Drought Scenarios Research Articles

Diverse responses of vegetation production to interannual summer drought in North America

Droughts are projected to occur more frequently with future climate change of rising temperature and low precipitation. However, its impact on regional and global vegetation production is not well understood, which in turn contributes to uncertainties to model carbon sequestration under drought scenarios. Using long-term continuous eddy covariance measurements (168 site-year), we present an analysis of the influences of interannual summer drought on vegetation production across 29 sites representing diverse ecoregions and plant functional types in North America. Results showed that interannual summer drought, which was evaluated by the increase in summer temperature or decrease in soil moisture, would cause reductions of both summer gross primary production (GPP) and net ecosystem production (NEP) in non-forest sites (e.g., grasslands and crops). On the contrary, forest ecosystems presented a very different pattern. For evergreen forests, lower summer soil moisture decreased both GPP and NEP; however, higher summer temperature only reduced NEP with no apparent impacts on GPP. Furthermore, summer drought did not show evident impacts on either summer GPP or NEP in deciduous forests, suggesting a better potential of deciduous forests in resisting summer drought and accumulating carbon from atmosphere. These observations imply diverse responses of vegetation production to interannual summer drought and such features would be useful to improve the strengths and weaknesses of ecosystem models to better comprehend the impacts of summer drought with future climate change.

Enhancing floral diversity to increase the robustness of grassland beetle assemblages to environmental change

AbstractIntensive grassland management has produced floristically species poor swards supporting a limited invertebrate fauna. Low cost seed mixtures can be used to increase floristic diversity and so diversify the food resource of phytophagous invertebrate. We quantify trophic links between plants and phytophagous beetles in grasslands established using three seed mixtures. Using food webs, we model secondary extinctions from the beetle communities caused by the loss of host‐plants. Plant species were eliminated according to three scenarios: (1) drought intolerant first; (2) low nutrient status first; (3) stress tolerant first. Diverse seed mixtures containing grasses, legumes, and nonlegume forbs, were more robust to secondary beetle extinctions. The highest diversity seed mixture increased robustness under scenarios of extreme drought in three out of four tested management regimes. Simple and low cost seed mixtures have the potential to promote landscape scale robustness to future environmental change for native invertebrates.

Estimation of flushing time in a monsoonal estuary using observational and numerical approaches

Estimation of flushing time (T F) in an estuary is important for water quality analysis, and it is one of the major transport time scales used in estuaries to quantify the hydrodynamic processes and for water resources management strategies. Thus, the main objective of the present study was to estimate the T F in the Mandovi estuary (a monsoonal estuary) on the west coast of India. In the study, field observations of salinity (FOS) and a numerical model are used to describe the T F during the south-west monsoon (heavy river discharge), post-monsoon (moderate river discharge) and pre-monsoon (negligible river discharge). T F was calculated for 12 (months) river discharge scenarios (the calculation was done under monthly mean flow conditions). Among the 12 scenarios, four scenarios were within an extremely low flow range: 0.8–2.2 m3s−1; four were in a moderate flow range: 4.3–67 m3s−1; and the remaining four were in a high flow range: 119.0–506.6 m3s−1. The T F calculated from FOS and numerical model showed good matches during the periods of heavy river discharge and moderate river discharge. The results from FOS (numerical model) showed that the T F was 1.12 (1.11) days for a river flow of 506.6 m3s−1 (during the south-west monsoon), and the T F reached 251.28 (592.38) days under extreme low flow of 0.8 m3s−1 (during the pre-monsoon). Regression equations fitted by power and exponential functions were derived from FOS and numerical model simulations to correlate T F with monthly mean river discharges. The power regression equation derived from FOS (numerical model) showed good statistical fit with data (r = −0.997 (−1.0)) for any given river discharge compared to the exponential regression equation (r = −0.81 (−0.80)). Hence, the power regression equation can be used for the rapid evaluation of the impact of drought (during the pre-monsoon) and flood (during the SW monsoon) scenarios in the estuary.

