Aridification Trend Research Articles

Element geochemical characteristics, provenance attributes, and paleosedimentary environment of the Paleogene strata in the Lenghu area, northwestern Qaidam Basin

The Lenghu area is a key exploration block in the northwestern Qaidam Basin. Due to the low exploration level, the provenance and paleosedimentary environment of the Paleogene strata is not clear. Based on the major and trace element contents and the carbon and oxygen isotopes of 547 samples collected from the Paleogene strata (E32, E31, and E1+2), this study investigated the provenance attributes and paleosedimentary environment of the entire Paleogene period. The samples from the Paleogene strata have relatively low contents of SiO2 (39.75%–61.81%) and Al2O3 (6.23%–20.48%) and high contents of La, Sc, and Co (223.07 ppm, 273.84 ppm, and 325.45, respectively). Moreover, the La–Th-Sc, Ti/Zr–La/Sc and SiO2–K2O/Na2O discrimination diagrams suggest that the tectonic environment of the provenance is an oceanic island arc. The Co/Th–La/Sc and Zr/TiO2-(V + Ni + Cr)/Al2O3 diagrams indicate that the provenance lithology of the study area is mafic rocks with a high degree of weathering. These results imply that the source rocks of the Paleogene strata are the mafic submarine volcanic rocks of the Tanjianshan group in the Saishiteng Mountains. The Sr/Cu, Sr/Rb, and Mg/Ca indexes indicate that the paleosedimentary environment had a humid climate with a trend of slight aridity. The Sr/Ba and Rb/K ratios and the isotope coefficient Z (calculated by carbon and oxygen isotopes) indicate that the paleosalinity of the water body was predominantly fresh water with a salty trend from the Early to the Late Paleogene. The paleoredox environment during the Paleogene sedimentation was relatively oxidized with a reduction trend based on the V/(V + Ni) and V/Cr values. This combined with the trend of increasing paleosalinity suggests that there was a relatively large lake transgression in the Late Paleogene.

Climate engineering to mitigate the projected 21st-century terrestrial drying of the Americas: a direct comparison of carbon capture and sulfur injection

Abstract. To mitigate the projected global warming in the 21st century, it is well-recognized that society needs to cut CO2 emissions and other short-lived warming agents aggressively. However, to stabilize the climate at a warming level closer to the present day, such as the “well below 2 ∘C” aspiration in the Paris Agreement, a net-zero carbon emission by 2050 is still insufficient. The recent IPCC special report calls for a massive scheme to extract CO2 directly from the atmosphere, in addition to decarbonization, to reach negative net emissions at the mid-century mark. Another ambitious proposal is solar-radiation-based geoengineering schemes, including injecting sulfur gas into the stratosphere. Despite being in public debate for years, these two leading geoengineering schemes have not been directly compared under a consistent analytical framework using global climate models. Here we present the first explicit analysis of the hydroclimate impacts of these two geoengineering approaches using two recently available large-ensemble (>10 members) model experiments conducted by a family of state-of-the-art Earth system models. The CO2-based mitigation simulation is designed to include both emission cuts and carbon capture. The solar-radiation-based mitigation simulation is designed to inject sulfur gas strategically at specified altitudes and latitudes and run a feedback control algorithm to avoid common problems previously identified such as the overcooling of the tropics and large-scale precipitation shifts. Our analysis focuses on the projected aridity conditions over the Americas in the 21st century in detailed terms of the potential mitigation benefits, the temporal evolution, the spatial distribution (within North and South America), the relative efficiency, and the physical mechanisms. We show that sulfur injection, in contrast to previous notions of leading to excessive terrestrial drying (in terms of precipitation reduction) while offsetting the global mean greenhouse gas (GHG) warming, will instead mitigate the projected drying tendency under RCP8.5. The surface energy balance change induced by sulfur injection, in addition to the well-known response in temperature and precipitation, plays a crucial role in determining the overall terrestrial hydroclimate response. However, when normalized by the same amount of avoided global warming in these simulations, sulfur injection is less effective in curbing the worsening trend of regional land aridity in the Americas under RCP8.5 when compared with carbon capture. Temporally, the climate benefit of sulfur injection will emerge more quickly, even when both schemes are hypothetically started in the same year of 2020. Spatially, both schemes are effective in curbing the drying trend over North America. However, for South America, the sulfur injection scheme is particularly more effective for the sub-Amazon region (southern Brazil), while the carbon capture scheme is more effective for the Amazon region. We conclude that despite the apparent limitations (such as an inability to address ocean acidification) and potential side effects (such as changes to the ozone layer), innovative means of sulfur injection should continue to be explored as a potential low-cost option in the climate solution toolbox, complementing other mitigation approaches such as emission cuts and carbon capture (Cao et al., 2017). Our results demonstrate the urgent need for multi-model comparison studies and detailed regional assessments in other parts of the world.

