Long Term Spatio-temporal Variations of Seasonal and Decadal Aridity in India

A comprehensive analysis of climate data(1958-2018)is carried out at the national scale in India to assess spatiotemporal variation in aridity.The aridity is analyzed using UNEP(United Nations Environment Programme)Aridity Index(AI),which is the ratio between Precipitation(P)and Potential Evapotranspiration(PET).Freely available Terra-Climate database,P and PET variables,offered an unprecedented opportunity for monitoring variations in AI and aridity index anomalies(AIA)at inter-seasonal and inter-decadal basis.The study also assesses longer term patterns of P and AI anomalies with vegetation anomalies.The results indicate that significant clustered areas with maximum dryness are located at west-central part of India,the state of Maharashtra.Overall,there is a gradual increase in the extent of arid zone during 60-year period and spatially maximum extent of percentage change in aridity area is observed.The change patterns of AI in India are largely driven by the changing patterns of precipitation.The maximum impact of decline in precipitation on AIA was observed during Kharif season frequently,for every 4-5 years during 1972-1992.The pattern repeated in the last few recent years(2013-2018),the decline in precipitation resulted increased aridity.The study also reveals that the availability and usage of irrigation sources have increased from 2014 to 2018.Thus,despite of less precipitation positive vegetation has been resulted in this period.The findings are important to understand the impacts of climate change on land use pattern,and land and water resource management.

A study on environmental aridity over northern and southern to Qinling Mountains under climate warming

Based on the data up to 1999 from hydroclimatological departments, this pape analyzes the climatic divide implications of the Qinling Mountains in regional response to the process of climate warming, due to which the grades of dryness/wetness (GDW) in 100 years show that the northern region has entered a drought period, while the southern is a humid period. In a course of ten years, the D-value of annual average air temperature over southern Shaanxi (the Hanjiang Valley) and the Central Shaanxi Plain (the Guanzhong Plain) has narrowed, i.e., the former with a slight change and the latter with rapid increase in temperature. Both regions were arid with the decrease in precipition D-value, namely the plain became warmer while the south was drier. The Qinling Mountains play a pronounced role in the climatic divide. The runoff coefficient (RC) of the Weihe River decreases synchronously with that of the Hanjiang due to climate warming. The RC of Weihe dropped from 0.2 in the 1950s to less than 0.1 in the 1990s. The Weihe Valley (the Guanzhong Plain) is practically an arid area due to shortage of water. The successive 0.5, 1.0°C temperature anomaly over China marks, perhaps, the improtant transition period in which the environment becomes more vulnerable than before. The study shows the obvious trend of environmental aridity, which is of help to the understanding of regional response to global climate change.

Characterizing the spatiotemporal variations of evapotranspiration and aridity index in mid-western China from 2001 to 2016

Mid-western China is one of the most sensitive and fragile areas on the Earth.Evapotranspiration(ET)is a key part of hydrological cycle in these areas and is affected by both global climate change and human activities.The dynamic changes in ET and potential evapotranspiration(PET),which can reflect water consumption and demand,are still unclear,and there is a lack of predictive capacity on drought severity.In this study,we used global MODIS(moderate-resolution imaging spectroradiometer)terrestrial ET(MOD16)products,Morlet wavelet analysis,and simple linear regression to investigate the spatiotemporal variations of ET,PET,reference ET(ET0),and aridity index(AI)in mid-western pastoral regions of China(including Gansu Province,Qinghai Province,Ningxia Hui Autonomous Region,and part of Inner Mongolia Autonomous Region)from 2001 to 2016.The results showed that the overall ET gradually increased from east to southwest in the study area.Actual ET showed an increasing trend,whereas PET tended to decrease from 2001 to 2016.The change in ET was affected by vegetation types.During the study period,the average annual ET0 and AI tended to decrease.At the monthly scale within a year,AI value decreased from January to July and then increased.The interannual variations of ET0 and AI showed periodicity with a main period of 14 a,and two other periodicities of 11 and 5 a.This study showed that in recent years,drought in these pastoral regions of mid-western China has been alleviated.Therefore,it is foreseeable that the demand for irrigation water for agricultural production in these regions will decrease.

