Increasing Drought Severity Research Articles

The role of species interactions for forest resilience to drought.

Increasing durations and frequencies of droughts under climate change endanger the sustainable functioning of forests worldwide. The admixture of species with complementary resource use may increase the resilience of forests towards drought; however, little is known about modifications of species interactions (i.e. facilitation and competition) by increasing drought severity in mixed forests. In particular, knowledge on the regulation of central ecohydrological processes, such as tree water fluxes, is lacking. Therefore, we conducted a literature review to assess the impact of species interactions on tree resilience (resistance + recovery) under increasing drought severity. The classification of studies into three drought classes suggested that beneficial species interactions, i.e. through improved water relations, were prevalent under mild droughts. However, with increasing drought, negative effects, such as interspecific competition, occurred. These negative interactions were prominent under extreme droughts, where even trees with complementary resource-use strategies competed for water resources. Fewer data are available on recovery of water fluxes. The limited evidence supported the patterns observed for drought resistance, with facilitation and complementarity of species in mixtures enhancing tree recovery after moderate droughts. However, after extreme droughts, competition effects and reduced recovery for some species were observed, which can strongly compromise tree resilience. While we acknowledge the importance of mixed forests for biodiversity, ecosystem services or pest resistance, we caution that beneficial species interactions may shift under extreme droughts. Thus, there is an urgent need to investigate species interaction effects on resilience in more depth to adapt forest trees to increasing drought stress.

Climate-change-driven growth decline of European beech forests

The growth of past, present, and future forests was, is and will be affected by climate variability. This multifaceted relationship has been assessed in several regional studies, but spatially resolved, large-scale analyses are largely missing so far. Here we estimate recent changes in growth of 5800 beech trees (Fagus sylvatica L.) from 324 sites, representing the full geographic and climatic range of species. Future growth trends were predicted considering state-of-the-art climate scenarios. The validated models indicate growth declines across large region of the distribution in recent decades, and project severe future growth declines ranging from −20% to more than −50% by 2090, depending on the region and climate change scenario (i.e. CMIP6 SSP1-2.6 and SSP5-8.5). Forecasted forest productivity losses are most striking towards the southern distribution limit of Fagus sylvatica, in regions where persisting atmospheric high-pressure systems are expected to increase drought severity. The projected 21st century growth changes across Europe indicate serious ecological and economic consequences that require immediate forest adaptation.

An Assessment of Proso Millet as an Alternative Summer Cereal Crop in the Mediterranean Basin

Proso millet (Panicum miliaceum L.) is a cereal well known for its ability to be successfully grown under drought and intense heat conditions, thus sustaining food security in arid regions. Considering that a trend of increasing drought severity is expected in the future in Southern Europe, solutions need to be found to enhance the resilience of agroecosystems to the effects of climate change. From this perspective, proso millet re-introduction could represent an interesting tool in reducing water consumption for grain production and in providing a new resource to farmers. The aim of this study was to characterize proso millet adaptability to drought and low-input field conditions in the Mediterranean environment, especially considering water-related traits, such as water use efficiency. Limited water-demanding crops and yield stability can contribute to the resilience of agroecosystems and their adaptation to climate change. A three-year field crop experiment was conducted in northern Italy to assess proso millet’s performance in terms of productivity and water status in rainfed agriculture conditions. It was compared to a conventional irrigated corn, a typical summer cereal of the area. All years of experimentation were characterized by adverse meteorological trends, in the full manifestation of the uncertainties of climate change. Despite such different conditions from an agro-meteorological point of view, proso millet showed, in non-irrigated conditions, stable yield and water use efficiency (on average 0.30 kg/m2 and 1.83 kg/m3, respectively), and good agronomic performance. Proso millet, therefore, seems to offer interesting traits for reintroduction on the European side of the Mediterranean Basin, representing a resource for farmers. Moreover, the shortness of the proso millet life cycle (on average 108 days) allows it to be used as a catch crop in the event of major crop failure, an event becoming more likely in the climate change scenario. Furthermore, the possibility of producing grain while saving water (and other production inputs), even in very hot and dry years, increases the sustainability of agricultural production and the resilience of agroecosystems.