Cenozoic moisture fluctuations on the northeastern Tibetan Plateau and association with global climatic conditions

Abstract The Cenozoic history of aridification in the Asian interior is thought to be intimately linked to uplift of the Tibetan Plateau and long-term global cooling. How fluctuating climatic conditions influenced regional moisture levels during the Cenozoic remains largely unknown. To infer moisture changes, we present oxygen isotope values of carbonates (δ18Ocarb) and carbon isotope values of long-chain n-alkanes (δ13Calk) from a continuous geological section in the Qaidam Basin, northwestern China. The section spans most of the Cenozoic Era, from ~52 to 5 million years ago (Ma), based on conventional chronology, whereas recently a drastically revised chronology has placed its basal age at ~26 Ma. The association of moisture changes with global climate largely depends on the chosen chronology. With the revised chronology, our records are inconsistent with existing moisture records from the Asian interior and do not show clear association with global climatic conditions. However, with the conventional chronology, our δ18Ocarb record shows a long-term aridification trend over the Cenozoic, whereas the δ13Calk suggests reduced moisture levels during the Oligocene. Both records consistently show enhanced aridity, notably during the Oligocene, ~20–17 Ma and after ~13 Ma, which largely corresponded to relatively cool global periods. Our records thus suggest that global climatic conditions during the Cenozoic exerted more influence on the moisture levels in the Asian interior than previously thought, if the conventional chronology is correct. Our study also highlights the importance of constructing a reliable chronology in order to make an association of Cenozoic terrestrial records with global climate.

Shifts in Growth Responses to Climate and Exceeded Drought-Vulnerability Thresholds Characterize Dieback in Two Mediterranean Deciduous Oaks

Drought stress has induced dieback episodes affecting many forest types and tree species worldwide. However, there is scarce information regarding drought-triggered growth decline and canopy dieback in Mediterranean deciduous oaks. These species face summer drought but have to form new foliage every spring which can make them vulnerable to hotter and drier conditions during that season. Here, we investigated two stands dominated by Quercus frainetto Ten. and Quercus canariensis Willd. and situated in southern Italy and Spain, respectively, showing drought-induced dieback since the 2000s. We analyzed how radial growth and its responses to climate differed between non-declining (ND) and declining (D) trees, showing different crown defoliation and coexisting in each stand by: (i) characterizing growth variability and its responsiveness to climate and drought through time, and (ii) simulating growth responses to soil moisture and temperature thresholds using the Vaganov–Shashkin VS-lite model. Our results show how growth responsiveness to climate and drought was higher in D trees for both oak species. Growth has become increasingly limited by warmer-drier climate and decreasing soil moisture availability since the 1990s. These conditions preceded growth drops in D trees indicating they were more vulnerable to warming and aridification trends. Extremely warm and dry conditions during the early growing season trigger dieback. Changes in the seasonal timing of water limitations caused contrasting effects on long-term growth trends of D trees after the 1980s in Q. frainetto and during the 1990s in Q. canariensis. Using growth models allows identifying early-warning signals of vulnerability, which can be compared with shifts in the growth responses to warmer and drier conditions. Our approach facilitates establishing drought-vulnerability thresholds by combining growth models with field records of dieback.

