Increased Frequency Of Droughts Research Articles

Climate change impacts on spatial and seasonal meteorological drought characteristics for the island of Ireland

AbstractUnderstanding how climate change is likely to impact on meteorological droughts is key to informing adaptation planning. For Ireland, little research has examined how droughts are likely to change in future. Here we examine changes in the monthly climate water balance, aridity index and changes in magnitude, frequency and duration of droughts using standardized drought indices for the island of Ireland derived from bias‐adjusted CORDEX simulations for the 2080s (2070–2099), forced with a high (RCP8.5) and moderate (RCP4.5) emissions pathway. Findings highlight that increases in potential evapotranspiration, driven by increasing temperature, together with changing seasonal rainfall patterns increase aridity in summer with water deficits extending into spring months, especially in the east and midlands by the end of the century. Increases in drought frequency and magnitude are also evident, with greatest increases for RCP8.5. Critically, increases are considerably greater for the standardized precipitation evapotranspiration index (SPEI) than for the standardized precipitation index (SPI), emphasizing the importance of using metrics that capture potential evapotranspiration in monitoring and assessing future drought risk. Summer and spring show the greatest increase in drought magnitude and frequency, most marked in the east of the island. By contrast, multiseasonal droughts, assessed using 6‐month accumulation periods show more modest changes in magnitude and duration. The resultant impacts of climate change on drought for Ireland would require considerable adaptation given the vulnerabilities exposed by the 2018 drought.

Pre- and post-drought conditions drive resilience of Pinus halepensis across its distribution range

Severe droughts limit tree growth and forest productivity worldwide, a phenomenon which is expected to aggravate over the next decades. However, how drought intensity and climatic conditions before and after drought events modulate tree growth resilience remains unclear, especially when considering the range-wide phenotypic variability of a tree species.We gathered 4632 Aleppo pine (Pinus halepensis Mill.) tree-ring width series from 281 sites located in 11 countries across the Mediterranean basin, representing the entire geographic and bioclimatic range of the species. For each site and year of the period 1950–2020, we quantified tree-growth resilience and its two components, resistance and recovery, to account for the impact of drought and the capacity to recover from it. Relative drought intensity of each year was assessed using SPEI (Standardized Precipitation Evapotranspiration Index), a climatic water deficit index. Generalized additive mixed models were used to explore the non-linear relationships between resilience and its two components and drought intensity, preceding and following years climatic conditions.We found that P. halepensis radial growth was highly dependent on the SPEI from September of the previous year to June of the current year. Trees growing under more arid bioclimates showed higher inter-annual growth variability and were more sensitive to drought, resulting in an increased response magnitude to pre-, during and post-drought conditions. In contrast to our expectations, drought intensity only slightly affected resilience, which was rather negatively affected by favorable preceding conditions and improved by favorable following conditions.Resilience and its components are highly dependent on preceding and following years climatic conditions, which should always be taken into account when studying growth response to drought. With the observed and predicted increase in drought frequency, duration and intensity, favorable conditions following drought episodes may become rare, thus threatening the future acclimation capacity of P. halepensis in its current distribution.

Recent evolution of flowering time across multiple European plant species correlates with changes in aridity

Ongoing global warming and increasing drought frequencies impact plant populations and potentially drive rapid evolutionary adaptations. Historical comparisons, where plants grown from seeds collected in the past are compared to plants grown from freshly collected seeds from populations of the same sites, are a powerful method to investigate recent evolutionary changes across many taxa. We used 21–38 years old seeds of 13 European plant species, stored in seed banks and originating from Mediterranean and temperate regions, together with recently collected seeds from the same sites for a greenhouse experiment to investigate shifts in flowering phenology as a potential result of adaptive evolution to changes in drought intensities over the last decades. We further used single nucleotide polymorphism (SNP) markers to quantify relatedness and levels of genetic variation. We found that, across species, current populations grew faster and advanced their flowering. These shifts were correlated with changes in aridity at the population origins, suggesting that increased drought induced evolution of earlier flowering, whereas decreased drought lead to weak or inverse shifts in flowering phenology. In five out of the 13 species, however, the SNP markers detected strong differences in genetic variation and relatedness between the past and current populations collected, indicating that other evolutionary processes may have contributed to changes in phenotypes. Our results suggest that changes in aridity may have influenced the evolutionary trajectories of many plant species in different regions of Europe, and that flowering phenology may be one of the key traits that is rapidly evolving.

