Reduction In Rainfall Research Articles

Hydrogeochemical Processes in Basement Areas Using Principal Component in Burkina Faso (West African Sahel)

The basement aquifers in Burkina Faso are increasingly exposed to groundwater pollution, largely due to socio-economic activities and climatic fluctuations, particularly the reduction in rainfall. This pollution makes the management and understanding of these aquifers particularly complex. To elucidate the processes controlling this contamination, a methodological approach combining principal component analysis (PCA) and multivariate statistical techniques was adopted. The study analyzed sixteen physicochemical parameters from 58 water samples. The primary objective of this research is to assess groundwater quality and deepen the understanding of the key factors influencing the spatial variation of their chemical composition. The results obtained will contribute to better planning of preservation and sustainable management measures for water resources in Burkina Faso. The results show that three principal components explain 72% of the variance, identifying anthropogenic inputs, with two components affected by mineralization and one by pollution. The study reveals that the groundwater is aggressive and highly corrosive, with calcite saturation. Water-rock interactions appear to be the main mechanisms controlling the hydrochemistry of groundwater, with increasing concentrations of cations and anions as the water travels through percolation pathways. PCA also revealed that the residence time of the water and leaching due to human activities significantly influence water quality, primarily through mineralization processes. These results suggest that rock weathering, coupled with reduced rainfall, constitutes a major vulnerability for aquifer recharge.

Ectomycorrhizal fungal community response to warming and rainfall reduction differs between co-occurring temperate-boreal ecotonal Pinus saplings.

Understanding the responses of ectomycorrhizal (ECM) fungi and their tree hosts to warming and reduced soil water availability under realistic future climate scenarios is essential, yet few studies have investigated how combined global change stressors impact ECM fungal community richness and composition as well as host performance. In this study, we leveraged a long-term factorial warming (ambient, + 1.7 ºC, + 3.2 ºC) and rainfall reduction (ambient, 30% reduced rainfall) experiment in northern Minnesota, USA to investigate the responses of two congeneric hosts with varying drought tolerances and their associated ECM fungal communities to a gradient of soil moisture induced by a combination of warming and rainfall reduction. Soil drying had host-specific effects; the less drought tolerant Pinus strobus had decreased stem growth and lower ECM fungal community richness (fewer ECM fungal Operational Taxonomic Units, OTUs), while the more drought tolerant Pinus banksiana experienced no decline in stem growth but had an altered ECM fungal community composition under drier, warmer soils. Taken together, the results of this study suggest that the combined effects of warming and decreased precipitation will largely be additive in terms of their impact on host performance and ECM fungal community richness, but that drier and warmer soil conditions may also differentially impact specific ECM fungal genera independently of host performance.

Climate change and exotic pathogens shift carbon allocation in Mediterranean mixed forests

Abstract Forecasting the effects of global change drivers on ecosystems is one of the most pressing challenges for scientists worldwide. Particularly, climate change and exotic pathogens might have a large impact on plant community dynamics and ecosystem functioning through changes in carbon uptake and sinks. Nevertheless, we still have a poor understanding of the combined effects of these two drivers on plant communities. Here, we explored the impact of rainfall reduction and exotic pathogens on the carbon balance of Mediterranean tree species. For this, we performed a 3‐year field experiment taking advantage of rainfall exclusion infrastructures (30% exclusion) installed in the southernmost European oak forests invaded by the aggressive exotic pathogen Phytophthora cinnamomi. We measured a set of 10 variables representative of tree carbon sources (photosynthetic rates) and sinks (primary production, reproduction, defence, and reserves) in adult trees of three species in two forest types: closed forests of Quercus suber and Q. canariensis, and open woodlands of Q. suber and Olea europaea. We found a large variability in the sensitivity of the different carbon sources and sinks to the effects of drought and pathogens, from variables highly sensitive to both factors (carbon fixation and reproduction, root chemistry) to variables only responsive to drought (litter production) or totally unresponsive (tree trunk, leaf chemistry). Although negative effects predominated, positive effects of rainfall exclusion were also detected in wet years, likely due to a reduction of pathogen abundance in drier soil. Trade‐offs between carbon sinks appeared in all tree species, but rainfall exclusion only modified trade‐offs in Q. suber, the species most susceptible to P. cinnamomi. Synthesis. We provide evidence on the complexity of the combined effects of abiotic (drought) and biotic (pathogens) global change drivers on carbon source and sinks of adult trees, including both negative direct effects and positive indirect effects. Our results showed that these effects varied among co‐existing species, particularly for carbon sinks directly related to tree demography (reproduction). Therefore, long‐term changes in the structure of Mediterranean mixed forests might be expected towards the dominance of species highly resistant to both drought and pathogens.