Calcic Vertisols in the upper Daptocephalus Assemblage Zone, Balfour Formation, Karoo Basin, South Africa: Implications for Late Permian Climate

ABSTRACT The fully continental succession of the Beaufort Group, Karoo Basin, South Africa, has been used in the development of environmental models proposed for the interval that spans the contact between the Daptocephalus to Lystrosaurus Assemblage Zones, associated by some workers with the end-Permian extinction event. An aridification trend is widely accepted, yet geochemical data indicate that the majority of in situ paleosols encountered in this interval developed in waterlogged environments. To date, the presence of calcic paleosols in the latest Permian can be inferred only from the presence of calcite-cemented pedogenic nodules concentrated in fluvial channel-lag deposits. Here, we report on the first empirical evidence of in situ calcic Vertisols found in the upper Daptocephalus Assemblage Zone near Old Wapadsberg Pass, one of eight classic localities in which the vertebrate turnover is reported in the Karoo Basin. Seven discrete intervals of calcic Vertisols, exposed over a very limited lateral extent, occur in an ∼ 25 m stratigraphic interval. Estimates of mean annual temperature and mean annual precipitation are calculated from geochemical measurements of one paleosol, and these estimates indicate that the prevailing climate at the time of pedogenesis was seasonally cold and humid. Correlation with adjacent stratigraphic sections indicates that the late Permian landscape experienced poorly drained and better-drained phases, interpreted to reflect a climate that varied between episodically dry and episodically wet. In contrast to a paleoenvironmental reconstruction of unidirectional aridification from strata in the Wapadsberg Pass region, this study provides new evidence for a wetting trend towards the Daptocephalus–Lystrosaurus Assemblage-Zone boundary.

Aridity Trends in Central America: A Spatial Correlation Analysis

Trend analyses are common in several types of climate change studies. In many cases, finding evidence that the trends are different from zero in hydroclimate variables is of particular interest. However, when estimating the confidence interval of a set of hydroclimate stations or gridded data the spatial correlation between can affect the significance assessment using for example traditional non-parametric and parametric methods. For this reason, Monte Carlo simulations are needed in order to generate maps of corrected trend significance. In this article, we determined the significance of trends in aridity, modeled runoff using the Variable Infiltration Capacity Macroscale Hydrological model, Hagreaves potential evapotranspiration (PET) and near-surface temperature in Central America. Linear-regression models were fitted considering that the predictor variable is the time variable (years from 1970 to 1999) and predictand variable corresponds to each of the previously mentioned hydroclimate variables. In order to establish if the temporal trends were significantly different from zero, a Mann Kendall and a Monte Carlo test were used. The spatial correlation was calculated first to correct the variance of each trend. It was assumed in this case that the trends form a spatial stochastic process that can be modeled as such. Results show that the analysis considering the spatial correlation proposed here can be used for identifying those extreme trends. However, a set of variables with strong spatial correlation such as temperature can have robust and widespread significant trends assuming independence, but the vast majority of the stations can still fail the Monte Carlo test. We must be vigilant of the statistically robust changes in key primary parameters such as temperature and precipitation, which are the driving sources of hydrological alterations that may affect social and environmental systems in the future.

GIS-based assessment of aridity over Punjab Province, Pakistan, by using climatic indices

Aridity is a severe concern for agricultural countries including Pakistan. For the assessment of aridity, the climate indices such as temperature, precipitation, and rainfall were used to estimate the aridity level worldwide. Similarly, a comprehensive analysis was conducted during 1980 to 2016 using Thornthwaite’s, Erinc, and Global aridity indices to examine aridity in Pakistan. For this, data from twelve metrological stations was used to analyze the variation and distribution of aridity using ArcGIS 10.5. The examined results showed that the aridity trend shifted from southern to northern Punjab gradually. Furthermore, temporal analysis and calculated values of selected indices showed that 32.91% area is covered by arid region. In addition, 6.99% area of observed station lied in the humid region whereas 35.09% area recorded in semi-arid regions during 36 years. Moreover, Rahim Yar Khan, Bahawalpur, Bahwalnagar, and Dera Ghazi Khan were evaluated as hyper-arid region, while Multan and Faisalabad stations were covered with 12.93% area of the arid region. On the other hand, Lahore and Multan cities were observed under humid region with the area of 27.56%. In addition, Mangla, Rawalpindi, and Murree consisted of 0.68% area and noted as very humid region. Findings of current study showed that increasing trend of aridity is the fluctuation in mean annual temperature and decreasing trends of rainfall. Thus, this research would be helpful to facilitate researchers and policy makers to contribute to use natural terrestrial water resources in sustainable manner to protect ecosystem.