Leaf morpho-physiology and phytochemistry of olive trees as affected by cultivar type and increasing aridity

The olive species(Olea europaea L.)is an ancient traditional crop grown under rainfed conditions in the Mediterranean Basin.In response to the growing national and international demand for olive oil,the olive cultivars are introduced into highly arid new bioclimatic areas.Subsequently,the morpho-physiology and phytochemistry of olive trees are potentially changing among cultivar types and geographical conditions.In the present work,we have undertaken an assessment on the impacts of geographical location and cultivar types on the leaf morpho-physiology and phytochemistry of olive trees.Thus,leaves of the two most cultivated olive tree varieties,Chemlal and Sigoise,were collected from three geographical regions(Setif,Batna,and Eloued)with increasing aridity in Algeria.Leaf samples from the geographical regions were analyzed using the standard physiological experiment,colorimetric method,and a chromatography assay.Leaves of both cultivars exhibited a significant variance in terms of the leaf shape index but not for the leaf tissue density,specific leaf weight,and specific leaf area.Photosynthetic pigment contents were affected by both cultivar type and geographical location,with the lowest pigment content recorded in the Sigoise cultivar from the Setif region.Compared with the Setif and Batna regions,dried leaves of both cultivars from the Eloued region showed the higher levels of the total polyphenol,total flavonoid,and total tannin,as well as a better antioxidant capacity.Liquid chromatography-mass spectrometry analysis of all leaf extracts identified the following phenolic acids as major compounds:oleuropein,naringin,apigenin-7-O-glucoside,kaempferol,quercetin,quercitrin,luteolin-7-O-naringenin,and quinic acid.Lower contents were found for p-Coumaric acid,trans-Ferulic acid,hyperoside,rutin,apigenin,caffeic acid,protocatechuic acid,o-Coumaric acid,and gallic acid.Also,epicatechin and catechin+were not found in the leaf extracts of the Sigoise cultivar.The leaf organic extracts in both cultivars displayed promising anti-cancer activity that was affected by geographical location and organic solvent polarity.Briefly,although increasing aridity and soil organic and mineral deficiency affected the leaf morpho-physiological parameters,both cultivars sustained a chemical richness,a good antioxidant,and an anti-tumoral capacity in leaves.Furthermore,the findings revealed that regardless the olive tree genotype,there was a significant impact of geographical location on the leaf morpho-physiology,bioactivity,and chemical composition,which may consequently modulate the growth and oil production of olive trees.

An Aridity Trend in China and Its Abrupt Feature in Association with the Global Warming

A distinct aridity trend in China in last 100 years is presented by applying a linear fitting to both the climate records and the hydrological records, which is supported by evidence of environmental changes and seems to be associated with a global warming trend during this period.The Mann Kendall Rank statistic test reveals a very interesting feature that the climate of China entered into a dry regime abruptly in about 1920's, which synchronized with the rapid warming of the global temperature at almost the same time.According to an analysis of the meridional profile of observed global zonal mean precipitation anomalies during the peak period of global wanning (1930-1940), the drought occurred in whole middle latitude zone (25°N-55°N) of the Northern Hemisphere, where the most part of China is located in. Although this pattern is in good agreement with the latitude distribution of the difference of zonal mean rates of precipitation between 4 × CO2 and 1 × CO2 simulated by climate model (Manabe and Wetherald, 1983), more studies are required to understand the linkage between the aridity trend in China and the greenhouse effect.The EOF analysis of the Northern Hemisphere sea level pressure for the season of June to August shows an abrupt change of the time coefficient of its first eigenvector from positive to negative in mid-1920's, indicating an enhancement of the subtropical high over Southeast Asia and the western Pacific after that time. This is an atmospheric circulation pattern that is favorable to the development of dry climate in China.