추계학적 모의유량을 이용한 한강수계 용수공급시스템의 장기지속가뭄 영향 평가

The Uncertainty of drought events can be regarded as supernatural phenomena so that the uncertainty of water supply system will be also uncontrollable. Decision making for water supply system operation must be dealt with in consideration of hydrologic uncertainty conditions. When ultimate small quantity of precipitation or streamflow lasts, water supply system might be impacted as well as stream pollution, aqua- ecosystem degradation, reservoir dry-up and river aesthetic waste etc. In case of being incapable of supplying water owing to continuation of severe drought, it can make the damage very serious beyond our prediction. This study analyzes comprehensively sustained drought impacts on the Han River Basin Water Supply System. Drought scenarios consisted of several sustained times and return periods for 5 sub-watersheds are generated using a stochastic hydrologic time series model. The developed drought scenarios are applied to assess water supply performance at the Paldang Dam. The results show that multi-year drought events reflecting spatial hydrologic diversity need to be examined in order to recognize variation of the unexpected drought impacts.

Any trait or trait-related allele can confer drought tolerance: just design the right drought scenario

Most traits associated with drought tolerance have a dual effect, positive in very severe scenarios and negative in milder scenarios, or the opposite trend. Their effects also depend on other climatic conditions such as evaporative demand or light, and on management practices. This is the case for processes associated with cell protection and with avoidance, but also for the maintenance of growth or photosynthesis, high water use efficiency, large root systems or reduced abortion rate under water deficit. Therefore, spectacular results obtained in one drought scenario may have a limited interest for improving food security in other geographical areas with water scarcity. The most relevant questions on drought tolerance are probably, 'Does a given allele confer a positive effect on yield in an appreciable proportion of years/scenarios in a given area or target population of environment (TPE)?'; 'In a given site or TPE, what is the trade-off between risk avoidance and maintained performance?'; and 'Will a given allele or trait have an increasingly positive effect with climate change?' Considerable progress has already occurred in drought tolerance. Nevertheless, explicitly associating traits for tolerance to drought scenarios may have profound consequences on the genetic strategies, with a necessary involvement of modelling.

A Hydroclimatological Assessment of Regional Drought Vulnerability: A Case Study of Indiana Droughts

Abstract Characterizing and developing drought climatology continues to be a challenging problem. As decision makers seek guidance on water management strategies, there is a need for assessing the performance of drought indices. This requires the adaptation of appropriate drought indices that aid in monitoring droughts and hydrological vulnerability on a regional scale. This study aims to assist the process of developing a statewide water shortage and assessment plan (WSP) for the state of Indiana by conducting a focused hydroclimatological assessment of drought variability. Drought climatology was assessed using in situ observations and regional reanalysis data. A summary of precipitation and evaporation trends, estimated drought variability, worst-case drought scenarios, drought return period, and frequency and duration was undertaken, using multiple drought indices and streamflow analysis. Results indicated a regional and local variability in drought susceptibility. The worst-case (200-yr return period) prediction showed that Indiana has a 0.5% probability of receiving 45% of normal precipitation over a 12-month drought in any year. Consistent with other studies, the standardized precipitation index (SPI) was found to be appropriate for detecting short-term drought conditions over Indiana. This recommendation has now been incorporated in the 2009 Indiana water shortage plan. This study also highlights the difficulties in identifying past droughts from available climatic data, and the authors’ results suggest a persistent, high degree of uncertainty in making drought predictions using future climatic projections.

A reply to ‘Multiyear versus single-year drought: a comment on Peck and Adams’