Spatial patterns of temperature, precipitation, and settlement dynamics on the Iberian Peninsula during the Chalcolithic and the Bronze Age

In light of recent climate changes, it is important to also gain knowledge about the spatial manifestation of past climate events and their potential impact on ancient societies across a wide range of different scenarios. Following this approach, we compare compilations of seasonal (winter and summer) as well as annual precipitation and temperature changes to a measure of human activity based on AMS 14C data of settlement sites from the Iberian Peninsula during the Chalcolithic and the Bronze Age – a period of major social turnover. Palaeoclimatic reconstructions show a long-term decrease in winter precipitation between 6000 and 3000 cal. BP (4050–1050 BCE). Superimposed to this long-term aridification trend was the 4.2 ka BP climate event, which manifested itself as a period of abrupt decrease in summer precipitation and/or an elongation of the summer dry period, but probably with constant winter precipitation from 4000 to 3800 cal. BP (2050–1850 BCE), particularly affecting the southeast of the Iberian Peninsula. Additionally, a winter cooling event across the Iberian Peninsula and its marginal seas occurred between 4400 and 4000 cal. BP (2450–2050 BCE) coinciding with Bond Event 3. By comparing human activities to the changes in seasonal and annual precipitation, new insight is gained into the causal relationships between climatic and social dynamics in the past. We show that winter precipitation potentially played a major role for the societies during the Chalcolithic and the Bronze Age of the southern Iberian Peninsula. While the El Argar culture at the south-eastern Iberian Peninsula boomed in spite of enhanced summer drought associated to the 4.2 ka BP climate event, decreasing winter precipitation was potentially contributing to a demographic decline in the southwest after 4800 cal. BP (2850 BCE) as well as to the bust of the El Argar culture in the southeast after 3600 cal. BP (1650 BCE) by limiting the agricultural strategies.

Cloud Cover over the Arabian Peninsula from Global Remote Sensing and Reanalysis Products

Abstract Clouds – their coverage, nature, and interactions with the energy budget of the planet – represent one of the primary sources of uncertainty in future climate prediction. Despite the crucial role of desert clouds in the distribution of water and energy budgets, their climatology is still largely incomplete. With arid regions projected to become dryer under global warming conditions, understanding the characteristics of their cloud cover can provide critical insights. In this work, cloud coverage was investigated over one of the Earth's most arid regions – the Arabian Peninsula. Four total cloud cover (TCC) products, namely the International Satellite Cloud Climatology Project H (ISCCP), the CM SAF Cloud, Albedo and Surface Radiation AVHRR 2 (CLARA) satellite datasets, the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP–NCAR) Reanalysis (R-2) (NCEP) and the ECMWF Interim Re-Analysis (ERA) reanalyses, were used to construct a climatology of desert clouds over the peninsula between 1984 and 2009, accounting for the different products' uncertainties and limitations. Satellite retrievals and reanalysis fields were first validated against ground observations from the United Arab Emirates, for which homogeneity assessments were conducted. The validation was done using statistical indicators, including Normalized Root Mean Square Errors (nRMSE), relative biases (rBIAS), and correlation coefficients, on monthly and seasonal scales. The ISCCP dataset resulted in the highest correlations with the ground observations (overall 0.38) and the lowest nRMSE (overall 0.54), while CLARA had the lowest rBIAS (overall 0.02). All products showed discrepancies when compared to the ground observations, both annually and on a seasonal basis. When extended to the entire Arabian Peninsula, the satellite and reanalysis products showed decreasing spring and increasing summer (except for ISCCP) TCC evolution across the region. At inter-annual scales, the TCC over the peninsula showed a significant discontinuity in 1998. This shift could be linked to the forcing of the El Nino Southern Oscillation on water vapor transport over the region, as well as to documented artifacts in satellite retrievals and model outputs. These discrepancies are indicative of a need for detailed assessments to be made of the uncertainties existing in TCC data for the Arabian Peninsula. Plain Language Summary Clouds represent a primary source of uncertainty in future climate predictions. This is particularly pronounced in dryland clouds, given their sporadic and intermittent nature. With global warming predicted to enhance aridification trends in terrestrial arid zones, historical cloudiness trends over arid and hyper arid regions are very important – yet their climatology to date is still largely incomplete. The quality of observations and/or model outputs are an important consideration, making validation and intercomparison assessments imperative. This work investigated cloud cover over the Arabian Peninsula, one of the most arid regions on the Earth. Four cloud cover datasets were used, derived from satellite measurements and atmospheric reanalysis model outputs. The selected study period was between 1984 and 2009. The four datasets were initially compared with observations taken at ground stations in the United Arab Emirates. The four products were then studied over the entire Arabian Peninsula. Results showed that cloud cover displayed marked seasonal characteristics and large inter-annual temporal evolution. An abrupt change in regional cloud cover time series was found to occur in 1998. This could be attributed to the forcing of the El Nino Southern Oscillation, although significant documented uncertainties in satellite products over this time span call for deeper investigations of this causal relation.