Trend Analysis in Rainfall, Reference Evapotranspiration and Aridity Index in Southern Senegal: Adaptation to the Vulnerability of Rainfed Rice Cultivation to Climate Change

Rainfall and evapotranspiration are two vital elements for food production under rainfed agriculture. This study aims at investigating the combined changes in these variables in the form of aridly index in the southern Senegal. The temporal trends in annual and monthly (from May to October) aridity index, rainfall and evapotranspiration are examined and adaptation strategies to the vulnerability of rainfed rice cultivation to the changes are developed. The results show a significant decreasing trend in annual rainfall at all study locations for the period 1922-2015. When analyzing the trends in sub-periods, there are two clear patterns in the annual rainfall series: a decreasing trend for the period 1922-1979 and a reversal increasing trend for the period 1980-2015. An increasing trend is also observed in annual reference evapotranspiration. The results reveal that the region will be drier with a significant increase in aridity at the annual and most monthly series. Appropriate adaptation strategies should be implemented to diminish the adverse influence of the increasing aridity on rice productivity for a sustainable agriculture.

Modeling the Asian Aridity during the Early Cenozoic

Asian aridity can be traced back to the early Cenozoic(e.g.,Guo et al.,2008;Licht et al.,2016;Li et al.,2018a).Previous modelling studies focus mainly on the monsoon climate during the early Cenozoic,and studies for the Asian aridity are still limited(e.g.,Huber and Goldner,2012;Zhang et al.,2012;Li et al.,2018b).Here Asian aridity during the early Cenozoic is investigated through climate modelling by changing atmospheric CO2 concentration,orbital parameters,and topography.

Year aridity index patterns in northwest China and the relationship to summer North Atlantic sea surface temperature

Aim to linking the variability of drought in northwest China to the oceanic influence of North Atlantic SSTs at the background of global warming and at the regional climate change shifting stages, year aridity index variations in northwest China and summer North Atlantic sea surface temperature （SST） variations are examined for the 44 a period of 1961-2004 using singular value decomposition （SVD） analysis. Results show that the SST anomalies （SSTA）in the North Atlantic in summer reflected three basic models. The first SVD mode of SST pattern shows a dipole - like variation with the positive center located at southwest and negative center at northeast of extratropical North Atlantic. And it strongly relates to the positive trend in AI variation in northwest China. The second coupled modes display the coherent positive anomalies in extratropical North Atlantic SST and the marked opposite trend of AI variability between north and south of Xinjiang. In addition, the lag correlation analysis of the first mode of SSTA and geopotential heights at 500 hPa variations also shows that the indication of the former influencing the latter configuration, which result in higher air temperature and less precipitation when the SSTA in the North Atlantic Ocean in summer motivated Eurasian circulation of EA pattern, further to influence the wet - dry variations in northwest China by the ocean-to - atmosphere forcing.

Main Influencing Factors of Climatic Aridity in the Most Serious Increasing Aridity Region of North Chi- na

Based on the data of monthly precipitation and other monthly meteorological elements of 661 meteorological stations over China from 1961 to 2013, the temporal evolution characteristics of aridity in Hetao area of North China which is drying significantly were studied by using REOF, and the effects of summer monsoon and meteorological factors on the aridity index were discussed. The results showed that climatic aridity in Hetac area of North China tended to increase with time during 1961 -2013. The annual variation and overall trend of climatic aridity in Hetao area of North China was mainly influenced by /SASM1 before the 1990s, and the degree of the influence weakened with global warming. There were certain differ- ences between annual and decadal variations in the effects of the meteorological elements on climatic aridity. The impact of the thermal factors on aridity index was more significant than the dynamic factor after the 1990s, revealing that climate warming aggravated climatic aridity in Hetao area of North China.