We appreciate Tihomir Ancev’s interest in our research on the economic consequences of multiyear droughts (Peck and Adams 2010). Ancev raises two concerns about our paper in their comment. First, he is concerned that our main conclusion (i.e. drought in one year can influence the effects of drought in subsequent years) may be an artefact of our representation of crop interdependencies as ‘agronomic rules.’ He asks, specifically, whether our conclusion would change if we allowed the model to make trade-offs between drought management and pest and disease management. Ancev’s second concern is that our conclusion does not hold for all drought scenarios we analysed. Because our conclusion does not hold universally (across all states of nature in the analysis), Ancev questions its validity. He closes by recommending an alternative approach that would compare the effects of single versus multiyear drought events. Ancev is correct that agricultural producers facing drought are not rigidly bound by agronomic rules, but instead face trade-offs between crops that help manage scarce water resources and those that help manage pests and diseases. Producers may violate agronomic rules if they are more concerned about mitigating the financial impact of drought in the current year than the financial impact of increased pests and diseases in future years. Continuous production functions would capture the yield effects of alternative crop sequences more precisely and allow marginal trade-offs between drought and pest/disease management. Unfortunately, we found no such production functions in the literature for our study area’s major crops (wheat, corn, sugar beets and onions). El-Nazer and McCarl (1986) estimated production functions for wheat and corn in the Pacific Northwest, but their study did not include beets or onions, so their production functions do not capture the yield effects of sugar beets or onions on wheat and corn, or vice versa. Nor were adequate production data available from the study area to estimate functions that capture crop interdependencies.

Genome-wide responses to drought in forest trees

Drought is a significant threat to forest health and the establishment of productive tree plantations. There is therefore great interest in understanding the mechanisms underpinning drought responses in forest trees. This review considers the means by which plants in general, and forest trees specifically, both detect and respond to water limitation. The review focuses on molecular-level responses to a drought stimulus, with an emphasis on responses that involve genome-wide reconfigurations in transcript abundance and protein complement in forest trees. A historical view of the molecular analysis of such responses shows a remarkable transition from understanding the impact of drought on individual genes to a more comprehensive picture of the suites of genes and proteins that constitute a drought response. Attention is paid to how this understanding might further the aims of preserving forest health and improve plantation productivity. The review suggests that genome-wide analysis of forest tree drought responses can be leveraged to provide new tools for conservation of adaptive variation and targets for selective breeding or directed modification of forest tree genotypes that can better contend with future drought scenarios.

Many-objective de Novo water supply portfolio planning under deep uncertainty

This paper proposes and demonstrates a new interactive framework for sensitivity-informed de Novo planning to confront the deep uncertainty within water management problems. The framework couples global sensitivity analysis using Sobol’ variance decomposition with multiobjective evolutionary algorithms (MOEAs) to generate planning alternatives and test their robustness to new modeling assumptions and scenarios. We explore these issues within the context of a risk-based water supply management problem, where a city seeks the most efficient use of a water market. The case study examines a single city’s water supply in the Lower Rio Grande Valley (LRGV) in Texas, using a suite of 6-objective problem formulations that have increasing decision complexity for both a 10-year planning horizon and an extreme single-year drought scenario. The de Novo planning framework demonstrated illustrates how to adaptively improve the value and robustness of our problem formulations by evolving our definition of optimality while discovering key tradeoffs.

Combined effects of soil moisture and carbaryl to earthworms and plants: Simulation of flood and drought scenarios

Studying tolerance limits in organisms exposed to climatic variations is key to understanding effects on behaviour and physiology. The presence of pollutants may influence these tolerance limits, by altering the toxicity or bioavailability of the chemical. In this work, the plant species Brassica rapa and Triticum aestivum and the earthworm Eisenia andrei were exposed to different levels of soil moisture and carbaryl, as natural and chemical stressors, respectively. Both stress factors were tested individually, as well as in combination. Acute and chronic tests were performed and results were discussed in order to evaluate the responses of organisms to the combination of stressors. When possible, data was fitted to widely employed models for describing chemical mixture responses. Synergistic interactions were observed in earthworms exposed to carbaryl and drought conditions, while antagonistic interactions were more representative for plants, especially in relation to biomass loss under flood-simulation conditions.

