Climate change is expected to exacerbate drought conditions over many global regions. However, the future risk posed by droughts depends not only on the climate-induced changes but also on the ...changes in societal exposure and vulnerability to droughts. Here we illustrate how the consideration of human vulnerability alters global drought risk associated with runoff (hydrological) and soil moisture (agriculture) droughts during the 21st-century. We combine the changes in drought frequency, population growth, and human development as a proxy of vulnerability to project global drought risk under plausible climate and socioeconomic development pathways. Results indicate that the shift toward a pathway of high greenhouse gas emissions and socioeconomic inequality leads to i) increased population exposure to runoff and soil moisture droughts by 81% and seven folds, respectively, and ii) a stagnation of human development. These consequences are more pronounced for populations living in low than in very high human development countries. In particular, Sub-Saharan Africa and South Asia, where the majority of the world's less developed countries are located, fare the worst in terms of future drought risk. The disparity in risk between low and very high human development countries can be substantially reduced in the presence of a shift toward a world of rapid and sustainable development that actively reduces social inequality and emissions. Our results underscore the importance of rapid human development in hotspots of drought risk where effective adaptation is most needed to reduce future drought impacts.
•We illustrate how vulnerability can shape 21st-century global drought risk.•Less developed countries are disproportionately impacted by future drought risk.•Drought risk is driven by increased exposure and human development stagnation.•Rapid human development substantially reduces drought risk disparity.
Spatiotemporal dynamics of global drought Herrera‐Estrada, Julio E.; Satoh, Yusuke; Sheffield, Justin
Geophysical research letters,
16 March 2017, Letnik:
44, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Understanding the evolution and physical drivers of drought is critical to informing forecasting efforts. One aspect that has seldom been explored is the joint evolution of droughts in space and ...time. Most studies fix the reference area and focus on their temporal variability or study their spatial heterogeneity over fixed durations. This work implements a Lagrangian approach by aggregating contiguous areas under drought into clusters. These clusters become the frame of reference and are tracked as they evolve through space and time. Clusters were identified from soil moisture data from the Climate Forecast System Reanalysis (1979–2009). Evapotranspiration, moisture fluxes, and precipitation were used to explore the relevance of possible mechanisms of drought propagation. While most droughts remain near their origin, the centroid of 10% of clusters traveled at least 1400–3100 km, depending on the continent. This approach also revealed that large‐scale droughts often lock into further growth and intensification.
Key Points
Droughts can displace hundreds of kilometers from their origin
Several regions experience high mobility and consistent displacement patterns of droughts
Droughts tend to lock into further growth and intensification after reaching a certain area and intensity
Plain Language Summary
Droughts are some of the most expensive natural disasters that society has to face, so understanding how they evolve and what are the physical mechanisms that control them is critical for improving our ability to predict them. Past research has focused mostly on how droughts evolve in time over a fixed region and how droughts of a given duration evolve in space. However, little work has been done to study how they evolve in time and space, simultaneously, leading to a significant gap in our understanding of these extreme events. In this work we identify individual drought events between 1979 and 2009 around the world and track them in space and time to analyze their characteristics and behaviors across different continents. We find that some droughts can travel hundreds of kilometers from where they originated (e.g., from the U.S. Southwest to the U.S. Midwest), and that after droughts have grown and become intense enough, they will tend to become even larger and more intense before conditions improve (i.e., conditions will tend to become worse before they become better).
Anthropogenic climate change is expected to affect global river flow. Here, we analyze time series of low, mean, and high river flows from 7250 observatories around the world covering the years 1971 ...to 2010. We identify spatially complex trend patterns, where some regions are drying and others are wetting consistently across low, mean, and high flows. Trends computed from state-of-the-art model simulations are consistent with the observations only if radiative forcing that accounts for anthropogenic climate change is considered. Simulated effects of water and land management do not suffice to reproduce the observed trend pattern. Thus, the analysis provides clear evidence for the role of externally forced climate change as a causal driver of recent trends in mean and extreme river flow at the global scale.