Response of southern African ungulate species to supplementary feeding during drought: Species‐specific differences in relative use, food choice and intraspecific behavioural interactions

AbstractIn southern Africa, climate change is increasing drought severity and duration. One way to mitigate drought‐induced food shortages is supplementary feeding, but ungulate responses are largely unstudied. Here, we analyse ~250 h of video footage from camera traps at feeding stations in South Africa during a year when rainfall was ~50% of the decadal average. Feeding station usage was highly uneven: eland (Taurotragus oryx), greater kudu (Tragelaphus strepsiceros), sable (Hippotragus niger) and white rhino (Ceratotherium simum) were over‐represented relative to their local population; and impala (Aepyceros melampus), blesbok (Damaliscus dorxas phillipsi) and zebra (Equus quagga) were under‐represented. In total, 81% of individuals at feeding stations fed (0%–90% for different species). Guarding behaviour was observed, especially by eland and kudu, potentially excluding other (smaller) species. Overall, 17% visits involving ≥2 individuals involved intraspecific aggression (highest for sable (40%) and eland (27%); low/absent otherwise); there were very few (n = 6) inter‐specific encounters. Lucerne and teff hay were consumed more frequently than Boskos (pellets), which was favoured by non‐target primates and ungulates showing guarding behaviour. As benefits of feeding are unequal, and can encourage guarding and intraspecific aggression, we suggest feeding should be done with caution, especially if the aim is to benefit specific species.

Winners and losers of climate warming: Declining growth in Fagus and Tilia vs. stable growth in three Quercus species in the natural beech–oak forest ecotone (western Romania)

Global warming and increasing drought severity are exposing temperate forests to increasing stress, challenging silvicultural decision making. Growth analyses in marginal tree populations at drought-induced range limits may provide valuable information on tree species’ adaptive potentials and species-specific climate turning points. We studied the climate sensitivity and resilience to drought of radial growth, and long-term growth trends of mesic and rear-edge populations of Fagus sylvatica in comparison to three oak species (Quercus petraea, Q. frainetto, Q. cerris) and Tilia tomentosa in natural ecotones from mesic beech to xeric oak forests along three elevation transects in western Romania. Radial growth of all species was positively influenced by summer precipitation and low drought intensity, and negatively by high summer temperatures. The basal area increment (BAI) of F. sylvatica and T. tomentosa has declined in the last 10–20 years with warming and a deterioration of the summer water balance, while the three Quercus species maintained stable growth rates, though at lower BAI levels, suggesting a negative relationship between mean BAI and drought resistance among the five species. Growth reductions during three severe drought events (2000, 2003, 2012) were stronger, and growth resilience lower, in F. sylvatica and T. tomentosa than in the Quercus species, pointing at a thermal limit of beech at June–August temperatures of 20–21 °C. As the climate of the studied ecotones is similar to the predicted climate at colline/submontane elevation in Central Europe in about 50 years, a decline in beech growth and vitality is likely also in drought-affected regions in the distribution centre with future warming. Our results demonstrate that choosing stress-tolerant Q. petraea (as well as Q. frainetto and Q. cerris) instead of more productive timber species is a relatively safe option for Central European forestry in a warmer climate.

Warming winter, drying spring and shifting hydrological regimes in Northeast China under climate change

As an important agriculture production area in the world and a flood prone area, future hydro-climate changes in winter and spring in Northeast China could have remarkable influence on spring water resources and flood. Yet, studies on future hydro-climate variations with special considerations of snow influences remain limited so far in the region. Here, we studied future winter and spring hydro-climate changes to the end of the century with special considerations of snow variations under the RCP2.6, RCP6.0 and RCP8.5 scenarios in Northeast China. A water and energy budget-based distributed biosphere hydrological model with improved snow physics was implemented. We find that winter and spring are warming 0.08 °C and 0.06 °C annually under 30 years moving average in RCP8.5. Air temperature increasing rate in winter is approximately two times higher than that in spring in 2030–2059. In this period, snow melt contribution to spring average runoff and maximum runoff decrease by at least 39% and 23%, respectively, and spring soil moisture decreases by 7%. The spring snow melt runoff peak will move from April to March under the warmest climate condition (i.e., 2070–2099 in RCP8.5). The earlier snow melt renders the snow melt contribution to total runoff decrease to almost zero in May, which could increase drought severity. This study sheds some lights on changes in hydrological regimes under climate change with a focus on snow melt and the influences in the entire Northeast China for the first time, and is helpful for adaption to future climate change.