The 2018 west-central European drought projected in a warmer climate: how much drier can it get?

Abstract. Projections of changes in extreme droughts under future climate conditions are associated with large uncertainties, owing to the complex genesis of droughts and large model uncertainty in the atmospheric dynamics. In this study we investigate the impact of global warming on soil moisture drought severity in west-central Europe by employing pseudo global warming (PGW) experiments, which project the 1980–2020 period in a globally warmer world. The future analogues of present-day drought episodes allow for investigation of changes in drought severity conditional on the historic day-to-day evolution of the atmospheric circulation. The 2018 west-central European drought is the most severe drought in the 1980–2020 reference period in this region. Under 1.5, 2 and 3 ∘C global warming, this drought episode experiences strongly enhanced summer temperatures but a fairly modest soil moisture drying response compared to the change in climatology. This is primarily because evaporation is already strongly moisture-constrained during present-day conditions, limiting the increase in evaporation and thus the modulation of the temperature response under PGW. Increasing precipitation in winter, spring and autumn limits or prevents an earlier drought onset and duration. Nevertheless, the drought severity, defined as the cumulative soil moisture deficit volume, increases considerably, with 20 % to 39 % under 2 ∘C warming. The extreme drought frequency in the 1980–2020 period strongly increases under 2 ∘C warming. Several years without noticeable droughts under present-day conditions show very strong drying and warming. This results in an increase in 2003-like drought occurrences, compounding with local summer temperature increases considerably above 2 ∘C. Even without taking into account a (potentially large) dynamical response to climate change, drought risk in west-central Europe is strongly enhanced under global warming. Owing to increases in drought frequency, severity and compounding heat, a reduction in recovery times between drought episodes is expected to occur. Our physical climate storyline provides evidence complementing conventional large-ensemble approaches and is intended to contribute to the formulation of effective adaptation strategies.

Wildfire severity alters soil microbial exoenzyme production and fungal abundances in the southern Appalachian Mountains

Climate change has increased drought frequency and duration that are exacerbated by increased temperatures globally. This effect has, and will continue, to increase fire occurrence across many regions of North America. In the southern Appalachian Mountains, wildfires with high burn severity occurred in 2016 due to increased drought and human activity. To investigate the effects of burn severity on soil physicochemical properties, microbial extracellular enzyme production, and microbial abundances in a temperate region, surface soils (0–15 cm) were collected from two sites (the Great Smoky Mountains National Park in Tennessee and the Nantahala National Forest in North Carolina, USA) spanning lightly, moderately, and severely burned areas, accompanied by adjacent unburned locations that act as controls. The soil samples were collected at three time points between 2017 and 2019 (i.e., 0.5, 1, and 2.5 years post-fire) among burn severity plots. Total hydrolytic enzyme production varied over time, with severe burn plots having significantly lower enzyme production at 2.5 years post-fire. Individual enzymes varied among burn severities and across time post-fire. Light burn plots showed greater carbon-specific (β-glucosidase and β-xylosidase) and phosphorus-specific (acid phosphatase) enzyme activities at 0.5 years post-fire, but this effect was transient. At 2.5 years post-fire, the β-xylosidase and acid phosphatase activities were lower in severe or moderate burn plots relative to the controls. In contrast, the activity of nitrogen-specific enzyme leucyl aminopeptidase was the lowest in severe burn plots at 0.5 years post-fire, but was the lowest in light burn plots at 2.5 years post-fire. The fungi:bacteria ratio declined with burn severity, indicating that fungi are sensitive or less resilient to high burn severity during recovery. These results suggest that wildfires alter trajectories for soil microbial structure and function within a 2.5-year timeframe, which potentially has long-term impacts on biogeochemical cycling.