Surrogate Climate Change Scenario and Projections with a Regional Climate Model: Impact on the Aridity in South America

The impact of global warming on the aridity in South America (SA) is investigated. For this purpose, the methodology for generating surrogate climate-change scenarios with a RCM is employed. For the present climate (CTRL) the RCM is initialized with and driven by ECMWF/ERA-Interim reanalysis data. Two aridity indices are used: the Budyko and the UNEP indices. The results for the CTR are in agreement with other model studies which indicate future warming;rainfall increases in southeastern South America, Ecuador and Peru and decreases in the central and eastern Amazon. In general the model reproduces the aridity in the continent compared with the observed data for both indices. The distribution of aridity over SA in surrogate climate-change scenario shows an increase of the dryness in the continent. Over Amazonia the aridity increases 23.9% (for the UNEP index) and 3.1% (for the Budyko index), suggesting that portions of the Amazonia forest are replaced by dry land area. The semi-arid zone over northeast Brazil expands westward, attaining the interior of north Brazil. In this region the aridity increases 20% (for the UNEP index) and 0.6% (for the Budyko index) indicating that areas of humid regime may be occupied by areas with dry land regime. The RCM was also integrated driven by the AOGCM ECHAM5/MPI-OM for the reference climate (CTRL2) and under A1B SRES scenario. The results for the present-day climate are similar in CTRL2 and CTRL, and are in agreement with CRU data. The distribution of the aridity for the present climate seems to be better represented in CTRL using both Budyko and UNEP indices. The changes in aridity (future climate minus control) are higher in the run forced by the A1B SRES scenario. Although the UNEP and Budyko indices show potentialities and limitations to represent the aridity distribution over SA, the changes in aridity due to a pseudo-scenario of global warming are higher using the UNEP index.

Effects of grazing intensity on seed production of Caragana stenophylla along a climatic aridity gradient in the Inner Mongolia Steppe,China

As the increases of climatic aridity and grazing intensity, shrubs play an increasingly important role in grassland ecosystem in arid and semi-arid regions, and its abundance also generally increases. However, the effects of climatic aridity and grazing intensity on sexual reproduction of shrubs in grassland remain largely unclear. In order to understand the effects of grazing intensity and climatic drought stress, and their interaction on seed production of shrub species, we examined the seed number, seed weight and seed yield of Caragana stenophylla under three grazing intensities （fenced, mild grazing and severe grazing） across a climatic aridity gradient （semi-arid, arid, very arid and intensively arid zones） in the Inner Mongolia Steppe, northern China during 2012-2013. The seed number, seed weight and seed yield gradually increased from the semi-arid to the very arid zones, but decreased from the very arid to the intensively arid zones in fenced plots. The seed number and seed yield decreased from the semi-arid to the intensively arid zones in mild and severe grazing treatment plots, therefore, grazing enhanced the suppression effect of climatic aridity on seed production of C. stenophylla. The seed number and seed yield gradually decreased as grazing intensity increased. The seed weight was highest in severe grazing plots, followed by the mild grazing plots and then the fenced plots. Precipitation varied interannually during the study period. We observed that the seed number seed weight and seed yield were lower in the low precipitation year （2013） than in the high precipitation year （2012）. As climatic drought stress increased, the negative effects of grazing on seed production of C. stenophylla also gradually increased. Our results indicated that climatic drought stress may contribute to the encroachment of C. stenophylla shrub in arid zones by promoting its seed production. However, grazing had negative effects on sexual reproduction of C. stenophylla, and the combined effects of drought stress and grazing seriously suppressed sexual reproduction of C. stenophylla in the intensively arid zone.

Asymmetric Drying and Wetting Trends in Eastern and Western China

As an important factor that directly affects agricultural production, the social economy, and policy implementation,observed changes in dry/wet conditions have become a matter of widespread concern. However, previous research has mainly focused on the long-term linear changes of dry/wet conditions, while the detection and evolution of the non-linear trends related to dry/wet changes have received less attention. The non-linear trends of the annual aridity index, obtained by the Ensemble Empirical Mode Decomposition(EEMD) method, reveal that changes in dry/wet conditions in China are asymmetric and can be characterized by contrasting features in both time and space in China. Spatially, most areas in western China have experienced transitions from drying to wetting, while opposite changes have occurred in most areas of eastern China. Temporally, the transitions occurred earlier in western China compared to eastern China. Research into the asymmetric spatial characteristics of dry/wet conditions compensates for the inadequacies of previous studies, which focused solely on temporal evolution;at the same time, it remedies the inadequacies of traditional research on linear trends over centennial timescales. Analyzing the non-linear trend also provides for a more comprehensive understanding of the drying/wetting changes in China.