Contrasted agronomical and physiological responses of five Coffea arabica genotypes under soil water deficit in field conditions.

Breeding programs have developed high-yielding Coffea arabica F1-hybrids as an adaptation against adverse conditions associated with climate change. However, theresponse to drought of coffee F1 hybrids has seldom been assessed. A trial was established with five C. arabica genotypes (2 pure lines: Catimor and Marsellesa and 3 F1 hybrids: Starmaya, Centroamericano and Mundo Maya) planted under the leguminous tree species Leuceana leucocephala. Coffee growth, yield and physiological responses were assessed under a rain-fed (control: CON) and a rainfall reduction treatment (RR) for 2 years. The RR treatment created a long-term rainfall deficit in a region with suboptimal temperature similar to those predicted by climate change scenarios. Moreover, the RR treatment reduced soil water content by 14% over 2 successive years of production and increased hydric stress of the three F1-hybrids (leaf water potentials averaged -0.8 MPa under RR compared with -0.4 MPa under CON). Under RR, coffee yields were reduced from 16 to 75% compared to CON. Mundo Maya F1 hybrid was the sole high-yielding genotype apable of sustaining its yield under RR conditions. Our results suggested that its significant increase in fine root density (CON = 300 and RR = 910 root.m-2) and its maintenance of photosynthetic rate (2.5 - 3.5 mmol CO2 m-2 s-1) at high evaporative demand might explain why this genotype maintained high yield under RR condition. This work highlights a possible drought tolerance mechanism in fruit bearing adult coffee trees where the plant fine root number increases to intake more water in order to preserve turgor and sustainphotosynthesis at high ETo and therefore conserves high yield in dry conditions.

Does soil type influence the occurrence of fire outbreaks in Cerrado, Brazil?

Forest fires associated with anthropic activities in Cerrado, Brazil, have been the main cause of the degradation of the biome. Thus, this study aims to understand the dynamics of fire foci and Gross Primary Production as a function of soil classes in an Environmental Preservation Area. This study combined soil types with meteorological variables of rainfall, soil moisture and air temperature to relate to fire occurrences and Gross Primary Production (GPP) for the years 2001–2020. For the evaluated period, there was an increase in temperature (±0.5 ºC) and a reduction in rainfall (±50 % in the driest years). The highest numbers of fire outbreaks were recorded in the areas corresponding to the Neossolos (Arenosols), followed by Latossolos (Ferralsols) between August and October. The future projection of the occurrence of foci for the next 10 years indicated that there would be an increase in the number of fire foci in all soil classes (700 %), especially for Neossolos. The future projection of GPP for the next 10 years indicates that there would be a reduction in coverage, especially for Gleissolo (Gleysol, 40–80 %). As a prevention strategy, attention should be doubled between August and October, as these months are the most conducive to fire outbreaks in the Cerrado.

Supporting the development of climate-resilient water safety plans through a risk-screening framework for drinking water source protection

ABSTRACT Climate change-induced impacts on water-quality challenge risk management of drinking water. Uncertainty around future changes and limited resources require approaches that enable prioritisation at regional or national scale for planning and adaptive intervention. This paper presents a framework for risk screening drinking water supplies, providing a staged approach to building the capacity for integrating climate change into risk management. The framework is applied to drinking water sources of the Scottish national drinking water provider, developing raw water trajectories for indicative water-quality parameters (water colour and Escherichia coli). It establishes baseline understanding of water-quality controls through multivariate statistical analysis. It incorporates climate and land-use change into the model using climate (UKCP18) and land-use projections. The results suggest potential higher organic carbon production in soils from increased production with higher temperature, combined with reduced dilution and drought effects from reductions in summer rainfall. For E. coli, risks arise through land-use change leading to potential agricultural intensification. The framework supports the targeted development of climate-resilient Water Safety Plans, prioritising systems most at risk of raw water-quality deteriorations. It emphasises source protection to maintain or improve regulatory compliance, minimise socioeconomic and environmental harms, and generate additional benefits.