Future Projection of Drought Risk over Indian Meteorological Subdivisions Using Bias-Corrected CMIP6 Scenarios

This study presents a comprehensive analysis of extreme events, especially drought and wet events, spanning over the past years, evaluating their trends over time. An investigation of future projections under various scenarios such as SSP-126, SS-245, and SSP-585 for the near (2023–2048), mid (2049–2074), and far future (2075–2100) using the bias-corrected Coupled Model Intercomparisons Project 6 (CMIP6) multi-model ensemble method was also performed. The Standard Precipitation Index (SPI), a simple yet incredibly sensitive tool for measuring changes in drought, is utilized in this study, providing a valuable assessment of drought conditions across multiple timescales. The historical analysis shows that there is a significant increase in drought frequency in subdivisions such as East MP, Chhattisgarh, East UP, East Rajasthan, Tamil Nadu, and Rayalaseema over the past decades. Our findings from a meticulous examination of historical rainfall trends spanning from 1951 to 2022 show a noticeable decline in rainfall across various regions such as Uttar Pradesh, Chhattisgarh, Marathwada, and north-eastern states, with a concurrent increase in rainfall over areas such as Gujarat, adjoining regions of West MP and East Rajasthan, and South Interior Karnataka. The future projection portrays an unpredictable pattern of extreme events, including droughts and wet events, with indications that wet frequency is set to increase under extreme SSP scenarios, particularly over time, while highlighting the susceptibility of the northwest and south peninsula regions to a higher incidence of drought events in the near future. Analyzing the causes of the increase in drought frequency is crucial to mitigate its worst impacts, and recent experiences of drought consequences can help in effective planning and decision-making, requiring appropriate mitigation strategies in the vulnerable subdivisions.

Spatial Heterogeneity of Vegetation Resilience Changes to Different Drought Types

AbstractResilience is a fundamental concept for vegetation health. The increasing drought frequency and severity may pose severe threat to vegetation resilience. However, it is still not clear how vegetation resilience is evolving in response to climate change in pivotal biographical zones. Here, we examined the resilience changes in terms of leaf area index (LAI, an indicator of canopy structure) and gross primary productivity (GPP, an indicator of carbon uptake) in responding to the Standardized Precipitation‐Evapotranspiration Index (SPEI) and vapor pressure deficit (VPD) over China's Loess Plateau and Qinling Mountains. Linking remote sensing variables and tree ring width allows the upscaling of plot‐based vegetation growth information. We further explored potential explanatory factors associated with the heterogeneous spatial distributions of resilience changes. Results revealed that the resilience of GPP weakened more than LAI in response to drought, suggesting that compared to LAI, productivity requires more time to recover to the pre‐drought levels. Regionally, the change of vegetation resilience on the Loess Plateau and in high‐altitude areas was highly susceptible to SPEI and VPD, respectively. The observed spatial heterogeneity in resilience changes was mainly attributed by climate zone, water deficit, and their interactions. Our findings provide direct and empirical evidence that the vegetation in the Loess Plateau and Qinling Mountains is gradually losing resilience. The results indicate that sustained ecosystem water deficit and atmospheric dryness will continue to threaten vegetation survival and terrestrial ecosystem service.

