Increasing Drought Severity Research Articles

Increased drought severity tracks warming in the United States’ largest river basin

Across the Upper Missouri River Basin, the recent drought of 2000 to 2010, known as the "turn-of-the-century drought," was likely more severe than any in the instrumental record including the Dust Bowl drought. However, until now, adequate proxy records needed to better understand this event with regard to long-term variability have been lacking. Here we examine 1,200 y of streamflow from a network of 17 new tree-ring-based reconstructions for gages across the upper Missouri basin and an independent reconstruction of warm-season regional temperature in order to place the recent drought in a long-term climate context. We find that temperature has increasingly influenced the severity of drought events by decreasing runoff efficiency in the basin since the late 20th century (1980s) onward. The occurrence of extreme heat, higher evapotranspiration, and associated low-flow conditions across the basin has increased substantially over the 20th and 21st centuries, and recent warming aligns with increasing drought severities that rival or exceed any estimated over the last 12 centuries. Future warming is anticipated to cause increasingly severe droughts by enhancing water deficits that could prove challenging for water management.

Spatiotemporal variations of drought in the Yunnan-Guizhou Plateau, southwest China, during 1960–2013 and their association with large-scale circulations and historical records

Abstract It is imperative that more powerful drought indicators are used to objectively quantify the characteristics of droughts. A revised reconnaissance drought index (RDI) was used to detect drought in the Yunnan-Guizhou Plateau (YGP), and the impacts of potential evapotranspiration, precipitation, and climate index anomalies were also considered. This will help to further elucidate the causes of meteorological droughts from a climate change perspective, and is of great importance in guiding future drought prediction and control. The non-parametric Mann-Kendall test was applied to identify points of change for meteorological droughts in the YGP during 1960–2013, and a cross wavelet analysis was used to reveal correlations between monthly climate indices and the RDI. The results are as follows: (1) The decreasing RDI trends (annual (−0.066/10a), summer (−0.18/10a), autumn (−0.196/10a), and winter (−0.056/10a)) indicate increasing drought severity, while the increasing trend in spring (0.084/10a) indicates a decreasing drought severity. However, these trends were insignificant, and no mutations occurred in the YGP during 1960–2013. (2) The drought duration was longest in the central, southern, northwestern, and northeastern edge of Yunnan Province (YP) and in the western parts of Guizhou Province (GP), while the drought severity was higher in the southwestern, eastern, and western edge of YP, and throughout GP. For the entire YGP, the duration and severity of droughts in the 1960s, 1980s, and 2000s was generally stronger than in 1970s and 1990s (3) Drought events that were identified by the RDI are consistent with those in historical records, but there are also inconsistencies during individual years. It was found that the RDI accounts for both the influence of precipitation and evaporation on drought: a decreased annual precipitation (84.6%) and an increased evaporation (40.7%) both contributed to decreased RDI (59.3%) for all stations. Therefore, the decrease in precipitation may lead to drought in the YGP. (4) The El Nino Southern Oscillation and the Arctic Oscillation play major roles in meteorological droughts in the YGP and affect the RDI over a relatively short timescale (1–8 years); severe droughts in spring occurred mainly during El Nino events, whereas both El Nino and La Nina events were associated with droughts in summer, autumn, and winter. Overall, severe droughts occurred more frequently during the El Nino event than during the La Nina event.

Exotic herbaceous species interact with severe drought to alter soil N cycling in a semi-arid shrubland