Climate change and extremes in the Mediterranean island of Cyprus: from historical trends to future projections

Cyprus is a European island state in the eastern Mediterranean climate change hotspot. Despite being a relatively small island, it has diverse climatic zones, ranging from semi-arid to subhumid in the mountains and humid on Mount Olympos. Given the accelerated rate of environmental change in the region, the present study aims to identify, and update observed trends of critical climate parameters, highlighting vulnerable climatic areas within the island. Moreover, since nationwide multi-model assessments of future climate conditions are limited or outdated, we aim to investigate the range of future climate projections using a 21-member EURO-CORDEX ensemble under pathways RCP2.6 and RCP8.5. Besides mean conditions, we analyze various extreme climate indicators relevant to socio-economic activities such as agriculture, biodiversity, tourism, energy and water resources. Our historical analysis revealed a statistically significant increasing temperature trend (0.4 °C–0.6 °C per decade), which is more pronounced during the summer and spring. Concerning precipitation, the observed trends are not as robust, nevertheless, the southeastern coast and the central regions near the capital city of Nicosia are substantially drier and more prone to further changes in precipitation regimes. The projections for the end of the 21st century, according to the high radiative forcing scenario (RCP8.5), indicate that Cyprus is likely to experience an annual temperature increase of over 4 °C and an approximate 20%–30% reduction in annual rainfall, relative to 1981–2000. These projections highlight an alarming trend that requires urgent attention and proactive measures to mitigate the potential impacts of climate change on the island.

Enhanced precipitation responses over the Tibetan Plateau following future Tambora-size volcanic eruption

Hydroclimate over the Tibetan Plateau (TP) notably influences the eco-environment of the Northern Hemisphere. Given its high elevation and complex topography, the climate in the TP shows a high sensitivity to anthropogenic warming and volcanic-induced cooling. The mechanism by which a future volcanic or similar radiative perturbation affects precipitation in the TP under an anthropogenic warming climate must be addressed not only to enable regional adaptation but deepen our understanding of how a climate system evolves under such a dual force. Here, based on the Community Earth System Model version 1.2 and ensemble simulations under pre-industrial and RCP8.5 scenarios, we showed that a Tambora-sized volcanic perturbation led to severe rainfall reduction over the south TP in the following summer (June–August). Evaporation response accounted for a minor and relatively constant share of precipitation reduction following the Clausius–Clapeyron scaling, whereas dynamic processes triggered an El Niño-like response in the eastern equatorial Pacific, which suppressed the Walker and Hadley circulation and contributed to drying anomalies. Global warming renders the post-Tambora hydroclimate responses with 30% higher severity as a result of the increased climatological moisture content and intensified El Niño response, which enhanced hydroclimate sensitivity and attenuated monsoon circulation. The results illustrate the amplification effect of global warming on the plateau's hydroclimate responses to external forcings, which may add another layer of uncertainty on climate adaptation in this already complex region.

Climate Change Impacts for Multipurpose Reservoir Planning: Basnagoda Reservoir, Sri Lanka

Climate change via rainfall and temperature changes poses threats to water resources. Traditionally, these variations are rarely considered in irrigation infrastructure planning. Integrating climate impacts into early irrigation planning ensures resilience and sustainability.This study aims to assess the climate change impacts on Basnagoda reservoir using a reservoir operation study, system designing and sizing, water use strategies and making recommendations as mitigation and adaptation strategies.This study employed reservoir operation model recommended in the Irrigation guideline, Sri Lanka to assess four climatic scenarios derived from predicted temperature and rainfall changes. Sensitivity analysis included reservoir sizing for the most critical scenario. Mitigation and adaptation methodologies such as 1) Reservoir capacity enhancement 2) Seasonal shifting 3) Conveyance enhancement were analyzed. Reservoir operations currently meet 100% of domestic demand, irrigating total 950 ha annually (380 ha Maha, 570 ha Yala) with environmental flow. Design capacity fulfils 78% of domestic demand, with environmental flow for projected period. The maximum cultivable area at the design stage while providing 25% of design domestic demand is 544 ha in Maha and 680 ha in Yala season. With a 20% rainfall reduction posing the worst scenario, domestic water fulfilment reduced to 20% (Maha) and 19% (Yala). Optimal reservoir capacity enhancement is 15%, expanding cultivable area to 390 ha, while providing 25% of design domestic demand. Conveyance enhancement increases cultivable area from reservoir water by 15%. This study is unique for integrating climate change impacts into reservoir infrastructure planning and design stages.