Natural and drought scenarios in an east central Amazon forest: Fidelity of the Community Land Model 3.5 with three biogeochemical models

[1] Recent development of general circulation models involves biogeochemical cycles: flows of carbon and other chemical species that circulate through the Earth system. Such models are valuable tools for future projections of climate, but still bear large uncertainties in the model simulations. One of the regions with especially high uncertainty is the Amazon forest where large-scale dieback associated with the changing climate is predicted by several models. In order to better understand the capability and weakness of global-scale land-biogeochemical models in simulating a tropical ecosystem under the present day as well as significantly drier climates, we analyzed the off-line simulations for an east central Amazon forest by the Community Land Model version 3.5 of the National Center for Atmospheric Research and its three independent biogeochemical submodels (CASA', CN, and DGVM). Intense field measurements carried out under Large Scale Biosphere-Atmosphere Experiment in Amazonia, including forest response to drought from a throughfall exclusion experiment, are utilized to evaluate the whole spectrum of biogeophysical and biogeochemical aspects of the models. Our analysis shows reasonable correspondence in momentum and energy turbulent fluxes, but it highlights three processes that are not in agreement with observations: (1) inconsistent seasonality in carbon fluxes, (2) biased biomass size and allocation, and (3) overestimation of vegetation stress to short-term drought but underestimation of biomass loss from long-term drought. Without resolving these issues the modeled feedbacks from the biosphere in future climate projections would be questionable. We suggest possible directions for model improvements and also emphasize the necessity of more studies using a variety of in situ data for both driving and evaluating land-biogeochemical models.

Development and application of a simulation model for changes in land-use patterns under drought scenarios

In arid and semiarid areas of northern China, one of the most vulnerable regional environments, water resources are a key constraint on socioeconomic development. We constructed a simulation model for land-use patterns under a drought transition (i.e., the increased frequency and duration of drought since the late 1970s in the Yongding River Basin study area) to account for the complexity of both the driving factors behind land-use change and the micro-level changes in land-use patterns. This model was a combination of the “top-down” system dynamics model, the “bottom-up” cellular automaton model, and the artificial neural network model. In this model, we considered the socioeconomic development and water resource restrictions, as well as the balance between the land-use requirements and the land supply. We then verified the model through a case study. The results demonstrated the value of constructing a simulation model driven by water resource constraints under the influence of drought. The spatial distribution of land uses in future scenarios will help support decision-making for sustainable regional development.

Modeling water ages and thermal structure of Lake Mead under changing water levels

Water age and thermal structure of Lake Mead were modeled using the 3-dimensional hydrodynamic Environmental Fluid Dynamics Code (EFDC). The model was calibrated using observed data from 2005 and then applied to simulate 2 scenarios: high-stage with an initial water level of 370.0 m and low-stage with a projected initial water level of 320.0 m. The high-stage simulation described predrought lake hydrodynamics, while the low-stage simulation projected how lake circulation could respond under significant lake drawdown, should drought conditions persist. The results indicate that water level drawdown plays an important role in thermal stratification and water movement of Lake Mead during receding water levels. The impact of the dropping water level on lake thermal stratification is more significant in shallow regions such as Las Vegas Bay. Depth-averaged (the mean value of 30 vertical layers) water temperature in the low-stage was estimated to increase by 4–7 C and 2–4 C for shallow (<20 m) and deep (>70 m) regions, respectively. Further, depth-averaged water age decreased about 70–90 d for shallow regions and 90–120 d for deep regions under the simulated drought scenario. Such changes in temperature and water age due to continuous drought will have a strong influence on the hydrodynamic processes of Lake Mead. This study provides a numerical tool to support adaptive management of regional water resources by lake managers.

Contrasting physiological responsiveness of establishing trees and a C4 grass to rainfall events, intensified summer drought, and warming in oak savanna

