Prolonged Drought Periods Research Articles

Extreme droughts drive tropical semi-arid eutrophic reservoirs towards CO2 sub-saturation

Abstract Aim: This study aimed to evaluate the carbon dioxide (CO2) dynamics in tropical semi-arid reservoirs during a prolonged drought period as well as to test if the trophic state affects the CO2 saturation. Methods This study was performed in four reservoirs located in the tropical semi-arid region in the northeast of Brazil. All samplings were performed between 9 and 12 am using a Van Dorn Bottle. Samples for partial pressure of carbon dioxide (pCO2 ) measurements were taken in the sub-surface as well as samples for total phosphorus and chlorophyll-a. Correlation analysis and linear regression were used to detect relations among the calculated pCO2, water volume and chlorophyll-a. Results The water level reduction due to atypical droughts caused chlorophyll-a concentrations to increase, which in turn, led to CO2 reduction in the water. However, CO2 concentrations were very variable and an alternation between CO2 sub-saturation and super-saturation conditions was observed. This paper showed that water volume and chlorophyll-a were important regulators of CO2 in the water, as well as important carbon balance predictors in the tropical semiarid reservoirs. Conclusions The results of this paper indicate that the eutrophication allied to drastic water level reductions lead to a tendency of autotrophic metabolism of these systems.

Estudo da variabilidade horária da temperatura e umidade do solo na área experimental do projeto Esecaflor-Caxiuanã-LBA

The ESECAFLOR Project artificially induces a prolonged drought period and studies the consequences on the flows of water and carbon dioxide in an Amazon Rainforest, assessing the impacts on the ecosystem in response to this exclusion of water in the soil, a fact similar to the influence of a event of El Niño. ESECAFLOR is located in the National Forest of Caxiuanã, in the municipality of Melgaço. The objective of this work is to study soil temperature and soil moisture variability in the Brazilian Amazon. The data used refer to a period of 3 years. The results indicated greater soil moisture variability in the control plot (A), when compared to the exclusion plot (B), due to the latter having water stress. In plot B, the soil moisture remained practically constant during the studied period. In relation to the soil temperature, the variations were small in both plots, but with higher values in plot B in relation to plot A, since much of the energy that reaches the surface is used as sensible heat for its heating. With the exclusion of water in the forest soil, the life cycle may suffer irreversible changes.

Titanium dioxide nanoparticle exposure reduces algal biomass and alters algal assemblage composition in wastewater effluent-dominated stream mesocosms

A 5-week mesocosm experiment was conducted to investigate the toxicity of titanium dioxide nanoparticles (TiO2NPs) to periphytic algae in an environmentally-realistic scenario. We used outdoor experimental streams to simulate the characteristics of central Texas streams receiving large discharges of wastewater treatment plant effluent during prolonged periods of drought. The streams were continually dosed and maintained at two concentrations. The first represents an environmentally relevant concentration of 0.05 mg L−1 (low concentration). The second treatment of 5 mg L−1 (high concentration) was selected to represent a scenario where TiO2NPs are used for photocatalytic degradation of pharmaceuticals in wastewater. Algal cell density, chlorophyll-a, ash-free dry mass, algal assemblage composition, and Ti accumulation were determined for the periphyton in the riffle sections of each stream. The high concentration treatment of TiO2NPs significantly decreased algal cell density, ash-free dry mass, and chlorophyll-a, and altered algal assemblage composition. Decreased abundance of three typically pollution-sensitive taxa and increased abundance of two genera associated with heavy metal sorption and organic pollution significantly contributed to algal assemblage composition changes in response to TiO2NPs. Benefits of the use of TiO2NPs in wastewater treatment plants will need to be carefully weighed against the demonstrated ability of these NPs to cause large changes in periphyton that would likely propagate significant effects throughout the stream ecosystem, even in the absence of direct toxicity to higher trophic level organisms.