Mediterranean-type ecosystems are increasingly threatened by climate change and exotic annual species, jeopardizing the native communities and their global biodiversity. In these systems, soil nitrogen (N) limits net primary production, and its availability can be influenced by both of these stressors. To understand the interactive effects of droughts and exotic herbaceous species on soil N, we monitored the temporal variability of soil inorganic N, net N mineralization, net nitrification, and NO3- leaching under native- and exotic-dominated stands exposed to rainfall manipulation plots in a Mediterranean-type shrub-dominated community. Increasing drought severity resulted in the accumulation of soil NH4+ and NO3-, with a more pronounced increase in exotic-dominated plots. Increased net N mineralization and net nitrification and reduced leaching losses were observed as mechanisms of inorganic N accumulation. In comparison to soils under native plants, soils under exotic plants had enhanced leaching losses upon soil rewetting. We propose that distinct traits of exotic annual herbaceous species associated with higher N inputs, faster turnover, and reduced temporal uptake determine the changes in N cycling in response to droughts. Severe droughts and exotic plants may produce a larger, more vulnerable pool of N that is prone to losses while providing a competitive advantage to promote exotic growth in these N-limited ecosystems.

How do herbivorous insects respond to drought stress in trees?

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant-insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon-based and nitrogen-based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap-sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought-induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO2 levels. There is a need for larger, temperate and tropical forest-scale drought experiments to look at herbivorous insect responses and their role in tree death.

Parched pines: a quantitative comparison of two multi‐year droughts and associated mass mortalities of bishop pine (Pinus muricata) on Santa Cruz Island, California

AbstractExtreme weather events such as droughts are expected to increase in severity and frequency as the climate changes; it is imperative that land managers be able to monitor associated changes in vegetation health efficiently and across large scales in order to mitigate or prepare for these events. This need motivated deeper study of the die‐off of bishop pine (Pinus muricata) on California's Santa Cruz Island during the 2012–2016 drought. These pines play a keystone role within the island's ecosystem and have experienced two severe droughts and associated mass die‐offs in the past 40 years. In an effort to compare these events, we used meteorological data to track changes in drought severity from 1985 to 2018 coupled with novel methods for forest monitoring to reveal dynamics not detectable by shorter‐duration studies. Leveraging 34 years of 30 m resolution Landsat imagery, we compared vegetation mortality between the two most severe droughts of that time period: 1987–1991 and 2012–2016. We used the slope of decline in the annual median value of three different Vegetation Indices (VIs; NBR, NDMI and NDVI) to compare mortality between the two drought events and to reveal spatial patterns of mortality within the bishop pine forests. Our results indicated that the 2012–2016 drought was the island's harshest in over a century and that it resulted in greater and more widespread mortality of vegetation within bishop pine stands than the 1987–1991 drought. The average VI decline was significantly greater during the 2012–2016 drought than the 1987–1991 drought by a factor of 1.89, 2.09 and 1.84 for NBR, NDMI and NDVI, respectively. Our results aligned with projections of increasing drought severity and associated tree mortality across the region. The temporal monitoring methods developed here can be adapted to study similar landscape scale changes over multiple decades in other forest ecosystems facing similar threats.

Beyond the extreme: recovery of carbon and water relations in woody plants following heat and drought stress.

Plant responses to drought and heat stress have been extensively studied, whereas post-stress recovery, which is fundamental to understanding stress resilience, has received much less attention. Here, we present a conceptual stress-recovery framework with respect to hydraulic and metabolic functioning in woody plants. We further synthesize results from controlled experimental studies following heat or drought events and highlight underlying mechanisms that drive post-stress recovery. We find that the pace of recovery differs among physiological processes. Leaf water potential and abscisic acid concentration typically recover within few days upon rewetting, while leaf gas exchange-related variables lag behind. Under increased drought severity as indicated by a loss in xylem hydraulic conductance, the time for stomatal conductance recovery increases markedly. Following heat stress release, a similar delay in leaf gas exchange recovery has been observed, but the reasons are most likely a slow reversal of photosynthetic impairment and other temperature-related leaf damages, which typically manifest at temperatures above 40 °C. Based thereon, we suggest that recovery of gas exchange is fast following mild stress, while recovery is slow and reliant on the efficiency of repair and regrowth when stress results in functional impairment and damage to critical plant processes. We further propose that increasing stress severity, particular after critical stress levels have been reached, increases the carbon cost involved in reestablishing functionality. This concept can guide future experimental research and provides a base for modeling post-stress recovery of carbon and water relations in trees.