Myeloid‐derived suppressor cells (MDSCs) play a crucial role in immunosuppression in tumor‐bearing hosts. MDSCs express arginase‐I and indoleamine 2,3‐dioxygenase; they suppress T‐cell function by ...reducing the levels of l‐arginine and l‐tryptophan, respectively. We examined the anticancer effects of supplementation of these amino acids in CT26 colon carcinoma‐bearing mice. Oral supplementation of l‐arginine or l‐tryptophan (30 mg/mouse) did not affect tumor growth, whereas oral supplementation of d‐arginine was lethal. Supplementation of l‐arginine showed a tendency to augment the efficacy of cyclophosphamide (CP). CP reduced the proportions of granulocytic MDSCs and increased the proportions of monocytic MDSCs in the spleen and tumor tissues of CT26‐bearing mice. l‐Arginine supplementation alone did not affect the MDSC subsets. CP treatment tended to reduce the plasma levels of l‐arginine in CT26‐bearing mice and significantly increased the number of tumor‐infiltrating CD8+ T cells. In addition, l‐arginine supplementation significantly increased the proportions of tumor peptide‐specific CD8+ T cells in draining lymph nodes. Importantly, additional supplementation of l‐arginine significantly increased the number of cured mice that were treated with CP and anti‐PD‐1 antibody. Totally, l‐arginine supplementation shows promise for boosting the therapeutic efficacy of chemoimmunotherapy.
Combination treatment with cyclophosphamide and anti‐PD‐1 antibody significantly suppressed the tumor growth, but did not exert a curative effect. However, the addition of l‐arginine supplementation boosted to complete regression in the majority of mice.
Abstract
Agricultural irrigation has significantly reshaped the land surface energy and water balance. Previous studies have well investigated its cooling effect on air temperature (
T
air
). ...However, its effect on increasing air humidity which can intensify the humid heat was often overlooked, particularly over urban areas with high population density, high
T
air
, and consequently greater exposure to moist heat stress. In this study, using state-of-the-art reanalysis data at a high spatial resolution (∼9 km), we evaluated how changes in area equipped for irrigation (AEI) around a city affect urban moist heat stress (UMHS) in more than 1000 cities in China and India. In addition to
T
air
, wet-bulb temperature (
T
WB
) and wet-bulb globe temperature (
T
WBG
), which consider humidity and are closer to the perceived temperature, were assessed. We found that although AEI expansion lowers urban
T
air
, irrigation increases
T
WB
and
T
WBG
due to increased air humidity, thereby exacerbating the UMHS. This ‘warming’ effect of irrigation is more evident in northern India where AEI has expanded significantly in recent decades, and is prominent in the pre-monsoon and post-monsoon seasons, when precipitation and air humidity are low. However, this effect is not evident in China due to the lower intensity of AEI expansion and differing climatic conditions. Overall, this study highlights the side-effect of irrigation on regional climate, providing crucial information for better understanding urban heat stress and for future city planning.
Abstract
Droughts that exceed the magnitudes of historical variation ranges could occur increasingly frequently under future climate conditions. However, the time of the emergence of unprecedented ...drought conditions under climate change has rarely been examined. Here, using multimodel hydrological simulations, we investigate the changes in the frequency of hydrological drought (defined as abnormally low river discharge) under high and low greenhouse gas concentration scenarios and existing water resource management measures and estimate the time of the first emergence of unprecedented regional drought conditions centered on the low-flow season. The times are detected for several subcontinental-scale regions, and three regions, namely, Southwestern South America, Mediterranean Europe, and Northern Africa, exhibit particularly robust results under the high-emission scenario. These three regions are expected to confront unprecedented conditions within the next 30 years with a high likelihood regardless of the emission scenarios. In addition, the results obtained herein demonstrate the benefits of the lower-emission pathway in reducing the likelihood of emergence. The Paris Agreement goals are shown to be effective in reducing the likelihood to the unlikely level in most regions. However, appropriate and prior adaptation measures are considered indispensable when facing unprecedented drought conditions. The results of this study underscore the importance of improving drought preparedness within the considered time horizons.
