will present a higher frequency of wet and dry events, which will generate a more variable rainfall regime affecting the economic activities of the area. The information obtained will be essential for decision-makers and agricultural producers because it will allow them to know the rainfall fluctuation in future situations.

Cover crops reduce soil resistance to penetration by preserving soil surface water content

Replacement of bare fallow in rotations by cover crops is a promising tool to reduce crusting, although the interactions with the soil moisture and the effect of the cover crop species are still not well understood. The objective of this work was to determine how cover crops modify the soil surface response to penetration and their relation with the soil water content. Two winter cover crops, barley (Hordeum vulgare L.) and vetch (Vicia sp. L.), were compared with a bare fallow treatment in a 10-year field experiment in central Spain. Soil resistance to penetration and soil water content were intensively measured (76 sampling dates) at two surface depths, using two types of surface penetrometers. Under the barley cover crop, the number of very dry events was reduced by around 20%, compared to the bare fallow. The soil resistance to penetration was closely related to the surface soil water content (R2 = 0.65) and cover crops affected it through soil moisture modification. In this line, the greater mulch provided by barley cover crop respect to vetch, increased the soil water content prior to main crop seeding, resulting in less resistance to penetration during this critical period. The good performance of barley resulted in a reduction of more than 60% of the soil resistance to penetration between the 3rd and 8th year of the experiment (7.2–2.9 kg cm−2, respectively). Even under bare fallow, soil strength was decreased after ten years with reduced tillage. Therefore, the maintenance of cover crop residues over surface soil together with reduced tillage enhanced the soil surface conditions and steadily reduced the risk of crust formation. Expected enhancement of main-crop germination, water infiltration, soil aeration and erosion mitigation may be attained by cover-cropping in degraded soils.

Analysis and Predictability of Dry Spell Lengths Observed in Synoptic Stations of Benin Republic (West Africa)

The complex behavior and predictability of the Dry Spell Lengths (DSL) series obtained in Benin synoptic stations, from 1951 to 2010 are analyzed in this paper using a fractal approach. The synoptic stations are located in Cotonou, Bohicon, Save (subequatorial climate), and Parakou, Natitingou, Kandi (Sudanian climate). The DSLs are computed by considering four thresholds level, R0 = {1.0, 1.5, 2.0 and 5.0} mm/day. The fractal trace is estimated for dry spell density by the mean of the “Dry Spell Spell” (DSS) n-index. The rescaled range method is used to determine the predictability of DSL. By analyzing the DSS, results show that low DSS n-index values (n-index 0.4) occur preferentially in the southern part. Therefore, during 1951-2010, the Sudanian region presents frequent wet spells, alternated with short dry spells than in the subequatorial one. However, a high degree of long dry spell persistence, followed by short dry events is observed in the subequatorial region than in the Sudanian one. The longest DSL is observed in the subequatorial region, especially in Cotonou. Except for the Kandi station, the DSLs series obtained at synoptic stations are characterized by persistence. Therefore, autoregressive processes could be applied to the DSL series. Generally, the physical process governing dry spells observed at Save, Natitingou, and Bohicon are consistently predictable than the process governing the stations of the Cotonou and Parakou. However, at Kandi station, the DSL process approximates the usual Brownian motion, and it is, therefore, unpredictable or difficult to predict.

Drying in newly intermittent rivers leads to higher variability of invertebrate communities

Abstract Aquatic invertebrate communities inhabiting intermittent rivers that are characterised by recurrent drying events (flow cessation or complete disappearance of surface water) often show rapid recovery upon flow resumption. Such rapid recovery is possible thanks to specific resistance and resilience traits that species adapted to river drying often exhibit. However, differences in community response to drying can be expected between historically drying (HD) networks—those IRs with a long history of flow intermittence—and recently drying (RD) networks, where drying is a novel, often human‐induced, phenomenon. The invertebrate species found in RD networks may lack the adaptations that are known to facilitate quick community recovery upon rewetting and could thus be dramatically affected by drying. Unfortunately, the responses of aquatic communities in RD networks are still poorly explored, limiting our capacity to predict and mitigate future biodiversity changes. Here, we compared the responses of aquatic invertebrate communities to drying in nine pairs of intermittent and perennial river reaches from HD networks across France and nine pairs from RD networks across the Czech Republic. Using both taxonomic and functional perspectives, differences in α‐ and β‐diversity patterns between perennial and intermittent sites were evaluated separately for HD and RD groups, and before and after drying over several years. Drying had stronger effects on taxonomic richness in RD compared to HD networks. In addition, drying greatly altered spatial and temporal β‐diversity in RD networks, but it marginally affected β‐diversity in HD networks. Communities of HD networks showed a higher proportion of resistant taxa than RD networks. These results suggest that recent drying can have, at least on a short time scale (i.e. years), stronger effects on aquatic communities in RD networks compared to those in HD networks. Because drying duration, frequency, and spatial extent are increasing with climate change, RD networks could soon reach tipping points, calling for long‐term monitoring of biodiversity in these novel ecosystems.

Plant Hydraulic Stress Strategy Improves Model Predictions of the Response of Gross Primary Productivity to Drought Across China

AbstractThe response of the terrestrial carbon cycle to droughts, which have recently increased in incidence and severity, is a hot topic in research, but the role played by vegetation water use strategies remains unclear. Both the soil moisture stress (SMS) and plant hydraulic stress (PHS) strategies are used in land surface models, but their performance in simulating the terrestrial carbon cycle and its response to droughts in various climatic zones remains uncertain. In this study, we used Community Land Model Version 5 to simulate gross primary productivity (GPP) across four different climatic subregions of China during 2000–2015 to investigate the roles played by PHS and SMS in the response of GPP to dry events and dry or rainy years in various climate zones. Simulated GPP with the two strategies were overestimated by 2.0–2.3% for the entire China compared to Moderate Resolution Imaging Spectroradiometer (MODIS) data. GPP simulated using PHS configuration fit eddy covariance and MODIS data better than that obtained using SMS across China, except for the Qinghai‐Tibet Plateau. PHS increased simulated GPP by 0.10–0.63 g C m−2 day−1 during dry events across different climatic regions because of root hydraulic lift but decreased GPP by 0.37–0.45 g C m−2 day−1 during growing season in the humid southeastern region because of high atmospheric vapor pressure deficit and root hydraulic descent. Simulations forced by data collected locally in China performed better than those forced by CRUNCEP7 global data at the site but worse at the regional scale, in particular for the Qinghai‐Tibet Plateau.

Disentangling the effects of climatic variability and climate extremes on the belowground biomass of C3- and C4-dominated grasslands across five ecoregions

Elucidating the variation in grassland belowground biomass (BGB) and its response to changes in climatic variables are key issues in plant ecology research. In this study, BGB data for five ecoregions (cold steppe, temperate dry steppe, savanna, humid savanna, and humid temperate) were used to examine the effects of climatic variability and extremes on the BGB of C3- and C4-dominated grasslands. Results showed that BGB varied significantly across the ecoregions, with the highest levels in cold steppe and the lowest in savanna. The results indicated that growing-season temperature, maximum and minimum temperatures and their interactions had significantly positive effects on the single-harvest BGB of C3 plants in colder ecoregions (i.e., humid temperate and cold steppe) and of C4 plants in arid ecoregions (i.e., temperate dry steppe and savanna). The single-harvest BGB of C3 plants in arid ecoregions and C4 plants in humid savanna ecoregion declined with increasing temperature during the growing season. Growing-season precipitation exerted significant positive effects on the single-harvest BGB of C4 plants in arid ecoregions. Annual temperature variables negatively impacted the annual BGB of humid temperate ecoregion, because of the dominance of C3 plants. Increasing cumulative growing-season precipitation elevated and the mean annual temperature reduced the annual BGB of both categories of plants in arid ecoregions. Compared with normal climates, extreme dry events during the growing season enhanced single-harvest BGB in colder ecoregions. The single-harvest BGB of C4 plants in savanna tended to increase during extreme wet and decrease during moderate dry events compared to normal climates. This study suggests that the differential effects of climatic variability and extremes on BGB can be explained by differences in plant types, and ecoregions. These findings on the responses of the BGB to climatic variability and extremes constitute important scientific evidence emphasizing the need to maintain ecosystem stability across ecoregions.

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.