Lianas have a seasonal growth advantage over co-occurring trees.

The seasonal growth advantage hypothesis posits that plant species that grow well during seasonal drought will increase in abundance in forests with increasing seasonality of rainfall both in absolute numbers and also relative to co-occurring plant species that grow poorly during seasonal drought. That is, seasonal drought will give some plant species a growth advantage that they lack in aseasonal forests, thus allowing them attain higher abundance. For tropical forest plants, the seasonal growth advantage hypothesis may explain the distribution of drought-adapted species across large-scale gradients of rainfall and seasonality. We tested the seasonal growth advantage hypothesis with lianas and trees in a seasonal tropical forest in central Panama. We measured the dry-season and wet-season diameter growth of 1,117 canopy trees and 648 canopy lianas from 2011 to 2016. We also evaluated how lianas and trees responded to the 2015-2016 El Niño, which was the third strongest el Niño drought on record in Panama. We found that liana growth rate was considerably higher during the dry-season months than the wet-season months in each of the five years. Lianas achieved one-half of their annual growth during the 4-month dry season. By contrast, trees grew far more during the wet season; they realized only one-quarter of their annual growth during the dry season. During the strong 2015-2016 El Niño dry season, trees essentially stopped growing, whereas lianas grew unimpeded and as well as during any of the previous four dry seasons. Our findings support the hypothesis that seasonal growth gives lianas a decided growth advantage over trees in seasonal forests compared to aseasonal forests, and may explain why lianas peak in both absolute and relative abundance in highly seasonal tropical forests. Furthermore, the ability of lianas to grow during a strong el Niño drought suggests that lianas will benefit from the predicted increasing drought severity, whereas trees will suffer, and thus lianas are predicted to increase in relative abundance in seasonal tropical forests.

Mechanisms and Early Warning of Drought Disasters: Experimental Drought Meteorology Research over China

Abstract A major experimental drought research project entitled “Mechanisms and Early Warning of Drought Disasters over Northern China” (DroughtEX_China) was launched by the Ministry of Science and Technology of China in 2015. The objective of DroughtEX_China is to investigate drought disaster mechanisms and provide early-warning information via multisource observations and multiscale modeling. Since the implementation of DroughtEX_China, a comprehensive V-shape in situ observation network has been established to integrate different observational experiment systems for different landscapes, including crops in northern China. In this article, we introduce the experimental area, observational network configuration, ground- and air-based observing/testing facilities, implementation scheme, and data management procedures and sharing policy. The preliminary observational and numerical experimental results show that the following are important processes for understanding and modeling drought disasters over arid and semiarid regions: 1) the soil water vapor–heat interactions that affect surface soil moisture variability, 2) the effect of intermittent turbulence on boundary layer energy exchange, 3) the drought–albedo feedback, and 4) the transition from stomatal to nonstomatal control of plant photosynthesis with increasing drought severity. A prototype of a drought monitoring and forecasting system developed from coupled hydroclimate prediction models and an integrated multisource drought information platform is also briefly introduced. DroughtEX_China lasted for four years (i.e., 2015–18) and its implementation now provides regional drought monitoring and forecasting, risk assessment information, and a multisource data-sharing platform for drought adaptation over northern China, contributing to the global drought information system (GDIS).