Changes in Aridity in Response to the Global Warming Hiatus

The global warming slowdown or warming hiatus, began around the year 2000 and has persisted for nearly 15 years. Most studies have focused on the interpretation of the hiatus in temperature. In this study, changes in a global aridity index （AI） were analyzed by using a newly developed dynamical adjustment method that can successfully identify and separate dynamically induced and radiatively forced aridity changes in the raw data. The AI and Palmer Drought Severity Index produced a wetting zone over the mid-to-high latitudes of the Northern Hemisphere in recent decades. The dynamical adjustment analysis suggested that this wetting zone occurred in response to the global warming hiatus. The dynamically induced AI （DAI） played a major role in the AI changes during the hiatus period, and its relationships with the North Atlantic Oscillation （NAO）, Pacific Decadal Oscillation （PDO）, and Atlantic Multi-decadal Oscillation （AMO） also indicated that different phases of the NAO, PDO, and AMO contributed to dif- ferent performances of the DAI over the Northern Hemisphere. Although the aridity wetting over the mid-to-high lat- itudes may relieve long-term drying in certain regions, the hiatus is temporary, and so is the relief. Accelerated glob- al warming will return when the NAO, PDO, and AMO revert to their opposite phases in the future, and the wetting zone is likely to disappear.

miR-340-5p靶向调控ARID1A对甲状腺癌活性、迁移和侵袭的影响

目的 探讨miR-340-5p靶向调控富含AT的相互作用结构域(ARID)1A对甲状腺癌活性、迁移和侵袭的影响。方法 通过实时荧光定-聚合酶链反应(RT-qPCR)和Western印迹检测miR-340-5p和ARID1A在甲状腺癌细胞中表达水平。通过噻唑蓝(MTT)和Transwell实验检测转染miR-340-5p抑制物后癌细胞活性、迁移和侵袭变化。双荧光素酶报告基因检测miR-340-5p和ARID1A的靶向结合关系。最后通过同时敲低miR-340-5p和ARID1A的回复实验验证miR-340-5p调控ARID1A影响癌症发展。结果 miR-340-5p在甲状腺癌细胞中明显高表达,ARID1A表达明显较低(P<0.05)。通过抑制BCPAP细胞中miR-340-5p表达明显减少了癌细胞活性、迁移和侵袭水平。miR-340-5p和ARID1A具有直接靶向结合关系。敲降ARID1A能够明显逆转miR-340-5p抑制物对BCPAP细胞活性、迁移和侵袭的抑制作用。结论 miR-340-5p是甲状腺癌中的促癌基因,ARID1A为miR-340-5p的靶标下游,miR-340-5p通过靶向调控ARID1A促进甲状腺癌细胞活性、迁移和侵袭。

Analysis of Dry-Wet Climate Change Characteristics and Main Influencing Factors in Main Grain Producing Area of Tibet from 1980 to 2021

Based on the daily meteorological observation data of seven meteorological stations in southern Tibet from 1980 to 2021 (April-October), the temporal and spatial variation characteristics and influencing factors of aridity index ( AI ) in the growing season of major grain producing areas in Tibet were studied by using climate tendency rate, Mann-Kendal test, Morlet wavelet analysis, GIS hybrid interpolation method, Pearson correlation coefficient, contribution rate analysis and other methods. The results showed that the average AI in the main grain producing areas of Tibet was 1.7, which belonged to the semi-arid area, and the overall trend was decreasing (humidifying) (-0.036/10 a). The linear decreasing trend was different in different regions, and the area around Lhatse County was the most significant (-0.26/10 a). AI had no obvious abrupt change, and had long- and medium-term fluctuation characteristics of 24 years, 6 years. The spatial distribution was uneven, and had the characteristics of ‘shrinking arid area and expanding humid area . The contribution rates of the main climate influencing factors of AI varied in different regions. In general, the contribution rates after quantification was as follows: precipitation (34.9%)>relative humidity (28.4%)>sunshine (19.9%)>maximum temperature (12.4%).