Projected changes in droughts and extreme droughts in Great Britain strongly influenced by the choice of drought index

Abstract. Droughts cause enormous ecological, economical and societal damage, and they are already undergoing changes due to anthropogenic climate change. The issue of defining and quantifying droughts has long been a substantial source of uncertainty in understanding observed and projected trends. Atmosphere-based drought indicators, such as the Standardised Precipitation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI), are often used to quantify drought characteristics and their changes, sometimes as the sole metric representing drought. This study presents a detailed systematic analysis of SPI- and SPEI-based drought projections and their differences for Great Britain (GB), derived from the most recent set of regional climate projections for the United Kingdom (UK). We show that the choice of drought indicator has a decisive influence on the resulting projected changes in drought frequency, extent, duration and seasonality using scenarios that are 2 and 4 ∘C above pre-industrial levels. The projected increases in drought frequency and extent are far greater based on the SPEI than based on the SPI. Importantly, compared with droughts of all intensities, isolated extreme droughts are projected to increase far more with respect to frequency and extent and are also expected to show more pronounced changes in the distribution of their event durations. Further, projected intensification of the seasonal cycle is reflected in an increasing occurrence of years with (extremely) dry summers combined with wetter-than-average winters. Increasing summer droughts also form the main contribution to increases in annual droughts, especially using the SPEI. These results show that the choice of atmospheric drought index strongly influences the drought characteristics inferred from climate change projections, with a comparable impact to the uncertainty from the climate model parameters or the warming level; therefore, potential users of these indices should carefully consider the importance of potential evapotranspiration in their intended context. The stark differences between SPI- and SPEI-based projections highlight the need to better understand the interplay between increasing atmospheric evaporative demand, moisture availability and drought impacts under a changing climate. The region-dependent projected changes in drought characteristics by two warming levels have important implications for adaptation efforts in GB, and they further stress the need for rapid mitigation.

Higher local intra- than interspecific variability in water- and carbon-related leaf traits among Neotropical tree species.

Intraspecific variability in leaf water-related traits remains little explored despite its potential importance in the context of increasing drought frequency and severity. Studies comparing intra- and interspecific variability of leaf traits often rely on inappropriate sampling designs that result in non-robust estimates, mainly owing to an excess of the species/individual ratio in community ecology or, on the contrary, to an excess of the individual/species ratio in population ecology. We carried out virtual testing of three strategies to compare intra- and interspecific trait variability. Guided by the results of our simulations, we carried out field sampling. We measured nine traits related to leaf water and carbon acquisition in 100 individuals from ten Neotropical tree species. We also assessed trait variation among leaves within individuals and among measurements within leaves to control for sources of intraspecific trait variability. The most robust sampling, based on the same number of species and individuals per species, revealed higher intraspecific variability than previously recognized, higher for carbon-related traits (47-92 and 4-33 % of relative and absolute variation, respectively) than for water-related traits (47-60 and 14-44 % of relative and absolute variation, respectively), which remained non-negligible. Nevertheless, part of the intraspecific trait variability was explained by variation of leaves within individuals (12-100 % of relative variation) or measurement variations within leaf (0-19 % of relative variation) and not only by individual ontogenetic stages and environmental conditions. We conclude that robust sampling, based on the same number of species and individuals per species, is needed to explore global or local variation in leaf water- and carbon-related traits within and among tree species, because our study revealed higher intraspecific variation than previously recognized.

Drought survival strategies differ between coastal and montane conifers in northern California

AbstractIncreasingly severe and prolonged droughts are contributing to tree stress and forest mortality across western North America. However, in many cases, we currently have poor information concerning how drought responses in forests vary in relation to competition, climate, and site and tree characteristics. We used annual tree ring evidence of 13C discrimination (Δ13C) and growth metrics to assess drought resistance and resilience for six conifer species at the intersection of several bioregions in northern California. Within each species' range in northern California, we collected competition and tree characteristics from 270 focal trees across sites that varied from wetter to drier habitat conditions (54 sites). Across sites, all six conifer species weathered the severe 2013–2015 drought with reasonably high resistance and post‐drought resilience. However, we found important differences in drought responses between coastal and montane species based on annual growth and Δ13C metrics. Broadly, the two coastal species showed consistent declines in drought resistance across successive drought years, whereas the four montane species maintained high drought resistance across drought years. More specifically, we found lower Δ13C and growth during drought years in coastal species, suggesting stomatal closure during drought with the potential for vulnerability to carbon depletion during long‐term drought. Conversely, Δ13C and growth were stable in montane species throughout the drought, which may contribute to hydraulic failure under increased drought frequency and/or severity. We also evaluated environmental factors that affect Δ13C using data from before and during the drought. These physiological models were consistent for the two coastal species, with a positive relationship between annual precipitation and Δ13C and a negative relationship between tree density and Δ13C. Conversely, the four montane models illustrated a greater importance of site conditions on drought responses for these species. Our findings show differential risk for drought stress across diverse conifers during severe drought. This work highlights the importance of site and tree characteristics in determining drought responses across cool, annually humid coastal habitats to seasonally dry montane habitats.

One yearlong analysis: The contribution of dewfall and distillation to rock- and cobble-inhabiting lichens in the Negev

With rain providing only circa 20 rainy days a year, dewfall is regarded as the main water source for crustose lichens inhabiting rocks and cobbles in the Negev. Nevertheless, no attempt was yet done to evaluate the role played by dewfall or distillation (water vapor that originates from the soil and may condense on the cobbles i.e., indirect rain water, IRW) in providing water to lithic crustose lichens. For this end, one yearlong measurements of non-rainfall water (NRW), i.e. vapor, dewfall, and fog that originate from the atmosphere, and IRW were measured by the cloth-plate method (CPM) and on two pairs of rock slabs and cobbles between October 1st, 2021 and September 30th, 2022, along with periodic temperature measurements. A total of 79 days of NRW and 48 days of IRW were recorded by the CPM, but when adding the days during which measurements were not conducted, the total days with NRW and IRW amounted to 92 and 74 days, respectively. Whereas the daily average NRW for the cobbles and rocks was 0.095 and 0.044 mm, respectively, it was respectively 0.117 and 0.069 mm for IRW. Previous work allowed us to calculate the daylight wetness duration for NRW (230.9 and 149.7 h for the cobbles and rocks, respectively) and IRW (203.4 and 158.6 h for the cobbles and rocks, respectively). When considering also direct wetting by rain (additional 33 h), the dry period provided 49.4% and 43.9% of the daytime wetness duration for the cobbles and rock slabs, respectively. NRW may thus contribute an approximately equal amount of water to that of rain, with cobbles benefiting more than rock slabs from both water sources. Climate change which may result in increased drought frequency and nocturnal warming may respectively result in lower IRW and NRW, negatively impacting lithobiont distribution.

Spatio-temporal characteristics of meteorological and agricultural drought indices and their dynamic relationships during the pre-monsoon season in drought-prone region of Bangladesh

The global water crisis has become a rising concern against the background of climate change, which is responsible for increasing drought frequency, a devastating natural hazard that severely affects the agricultural sector of a nation. Due to the geographical position, spatial variation in seasonal precipitation patterns, and groundwater table, the northwestern part of Bangladesh is one of the most drought-prone regions with extensive irrigation practices. In recent decades, the frequency of meteorological drought has significantly increased, but its dynamic relationship with agricultural drought is still unclear. In this research, we aim to study the meteorological and agricultural drought conditions and their dynamic relationships during the pre-monsoon season (March-May) in northwest Bangladesh. For this, we analyzed the 3-month standardized precipitation index (SPI), Palmer drought severity index (PDSI), and 3-month standardized precipitation evapotranspiration index (SPEI) to study the meteorological drought, and the normalized difference vegetation index (NDVI), land surface temperature (LST), vegetation condition index (VCI), temperature condition index (TCI), and vegetation health index (VHI) using MODIS to study the agricultural drought. Results revealed that SPI-3 and SPEI-3 during the pre-monsoon increased, while PDSI decreased. Agricultural drought indices showed a better VHI status in 2021. The Pearson correlation among these indices represented no correlation between meteorological and agricultural drought. This research identified that the relationship between VHI and SPI-3 might not be positive in all cases, especially in extensively irrigated regions. Therefore, it is important to consider hydrological drought indices to improve the understanding and accuracy of drought assessment.