Water scarcity severely impairs food security and economic prosperity in many countries today. Expected future population changes will, in many countries as well as globally, increase the pressure on ...available water resources. On the supply side, renewable water resources will be affected by projected changes in precipitation patterns, temperature, and other climate variables. Here we use a large ensemble of global hydrological models (GHMs) forced by five global climate models and the latest greenhouse-gas concentration scenarios (Representative Concentration Pathways) to synthesize the current knowledge about climate change impacts on water resources. We show that climate change is likely to exacerbate regional and global water scarcity considerably. In particular, the ensemble average projects that a global warming of 2 °C above present (approximately 2.7 °C above preindustrial) will confront an additional approximate 15% of the global population with a severe decrease in water resources and will increase the number of people living under absolute water scarcity (<500 m3 per capita per year) by another 40% (according to some models, more than 100%) compared with the effect of population growth alone. For some indicators of moderate impacts, the steepest increase is seen between the present day and 2 °C, whereas indicators of very severe impacts increase unabated beyond 2 °C. At the same time, the study highlights large uncertainties associated with these estimates, with both global climate models and GHMs contributing to the spread. GHM uncertainty is particularly dominant in many regions affected by declining water resources, suggesting a high potential for improved water resource projections through hydrological model development.
This paper describes a novel synthetic approach for three- and four-armed cage-shaped polymers based on the topological conversion of the corresponding trefoil- and quatrefoil-shaped precursors. The ...trefoil- and quatrefoil-shaped polymers were synthesized by the following three reaction steps: (1) the t-Bu-P4-catalyzed ring-opening polymerization of butylene oxide using multiple hydroxy- and azido-functionalized initiators to produce the three- or four-armed star-shaped polymers possessing three or four azido groups at the focal point, respectively, (2) the ω-end modification to install a propargyl group at each chain end, and (3) the intramolecular multiple click cyclization of the clickable star-shaped precursors. The topological conversion from the trefoil- and quatrefoil-shaped polymers to the cage-shaped polymers was achieved by the catalytic hydrogenolysis of the benzyl ether linkages that had been installed at the focal point. The amphiphilic cage-shaped block copolymers together with the corresponding trefoil- and quatrefoil-shaped counterparts were synthesized in a similar way using 2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether as a hydrophilic monomer and decyl glycidyl ether as a hydrophobic monomer. Interestingly, significant changes in the critical micelle concentration and micellar morphology were observed for the amphiphilic block copolymers upon the topological conversion from the trefoil- and quatrefoil-shaped to cage-shaped architectures.
We compare ensembles of water supply and demand projections from 10 global hydrological models and six global gridded crop models. These are produced as part of the Inter-Sectoral Impacts Model ...Intercomparison Project, with coordination from the Agricultural Model Intercomparison and Improvement Project, and driven by outputs of general circulation models run under representative concentration pathway 8.5 as part of the Fifth Coupled Model Intercomparison Project. Models project that direct climate impacts to maize, soybean, wheat, and rice involve losses of 400–1,400 Pcal (8–24% of present-day total) when CO2 fertilization effects are accounted for or 1,400–2,600 Pcal (24–43%) otherwise. Freshwater limitations in some irrigated regions (western United States; China; and West, South, and Central Asia) could necessitate the reversion of 20–60 Mha of cropland from irrigated to rainfed management by end-of-century, and a further loss of 600–2,900 Pcal of food production. In other regions (northern/eastern United States, parts of South America, much of Europe, and South East Asia) surplus water supply could in principle support a net increase in irrigation, although substantial investments in irrigation infrastructure would be required.
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