Analysis of the Drought Impact as an Extreme Climatic Event in Sudan

This study aimed to investigate drought as an extreme climatic event in Sudan by utilizing the Anomaly and Standard Precipitation Index (SPI). This research employed high-resolution Climate Hazards Group Infrared Precipitation with Station (CHIRPS) data to analyze the temporal and spatial distribution of rainfall in Sudan from 2001 to 2015. Notably, the analysis compared the annual average precipitation to specific drought events and calculated the Standardized Precipitation Index (SPI). The results indicate a striking frequency of drought occurrence in Sudan, with SPI values suggesting similarities between drought and wet years. It is recommended to compute the SPI for individual stations rather than rely solely on area averages. Despite the comparable SPI values between the drought and wet years, this study emphasizes the profound impact of drought as a recurring phenomenon in Sudan. These findings emphasize the urgent need for proactive drought management and mitigation strategies in Sudan to effectively address the consequences of this climatic challenge.

History and variability of Asian interior aridity recorded by eolian flux in the Chinese Loess Plateau during the past 7 Ma

Eolian flux in the Chinese Loess Plateau was reconstructed by measuring the dry bulk density and CaCO3 content of the late Cenozoic loess-paleosol-red clay sequences in the Lingtai profile. Comparison of eolian flux variation between the Lingtai profile and the ODP sites 885/886 in the North Pacific shows a significant wet-dry variability in addition to a gradual drying trend in the dust source regions in interior Asia. Especially, the increase of eolian fluxes from both continental and pelagic eolian sediments indicates a sharp drying of the dust source regions between 3.6 and 2.6 MaBP, which might be attributed to the tectonic uplift of the Tibetan Plateau, which cut down the moisture input to the interior Asia. The average value and variability of eolian flux are higher after 2.6 MaBP than before, which may be related to the Quaternary climatic fluctuations on the glacial-interglacial timescale after the commencement of major Northern Hemisphere Glaciations. The eolian fluxes of the Lingtai profile and Core V21-146 in northwest Pacific show a synchronous variation on the 104-105 a timescale, indicating that the flux variations from both continental and marine records are closely correlated to the Quaternary climatic fluctuation forced by the ice volume changes on a global scale.

Aridity/humidity status of land surface in China during the last three decades

To clarify aridity/humidity status of land surface is helpful for studying environmental background and regional differences, seeking causes of environmental change, and providing a scientific basis for researches on climate change in the future. In this paper, the authors calcu- lated potential evapotranspiration of China using data from 616 meteorological stations during the period of 1971―2000 with the Penman-Monteith model recommanded by FAO in 1998. Vy- sothkii’s model was used to calculate aridity/humidity index. Then the calculated results of sta- tions were interpolated to land surface using ArcGIS. Results show that the annual average po- tential evapotranspiration is 400―1500 mm in the whole country, 600―800 mm in most parts of it; and 350―1400 mm in growing season (April―Octobor), which is nearly 200 mm less than the annual average. According to the aridity/humidity indexes of 1.0, 1.5 and 4.0, the aridity/humidity status is categorized to four types, namely, humid, subhumid, semiarid and arid. A majority of stations (76%) are more humid in growing season than the annual average. Results of com- prisons between the distribution map of aridity/humidity index with that of precipitation and vegetation indicate a good consistence of aridity/humidity status with natural environment. Therefore potential evapotranspiration calculated with modified FAO’s Penman-Monteith model in combination with aridity/humidity index that considers water balance can more reasonably explain the actual land surface aridity/humidity status of China.