Future dry-wet climatic characteristics and drought trends over arid Central Asia

Understanding the future drought condition is critical to coping with the challenge of climate change. This study evaluated the simulation capability of 30 Global Climate Models (GCMs) provided by the Coupled Model InterComparison Project Phase 6 (CMIP6) in simulating precipitation (P), potential evapotranspiration (PET) and temperature (T) in arid Central Asia (ACA), and estimated the dry-wet climatic characteristics and trends under four SSP-RCPs (Shared Socio-economic Path-Representative Concentration Path scenarios, SSP126, SSP245, SSP370, and SSP585). Results show that the 30 CMIP6 GCMs have robust simulation ability for precipitation, potential evapotranspiration, and temperature (p < 0.01) over arid Central Asia. The delta-corrected multi-model ensemble mean (Delta-MME) outperforms GWR-corrected one (GWR-MME) and single models. In the future, the precipitation, potential evapotranspiration, and temperature will increase at different rates under the four SSP-RCPs. Uzbekistan, Kazakhstan, Kyrgyzstan and Tajikistan are the regions with faster precipitation and temperature rise, and the northern of arid Central Asia are the main area with the rapid growth of potential evapotranspiration. Arid Central Asia will face more severe drought, especially under high emission scenarios. In the near-term the drought will reduce at a certain extent, but the trend of drought will still be prominent in the mid and long term. Overall, drought in arid Central Asia will show an overall characteristic of decreasing drought number but increasing drought frequency, drought duration, and drought intensity. Drought risk is likely to be higher in Xinjiang of China, Turkmenistan and Uzbekistan. The research can provide a scientific basis for the decision-making of water resources planning and management and socio-economic development of arid Central Asia.

Projection of future extreme meteorological droughts using two large multi-member climate model ensembles

Several studies have looked at the evolution of droughts in a changing climate in various locations and have typically found that droughts are expected to become more severe in the future. However, relatively little work has been done on extreme droughts. This study focuses on the evolution of extreme meteorological droughts over near (2036–2065) and far (2071–2100) future time periods. Monthly precipitation from two large multi-member climate model ensembles: the Canadian Earth System Model (CanESM2) 50-member ensemble and the Community Earth System Model (CESM1) 40-member ensemble, was used to calculate the Standard Precipitation Index (SPI) to quantify and explore the evolution of future meteorological droughts. The use of these large ensembles allows for the calculation of the 20- and 100-year droughts return period and offers a unique perspective into those rare events.Both climate models project increases in extreme meteorological drought frequency over many of the world’s regions. The spatial patterns of regions with worsening droughts generally match those of projected change in mean annual precipitation, although the former is more extensive, indicating that changes in internal variability will increase drought frequency even in some regions projected to see increased mean annual precipitation. The projected increase in meteorological drought frequency is more significant for short-term JJA droughts, and for the larger return periods. Large increases in frequency are observed in many regions, all the way up to 20 times for the historical100-year JJA drought indicating a return period shift from 100 to 5 year.Considering the significant predicted increases in temperature, it follows that future changes for both agricultural (soil water deficit) and hydrological droughts (low stream levels), which result from the interaction between precipitation deficit and temperature (as well as other variables), will be even more severe.

Sustainable intensification with irrigation raises farm profit despite climate emergency