Spatial and temporal variation in rainy season droughts in the Indonesian Maritime Continent

Spatial and temporal droughts during rainy seasons are important climatic aspects to consider in water resources management. The dry spell index, a time-independent index that considers the characteristic of dry days, dry spell, seasonal length and evaporation rate in drought severity estimation, is supporting the analyses of the spatiotemporal variations of drought severity in the rainy season of the Indonesian Maritime Continent (IMC) between 1998 and 2018. The rainy season was determined using a modified anomalous accumulation. The results showed that an increase in dry spells produced a consistently increasing temporal drought during the rainy season across the IMC. Meanwhile, spatial variation suggested that although there is an increase in the rainy season total accumulated precipitation and duration, a large area within the monsoon regime also experiences increased drought severity, indicating more frequent extreme precipitation. Regional drought severity was classified as normal with a tendency of an increasing area under dry categories. Overall, the rainy season drought has increased in the IMC from 1998 to 2018, elevating the threats of reduced agricultural production.

Potato Response to Drought Stress: Physiological and Growth Basis.

Drought poses a major challenge to the production of potatoes worldwide. Climate change is predicted to further aggravate this challenge by intensifying potato crop exposure to increased drought severity and frequency. There is an ongoing effort to adapt our production systems of potatoes through the development of drought-tolerant cultivars that are appropriately engineered for the changing environment. The breeding of drought-tolerant cultivars can be approached through the identification of drought-related physiological and biochemical traits and their deployment in new potato cultivars. Thus, the main objective of this study was to develop a method to identify and characterize the drought-tolerant potato genotypes and the related key traits. To achieve this objective, first we studied 56 potato genotypes including 54 cultivars and 2 advanced breeding lines to assess drought tolerance in terms of tuber yield in the greenhouse experiment. Drought differentially reduced tuber yield in all genotypes. Based on their capacity to maintain percent tuber yield under drought relative to their well-watered controls, potato genotypes differed in their ability to tolerate drought. We then selected six genotypes, Bannock Russet, Nipigon, Onaway, Denali, Fundy, and Russet Norkotah, with distinct yield responses to drought to further examine the physiological and biochemical traits governing drought tolerance. The drought-induced reduction in tuber yield was only 15–20% for Bannock Russet and Nipigon, 44–47% for Onaway and Denali, and 83–91% for Fundy and Russet Norkotah. The tolerant genotypes, Bannock Russet and Nipigon, exhibited about a 2–3-fold increase in instantaneous water-use efficiency (WUE) under drought as compared with their well-watered controls. This stimulation was about 1.8–2-fold for moderately tolerant genotypes, Onaway and Denali, and only 1.5-fold for sensitive genotypes, Fundy, and Russet Norkotah. The differential stimulation of instantaneous WUE of tolerant and moderately tolerant genotypes vs. sensitive genotypes was accounted for by the differential suppression of the rates of photosynthesis, stomatal conductance, and transpiration rates across genotypes. Potato genotypes varied in their response to leaf protein content under drought. We suggest that the rates of photosynthesis, instantaneous WUE, and leaf protein content can be used as the selection criteria for the drought-tolerant potato genotypes.

Effects of Soil Amendment With Wood Ash on Transpiration, Growth, and Metal Uptake in Two Contrasting Maize (Zea mays L.) Hybrids to Drought Tolerance.

Wood ash as a soil amendment has gained wide spread acceptance in the recent years as a sustainable alternative to chemical fertilizers, although information regarding the effects of its application on maize growth and yield in the context of climate change and increasing drought severity is lacking till date. In the present study, field and pot trials were carried out at the experimental farm of the University of Padova at Legnaro (NE Italy) in a silty-loam soil in order to investigate the effects of soil amendment with wood ash (0.1% w/w, incorporated into the 0.2-m top soil) on the bioavailability of mineral elements and their uptake by maize. Characteristics analyzed included plant growth, leaf transpiration dynamics, and productivity in two contrasting hybrids, P1921 (drought sensitive) and D24 (drought tolerant). Wood ash contained relevant amounts of Ca, K, Mg, P, and S, and hazardous levels of Zn (732 mg kg−1), Pb (527 mg kg−1), and Cu (129 mg kg−1), although no significant changes in total soil element concentration, pH, and electrical conductivity were detected in open field. Ash application led to a general increasing trend of diethylene triamine penta-acetic acid (DTPA)-extractable of various elements, bringing to higher grain P in D24 hybrid, and Zn and Ni reductions in P1921 hybrid. Here, the results demonstrated that ash amendment enhanced shoot growth and the number of leaves, causing a reduction of harvest index, without affecting grain yield in both hybrids. The most relevant result was a retarded inhibition of leaf transpiration under artificial progressive water stress, particularly in the drought-tolerant D24 hybrid that could be sustained by root growth improvements in the field across the whole 0–1.5 m soil profile in D24, and in the amended top soil in P1921. It is concluded that woody ash can be profitably exploited in maize fertilization for enhancing shoot and root growth and drought tolerance, thanks to morphological and physiological improvements, although major benefits are expected to be achieved in drought tolerant hybrids. Attention should be payed when using ash derived by metal contaminated wood stocks to avoid any health risk in food uses.