AbstractClimate warming and drought may alter tree establishment in savannas through differential responses of tree seedlings and grass to intermittent rainfall events. We investigated leaf gas exchange responses of dominant post oak savanna tree (Quercus stellata and Juniperus virginiana) and grass (Schizachyrium scoparium, C4 grass) species to summer rainfall events under an ambient and intensified summer drought scenario in factorial combination with warming (ambient, +1.5 °C) in both monoculture and tree‐grass mixtures. The three species differed in drought resistance and response of leaf gas exchange to rainfall events throughout the summer. S. scoparium experienced the greatest decrease in Aarea (−56% and −66% under normal and intensified drought, respectively) over the summer, followed by Q. stellata (−44%, −64%), while J. virginiana showed increased Aarea under normal drought (+13%) and a small decrease in Aarea when exposed to intensified summer drought (−10%). Following individual rainfall events, mean increases in Aarea were 90% for S. scoparium, 26% for J. virginiana and 22% for Q. stellata. The responsiveness of Aarea of S. scoparium to rainfall events initially increased with the onset of drought, but decreased dramatically as summer drought progressed. For Q. stellata, Aarea recovery decreased as drought progressed and with warming. In contrast, J. virginiana showed minimal fluctuations in Aarea following rainfall events, in spite of declining water potential, and warming enhanced recovery. J. virginiana will likely gain an advantage over Q. stellata during establishment under future climatic scenarios. Additionally, the competitive advantage of C4 grasses may be reduced relative to trees, because grasses will likely exist below a critical water stress threshold more often in a warmer, drier climate. Recognition of unique species responses to critical global change drivers in the presence of competition will improve predictions of grass–tree interactions and tree establishment in savannas in response to climate change.

Simulation and Multi-Objective Management of Coastal Aquifers in Semi-Arid Regions

Groundwater is the main water resource in many semi-arid coastal regions and water demand, especially in summer months, can be very high. Groundwater withdrawal for meeting this demand often causes seawater intrusion and degradation of water quality of coastal aquifers. In order to satisfy demand, a combined management plan is proposed and is under consideration for the island of Santorini. The plan involves: (1) desalinization (if needed) of pumped water to a potable level using reverse osmosis and (2) injection into the aquifer of biologically-treated waste water. The management plan is formulated in a multi-objective, optimization framework, where simultaneous minimization of economic and environmental costs is desired, subject to a constraint so that cleaned water satisfies demand. The decision variables concern the well locations and the corresponding pumping and recharging rates. The problem is solved using a computationally efficient, multi-objective, genetic algorithm (NSGAII). The constrained multi-objective, optimization problem is transformed to an unconstrained one using a penalty function proportional to constraint violation. This extends the definition of the objective function outside the domain of feasibility. The impact of prolonged droughts on coastal aquifers is investigated by assuming various scenarios of reduced groundwater recharge. Water flow and quality in the coastal aquifer is simulated using a three-dimensional, variable density, finite difference model (SEAWAT). The method is initially applied to a test aquifer and the trade-off curves (Pareto fronts) are determinedl for each drought scenario. The trade-off curves indicate an increase on the economic and environmental cost as groundwater recharge reduces due to climate change.

Scenario-based assessment and management of water resources in mid-Himalayan micro-watersheds with limited data availability

A conceptual hydrological water balance model has been developed and employed to assess the water availability in a mid-Himalayan watershed and analyse the dynamics of water supply and its utilization under different scenarios arising out of present and future developments. The model was calibrated and validated using daily runoff and rainfall data at different locations in the watershed. The water availability in streams and springs to meet the human, animal and crop requirements was assessed, and was found to vary in different quarters of the year with inequalities existing in different parts of the watershed. The model was successfully applied to analyse the impact of land-use changes and weather aberrations on water availability in the present and future scenarios. The drought scenarios are more critical in causing water scarcity in a given location, compared to the impact of land-use changes. The findings can be applied for assessing, planning and allocation of water resources among different sectors of water use in hilly areas and to make informed decisions during critical periods of water scarcity.

Managing population and drought risks using many‐objective water portfolio planning under uncertainty

This study contributes a many‐objective analysis of the tradeoffs associated with using the portfolio planning approach for managing the urban water supply risks posed by growing population demands and droughts. The analysis focuses on four supply portfolio strategies: (1) portfolios with permanent rights to reservoir inflows, (2) adaptive options contracts added to the permanent rights, (3) rights, options, and leases, and (4) rights, options, and leases subject to a critical reliability constraint used to represent a maximally risk averse case. The portfolio planning strategies were evaluated using a 10 year Monte Carlo simulation of a city in the Lower Rio Grande Valley (LRGV) within Texas. Our solution sets provide the tradeoff surfaces between portfolios' expected values for cost, cost variability, reliability, surplus water, frequency of using leases, and dropped (or unused) transfers of water. Using an additional severe drought scenario, this work shows that leases and options can reduce the potential for critical supply failures when urban supply systems must contend with unexpected and severe extremes in both demand and water scarcity. In summary, this paper contributes a framework that couples interactive visualization and many‐objective optimization to innovate urban water portfolio planning under uncertainty. The many‐objective analysis of the LRGV case study shows that effective water portfolio planning can simultaneously improve the costs, efficiency, and reliability of urban water supply while ensuring adaptability and resiliency to future changes.