Assessment of Irrigated Agriculture Vulnerability under Climate Change in Southern Italy

Climate change in Mediterranean countries is anticipated to have a strong impact on water availability by exacerbating drought conditions and water scarcity. In this context, efficient irrigation practices are becoming essential for sustaining crop production. This work assesses vulnerability of irrigated agriculture for six irrigation districts and their associated reservoirs in Mediterranean areas across Italy under climate change (1976–2005 versus 2036–2065; RCP 4.5 and 8.5), evaluating changes in irrigation requirements, evaporation from reservoirs, and the availability of freshwater supplies. Irrigation requirements are estimated through a crop water model (SIMETAW_R) integrated into a GIS platform, while inflows to reservoirs are hydrologically modelled as partitioning of precipitation contributing to runoff. Results are aggregated into indicators that show the general decreasing resilience and increasing vulnerability of irrigated agriculture under climate change conditions in each case study. The highest percentage of allowable water losses for irrigation is estimated in the Cuga-Alto Temo system, during the prolonged drought period, to be able to satisfy irrigation demand for less than a year. Climate change may only partially affect irrigation in resilient systems, in which storage capacity and the water level entering into the reservoir are considerably higher than the water distribution volumes.

Exploring adaptations of groundnut cropping to prevailing climate variability and extremes in Limpopo Province, South Africa

Adapting groundnut production to the high climatic variability and extremes prevailing in Limpopo (South Africa) requires season- and site-specific exploitation of genotype x environment x management interactions. Notably, the El Niño-Southern Oscillation phenomenon (ENSO) causes distinctive seasonal rainfall anomalies in the province: Weather records over the period 1955–2010, showed El Niño years with an average of 296 mm growing season rainfall, neutral years with 349 mm and La Niña with 434 mm. We hypothesized that (i) early planting date is crucial for ensuring high productivity of groundnut and (ii) early maturing cultivars can ensure satisfactory production even in El Niño years, both options aiming at escaping prolonged periods of drought. To evaluate our hypotheses, we conducted a three year on-station trial with three planting dates and two cultivars, a one year trial at two sites comparing the two cultivars, tested crop model APSIM against field trial data, and, finally, performed long-term gridded crop model simulation runs for all cultivated land (i.e. 14,739 grid cells at a resolution 0.01°) in Limpopo exploring the effect of the cultivars and planting dates on groundnut yield. Field trials showed that early planting was superior to later plantings, irrespective of the weather year. Even in the very dry El Niño year 2016, yields of more than 1000 kg/ha were achieved with early planting, while planting later was not possible due to severe soil water deficits. Cultivar ICGV 03796 performed slightly better than ICGV 99257 due to faster ground cover closure, but no difference in phenology was observed. After evaluation of the model against the field trial data was found satisfactory, APSIM simulations showed that highest yields were achieved in La Niña years (median 996 kg/ha across all grids) and smallest in El Niño years (654 kg/ha across all grids). However, as in the field trials, we observed on average over all grid cells higher grain yields for early planting for all weather years as effective rainfall captured was higher than for later plantings. Longer growth duration by cultivar ICGV 03796 appeared to be more productive than an earlier maturing cultivar that we added into the simulation analysis as a third cultivar. However, a closer look at the spatial pattern of the simulation analysis revealed that for the generally drier regions of Limpopo, this cultivar with shorter growth duration would indeed be more productive in El Niño years. It showed that such season-specific adaptation would increase yields only by 2.9% for Limpopo province in total, but yield gains of more than 10% could be obtained for 11.3% of the grid cells in El Niño years. Hence, this study demonstrated that management recommendations at provincial scale explicitly need to consider in more detail a site- and season-specific approach.