Paleoenvironmental conditions and drainage evolution of the central Anatolian lake system (Turkey) during late Miocene to Pliocene surface uplift

Abstract Continued Africa-Eurasia convergence resulted in post–11 Ma surface uplift of the Central Anatolian Plateau (CAP) and the westward escape of the Anatolian microplate. Contemporaneously, a central Anatolian fluvio-lacustrine system developed that covered extensive parts of the rising CAP. Today, the semi-arid CAP interior—except for the Konya closed catchment—drains toward the Black Sea, the Mediterranean Sea, and the Persian Gulf. Lake connectivity and drainage patterns of the fluvio-lacustrine system in the evolving plateau region are, however, largely unknown. Here, we present sedimentological and stable isotopic (δ13C and δ18O) data (N = 665) from 13 well-dated lake sections covering the former fluvio-lacustrine depocenters of the southern CAP. Persistently (>1 m.y.) stable paleoenvironmental and hydrological conditions suggest that a low-relief environment characterized the southern CAP during plateau uplift. Throughout the late Miocene, various open and closed lakes of the southern CAP drained into closed, terminal lakes within the plateau interior. Sedimentation east of the Tuz Gölü fault ceased during the early Pliocene (ca. 5.3–3.6 Ma), when the eastern CAP became connected to marine base level as a result of river incision shortly after the switch from regional compression to extension. A final phase of lacustrine carbonate sedimentation characterizes most sampled basins, yet occurred asynchronously over the extent of the CAP. Therefore, the final episode of lacustrine sedimentation is unlikely to have been the result of a climatic event, consistent with the absence of a clear aridification trend in the lacustrine δ18O data. Rather, capping carbonates reflect the interplay of surface uplift and transition from inward- to outward-drained plateau regions and concomitant lake reorganization during the formation of the CAP and its margins.

Spatial Shift of Aridity and Its Impact on Land Use of Syria

Expansion of arid lands due to climate change, particularly in water stressed regions of the world can have severe implications on the economy and people’s livelihoods. The spatiotemporal trends in aridity, the shift of land from lower to higher arid classes and the effect of this shift on different land uses in Syria have been evaluated in this study for the period 1951–2010 using high-resolution monthly climate data of the Terrestrial Hydrology Research Group of Princeton University. The trends in rainfall, temperature and potential evapotranspiration were also evaluated to understand the causes of aridity shifts. The results revealed an expansion of aridity in Syria during 1951–1980 compared to 1981–2010. About 6.21% of semi-arid land was observed to shift to arid class and 5.91% dry-subhumid land to semi-arid land between the two periods. Analysis of results revealed that the decrease in rainfall is the major cause of increasing aridity in Syria. About 28.3% of agriculture land located in the north and the northwest was found to shift from humid to dry-subhumid or dry-subhumid to semi-arid. Analysis of results revealed that the shifting of drylands mostly occurred in the northern agricultural areas of Syria. The land productivity and irrigation needs can be severely affected by increasing aridity which may affect food security and the economy of the country.