Physiological, developmental and growth responses to desiccation induced stress in four seed coat colour varieties of Vigna unguiculata (L. Walp).

Cowpea (Vigna unguiculata L. Walp) is a widely grown leguminous crop in Ghana. This study was conducted using four varieties of cowpea based on the colour of the seed coat namely; red, brown, black and cream cowpea varieties, and were subjected to three different watering regimes, namely: Normal, moderate and severe water stress regimes. These different watering regimes were used as potential screening criteria to determine their drought tolerance ability. We monitored changes in physiological, morphological and yield traits due to the effects of four seed coat colour varieties and imposed water regimes. The effects of seed coat colour on relative water content (RWC) was significant (F = 13.15; p ≤ 0.05). Red variety recorded the highest RWC (60.14%) with the lowest RWC (50.71%) in the Black seed colour, all under severe water stress. The Red and Cream seed coats had a soil moisture content (SMC) of 62.61 and 48.70% respectively when the severe water stress treatment was considered. There was a decreasing trend in chlorophyll content for all four cowpea varieties. The Brown and Red varieties recorded the highest chlorophyll contents under moderate and severe water stress respectively. Proline concentrations were high with increasing drought severity. The Red cowpea variety recorded the maximum concentration of free proline (5.7 µg/g) under severe water stress. Mean seed weight in Red seed coat, subjected to severe water stress, was 0.48 g. Results in this experiment revealed that the Red seed coat colour appeared to be tolerant to severe water stress compared to Cream, Black and Brown seed coats. Key words: Cowpea, seed coat colour, water stress, relative water content, soil moisture content.

Friend or foe? The role of biotic agents in drought-induced plant mortality

Plant mortality is a complex process influenced by both biotic and abiotic factors. In recent decades, widespread mortality events have been attributed to increasing drought severity, which has motivated research to examine the physiological mechanisms of drought-induced mortality, particularly hydraulic failure. Drought-based mortality mechanisms are further influenced by plant interactions with biota such as neighboring plants, insect pests, and microbes. In this review, we highlight some of the most influential papers addressing these biotic interactions and their influence on plant mortality. Plant–plant interactions can be positive (facilitation), neutral, or negative (competition), depending on drought intensity and neighbor identity. For example, stand-scale mortality likely increases with basal area (an index of competition). However, the diversity of forest stands matters, as more diverse forests suffer less mortality from drought than species-poor forests. Dense forest stands also increase bark beetle attack frequency, which can exacerbate drought stress and mortality, particularly for fast-growing species with lower defense allocation. In some cases, however, drought stress can alleviate biotic attack, depending on feedbacks between plant and pest physiology. Finally, plant interactions with beneficial microorganisms can increase drought tolerance, reduce the likelihood of mortality, and even extend plant distributions into drier habitats. Our review suggests more work is needed in natural herbaceous plant communities as well as dry tropical ecosystems where mortality mechanisms are less understood. Overall, relatively few studies directly link biotic interactions with the physiological mechanisms of mortality. Simultaneous manipulations of biotic interactions and measurements of physiological thresholds (e.g., xylem cavitation) are needed to fully represent biotic interactions in predictive models of plant mortality.

A stand level application of efficiency analysis to understand efficacy of fertilization and thinning with drought in a loblolly pine plantation

Loblolly pine (Pinus taeda L.) is the most important and productive commercial timber species in the southern USA. Common plantation management practices such as fertilization and thinning could become inefficient and economically disadvantageous given anticipated climate change effects, such as increased drought severity, especially in the drier Upper Gulf region of the south-central USA. To calculate technical and economic efficiency, we used data envelopment analysis (DEA) to assess the ability of fertilized, thinned, and drought-induced loblolly pine plots in southeastern Oklahoma (n = 32) to turn volume growth and stand density (inputs) into timber products- pulpwood, chip-n-saw, sawtimber- and stored carbon (outputs) across 21, 26, and 31-year rotations. The highest efficiencies were for the fertilized-thinned treatments. We found that thinned stands remain technically, economically, and overall efficient as rotation age increased. Non-thinned stands had lower efficiencies than thinned stands and exhibited a 28% decrease in overall efficiency between ages 21 and 31. Drought decreased overall efficiency by at least 11% when rotation age was 26 years or longer. Fertilization with drought decreased overall efficiency on average by 24%. The results reiterate the importance of thinning to efficiently mediate drought conditions and should remain a staple of plantation silviculture. Results also indicate that fertilization is not likely to help ameliorate drought impacts, from an efficiency standpoint. Study results will benefit practitioners in gauging active forest management decisions and their likely outcomes from a resource efficiency perspective.

Intrinsic non-stomatal resilience to drought of the photosynthetic apparatus in Coffea spp. is strengthened by elevated air [CO2

Growing water restrictions associated with climate changes constitute daunting challenges to crop performance. This study unveils the impacts of moderate (MWD) or severe (SWD) water deficit, and their interaction with air [CO2], on the photosynthetic apparatus of Coffea canephora Pierre ex A. Froehner cv. Conilon Clone 153 (CL153) and Coffea arabica L. cv. Icatu. Seven year-old potted plants grown under 380 (aCO2) or 700μll -1 (eCO2) [CO2] gradually reached predawn water potentials between -1.6 and -2.1MPa (MWD), and below -3.5MPa (SWD). Under drought, stomata closure was chiefly related to abscisic acid (ABA) rise. Increasing drought severity progressively affected gas exchange and fluorescence parameters in both genotypes, with non-stomatal limitations becoming gradually dominating, especially regarding the photochemical and biochemical components of CL153 SWD plants. In contrast, Icatu plants were highly tolerant to SWD, with minor, if any, negative impacts on the potential photosynthetic functioning and components (e.g., Amax, Fv/Fm, electron carriers, photosystems (PSs) and ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) activities). Besides, drought-stressed Icatu plants displayed increased abundance of a large set of proteins associated with the photosynthetic apparatus (PSs, light-harvesting complexes, cyclic electron flow, RuBisCO activase) regardless of [CO2]. Single eCO2 did not promote stomatal and photosynthetic down-regulation in both genotypes. Instead, eCO2 increased photosynthetic performance, moderately reinforced photochemical (PSs activity, electron carriers) and biochemical (RuBisCO, ribulose-5-phosphate kinase) components, whereas photoprotective mechanisms and protein abundance remained mostly unaffected. In both genotypes, under MWD, eCO2 superimposition delayed stress severity and promoted photosynthetic functioning with lower energy dissipation and PSII impacts, whereas stomatal closure was decoupled from increases in ABA. In SWD plants, most impacts on the photosynthetic performance were reduced by eCO2, especially in the moderately drought affected CL153 genotype, although maintaining RuBisCO as the most sensitive component, deserving special breeder's attention to improve coffee sustainability under future climate scenarios.

Climate-growth relationships for Aspidosperma tomentosum Mart. in South American tropical dry forests

The precise demarcation and cross-dating of tree rings in Aspidosperma tomentosum Mart., a valuable timber species in the tropical dry forests of South America, were used to develop the first well-replicated chronology covering the period 1843–2015. A. tomentosum Mart. tree growth is strongly regulated by soil water availability prior to and during the current growing season. In the context of increased drought severity due to climate change, determining of climate influences on A. tomentosum Mart. radial growth is necessary to establish appropriate guidelines for the management, conservation and restoration of this species, currently affected by extreme weather events, extensive fires and deforestation in the Chiquitania forests, Bolivia. Tropical forest ecosystems play a critical role in the functioning of the Earth; thus, a better understanding of the influences of climate on tree growth is needed to estimate changes in forest productivity and consequently in carbon sink variations at regional and global scales. In the context of global environmental changes, our study aimed at using the growth rings of A. tomentosum Mart. to establish the relationships between radial growth and climatic variations. The anatomical characterization of the wood elements facilitated the precise annual band delimitation and the rejection of samples with false rings and growth anomalies. A tree-ring chronology was developed using traditional dendrochronological methods and the relationships with climate determined using correlation functions. The chronology is based on 20 individuals and covers the period 1843–2015. Tree-ring statistics indicate an important common signal in growth variations between trees (R-bar = 0.31, EPS = 0.90). Interannual variations in A. tomentosum Mart. are directly related to total annual precipitation (r = 0.76) and inversely to mean annual temperature (r = − 0.44). These relationships are similar to those documented for other commercial species (Centrolobium microchaete, Schinopsis brasiliensis) from tropical dry forests in South America, suggesting a consistent climatic influence on tree growth at a regional scale. The strong dependence of tree growth on climate variability is a major concern, as climate change scenarios for tropical dry forests in South America predict an increase in the frequency and intensity of droughts, which in turn would reduce the A. tomentosum Mart. growth during the twenty-first century.

Atmospheric Circulation as a Factor Contributing to Increasing Drought Severity in Central Europe

AbstractLong‐lasting and severe droughts seriously threaten agriculture, ecosystems, and society. Summer 2018 in central Europe was characterized by unusually persistent heat and drought, causing substantial economic losses, and became a part of a several years long dry period observed across this region. This study assesses the magnitude of the recent drought within a long‐term context and links the increased drought severity to changes in atmospheric circulation. Temporal variability of drought conditions since the late 19th century was analyzed at seven long‐term stations distributed across the Czech Republic using the Palmer Drought Severity Index and the Standardized Precipitation Evaporation Index. The Palmer Z Index and a variation of the Standardized Precipitation Evaporation Index were used to study rapidly emerging short‐term droughts and to link these episodes to atmospheric circulation. Changes in circulation were analyzed through circulation types calculated from flow strength, direction and vorticity in mean sea level pressure data from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis for 1948–2018. Increasing drought severity across the Czech Republic with record‐low values of the drought indices during 2015–2018 was found. The trend was distinctive in both vegetation (April–September) and cold (October–March) periods. The tendency toward more severe droughts in recent decades was linked to changes in frequency of dry and wet circulation types, highlighting the important role of atmospheric circulation in regional climate. It remains an open question whether the significantly increasing frequency of dry circulation types in the vegetation period is related to climate change, or rather represents multidecadal climate variability.

Resilience to drought of dryland wetlands threatened by climate change

Dryland wetlands are resilient ecosystems that can adapt to extreme periodic drought–flood episodes. Climate change projections show increased drought severity in drylands that could compromise wetland resilience and reduce important habitat services. These recognized risks have been difficult to evaluate due to our limited capacity to establish comprehensive relationships between flood–drought episodes and vegetation responses at the relevant spatiotemporal scales. We address this issue by integrating detailed spatiotemporal flood–drought simulations with remotely sensed vegetation responses to water regimes in a dryland wetland known for its highly variable inundation. We show that a combination of drought tolerance and dormancy strategies allow wetland vegetation to recover after droughts and recolonize areas invaded by terrestrial species. However, climate change scenarios show widespread degradation during drought and limited recovery after floods. Importantly, the combination of degradation extent and increase in drought duration is critical for the habitat services wetland systems provide for waterbirds and fish.

Human-induced changes in Indonesian peatlands increase drought severity

Indonesian peatlands are critical to the global carbon cycle, but they also support a large number of local economies. Intense forest clearing and draining in these peatlands is causing severe ecological and environmental impacts. Most studies highlighted increased carbon emission in the region through drought and large‐scale fires, further accelerating peatland degradation. Yet, little is known about the long-term impacts of human-induced disturbance on peatland hydrology in the tropics. Here we show that converting natural peat forests to plantations can significantly alter the hydrological system far worse than previously recognized, leading to amplified moisture stress and drought severity. This study quantified how human-induced changes to Indonesian peatlands have affected drought severity. Through field observations and modelling, we demonstrate that canalization doubled drought severity; logging and starting plantations even quadrupled drought severity. Recognizing the importance of peatlands to Indonesia, proper management, and rehabilitating peatlands remain the only viable option for continued plantation use.

Assessment of impacts of potential climate change on meteorological drought characteristics at regional scales

AbstractDrought patterns are better understood by analysing the joint dependence among long‐term drought characteristics: severity, duration, and frequency. Changes in these drought characteristics are also likely due to potential climate change, for instance, increased drought severity and duration, increased frequency of drought events, and increased spatial extent of drought impacts. In this study, we performed a regional‐scale analysis of potential changes in meteorological drought characteristics in a tropical region in India under a warming future climate scenario. The meteorological drought characteristics were computed using the Standardized Precipitation Index. The Coordinated Regional Downscaling Experiment South Asia Regional Climate Model future precipitation simulation under the RCP 4.5 scenario was bias‐corrected and utilized for future drought frequency analysis. Regionalization of meteorological drought characteristics was performed using the simple k‐means clustering technique to identify the homogeneous regions for baseline and future periods. Bivariate copula was utilized to model the dependence among the drought characteristics in order to develop the S‐D‐F curves. The changes in regionalization and regional S‐D‐F curves under future potential climate change were then investigated. The results of the study suggest an increase in drought severity by 2–3% for long‐term droughts (duration more than 5 months) in the future as indicated by upward shift and changes in the slope of the regional S‐D‐F curves. There is a projected increase in the occurrence of long‐term droughts in the future when compared to short‐term (duration of 1 to 3 months) droughts. We also observed a considerable spatial shift of drought hotspots, the severe drought‐prone regions lie in the eastern part of the study region in the future. Future projections of regional S‐D‐F curves and Spatio‐temporal drought characteristics obtained from the proposed framework may be utilized for devising drought mitigation strategies.

Elevated air [CO2] improves photosynthetic performance and alters biomass accumulation and partitioning in drought-stressed coffee plants

Coffee (Coffea arabica L.) is an important global commodity grown in tropical areas where increased drought severity and frequency are believed to become progressively important due to climate changes. Nonetheless, elevated air [CO2] is thought to be able to mitigate heat and drought stresses. In this study, we tested how carbon assimilation and use are affected by elevated [CO2] in combination with a progressive drought, and how this could impact shifts on biomass accumulation and partitioning. For that, we cultivated coffee plants in open top chambers under greenhouse conditions. Plants grown in 12-L pots were then submitted to ambient (386 ± 20 ppm) or elevated (723 ± 83 ppm) [CO2] during approximately seven months, as well as to varying soil water availabilities (100, 50, 37.5, 25 or 20 % of soil field capacity). Our results demonstrate that elevated [CO2] improved carbon assimilation rates (>60 %) with unaltered stomatal conductance and no signs of photosynthetic downregulation. This was accompanied by increases in water-use efficiency, respiration rates and biomass accumulation regardless of watering, and decreased photorespiration rates and oxidative pressure under drought. Improved growth under elevated [CO2] was more evident under drought than under full irrigation, and was unlikely to have been associated with global changes on hormonal pools, but rather with shifts on carbon fluxes. Finally, elevated [CO2] promoted key allometric adjustments linked to drought tolerance, e.g., more biomass partitioning towards roots with greater root length. Collectively, our results offer novel and timely information on the mitigating ability of elevated [CO2] on the photosynthetic performance and growth of coffee plants under drought conditions.

Refuges and ecological traps: Extreme drought threatens persistence of an endangered fish in intermittent streams.

Recent droughts raise global concern over potential biodiversity loss and mitigating impacts to vulnerable species has become a management priority. However, drought impacts on populations are difficult to predict, in part, because habitat refuges can buffer organisms from harsh environmental conditions. In a global change context, more extreme droughts may turn previously suitable habitats into ecological traps, where vulnerable species can no longer persist. Here, we explore the impacts of California's recent record‐breaking drought on endangered juvenile Coho salmon. We estimated the variability of cumulative salmon survival using mark–recapture of nearly 20,000 tagged fish in intermittent stream pools during a 7‐year period encompassing drought and non‐drought conditions. We then determined the relative importance of physical habitat, streamflow, precipitation, landscape, and biological characteristics that may limit survival during drought. Our most striking result was an increase in the number of pools with reduced or zero survival during drought years and a coincident increase in spatial variability in survival among study reaches. In nearly half of the stream pools, salmon survival during drought was similar to mean survival of pools assessed during non‐drought years, indicating some pools had remarkable resistance (ability to withstand disturbance) to extreme drought. Lower survival was most attributable to longer duration of disconnection between upstream and downstream habitats, a consequence of increasing drought severity. Our results not only suggest that many pools sustain juvenile salmon in non‐drought years transition into ecological traps during drought but also highlight that some pools serve as refuges even under extreme drought conditions. Projected increases in drought severity that lead to longer droughts and greater habitat fragmentation could transform an increasing proportion of suitable habitats into ecological traps. Predicting future impacts of drought on Coho salmon and other sensitive species will require identification and protection of drought refuges and management strategies that prevent further habitat fragmentation.