Incidence of Potato Virus “Y” and Aphid Flights in Potato (Brașov, 2014-2016)

This study aimed to provide updated information on incidence of PVY in seed potatoes (Carrera, Red Lady, Hermes, Riviera, Christian and Roclas varieties) produced in trials at Braşov, where the aphids flight was monitored three years (2014, 2015 and 2016). Another goal of this research was to identify the symptoms of PVY infected material, find positive by ELISA tests in the previous year’s crops. The highest level of PVY and PVYN infection was observed in 2015 for all potato varieties planted in the lot trials. In 2015, the periods of prolonged drought in July and August were responsible for the high incidence of PVY in the potato trials studied, compared with the infection level of the material in the other two years (2014 and 2016). There were some deviations in 2015 concerning to abundance and dynamics of aphid population, potentially PVY vectors. The peak period for aphid attack was the third decade of May - the first decade of June, a very vulnerable period for potato crop. In this year, aphid activity significantly offset the general trend. Experiments conducted in Braşov indicate that many PVY infected plants did not visually express symptoms and could be a good inoculum ready for the time when aphids vectors are typically at their highest levels.

Climate-change potential effects on the hydrological regime of freshwater springs in the Italian Northern Apennines

In large areas of the Italian Northern Apennines, hundreds of low-yield springs provide water for drinking and industrial purposes, with short groundwater flow paths being formed within fractured sedimentary rock units. This hydrogeological setting results in spring water discharges that closely follow meteoric water recharge patterns, leading to low-flow periods concentrated in the summer/early autumn. Therefore, the springs' outflow can be very sensitive to a shortage in water recharge, as it was the case in 2003 and 2017, when a prolonged period of drought caused severe water management issues. This work analyses how a group of such springs responds to climate change. In particular, we first validated a hydrological rainfall-runoff model on the basis of daily discharge data collected between 2013 and 2016. Then, outflows were simulated for baseline (1984–2013) and future periods (2021–2050) using weather data provided by five RCM-GCM combinations. Finally, we performed statistical analyses aiming to examine the intra-annual variability in discharge rates, low-flow indices, flow-duration curves and the length of low-flows. Results show no evidence of change in mean annual discharges, but future climate estimates suggest a slight change to seasonal discharges in the future, with a marked increase of discharge during winter and spring, and a decrease in summer and autumn. Q(95) and 7Q10 low-flow indices (i.e. the daily discharge exceeded 95% of the time and the minimum weekly discharge associated with a 10-year recurrence interval, respectively) are significantly affected by the climate change (−21.8% and −25.0%, respectively), while droughts are expected to be more frequent: the number of years with a consecutive low-flow between 51 and 100days to increase by a third, and between 101 and 150 to duplicate.

Biometric, physiological and anatomical responses of Passiflora spp. to controlled water deficit

The species of passion fruit (Passiflora spp.) are cultivated commercially for food, medicinal and ornamental purposes, especially in tropical regions of the planet subject to intense seasonal drought. This study assessed biometric, physiological, and anatomical responses of P. edulis, P. gibertii, P. cincinnata, P. alata and P. setacea to controlled water deficit. Seedlings with five months of age were subjected to soil water deficit imposed by irrigation suspension until the complete stomatal closure. All assessed species were susceptible to water deficit, with 50–75% reduction in vegetative growth, even though distinct mechanisms of coexistence with this stress were demonstrated by the evaluated genotypes. P. gibertii and P. edulis showed vigorous growth, quick closing and stomatal opening in response to soil water content, the first being more efficient in extracting water from the substrate even with lowest soil water storage. The effects of water deficit were postponed in P. setacea and P. cincinnata, which showed reduced leaf area and stomatal conductance even under irrigation, particularly in P. setacea. P. alata showed large leaf area but lower stomatal conductance and decreased root system by irrigation suspension. P. alata was the species that showed the most anatomical changes resulting from water deficit, such as reductions in the thickness of the leaf blade, adaxial epidermis, palisade parenchyma, and spongy parenchyma. On the other hand, P. setacea was the species that showed greatest ability to survive under water restriction due to tolerate prolonged drought periods with minor anatomical changes when compared to the control.