Lessons learnt from semi-arid wetland degradation. Las Tablas de Daimiel National Park

The Tablas de Daimiel National Park wetland developed in an area characterized by the cyclic nature of droughts, excessive aquifer exploitation and an evident aridification trend driven by climate change. The park and its surroundings have been exploited since prehistoric times and they are currently deeply anthropized to the point that both the physical survival of the wetland as well as its ecological function entirely depend on human action. A severe drought between 2006 and 2009 together with the drawdown of the water table caused the dry out of the system, reed overgrowth, disappearance of cut-sedge and sub-aquatic Chara spp. meadows and a smouldering peat fire. During this same period surface water, soil and groundwater were sampled for physical, hydrological and hydrochemical characterization. Upon drainage, the system functions as an artificial recharge system and becomes eutrophic showing large nutrient and salt content in soils and water. High water transmissivity capacities in the unsaturated zone and anthropic park management (soil compacted by heavy machinery, recirculation of low quality groundwater, reed reaping, water transfers, etc.) condition groundwater pollution. Increased knowledge of the physical-environment has allowed us to build a conceptual model of the surface water – groundwater interactions and to develop management tools to support the park management during a system dry out. Amongst these actions, we propose an unsaturated flow model for soil moisture simulation than can be used to predict critical soil water content for reed overgrowth or peat combustion risk.

Drought characteristics and its impact on changes in surface vegetation from 1981 to 2015 in the Yangtze River Basin, China

AbstractLocated in the subtropical monsoon climate area of China, the Yangtze River Basin (YRB) had been frequently affected by drought events recently. Based on standardized precipitation evapotranspiration Index (SPEI) and enhanced vegetation index (EVI), the characteristics of drought in the YRB and the influence of drought on vegetation in different seasons were investigated by maximum correlation (Rmax) between 1981 and 2015. The results showed that: (a) Droughts occurred frequently but had no obvious regularity in the YRB from 1981 to 2015. The drought intensity in autumn and winter were slightly higher than that in spring and summer. The autumn droughts in Sichuan Basin were the most serious, followed by the spring droughts in the middle and lower reaches of the YRB; (b) Annual SPEI series at 102 stations exhibited a downward trend and 72 stations exhibited an upward trend. There was no station showing a significant downward trend and two stations showing a significant upward trend. There was a drying trend in autumn and winter, and a wetting trend in spring and summer. The eastern area of the YRB shows a more arid trend in spring and autumn, as well as in the southwest in winter; (c) 90% of YRB showed a significant positive correlation (p < .05) between SPEI and EVI during the growing season (March–October), and the vegetation was more sensitive to short‐term and medium‐term drought. However, there were spatial and seasonal differences in the impact of drought on vegetation. Different types of land cover had different responses to droughts. Grasslands and croplands were more sensitive to droughts, grasslands at low elevation was dominated by short‐term droughts, while at high elevation was influenced by medium‐long‐ and long‐term droughts. Croplands and woodlands were more vulnerable to short‐term droughts.

Temporal and spatial evolution trends of drought in northern Shaanxi of China: 1960–2100

Drought prediction and assessment are the basis for addressing climate change and extreme weather. Northern Shaanxi is an important energy base and ecological barrier in China. Mitigating the threat of drought is necessary for sustainable development of the economy and society of the region. There are great uncertainties in drought predication because of climate change. Based on historical meteorological data and a multi-model ensemble mean value, temporal and spatial variation characteristics of drought in northern Shaanxi during the historical time period (1960–2018) and the future time period (2020–2100) were analyzed by detrending, Mann–Kendall trend test (MK), empirical orthogonal function spatial analysis (EOF), and wavelet analysis. The results show that the multi-model ensemble mean value provides a better simulation of precipitation and temperature in northern Shaanxi. The application of the Standardized Precipitation Evapotranspiration Index (SPEI) in the region is superior to the Standardized Precipitation Index (SPI) and self-calibrated Palmer Drought Index (sc-PDSI). The interannual dry and wet changes in the northern Shaanxi region during the historical period (1960–2018) can be divided into two periods. Overall, the drought index showed a significant decrease, and spring drought increased. In the future, precipitation and temperature in the region will increase from south to north, with the largest increase in the west. In the middle and late twenty-first century, due to the significant increase in temperature, the aridification trend in northern Shaanxi may be aggravated, which is consistent with the trend of drought in northern China. The future of spring drought is grim, and summer drought has an increasingly frequent trend. Making full use of water resources and accelerating the construction of the Yellow River diversion project are effective ways to alleviate drought and water shortage in the region.