Changing characteristics of meteorological droughts in Nigeria during 1901–2010

The objective of this study was to assess the changes in the severity and return periods of meteorological droughts during major cropping seasons of Nigeria for the period 1901–2010 in order to understand the impacts of climate variation on seasonal droughts. Gauge-based gridded global precipitation climatology center (GPCC) rainfall and climate research unit (CRU) potential evapotranspiration (PET) data having a spatial resolution of 0.5° were used for the reconstruction of droughts using standardized precipitation evapotranspiration index (SPEI). SPEI values were fitted with the best distribution function to estimate seasonal droughts return periods and the modified Mann-Kendall test was used to assess the secular changes in climate variables and drought index. The temporal variations in droughts and their interrelations with rainfall and temperature trends were assessed using a 50-year moving window with a 10-year time step. The results showed that meteorological drought severity has increased for all the cropping seasons of Nigeria. Temperature was found to be the dominating factor for defining droughts in semi-arid regions in the north while rainfall in the monsoon and tropical savanna climatic zones dominates in the south. Rises in temperature in the range of 0.14–0.42 °C/decade and almost no change in rainfall have caused decreases in SPEI up to −0.25/decade in some regions. The number of grid points with decreasing SPEI was found to vary between 50 out of 323 for millet and 152 for yam growing season. The moderate droughts were found to become more frequent compared to other classes of droughts. Amongst the cropping seasons, the highest increases in drought frequency were observed during corn growing season. The highest decrease in the median value of the return period of moderate, severe and extreme droughts during the two corn growing seasons were observed to be 6.25, 12.86 to 13.20, 23.15 to 24.31 years in 1901–1950 to 6.25, 12.92 to 12.94, 23.51 to 23.64 in 1961–2010. Compared to other drought severities, the return periods of the moderate droughts were found to decrease more. A general decrease in the return periods of droughts indicates more frequent droughts during all cropping seasons of Nigeria. Therefore, it can be concluded that the rising temperature due to global warming would increase drought severity and frequency in all the cropping seasons of Nigeria.

Influence of Internal Variability and Global Warming on Multidecadal Changes in Regional Drought Severity over the Continental United States

AbstractMeteorological droughts in the continental United States (CONUS) are known to oscillate at the multidecadal time scale in response to the sea surface temperatures (SST) variability over the Pacific Ocean and the North Atlantic Ocean. While previous studies have focused on understanding the influence of SST oscillations on drought frequency over the CONUS, this information has not been integrated with global warming for future drought risk assessment at the decadal scale. In this study, we use the support vector machines (SVMs) to handle correlation between input variables for quantifying the influence of internal variability [Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO)] and global warming on the decadal changes in the severity of seasonal droughts over the CONUS during 1901–2015. The regional drivers of drought severity identified using SVMs are used for the assessment of decadal drought risk in the near future. We find internal variability as the dominant driver of decadal changes in drought severity in the southern and central Great Plains and global warming as the dominant driver for the southeastern and southwestern United States. In the southern Plains, the existing pattern of increasing drought severity is likely to persist in the near future if AMO and PDO remain in their positive and negative phases, respectively, while global warming is likely to contribute to increasing drought severity in the Southeast and Southwest. This study suggests an emerging role of global warming in drought risk over the southern states, where near-term climate change adaptation is necessary.

Investigating drought in Apulia region, Italy using SPI and RDI

The Apulia region is highly vulnerable to meteorological and hydrological droughts, due to its low rainfall and higher agricultural water demand. In this study, we investigated the spatial and temporal drought characteristics in the Apulia region based on the Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) for the period 1960–2013. SPI was derived based on precipitation, whereas RDI was derived based on both precipitation and potential evapotranspiration. The overall objective is to identify whether these two selected drought indices are able to characterize drought equally or they differ in space and time. Results indicated that the number of drought events decreases and the average drought duration increases by increasing the time scale of the SPI and RDI. The RDI metrics was able to represent a more severe drought event compared to SPI. There is an increasing drought severity trend in the western part of Apulia and a decreasing drought severity trend in the eastern region. The study also shows that temperature (and so potential evapotranspiration) plays an important role in distinguishing drought characteristics between RDI and SPI.

Impacts of climate variability and change on seasonal drought characteristics of Pakistan

Assessment of the influence of climate variables on drought characteristics is important for adaption to changing pattern of droughts due to climate change. The objective of this study is to assess the changing characteristics of droughts due to climate variability and change during two major cropping seasons (Rabi and Kharif) for the period 1901–2010 over the diverse climate of Pakistan. The gauge-based gridded precipitation and temperature data with a spatial resolution of 0.5° is used for the reconstruction of droughts using standardized precipitation evapotranspiration index (SPEI). The temporal variations in droughts and their relationships with precipitation and temperature are assessed using a 50-year moving window with a 10-year time step. The annual maximum series (AMS) approach is used to estimate the return periods of seasonal droughts and the modified Mann-Kendal trend test is applied to assess the significance of trends in climate variables and drought index. The results showed that drought severity is increasing in the predominantly arid and semi-arid regions for both cropping seasons, while it is decreasing in western disturbance (WD) influenced high winter precipitation region during Rabi season. Temperature is found as the dominating factor for defining droughts in arid and semi-arid regions while the precipitation in WD influenced region. An increase in temperature in the range of 0.001 to 0.025 °C per year and almost no change in precipitation have caused decreases in Rabi SPEI in the range of −0.011 to −0.025 per year in the arid region. On the other hand, increases in precipitation in the range of 1.01–2.0 mm/year have caused increases in Kharif SPEI in WD influenced region in the range of 0.016–0.02 per year. However, rises in temperature in most part of the country has caused an increase in drought frequency in both seasons in the areas where droughts are less frequent. The results indicate that rising temperature due to global warming would increase drought severity and frequency in most part of the predominantly arid country.

Photosynthetic gas-exchange and PSII photochemical acclimation to drought in a native and non-native xerophytic species (Artemisia ordosica and Salix psammophila)

The mechanisms of plant photosynthetic acclimation to drought remains incomplete. We examined the photosynthetic performance through plant photosystem-fluorescence response to a long-lasting, anomalous summer drought (i.e., lasting for 61 days, with soil water content <0.1 m3·m−3) and subsequent post-drought recovery of a native and a non-native desert shrub species (Artemisia ordosica and Salix psammophila, respectively) growing in northwest China. Key indicators to the examination are derived estimates of plant stomatal conductance (gs), transpiration (Tr), water use efficiency (WUE), maximum and actual photochemical efficiency (Fv/Fm and ФPSII), non-photochemical quenching (NPQ), and leaf photosynthesis (PN) from simultaneous, continuous in situ measurements of gas exchange and chlorophyll fluorescence. Chlorophyll fluorescence-associated indicator “Fv/Fm” for both species was down regulated in response to deficits in soil water content (SWC), with differential SWC thresholds of 0.07 and 0.08 m3 m−3 for A. ordosica and S. psammophila, respectively. The results revealed that both species acclimate to summer drought by a stomatal-regulation mechanism of reducing gs and WUE and by a PSII NPQ mechanism of dissipating the excessive light energy, indicative of a water-conservation strategy in the acclimation to drought. In comparison with the non-native species, the native species generally had greater photosynthetic performance under water-deficit conditions demonstrating higher transpiration, net CO2 assimilation, and greater PSII photochemical efficiency. Lower WUE and greater drought resistance and resilience, combined with minor changes in PSII photochemical efficiency are consistent with a well-defined water-conservation response by A. ordosica. The results support the hypothesis that native desert-shrub species can potentially outperform non-native shrub species, due to stronger resistance and faster overall recovery from long-lasting drought. Therefore, with increased drought severity and duration anticipated with future climate change, the native shrub species is suggested to be used in desertification control and ecological restoration for sustainable ecosystem management.

Growth and physiological responses of subalpine forbs to nitrogen and soil moisture: investigating the potential roles of plant functional traits

Anthropogenic inputs of biologically available nitrogen (N) and climate change are simultaneously altering N and soil moisture availability in terrestrial ecosystems. Yet, plant responses to concurrent changes in both N and soil moisture in non-grassland ecosystems remain poorly understood. Our objective was to investigate how rooting depth and N-fixing ability—two functional traits we expected to mediate soil moisture and N limitations—influence forb responses to N and soil moisture availability in the Rocky Mountains USA. We assessed the growth and physiological responses (i.e., chlorophyll fluorescence, transpiration rate, and floral display) of four subalpine forb species to N additions across a naturally-occurring soil moisture gradient during one growing season. Soil moisture had a stronger positive effect on growth in shallow-rooted species and N additions had a stronger positive effect on photosynthetic capacity in species without N-fixing abilities. Transpiration rates were not consistent with soil moisture limitations expected for shallow-rooted species, and soil moisture and N had a neutral or negative influence on maximum floral displays across species. Nitrogen and soil moisture appeared to each limit separate response variables in some cases and we did not observe any N × soil moisture interactions. These findings suggest that shallow-rooted species may be more vulnerable to increased drought severity and that increased N availability may disproportionately benefit species without N-fixing abilities. However, mixed support for our hypotheses suggests that environmental conditions and functional traits not evaluated here likely influence subalpine plant responses to soil moisture and N availability.

Water-induced variation in yield and quality can be explained by altered yield component contributions in field-grown cotton

Novel yield component traits and fiber quality indices have been recently developed by breeders to screen for desirable cotton (Gossypium hirsutum L.) lines, but assessing these components in response to water-induced yield variability has received little attention. We investigated the hypothesis that differential sensitivities of whole-crop and intra-boll yield components to drought will largely explain water-induced yield and fiber quality variation in cotton. To test this hypothesis, two cotton cultivars were grown in the field under five contrasting irrigation regimes during the 2013 and 2014 growing seasons near Camilla, GA. Measurements included predawn leaf water potential (ΨPD) throughout the growing season and extensive yield component and fiber quality assessments at the end of the season. Water-induced yield variability was primarily associated with ΨPD at the flowering and boll development phase of crop growth. Boll density (bolls ha−1) was the dominant driver of drought-induced yield loss, but reduced boll mass and seed number per boll also contributed somewhat to yield loss. By comparison, increased drought severity decreased fiber density but increased individual fiber mass, producing a peak in total fiber weight per seed at a −0.7 MPa ΨPD irrigation threshold and increasing lint percentage in stressed treatments. Thus, the negative impacts of drought on overall boll mass and seed number per boll are partially offset by increased dry matter partitioning toward fiber growth. Fiber length declined with increased drought severity, whereas fiber micronaire increased in the most severely stressed treatments. This indicates that increasing drought severity during flowering and boll development decreases the number of individual fibers per seed and their final length, but their thickness is increased. The end result is a decline in the overall fiber quality index (Q-score) under drought stress.

Positive biodiversity–productivity relationships in forests: climate matters

While it is widely acknowledged that forest biodiversity contributes to climate change mitigation through improved carbon sequestration, conversely how climate affects tree species diversity-forest productivity relationships is still poorly understood. We combined the results of long-term experiments where forest mixtures and corresponding monocultures were compared on the same site to estimate the yield of mixed-species stands at a global scale, and its response to climatic factors. We found positive mixture effects on productivity using a meta-analysis of 126 case studies established at 60 sites spread across five continents. Overall, the productivity of mixed-species forests was 15% greater than the average of their component monocultures, and not statistically lower than the productivity of the best component monoculture. Productivity gains in mixed-species stands were not affected by tree age or stand species composition but significantly increased with local precipitation. The results should guide better use of tree species combinations in managed forests and suggest that increased drought severity under climate change might reduce the atmospheric carbon sequestration capacity of natural forests.

Protective Effects of Nitric Oxide on Photosynthetic Stability and Performance of Silybum marianum under Water Deficit Conditions

Core Ideas Milk thistle is a medicinal plant cultivating for production of silymarin and oil.The results our work showed that with the application of SNP photosynthesis, pigments content, and water status were improved in the drought stress condition and as a result significant increases in secondary metabolites production and grain yield was observed.Overall, this study suggest that application of 100 µM SNP and using Sari ecotype can be recommended for maximizing crop yield under drought stress in semiarid environment. Milk thistle is a medicinal plant cultivated for production of silymarin and oil. Nitric oxide as an active molecule, plays an important role in plant’s reaction to drought stress. In this study, we investigated the role of sodium nitroprusside (SNP) as a nitric oxide donor for tolerance enhancement of drought in two genotypes of milk thistle in a 2‐yr field experiment. With increasing drought severity, photosynthetic rate and stomatal conductance of milk thistle decreased significantly. The exogenous application of SNP significantly compensated for the negative effects of drought on photosynthetic rate by 40%, but also reduced stomatal conductance during 6 d after withholding irrigation. Drought stress significantly decreased pigments content and this affect was compensated by applying SNP in both genotypes. Among yield components, the number of heads per plant showed the highest sensitivity to drought stress followed by seed weight, while all yield components responded significantly to the application of SNP. Withholding irrigation significantly decreased seed yield in both genotypes and years. Averaged over 2 yr, application of 100 µM SNP in Sari ecotype at the stage of stem elongation and anthesis significantly improved seed yield by 38 and 33%, respectively, compared with the non‐application of SNP. However, in the Hungarian cultivar, SNP only led to a significant increase of 29% in seed yield during anthesis stress. Overall, this study suggest that application of SNP at a rate of 100 μM had potential to ameliorate the adverse effect of drought stress on photosynthetic rate and seed yield of milk thistle.

Forest resilience to drought varies across biomes.

Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species-level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree-ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring-width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994-1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi-arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi-arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards.

Exploring Historical and Projection of Drought Periods in Cirebon Regency, Indonesia

Climate hazards that affect drought could have an impact on agricultural production. Cirebon Regency as one of West Java's food supply areahas experienced hydrological drought because ofclimate variability. Hence, there were many rice fieldswhich lack of water sources for irrigation and resulted in crop failure. Accordingly, this study aims to explore the historical and projection of drought periods as well as the severity of droughts in Cirebon Regency, Indonesia. Interpretation of weather and climate data and Standardized Precipitation Index (SPI) were employed for methods of this studyby using rainfall data only. Based on baseline data (1986-2017) from Jatiwangi Meteorological Stationand Global Circulation Model (GCM) projection simulation (2020-2045) under the Representative Concentration Pathways (RCP) 4.5 scenario, the SPI analysis results show that the drought periodsare predicted to shift in the future with increasing drought severity. This study concludes that climate variability that affects future dry rainfall will still happen in uncertain month periods.Therefore, climatic information is needed in the vulnerable area to reduce the potential impactsthat will occur in the future.

Grazing and edaphic properties mediate soil biotic response to altered precipitation patterns in a semiarid prairie

Global circulation models predict shifts in precipitation patterns in arid and semiarid ecosystems worldwide. Independently of changes in total precipitation, rainfall is expected to concentrate in less frequent but larger events, and this redistribution will increase drought severity in biomes naturally controlled by precipitation pulses and water availability. This study focuses on effects of altering rainfall patterns on the soil food web of a semiarid prairie, and on impacts of grazing on soil food web resilience to climate change. We worked in a greenhouse with undisturbed soil monoliths extracted from grazed and ungrazed field plots. We planted all monoliths with Bouteloua gracilis that was the dominant grass at the experimental site, and let the grass establish before applying two different rainfall treatments over a five-month period, equivalent to the duration of the growing season in the area. We simulated the current rainfall pattern in the experimental area and also an altered rainfall pattern consisting of concentrating the total growing season precipitation in half the number of rain events. Rainfall concentration increased the amplitude of the water pulse and lengthened the dry periods between rain events thus worsening soil water stress. We analyzed the experimental monoliths for effects of rainfall pattern and grazing management C and N content, soil organic matter mineralization and soil biota abundance and functional diversity. Based on the experimental data, we simulated soil food web stability and mineralization capacity. We concluded that (a) rainfall concentration causes loss of key soil functional groups and reinforces soil food web stability, (b) organic matter mineralization by the soil food web decreases with rainfall concentration, (c) coarse-textured soils are more responsive than fine-textured soils to modifications of the rainfall regime, (d) soil food web responsiveness to changing rainfall regime is higher in grazed prairies than in prairies excluded from herbivores.