Regional variation in Holocene climate quantified from pollen in the Great Plains of North America

ABSTRACTThe Great Plains experienced extreme fluctuations in precipitation and temperature throughout the Holocene, but these fluctuations have been difficult to quantify systematically across the region. Pollen has long been used as a proxy for reconstructing climate changes, but its power is limited if a region is devoid of modern pollen samples to facilitate comparison with known climate conditions. Here, we present a set of pollen‐climate transfer functions developed using weighted‐averaging partial least squares to reconstruct mean annual precipitation (MAP), mean temperature of the coldest month (MTcold) and mean temperature of the warmest month (MTwarm). At the foundation of these transfer functions is a new set of 141 modern pollen samples that specifically cover the climate space of the Great Plains. These functions quantify the relationship between pollen assemblages and modern climate in this region (r = 0.928, 0.838 and 0.897 for MAP, MTcold and MTwarm, respectively). We applied these functions to three previously established pollen records taken from lacustrine sites in the region – Fox Lake, MN; Moon Lake, ND; and Kettle Lake, ND – to reconstruct precipitation and temperature at these sites throughout the Holocene. Annual precipitation reconstructed with these transfer functions at Moon Lake and Kettle Lake does not capture a severe, prolonged period of drought during the mid‐Holocene as seen in many other proxy records from these sites and from the region. Reconciliation of these results involves both the autecology of Ambrosia and the inability of any pollen surface samples to capture seasonal and short‐term variability in precipitation. Thus, the transfer functions correctly reconstruct periodic wet summers and a disturbance factor favouring Ambrosia, but miss the effects of reduced winter precipitation and increased frequency of severe drought. The problem revealed here may be more general to biomes with higher frequency disturbance regimes and more weedy species.

Effect of replacing wheat bran with spineless cactus plus urea in sugarcane-based diets for sheep

In times of drought, the availability of feed is reduced, and the use of concentrate ingredients, such as wheat bran, becomes costly for animal production. Thus, the use of spineless cactus emerges as a potential solution to the shortage of feed and water during prolonged drought periods. The objective of this study was to evaluate the effects of replacing wheat bran with spineless cactus plus urea (0%, 25%, 50%, 75%, and 100%) in sugarcane-based diets for sheep on nutrient intake, feeding behaviour, nitrogen balance and microbial protein synthesis. Five male Santa Ines sheep with average initial bodyweight of 34.0 ± 3.6 kg were used in a 5 × 5 Latin square. The maximum intakes of dry matter (DM) (1414 g/day), organic matter (OM) (1281 g/day), crude protein (CP) (204 g/day), neutral detergent fibre corrected for ash and protein (NDFap) (425 g/day), and total digestible nutrients (TDN) (890 g/day) were estimated with replacement levels of 80.2%, 75.3%, 88.6%, 50.5%, and 79.3% respectively. Feeding behaviour was not altered by replacing wheat bran with spineless cactus plus urea. Nitrogen retention increased by 0.10 g/day, while plasmatic urea nitrogen increased by 0.20 mg/day for every 1% level of replacement. The maximum production of microbial nitrogen (15.9 g/day) and microbial protein synthesis (99.4 g/day) were estimated with replacement levels of 45.8 and 45.7%, respectively. It is concluded that up to 80% wheat bran could be replaced with spineless cactus plus urea in sugarcane-based diets for sheep. Keywords: Alternative feed, drought, feeding behaviour, intake, microbial protein

Using geographical information system to generate a drought risk map for rice cultivation: Case study in Babahoyo canton (Ecuador)