Seasons of Drought in Slovakia During the Period from 1957 to 2016

Abstract The aim of the paper was to describe the occurrence of dry seasons in Slovakia. Dry seasons in the period from 1957 to 2016 were determined according to the monthly Palmer Drought Severity Index (PDSI). For this purpose, ten sites based on limit climatic parameters were chosen – Bratislava, Piešťany, Hurbanovo, Čadca, Sliač, Boľkovce, Poprad, Košice, Milhostov, and Kamenica nad Cirochou. The results showed the alternation of dry and wet episodes and the variability of weather not only over time, but also over space. The analysis of linear trends showed that the arid trend was identified on most sites (9 localities).

Analysis for Spatio-Temporal Variation Characteristics of Droughts in Different Climatic Regions of the Mongolian Plateau Based on SPEI

Continuous climate warming in the last few decades has led to global climate anomalies, resulting in frequent drought events in arid/semiarid regions with fragile and sensitive ecological environment. The Mongolian Plateau (MP) is located at the mid-latitude arid/semiarid climate region, which is deemed as the most sensitive region in response to global climate change. In order to understand the spatiotemporal characteristics of droughts in Mongolian Plateau under changing climate, we divided the study area into three climatic regions via Köppen climate classification. Then, the seasonal and annual drought trends were analyzed by standardized precipitation evaporation index (SPEI), which is a function of monthly mean temperatures, highest temperatures, lowest temperatures and precipitations, collected from the 184 meteorological stations from 1980 to 2015. Mann–Kendall (MK) test was employed to detect if there is an abrupt change of annual drought, while the empirical orthogonal function method (EOF) was adopted to investigate the spatiotemporal characteristics of droughts across the Mongolian Plateau. Results from MK test illustrated that the SPEI-12 exhibited statistically significant downward trends (a < 0.05) for all three climatic regions of the Mongolian Plateau. EOF spatial analysis indicated that Region III experienced the most severe drought from 1980 to 2015. During the 35 years period, an abrupt change of drought was detected in 1999. Before year 1999, the climate was relatively humid. However, the entire region became more arid after year 1999, reflected by remarkably increased frequency and intensity of drought. SPEI-3 revealed the trend of drought at seasonal scale. We found that drought became more severe in spring, summer, and fall seasons for the entire MP. However, winter became more humid. Different climate regions exhibited quite different drought seasonality: Region I experienced a severe arid trend in summer and fall. For Region II and III, summer became more arid. All three regions became more humid in winter season, especially for Region I, with the Sen’s slope of 0.0241/a.

Independent Aridity and Drought Pieces of Evidence Based on Meteorological Data and Tree Ring Data in Southeast Banat, Vojvodina, Serbia

In this study, aridity data and tree ring data were collected in Northern Serbia, in Southeast (SE) Banat, a subregion within Vojvodina, and Vojvodina at large. They were each investigated independently. The De Martonne Aridity Index and the Forestry Aridity Index are derived from examining the relationship between precipitation and surface air temperature data sets sourced from seven meteorological stations in SE Banat, and from 10 meteorological stations located in Vojvodina as a whole. Vojvodina is a large territory and used as the control area, for the period 1949–2017. The Palmer Drought Severity Index was derived for the period 1927–2016, for both SE Banat and the totality of Vojvodina. The results of the Tree Ring Width Index were obtained from samples collected in or around the villages of Vlajkovac and Šušara, both located in SE Banat, for the period 1927–2017. These tree ring records were compared with three previous aridity and drought indices, and the meteorological data on the surface air temperature and the precipitation, with the objective being to evaluate the response of tree growth to climate dynamics in the SE Banat subregion. It was noted that the significant positive temperature trends recorded in both areas were too insufficient to trigger any trends in aridity or the Tree Ring Width Index, as neither displayed any change. Instead, it appears that these climatic parameters only changed in response to the precipitation trend, which remained unchanged during the investigated period, rather than in response to the temperature trend. It appears that the forest vegetation in the investigated areas was not affected significantly by climate change in response to the dominant temperature increase.