Land use practices and ectomycorrhizal fungal communities from oak woodlands dominated by Quercus suber L. considering drought scenarios

Oak woodlands in the Mediterranean basin have been traditionally converted into agro-silvo-pastoral systems and exemplified sustainable land use in Europe. In Portugal, in line with the trend of other European countries, profound changes in management options during the twentieth century have led to landscape simplification. Landscapes are dynamic and the knowledge of future management planning combining biological conservation and soil productivity is needed, especially under the actual scenarios of drought and increasing evidence of heavy oak mortality. We examined the ectomycorrhizal (ECM) fungal community associated with cork oak in managed oak woodlands (called montado) under different land use practices, during summer. ECM fungal richness and abundance were assessed in 15 stands established in nine montados located in the Alentejo region (southern Portugal), using morphotyping and ITS rDNA analysis. Parameters related to the montados landscape characteristics, land use history over the last 25 years, climatic and edaphic conditions were taken into account. Fifty-five ECM fungal taxa corresponding to the most abundant fungal symbionts were distinguished on cork oak roots. Cenococcum geophilum and the families Russulaceae and Thelephoraceae explained 56% of the whole ECM fungal community; other groups were represented among the community: Cortinariaceae, Boletaceae, Amanita, Genea, Pisolithus, Scleroderma, and Tuber. There were pronounced differences in ECM fungal community structure among the 15 montados stands: C. geophilum was the only species common to all stands, tomentelloid and russuloid species were detected in 87-93% of the stands, Cortinariaceae was detected in 60% of the stands, and the other groups were more unequally distributed. Ordination analysis revealed that ECM fungal richness was positively correlated with the silvo-pastoral exploitation regime and low mortality of cork oak, while ECM fungal abundance was positively correlated with extensive agro-silvo-pastoral exploitation under a traditional 9-year rotation cultivation system and recent soil tillage. The effects of land use on the ECM fungal community and its implications in different scenarios of landscape management options, oak mortality, and global warming are discussed.

Bottlenecks, Drought, and Oil Price Spikes: Impact on U.S. Ethanol and Agricultural Sectors

We project U.S. ethanol production and its impact on planted acreage, crop prices, livestock production, trade, and retail food costs. The projections are made using a multicommodity, multicountry, partial equilibrium model. Results indicate that expanded U.S. ethanol production will cause long-run crop prices to increase. In response to higher feed costs, livestock farmgate prices increase enough to cover the feed cost increases. If crude oil prices increase, the U.S. ethanol sector expands. Results of a 1988-type drought scenario combined with a large mandate for ethanol consumption show higher crop prices, a drop in livestock production, and higher food prices.

Modelling of lake—groundwater interaction in Turkey

A regional steady state groundwater flow model was developed for the Yalvac basin located in the watershed of Lake Egirdir, the second largest freshwater lake in Turkey. Determination of lake–groundwater interaction is an important step in taking proactive measures for optimal and beneficial use of water resources from the water management perspective. The geological structure around the lake and its surrounding aquifer system makes the modelling challenging. The hydrogeologic units in the groundwater system exhibit both confined/unconfined conditions: they are not horizontal, yet some of them are nearly vertical, which does not allow use of the ‘horizontal-layer’ concept of Modflow. The model demonstrated that it is a useful tool for planning and managing the water resources in the region by determining immeasurable components of classical water budget calculations, the groundwater inflow/outflow components, which are generally required for management of lakes. The groundwater discharge to Lake Egirdir through the Yalvac basin was estimated by means of the model. Two scenarios of hypothetical drought and wet conditions were simulated and evaluated from water resources management and groundwater–lake interaction perspectives.