Societal Impact StatementDespite comprising a small proportion of global agricultural land use, irrigated agriculture is enormously important to the global agricultural economy. Burgeoning food demand driven by population growth—together with reduced food supply caused by the climate crisis—is polarising the existing tension between water used for agricultural production versus that required for environmental conservation. We show that sustainable intensification via more diverse crop rotations, more efficient water application infrastructure and greater farm area under irrigation is conducive to greater farm business profitability under future climates.Summary Research aimed at improving crop productivity often does not account for the complexity of real farms underpinned by land‐use changes in space and time. Here, we demonstrate how a new framework—WaterCan Profit—can be used to elicit such complexity using an irrigated case study farm with four whole‐farm adaptation scenarios (Baseline, Diversified, Intensified and Simplified) with four types of irrigated infrastructure (Gravity, Pipe & Riser, Pivot and Drip). Without adaptation, the climate crisis detrimentally impacted on farm profitability due to the combination of increased evaporative demand and increased drought frequency. Whole‐farm intensification—via greater irrigated land use, incorporation of rice, cotton and maize and increased nitrogen fertiliser application—was the only adaptation capable of raising farm productivity under future climates. Diversification through incorporation of grain legumes into crop rotations significantly improved profitability under historical climates; however, profitability of this adaptation declined under future climates. Simplified systems reduced economic risk but also had lower long‐term economic returns. We conclude with four key insights: (1) When assessing whole‐farm profit, metrics matter: Diversified systems generally had higher profitability than Intensified systems per unit water, but not per unit land area; (2) gravity‐based irrigation infrastructure required the most water, followed by sprinkler systems, whereas Drip irrigation used the least water; (3) whole‐farm agronomic adaptation through management and crop genotype had greater impact on productivity compared with changes in irrigation infrastructure; and (4) only whole‐farm intensification was able to raise profitability under future climates.

Responses of a semiarid grassland to recurrent drought are linked to community functional composition.

Recurrent droughts are an inevitable consequence of climate change, yet how grasslands respond to such events is unclear. We conducted a 6-year rainfall manipulation experiment in a semiarid grassland that consisted of an initial 2-year drought (2015-2016), followed by a recovery period (2017-2018) and, finally, a second 2-year drought (2019-2020). In each year, we estimated aboveground net primary productivity (ANPP), species richness, community-weighted mean (CWM) plant traits, and several indices of functional diversity. The initial drought led to reduced ANPP, which was primarily driven by limited growth of forbs in the first year and grasses in the second year. Total ANPP completely recovered as the rapid recovery of grass productivity compensated for the slow recovery of forb productivity. The subsequent drought led to a greater reduction in total ANPP than the initial drought due to the greater decline of both grass and forb productivity. The structural equation models revealed that soil moisture influenced ANPP responses directly during the initial drought, and indirectly during the subsequent drought by lowering functional diversity, which resulted in reduced total ANPP. Additionally, ANPP was positively influenced by CWM plant height and leaf nitrogen during the recovery period and recurrent drought, respectively. Overall, the greater impact of the second drought on ecosystem function than the initial drought, as well as the underlying differential mechanism, underscores the need for an understanding of how increased drought frequency may alter semiarid grassland functioning.

Body size dictates physiological and behavioural responses to hypoxia and elevated water temperatures in Murray cod (Maccullochella peelii).

Increasing drought frequency and duration pose a significant threat to fish species in dryland river systems. As ectotherms, fish thermal and hypoxia tolerances directly determine the capacity of species to persist in these environments during low flow periods when water temperatures are high and waterbodies become highly stratified. Chronic thermal stress can compound the impacts of acute hypoxic events on fish resulting in significant fish mortality; however, it is not known if all size classes are equally susceptible, or if the allometric scaling of physiological processes means some size classes are disproportionately affected. We investigated the physiological responses of Murray cod (Maccullochella peelii) over a four-fold body size range (0.2-3000g) to acute changes in water temperature and oxygen concentration following 4 weeks of acclimation to representative spring (20°C) and summer (28°C) water temperatures. We recorded maximum thermal tolerance (CT max), oxygen limited thermal tolerance (PCTmax ), lowest tolerable oxygen level (as the oxygen level at which lose equilibrium; O2,LOE), gill ventilation rates and aerial surface respiration threshold, blood oxygen transport capacity and lactate accumulation. Acclimation to elevated water temperatures improved thermal and hypoxia tolerance metrics across all size classes. However, body size significantly affected thermal and hypoxia responses. Small M. peelii were significantly less hypoxia tolerant than larger individuals, while larger fish were significantly less thermal tolerant than smaller fish. Hypoxia constrained thermal tolerance in M. peelii, with both small and large fish disproportionally compromised relative to mid-sized fish. Our findings indicate that both very small/young (larvae, fry, fingerlings) and very large/older M. peelii in dryland rivers are at significant risk from the combined impacts of a warming and drying climate and water extraction. These data will inform policy decisions that serve to balance competing demands on precious freshwater resources.