Origin of the Red Earth sequence on the northeastern Tibetan Plateau and its implications for regional aridity since the middle Miocene

The Red Earth deposit around Xining, northeastern Tibetan Plateau, has been studied in terms of soil micro-structure, grain-size distribution, major- and trace-element chemistry and magne- tostratigraphy. Field investigations indicate that the Red Earth sequence consists of 25 visually de- finable yellow-brown and weakly-developed soils interbedded with reddish strongly-developed soils, and has a similar structure to the aeolian Red Clay deposit on the Chinese Loess Plateau. Grain-size analysis shows that the Red Earth deposit is very fine-grained with a negligible sand fraction (>63 μm). Thin-section observations under light microscopy show that the deposit has a clayey texture and the coarse fraction (>10 μm) mainly consists of quartz, feldspar and micas. Pyroxene and hornblende were also observed. This mineralogical composition of the coarse fraction is similar to that of the Quaternary loess. In addition, all of the mineral grains are semi angular semi-angular and are gener- ally finer than 63 μm. There is a good agreement between the major and minor trace element chem- istry of loess-soil units and the Red Earth deposit. The REE distributions of the loess-soil and the Red Earth deposit are similar in shape, with enriched LREE and fairly flat HREE profiles and a clear nega- tive Eu anomaly. The geochemical characteristics of the Red Earth deposit are also identical to those of upper continental crust, thus indicating a wind-blown origin. Magnetostratigraphic investigation shows that onset of the Red Earth deposition predates 11.4 Ma BP (13.6 Ma at a nearby site). The distribution of the reported Miocene aeolian loess at Qin’an of the Loess Plateau is still unknown. Our results indicate that this aeolian deposit had extended to the northeastern Tibetan Plateau by at least the middle Miocene. The similarity of the element geochem- istry between the Red Earth deposit and the overlying loess shows that they may have similar sources and dynamic transport system, and may indicate that the aridification of the interior of the Tibetan Plateau and central Asia began by at least the middle Miocene. Compared with the last intergla-cial-glacial loess, the grain-size of the Red Earth deposit is finer. This may indicate a lower energy transport agent and/or aridity in the dust source region. However, changes in grain-size and other proxies indicate many climatic fluctuations, with two important shifts at 9.61-9.91 Ma and 7-8 Ma. In addition, the grain-size record shows a shift from a high-frequency and high-amplitude pattern to a low-frequency and low-amplitude pattern at around 10.4 Ma and may indicate a significant environ- mental event at this time. Previous research has shown that the intensity of the southwest Asian monsoon increased at this time, coincident with heavier foraminiferal oxygen isotope values and a sharp fall in sea-level. Thus the environmental event in the Northeast Tibetan Plateau at 10.4 Ma may have global implications.

Aridity trend and response to vegetation restoration in the loess hilly region of northern Shaanxi Province

Detecting variation trend in dry-wet conditions can provide information for devel- oping strategic measures to mitigate the impacts of global warming, particularly in dry regions Taking the hilly region of northern Shaanxi on the Loess Plateau as a case area, this study analyzed the trend of aridity variation during 1981-2012, and explored the effect of vegetation restoration promoted by the Grain-for-Green （GFG） program implemented in 1999. The re- sults indicated that the aridity in the region was non-significantly increased by 0.88% per year during 1981-2012, showing a drying trend. This drying trend and amplitude were changed by the influence of vegetation restoration promoted by the GFG program, based on two findings. The first one was that the aridity variation tended to increase during 1981-1999 while it turned to decrease during 2000-2012, with the regional mean relative change rate changed from 2.45% to -1.06%. This distinction was more remarkable in the loess gully region, where the vegetation was improved more obviously. The second one was that the mean vegetation coverage as indicated by EVI increased by 0.90% to 4.32% per year at county level, while the aridity decreased by 0.14% to 2.32% per year during 2000-2012. The regression analysis using the mean county data indicated that the change rate of aridity was negatively related to that of EVI with the coefficient of determination （R2） of 0.56, illustrating that around half of the aridity decline was explained by the EVI change. The mechanism of this effect was compli- cated, but it was found that the wind speed decline induced by the vegetation improvement could be an important contributor. It is concluded that the region became drier during 1981-2012, but the eco-restoration reduced the drying speed. However, this conclusion is involved in uncertainties, and further study based on experiments is needed to confirm the effect of the GFG-promoted vegetation restoration.