Extreme weather events are occurring more frequently, and they affect people, infrastructure and crops. Drought is one of the most important hazards that threaten agriculture and livestock. Such adverse events can result in yield losses over large cropping areas. It is difficult for farmers to cope with prolonged periods of drought. In the absence of government support, rainfed farmers have very limited adaptation capabilities. In this study, we used geographical information system (GIS) tools to generate a drought risk map (DRM) for rice cropping in Babahoyo Canton, Ecuador. This map represents production risks incurred through the onset of a drought event based on the interaction between vulnerability and threat. The vulnerability of rice cropping is determined through a soil land evaluation for rice cropping and the availability of water during the crop cycle rather than approaching the issue based on drought indices, such as the standard precipitation index (SPI). Threat is the likelihood of the occurrence of a drought event that affects rice crops. The DRM was compared to another drought risk map that was generated based only on climatic variables as risk factors (DRcM). We adjusted the DRM and DRcM by adding a layer of operational irrigation projects and by removing drought hazards from areas that are currently irrigated. Based on Normalized difference vegetation index (NDVI) temporal series and drought claims insurance data, the obtained DRM and DRcM were validated. Both maps show a significant relationship between zone classification and NDVI values. However, the DRM adjusted better to insurance data than the DRcM, which does not consider soil variables. The DRM is an effective tool for agricultural risk management decision-making and it serves as an important source of information that could be used for index-based insurance implementation.

Competition for light and water in a coupled soil-plant system

It is generally accepted that resource availability shapes the structure and function of many ecosystems. Within the soil-plant-atmosphere (SPA) system, resource availability fluctuates in space and time whereas access to resources by individuals is further impacted by plant-to-plant competition. Likewise, transport and transformation of resources within an individual plant is governed by numerous interacting biotic and abiotic processes. The work here explores the co-limitations on water losses and carbon uptake within the SPA arising from fluctuating resource availability and competition. In particular, the goal is to unfold the interplay between plant access and competition for water and light, as well as the impact of transport/redistribution processes on leaf-level carbon assimilation and water fluxes within forest stands. A framework is proposed that couples a three-dimensional representation of soil-root exchanges with a one-dimensional description of stem water flow and storage, canopy photosynthesis, and transpiration. The model links soil moisture redistribution, root water uptake, xylem water flow and storage, leaf potential and stomatal conductance as driven by supply and demand for water and carbon. The model is then used to investigate plant drought resilience of overstory-understory trees simultaneously competing for water and light. Simulation results reveal that understory-overstory interactions increase ecosystem resilience to drought (i.e. stand-level carbon assimilation rates and water fluxes can be sustained at lower root-zone soil water potentials). This resilience enhancement originates from reduced transpiration (due to shading) and hydraulic redistribution in soil supporting photosynthesis over prolonged periods of drought. In particular, the presence of different rooting systems generates localized hydraulic redistribution fluxes that sustain understory transpiration through overstory-understory interactions. Such complex SPA dynamics cannot be properly summarized by equivalent ecosystem-scale Resistor-Capacitor (RC) representation. However our results show that, with proper averaging across water flow paths, RC models can provide reasonable estimates of stand-level water and carbon fluxes during inter-storm periods.

Policy entrepreneurs in international river basins\u2014getting climate adaptation on the cross-border water policy agenda

In this study, we look at the role which water policy entrepreneurs play in promoting and stimulating climate adaptation measures in international river basins. In a Dutch-German case study in the Rhine delta, we explore the range of strategies that policy entrepreneurs employ in cross-border water management to effectively anchor and embed climate adaptation in the water policy debate.We focus on climate adaptation on the local and regional scale in the Deltarhine region where increased flooding and prolonged drought periods are expected under the current climate change scenarios with a considerable impact on flood protection, agricultural activities, drinking water and ecosystem development.We analyse the impact of policy entrepreneurs while coping with the challenging cross-border setting and dealing with structural differences in national systems such as the legal and institutional framework. It is shown that whilst the European water guidelines advocate a river basin approach across borders, the guidelines do not (yet) play a catalyst role regarding climate adaptation, and the presence and activities of policy entrepreneurs contribute in putting climate adaptation on the cross-border policy agenda.Finally, marked differences in the presence of entrepreneurs in Germany and the Netherlands are observed for which two important complementary explanations are offered relating to contextual elements of power asymmetry and dependency as well as different policy styles and organisational cultures in both countries.