Responses of soil seed banks to drought on a global scale

The global increase in drought frequency and intensity in large areas has potentially important effects on soil seed banks (SSBs). However, a systematic evaluation of the impact of drought on SSBs at a global scale has not yet been well understood. We evaluated the effects of drought on SSBs and identified the association key drivers in the current meta-analysis. The overall effects of drought on soil seed density and richness were weak negative and positive, respectively. Drought significantly increased soil seed density by 11.94 % in forest ecosystem, whereas soil seed richness were significantly increased in vascular plants (7.39 %). Linear mixed-effect results showed that soil seed density and richness significantly reduced as increasing drought intensity. In addition, geography (altitude) has significance in controlling the lnRR of soil seed density by altering climate (mean annual precipitation, drought) and soil properties (pH, soil organic carbon, and clay content) in the structural equation model, whereas soil seed richness was controlled by geography (altitude, and latitude) via climate (mean annual precipitation). In summary, the results suggested the size of SSBs response to drought and its relationship with drought intensity in terrestrial ecosystems, it may shed light on ecosystem restoration, succession, and management using SSBs when estimating the future drought.

How do understory trees deal with small canopy openings? The case of release in growth following drought-induced tree mortality

Hotter droughts have become important drivers of change in the structure of forest canopy, and the role of structural loss of overstory trees is gaining attention as an important factor that would trigger changes in understory behavior. The projection of understory individuals, allows us to analyze the potential future of the forests. Through a dendroecological approach, we evaluated growth responses in understory Austrocedrus chilensis trees growing underneath canopy that experienced tree mortality as a consequence of severe droughts occurred in Patagonia Argentina. We analyze the climatic response, tree growth patterns and drought resilience of understory components in three A. chilensis mixed forests. Tree growth was significantly reduced by drought, highlighting the climatic sensitivity of understory individuals; but indirectly, tree growth also showed releases associated with the openings due to canopy mortality. Thus, we found that understory tree growth increased over time. Our results demonstrated that growth performance of understory A. chilensis trees become largely modeled by a combination of the releases associated with changes of the canopy and their ability to withstand adverse weather conditions. We were able to show a clear capacity of understory A. chilensis to cope with drought events by increasing its growth, taking advantage of the disturbance in the upper layers of the canopy, while resisting successive dry years. However, the shadier environment underneath canopy did not buffered drought conditions, and understory A. chilensis trees suffers the effects of droughts. Considering an increase in drought frequency and intensity in climate predictions, with the consequent openings due to overstory tree mortality, understory species behavior will result as a complex interaction among a potential increase in understory vulnerability to more severe droughts, and the opportunity of canopy ascension.

Past experience of drought, drought risk perception, and climate mitigation and adaptation decisions by farmers in New Zealand

ABSTRACT We analyze the perception of farmers in New Zealand with regards to future drought risk as shaped by climatic change and the implications of these perceptions for climate mitigation and adaptation actions that these farmers choose to pursue. The policy options examined include reducing greenhouse gas emissions, strengthening climate resilience, and using water resources more efficiently. Almost all farmers in New Zealand expect an increase in drought frequency and intensity by 2050. We also find that age, gender, and education are correlated with future drought risk perceptions by farmers. Female farmers and farmers with higher education are more concerned about future droughts. Importantly, drought perception of farmers is associated with their climate-related mitigation and adaptation preferences. If farmers perceive an increase in drought risk by 2050, they will focus more on reducing greenhouse gas emissions, increasing the climate resilience of their farms, and trying to improve their use of water resources. Understanding how drought risk perceptions are shaped, and specifically their role in determining mitigation and adaptation decisions, may shed some useful light that can improve policy responses to the risks of droughts and climate change more broadly.