Re-evaluation of an early sphenacodontian synapsid from the Lower Permian of England

ABSTRACTThe holotypic isolated maxilla of the early sphenacodontianHaptodus grandisfrom the Cisuralian of England is revisited. A unique character combination includes haptodontine-grade traits like less specialised teeth and a high number of precanines, but at the same time a shortened lacrimal that is separated from the naris, which is strongly diagnostic of Sphenacodontoidea. As the specimen cannot be assigned to any known taxon, the new taxonHypselohaptodus grandisgen. nov. is proposed. Comparison with other sphenacodontians reveals a mosaic distribution of maxillary features, most significantly regarding the precanine region. Preliminary character histories precludeHypselohaptodusfrom Sphenacodontidae, but suggest a haptodontine-grade or basal therapsid position. The latter hypothesis is substantiated by an ecological model of episodic wet phases in an overall trend of aridification throughout the Permian, to explain the rareness of non-sphenacodontid sphenacodontians in the fossil record. Also from the early Permian of England, an isolated dentary has previously been assigned toOphiacodon, but can be shown to be either a sphenacodontian, possibly affiliated withHypselohaptodus, or a robust,Stereorhachis-like ophiacodontid. The absence ofOphiacodonin the intramontaneous Permian basis of Europe is explained by a narrow environmental tolerance range requiring limnic connection with lowland basins.

ESTIMATING THE CHANGE OF VEGETATION COVERAGE OF THE UPSTREAM OF MINJIANG RIVER BY USING REMOTE-SENSING IMAGES

The upstream of Minjiang River, which was one of the main water sources for Chengdu Plain and the Yangtze River, was selected as the study area in the paper. With a series of cloud-free Landsat TM/OLI images acquired on June 24, 1994 and June 1, 2014, the vegetation coverage of the study area was calculated based on the vegetation index and dimidiate pixel model. The temporal and spatial changes of vegetation coverage were analyzed with digital elevation model and county area. The average vegetation coverage of the study area was decreased from 68.97% in 1994 to 60.39% in 2014. The analysis results showed that vegetation changes were closely related to topographical characteristics. The proportion of vegetation degradation area increased with the elevation increase and vegetation degradation was the most serious at the elevation range from 3500 m to 4500 m. The vegetation degeneration was the most obvious in Wenchuan County and Songpan County. Geological hazards caused by the earthquake and human disturbance were the main cause of the vegetation degradation and the aridity trend in the study area was another important factor.

Chemical weathering and erosion responses to changing monsoon climate in the Late Miocene of Southwest Asia

AbstractThe late Miocene is a time of strong environmental change in SW Asia. Himalayan foreland stable isotope data show a shift in the dominant vegetation of the flood plains away from trees and shrubs towards more C4 grasslands at a time when oceanic upwelling increased along the Oman margin. We present integrated geochemical and colour spectral records from International Ocean Discovery Program Site U1456 in the eastern Arabian Sea to reconstruct changing chemical weathering and erosion, as well as relative humidity during this climatic transition. Increasing hematite/goethite ratios derived from spectral data are consistent with long-term drying after c. 7.7 Ma. Times of dry conditions are largely associated with weaker chemical alteration measured by K/Rb and reduced coarse clastic flux, constrained by Si/Al and Zr/Al. A temporary phase of increased humidity from 6.3 to 5.95 Ma shows a reversal to stronger weathering and erosion. Wetter conditions can result in both more and less alteration due to the nonlinear relationship between weathering rates, precipitation and sediment transport times. Trends in relative aridity do not follow existing palaeoceanographic records and are not apparently linked to changes in Tibetan or Himalayan elevation, but more closely correlate with global cooling. An apparent opposing trend in the humidity evolution in the Indus compared to southern China, as tracked by spectrally estimated hematite/goethite, likely reflects differences in the topography in the Indus compared to the Pearl River drainage basins, as well as the generally wetter climate in southern China.