Identifying and Separating Pandora Moth Outbreaks and Climate from A 1500-Year Ponderosa Pine Chronology from Central Oregon

Abstract We reconstruct pandora moth (Coloradia pandora Blake) outbreaks and climate from a 1572-year (435–2006 CE) ponderosa pine (Pinus ponderosa Dougl. ex Laws.) chronology from a lava flow in central Oregon. We took samples from 128 living trees and remnant logs and crossdated the samples using skeleton plots and COFECHA for quality control. After cutting out and removing those time periods from the chronology during which insects become the main limiting factor to growth, we examine the response of tree rings to climate. Evidence of species longevity (up to 877 years), presence of periodic pandora moth defoliations (13 total), and a significant relationship with the Palmer Drought Severity Index were observed (R2 = 0.34, p < 0.001). Suppressions related to pandora moth outbreaks were recorded back to 618 CE, with a mean return interval of 104 years. Previous-fall to current-spring PDSI was reconstructed over 1376 years (630–2006 CE), where the most prolonged drought periods were 1136–1166 CE and the ...

A review of the massive Chilean palm Jubaea chilensis

Diversa información sobre la palma chilena Jubaea chilensis, una especie endémica de los ecosistemas mediterráneos chilenos, ha sido generada a lo largo de los dos últimos siglos. El objetivo de esta revisión es reunir en un documento toda la información a la fecha sobre esta especie. Variadas fuentes de información fueron consideradas, desde donde la información reunida fue sistematizada y analizada para ser presentada en cinco temas generales. J. chilensis pertenece a la familia Arecaceae, y puede alcanzar 33 m de altura y dos metros de diámetro, convirtiéndola en una de las más masivas del mundo. Es la palmera más austral de América, y debido a su masividad, puede resistir periodos prolongados de sequía y bajas temperaturas. Es por esto que esta especie es utilizada como ornamental en muchos países. Su población original ha disminuido drásticamente en los últimos siglos debido al cambio de uso de suelo y las cosechas. A pesar de que ahora es una especie protegida, la palma chilena presenta un estado de conservación vulnerable. Sus principales amenazas, como la cosecha indiscriminada de sus frutos y la disminución de la cobertura vegetal, han permitido que las poblaciones de palmas envejezcan sin una regeneración apropiada. Más investigación al nivel de especie es altamente recomendada. Tres áreas temáticas deberían ser el foco para profundizar el conocimiento sobre la especie: su biología, específicamente en términos de ecofisiología y reproducción; determinar sus requerimientos ambientales; y, como resultado de la aplicación del conocimiento de las primeras dos temáticas, la reconstrucción de sus poblaciones naturales.

The hydrogeological and paleoclimatic factors in the Bronze Age Motillas Culture of La Mancha (Spain): the first hydraulic culture in Europe

Recent studies indicate that the motillas (Chalcolithic and Bronze Age settlements in La Mancha, Spain) could have constituted the most ancient groundwater collection system at regional scale in Europe. This paper presents the first hydrogeoarchaeological study at the regional level in La Mancha. The research includes borehole drilling and hydrogeological analysis of the territory on which the motillas are settled. The resulting data confirm a relationship between the geological substrate and the spatial distribution of the motillas, sited where groundwater was accessible by means of prehistoric technology. The motillas were built during the climatic event known as 4.2 ka cal BP, in a time of environmental stress after a period of severe and prolonged drought. In these environmental conditions, the construction of these wells was a successful solution that lived on for nearly a millennium and played a major part in the processes of change towards a more complex, hierarchical society.

New Technologies in Agriculture [Guest Editorial

By 2050, the world population is projected to increase by 35% to approximately 9.7 billion, and crop production needs to double to feed that population according to a United Nations report. Historically, to meet such challenges, the solution has been to clear more land and grow more crops, which increases the constraints on available resources and negatively impacts our fragile planet. This solution may not be sustainable, given the fact that our planet is facing changes in climate patterns with destructive weather and prolonged periods of drought. Therefore, alternative solutions must be found to balance food security, world stability, and sustainability for future generations.