Climatic effects on aflatoxin contamination of maize

Aflatoxins are frequent contaminants of maize especially in the face of climate change with deleterious health and socio-economic impacts. South Africa is ranked 9th maize exporter globally; hence, insights need to be gained in terms of the maize value chain in South Africa with respect to aflatoxin contamination to evaluate consumers’ exposure. High-performance liquid chromatography (HPLC) technique was used in this study to quantify aflatoxins in South African commercial maize. One thousand and twenty-eight (1028) maize samples were collected across six distinct agro-climatic regions over five harvest seasons (2017 – 2021). A total of 205 samples (19.94 %) were found to be contaminated with aflatoxins, with mean total aflatoxin concentration of 64.17 ppb amongst the contaminated samples, which is above the SA regulatory limit of 20 ppb for animal consumption. The year 2018 recorded the highest mean total aflatoxin value while North-West agro-climatic region had the highest mean total aflatoxin value. Drastic reduction in average rainfall significantly influence aflatoxin contamination of South African maize.

Hydrological Changes in a Fruit Growing Area Under the Influence of Climate Change: on the Amazon Coast

Objective: The objective of this study is to investigate the water consumption of the mango orchard using the method proposed by Thornthwaite and Mather (1955), called Climatological Water Balance, with the aim of assisting in agricultural planning and decision making. Theoretical Framework: The Climatological Water Balance was initially developed with the aim of characterizing the climate of a region, in order to be used in the climate classification developed by Thornthwaite in the 1940s. Later, this method began to be used for agronomic purposes given the great interrelationship of agriculture with climatic conditions. Method: The methodology adopted for this research comprises the information used in the preparation of the water balance and was acquired by instrumentation implemented at the experimental hose site in the village of Cuiarana, district of Salinópolis in the northeast of the state of Pará. The meteorological data were obtained in the Project tower LBA where are measured, by automatic instrumentation, such as: average air temperature (Tar) the relative air humidity (RH) through the HMP45 probe, the Rain acquired by the CSI MODEL TB4-L RAIN GAGE ​​from Campbell Scientific, the collection of data was carried out using a datalogger with recording every 10s and storage of the average every 10 min. Results and Discussion: The results obtained revealed an increase in air temperature mainly in El-niño years and with a strong reduction in rainfall in these years of approximately 30 to 40% in the annual accumulation. These results imply a reduction in productivity and the regional and local impact of the hydrological cycle. Research Implications: The practical and theoretical implications of this research are discussed, providing insights into how the results can be applied or influence practices in the field of fruit growing. These implications may include the importance of the vegetation cover of the mango orchard on the socio-environmental quality of the village of Cuiarana. Originality/Value: This study contributes to the literature on mango crops that are not irrigated, it also makes it possible to optimize sowing times, taking into account the average water availability in the studied region, resulting in a more efficient use of rainfall for agricultural production. The relevance and value of this research are evidenced by the fact that the study in the northeast of Pará is still precarious in terms of water consumption by the plant in a region with water deficiency.

Foraging habitat use by sympatric Cuvier’s Gazelle, Dama Gazelle, and Dorcas Gazelle on a private reserve in Morocco

Abstract Habitat use influences the survival and fitness of animals. Habitat quality and food availability in spring and summer are crucial determinants of ungulate population dynamics, peaking in spring and drastically decreasing in summer in Mediterranean region. Here, over a 2-year period we examine foraging habitat use in both spring and summer of 3 threatened gazelle species living in sympatry in a private reserve in Morocco: Cuvier’s Gazelle (Gazella cuvieri), Dama Gazelle (Nanger dama), and Dorcas Gazelle (G. dorcas). We observed differences among species—Cuvier’s Gazelle foraged in woodland, Dama Gazelle in grassland, and Dorcas Gazelle in scrubland—with differences being mediated by seasonal effects as all species broadened their foraging habitat use in summer. We observed differences between years in foraging patterns of Dama Gazelle and Dorcas Gazelle, reflecting greater herb and scrub cover in 2018, potentially related to greater rainfall. Given the seasonal and annual differences observed, reductions in rainfall predicted with the progression of changing climatic conditions in the Mediterranean basin would reduce the availability of food resources and heighten the vulnerability of these species. The study illustrates interspecific coexistence through food resource partitioning of the 3 species, contributing to support conservation management actions of their populations in setting up structured reintroduction programs within their range.

Soil water consumption along the profile in response to soil water content variations in a black locust plantation with a rainfall exclusion in Loess Plateau

Soil drying is frequently observed in mature forests in water-limited regions, and poses a threat to sustainable development of the ecosystems. Herein, we assessed the effects of rainfall reduction on the water-use characteristics of a black locust (Robinia pseudoacacia) plantation in a sub-humid region of the Loess Plateau, China. Paired plots were established in the plantation, including a treatment with 30 % throughfall exclusion and a control. We comparatively investigated the dynamics of soil water content (SWC) throughout the profile in the two plots after four years of the treatment and determined the contribution of soil water storage (SWS) in each soil layer to water consumption according to the SWS budget. While SWC across the profile in the control plot showed general responses to replenishment and consumption under rainy and dry weather conditions, respectively, the treatment plot had smaller replenishment and consumption in deep layers, causing an aggravated deficiency in SWS and the formation of a temporary dried soil layer (DSL) at a depth of 55–100 cm. The cumulative decrement in SWS during each dry event (consecutive rainless days of ≥ 5-day duration) in the control plot was significantly correlated with SWC at 100–160 cm, suggesting a substantial contribution of water consumption from this layer. However, the treatment plot showed a major contribution to water consumption from the 0–100 cm soil layer during dry events. The vertical distribution of the root system supports these findings, which differed from our hypothesis that deep soil water would be used in response to reduced rainfall input. The distribution of fine root density in the treatment plot was relatively shallower (0–22 and 0–73.1 cm accounting for 50 % and 90 % of fine roots, respectively) than in the control plot (0–31.2 and 0–103.5 cm for corresponding values). These findings indicate that soil water deficiency resulted in the formation of DSL, which hindered water consumption and root development deeper in the soil profile. The severity and recovery of the DSL may be jointly determined by the vertical distribution of SWS and transpiration demand of the plantation. These findings provide insights for water resource management and sustainable development of the plantations in this region.

The 2022-23 drought in the South American Altiplano: ENSO effects on moisture flux in the western Amazon during the pre-wet season

The 2022-23 hydrological year in the Lake Titicaca, Desaguadero River, and Lake Poopó hydrological system (TDPS) over the South American Altiplano constituted a historically dry period. This drought was particularly severe during the pre-wet season (October–December), when the TDPS and the adjacent Andean-Amazon region experienced as much as 60% reductions in rainfall. Consequently, Titicaca Lake water levels decreased by 0.05 m from December to January, which is part of the rising lake level period of normal conditions. Such conditions have not been seen since the El Niño-related drought of 1982-83. Using a set of hydroclimatic, Sea Surface Temperature (SST) and atmospheric reanalysis datasets, we find that this new historical drought was associated with enhanced southerly moisture flux anomalies, reducing the inflow of moisture-laden winds from the Amazon basin to the TDPS. Such anomalies in moisture transport were not seen since at least the 1950s. The atmospheric dynamics associated with this drought are related to La Niña SST anomalies via subtropical teleconnections associated with Rossby wave trains towards South America, further extended by subtropical Atlantic Ocean SST anomalies. This feature reduced the atmospheric moisture inflow from the Amazon and weakened the development of the Bolivian High in the upper troposphere. These results document a new atmospheric mechanism related to extreme droughts in the TDPS associated with La Niña SST anomalies during the pre-wet season. This goes beyond the traditional understanding of El Niño events, especially the strongest ones, being associated with dry conditions in the TDPS during the wet season (December–March).

Warming and rainfall reduction alter soil microbial diversity and co-occurrence networks and enhance pathogenic fungi in dryland soils

In this 9-year manipulative field experiment, we examined the impacts of experimental warming (2 °C, W), rainfall reduction (30 % decrease in annual rainfall, RR), and their combination (W + RR) on soil microbial communities and native vegetation in a semi-arid shrubland in south-eastern Spain. Warming had strong negative effects on plant performance across five coexisting native shrub species, consistently reducing their aboveground biomass growth and long-term survival. The impacts of rainfall reduction on plant growth and survival were species-specific and more variable. Warming strongly altered the soil microbial community alpha-diversity and changed the co-occurrence network structure. The relative abundance of symbiotic arbuscular mycorrhizal fungi (AMF) increased under W and W + RR, which could help buffer the direct negative impacts of climate change on their host plants nutrition and enhance their resistance to heat and drought stress. Indicator microbial taxa analyses evidenced that the marked sequence abundance of many plant pathogenic fungi, such as Phaeoacremonium, Cyberlindnera, Acremonium, Occultifur, Neodevriesia and Stagonosporopsis, increased significantly in the W and W + RR treatments. Moreover, the relative abundance of fungal animal pathogens and mycoparasites in soil also increased significantly under climate warming. Our findings indicate that warmer and drier conditions sustained over several years can alter the soil microbial community structure, composition, and network topology. The projected warmer and drier climate favours pathogenic fungi, which could offset the benefits of increased AMF abundance under warming and further aggravate the severe detrimental impacts of increased abiotic stress on native vegetation performance and ecosystem services in drylands.

Rainfall projections under different climate scenarios over the Kaduna River Basin, Nigeria

This research aimed to assess changes in mean and extreme rainfall within the Kaduna River Basin (KRB), specifically examining the implications of two Representative Concentration Pathways (RCPs)—4.5 and 8.5 scenarios. Employing a quantile mapping technique, this study corrected inherent biases in four Regional Climate Models, enabling the examination of mean precipitation and six indices capturing extreme precipitation events for the 2050s. These findings were compared against a historical reference period spanning from 1981 to 2010, considering the basin's upstream and downstream segments. Results revealed an average annual rainfall reduction under scenarios 4.5 (21.39%) and 8.5 (20.51%) across the basin. This decline exhibited a more pronounced impact on monthly rainfall during the wet season (April to October) compared to the dry season (November to March). Notably, a substantial decrement in wet indices, excluding consecutive wet days (CWD), was foreseen in both seasons for the upstream and downstream areas, signalling an impending drier climate. The anticipated rise in consecutive dry days (CDD) is poised to manifest prominently downstream attributed to global warming-induced climate change brought on by increased anthropogenic emissions of greenhouse gases. These findings accentuate a heterogeneous distribution of extreme rainfall, potentially leading to water scarcity issues throughout the KRB, especially impacting upstream users. Moreover, the projections hint at an increased risk of flash floods during intense wet periods. Consequently, this study advocates the implementation of targeted disaster risk management strategies within the KRB to address these foreseeable challenges.

Pathways of ice multiplication in nimbostratus clouds during the Indian summer monsoon

The present study illustrates the microphysical parameters of nimbostratus clouds during the Indian summer monsoon using airborne and radar observations conducted as part of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX), and simulations with the Weather Research and Forecasting (WRF) model. The study also analyzes the impact of secondary ice production (emphasizing the microphysical pathways of Hallett-Mossop (HM) as represented in the models) on cloud processes using model sensitivity simulations. The effect of possible pathways of riming during the HM process is the focus of the sensitivity simulations. Aircraft observations showed higher ice particle concentrations in the Hallett–Mossop zone (−3 °C to - 8 °C) along with the existence of smaller and larger cloud droplets, rimed needles, columns, and snow particles. Observations strongly suggested the active presence of the HM process in this cloud. The observed mean values of microphysical parameters including liquid water content, ice number concentrations, and maximum vertical velocity, agreed well with model simulations. The number concentration and water content of ice crystals and snow decreased in the HM zone during the HM inactive case. A reduction in rainfall is also observed in the absence of HM. HM increases convection as it causes a sudden increase in the number concentration of small ice particles, which causes rainwater to freeze quickly and water vapour to be consumed by diffusional growth. Latent heating is produced by both effects, which energizes the convection.

Climate change and human impacts on aquatic communities at Etoliko Lagoon in western Greece

The Etoliko Lagoon in western Greece has experienced extensive human modification since the 20th century, both on the surrounding land and in the aquatic environment. To examine human impacts and disentangle climatic from anthropogenic changes, we present a suite of biomarker records that span the past two centuries (∼1790–2011). Specifically, we use terrigenous (n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and phytosterols) and aquatic (dinosterol, brassicasterol, cholesterol, and stigmasterol) biomarkers to document changes in nutrient inputs, combustion, and algal productivity. During most of the 19th and 20th centuries, aquatic communities respond to temperature, forced mainly by solar irradiance and volcanic activity, and precipitation, controlled largely by summer and winter North Atlantic Oscillation (NAO) patterns that determine freshwater runoff. PAHs illustrate the acceleration of coal combustion during the 1800s, and declining concentrations since the 1950s correspond to the implementation of emission controls and reductions in rainfall that likely inhibited PAH transport. As human pressures increased in the late 1900s and water column anoxia grew, the absence of a clear human waste and eutrophication signal suggests that other factors also contributed to limited oxygen availability. Overall, environmental degradation of the late 20th and early 21st centuries is clear and can be attributed to a combination of especially arid conditions and human interferences that altered lagoon hydrography, trophic state, and aquatic community composition.

Contrasting aerosol effects on shallow and deep convections during the Mei-yu season in China

Convective clouds during the Mei-yu season contribute significantly to the total rainfall and related disasters over the middle and lower reaches of the Yangtze River in China. Studying the effects of aerosols on convective clouds is of great importance to weather and climate research. However, there are still many open questions to address. This study investigated the effects of aerosol on convections with different cloud geometrical thickness (CGT) bins during the 2018 Mei-yu season, which lasted for 17 days from 18 June to 5 July. Contrasting aerosol effects on shallow and deep convective clouds were revealed by means of anthropogenic aerosol experiments in the Weather Research and Forecasting model with Chemistry (WRF-Chem). Specifically, increased anthropogenic aerosols lead to a 9% reduction in total rainfall and a 7.17% decrease in convection occurrences during the Mei-yu season. After adopting a methodology that stratifies the convective clouds by fixing the CGT, we found that increasing aerosols suppress shallow convections with CGT <4 km and invigorate deep convections with CGT >4 km. Increased aerosols enhance the scattering of shortwave radiation, resulting in cooling of the surface air and increasing the stability of the regional lower atmosphere, potentially suppressing shallow convection. Meanwhile, in deep convection, with its stronger updraft and more latent heat, convective invigoration occurs under polluted conditions due to the aerosol-related microphysical and dynamical responses. Considering the high-humidity environment during the Mei-yu season, additional relative humidity tests show that the competing aerosol effects come from convective core invigoration and convective periphery processes which enhance evaporation and dissipation, demonstrating relative humidity is a critical factor in maintaining the net aerosol effects on convections. These results contribute to a better understanding of the effects of anthropogenic aerosols on convections during the Mei-yu season and the competing effects of aerosols depending on the ambient environmental conditions.

The Responses of Soil Nitrogen Transformations to Rainfall Reduction Mainly Occurred in the Early Growing‐Season in a Temperate Meadow

AbstractDrought is expected to increase in temperate regions in the coming decades due to global climate change and will strongly affect nitrogen (N) transformation and balance. However, the underlying mechanisms (soil microenvironment vs. biotic community) of rainfall reduction induced changes in soil N transformation rates, and whether the responses of soil N transformation rates to rainfall reduction vary over time remains poorly understood. In this study, we experimentally examined rainfall reduction effects on soil N transformation rates over two (the second and third experimental years) growing‐seasons in a temperate meadow. We applied four treatments: ambient rainfall, 30%, 50%, and 70% reduction in rainfall. Our findings demonstrated that, 70% rainfall reduction significantly decreased the average net N mineralization and nitrification rates by 68.4% and 72.0%, respectively. Soil nitrous oxide emission was profoundly varied between the experimental years, with it was sensitive no only to changes in annual precipitation amount, but also to seasonal distribution, the highest emissions appeared at the early growing‐season. Moreover, plant diversity, microbial biomass, and soil NO3−‐N content mainly regulated soil N transformation rates in response to rainfall reduction in the greater annual precipitation year; but soil N transformation rates were mainly controlled by soil water content in the less annual precipitation year. We suggest that to accurately project future ecosystem functions and improving the prediction of N cycling responses to changing precipitation patterns, stronger focus should be allocated not only to changes in precipitation amounts, but also to inter‐ and intra‐annual differences in precipitation distribution.