Intensifying postfire weather and biological invasion drive species loss in a Mediterranean-type biodiversity hotspot

Prolonged periods of extreme heat or drought in the first year after fire affect the resilience and diversity of fire-dependent ecosystems by inhibiting seed germination or increasing mortality of seedlings and resprouting individuals. This interaction between weather and fire is of growing concern as climate changes, particularly in systems subject to stand-replacing crown fires, such as most Mediterranean-type ecosystems. We examined the longest running set of permanent vegetation plots in the Fynbos of South Africa (44 y), finding a significant decline in the diversity of plots driven by increasingly severe postfire summer weather events (number of consecutive days with high temperatures and no rain) and legacy effects of historical woody alien plant densities 30 y after clearing. Species that resprout after fire and/or have graminoid or herb growth forms were particularly affected by postfire weather, whereas all species were sensitive to invasive plants. Observed differences in the response of functional types to extreme postfire weather could drive major shifts in ecosystem structure and function such as altered fire behavior, hydrology, and carbon storage. An estimated 0.5 °C increase in maximum temperature tolerance of the species sets unique to each survey further suggests selection for species adapted to hotter conditions. Taken together, our results show climate change impacts on biodiversity in the hyperdiverse Cape Floristic Region and demonstrate an important interaction between extreme weather and disturbance by fire that may make flammable ecosystems particularly sensitive to climate change.

137 - A Proposal of Multi-Dimensional Evaluation of Elderly Patients Affected by MDS: The “No-Chain” Algorithm

Understanding the long-term natural flow regime of rivers enables resource managers to more accurately model water level variability. Models for managing water resources are important in Florida where population increase is escalating demand on water resources and infrastructure. The Suwannee River is the second largest river system in Florida and the least impacted by anthropogenic disturbance. We used new and existing tree-ring chronologies from multiple species to reconstruct mean March–October discharge for the Suwannee River during the period 1550–2005 CE and place the short period of instrumental flows (since 1927 CE) into historical context. We used a nested principal components regression method to maximize the use of chronologies with varying time coverage in the network. Modeled streamflow estimates indicated that instrumental period flow conditions do not adequately capture the full range of Suwannee River flow variability beyond the observational period. Although extreme dry and wet events occurred in the gage record, pluvials and droughts that eclipse the intensity and duration of instrumental events occurred during the 16–19th centuries. The most prolonged and severe dry conditions during the past 450 years occurred during the 1560s CE. In this prolonged drought period mean flow was estimated at 17% of the mean instrumental period flow. Significant peaks in spectral density at 2–7, 10, 45, and 85-year periodicities indicated the important influence of coupled oceanic-atmospheric processes on Suwannee River streamflow over the past four centuries, though the strength of these periodicities varied over time. Future water planning based on current flow expectations could prove devastating to natural and human systems if a prolonged and severe drought mirroring the 16th and 18th century events occurred. Future work in the region will focus on updating existing tree-ring chronologies and developing new collections from moisture-sensitive sites to improve understandings of past hydroclimate in the region.

The twenty‐first century Colorado River hot drought and implications for the future

AbstractBetween 2000 and 2014, annual Colorado River flows averaged 19% below the 1906–1999 average, the worst 15‐year drought on record. At least one‐sixth to one‐half (average at one‐third) of this loss is due to unprecedented temperatures (0.9°C above the 1906–1999 average), confirming model‐based analysis that continued warming will likely further reduce flows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend toward greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a significant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River flow sensitivity to temperature combined with a large number of recent climate model‐based temperature projections indicate that continued business‐as‐usual warming will drive temperature‐induced declines in river flow, conservatively −20% by midcentury and −35% by end‐century, with support for losses exceeding −30% at midcentury and −55% at end‐century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River flows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur.