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Based on experimental data, this study presents a model of the dynamic growth of a thermally grown oxide (TGO) in thermal barrier coatings (TBCs) during thermal cycling. The model was solved using the finite element method. The thermal stress results of the model were compared with experimental results to verify the accuracy of the model. The stress analysis revealed that the combined effect of radial tensile stress and circumferential compressive stress can lead to the delamination of TBCs in a buckling form, which can induce the formation of cracks in TBCs along the axial direction. This observation was consistent with the conclusions drawn from the experimental results. Crack initiation and propagation result from the action of the maximum shear and radial stresses. In addition, the relationship between buckling failure and microscopic cracks was investigated. Thermal cycling induces radial and circumferential cracks, leading to buckling, delamination, and ultimate coating failure as the radial and circumferential cracks interact at the interface. [ABSTRACT FROM AUTHOR]

The thin-wall effect of single crystal superalloys refers to the phenomenon that when the thickness of the sample and the part is less than 1 mm, the lasting life is reduced, the creep rate is increased and other mechanical properties are significantly attenuated. With the development of the internal cooling structure of advanced aero-engine single crystal blade parts, the structural thickness of some areas decreases, making it a typical thin-walled structure. Thus, it is of great engineering significance to consider the thin-wall effect in the thin-wall region during the design and manufacture of blades. Creep performance is one of the most important properties of superalloys for turbine blade application. This paper summarizes the thin-wall effect in creep performance of the superalloys as well as some advanced experimental equipment in the study of thin-wall effect. Research on thin-wall debit effect of superalloys can be divided into two categories, one is the cause of thin-wall debit, including the relative enhancement of oxidation, more significance in anisotropy, changes in micro structure and the initiation or growth of defects, and the factors that influence the thin-wall debit effect including experimental conditions (temperature, stress, etc.), the processing methods (casting, machining), geometric shape (rectangular cross-section, ring cross-section, film cooling holes). Research on thin-wall debit effect is within the scope of engineering application, as a part of "component level/analog component level" in "building block" verification and evaluation technology, thin-wall debit effect research under service environment or near-service environment conditions is more valuable for application. For this purpose, a variety of advanced experimental equipment platforms have been developed to simulate one or several coupled service conditions (high temperature, high pressure, corrosion/erosion, centrifugal loading) of the blade in the engine. Future research on thin-wall effects should be carried out under conditions closer to actual service conditions by preparing specimens according to the actual blade manufacturing process and conducting experiments on the equipment that simulates the service environment. [ABSTRACT FROM AUTHOR]

With the global energy transition and increasing environmental requirements, hydrogen-mixed gas turbines as a high-efficiency and low-emission energy conversion equipment has been widely concerned. This paper reviews the development status of hydrogen-mixed gas turbines domestically and internationally, analyzes the characteristics of hydrogen combustion in gas turbines, explores the impact of hydrogen combustion on complex components and the application of high-temperature materials, and analyzes the performance requirements for hot-end component materials operating under high temperature, high pressure, and corrosive conditions, as well as the main challenges and potential solutions in current material development. The effects of water vapor and hydrogen embrittlement during hydrogen combustion on gas turbine alloys and thermal barrier coatings are discussed in detail. Water vapor accelerates the oxidation and corrosion of alloys, leading to a decline in mechanical properties. Furthermore, hydrogen embrittlement significantly affects the toughness and durability of alloys, increasing the risk of crack propagation and fracture. In terms of the problems, future research should focus on multi-field coupling simulations and accelerated corrosion tests, considering the factors such as temperature, pressure, and different atmospheres to establish realistic environment simulators to evaluate alloy and coating performances. Additionally, the combined effects of hydrogen and water vapor on high-temperature alloys and thermal barrier coatings should be emphasized. This includes investigating the diffusion mechanisms of hydrogen in alloys, interactions with lattice defects, and the microscopic processes leading to hydrogen embrittlement. Building oxidation models in high-temperature water vapor environments, clarifying the dissociation and adsorption mechanisms of water vapor at high temperatures, the hydroxylation of protective oxide films Al2O3 and Cr2O3, and the growth behavior of non-protective oxides(e.g., spinel) are also essential. [ABSTRACT FROM AUTHOR]

In recent decades, China has experienced substantial climate change and significant vegetation greenness due to the extensive implementation of artificial ecological restoration programs. However, the quantitative contributions of climatic and anthropogenic drivers to the national variations in associated evapotranspiration (ET) and gross primary productivity (GPP) over China at different climate zoning sub-regions remain unclear. Based on the analysis of climate factor and vegetation disturbance trends created by anthropogenic activities, this study constructed a remote sensing-based ecological model consisting of Penman–Monteith–Leuning (PML) and light use efficiency (LUE) components. The proposed model simulated the spatiotemporal changes in ET and GPP between 1999 and 2018 over China. The contributions of climatic factors and anthropogenic activities to ET and GPP variations were quantitatively calculated by ridge regression. The results show that (1) both interannual ET and GPP markedly increased, by 1.32 mm yr−1 and 8.01 g C m−2 yr−1, respectively; (2) vegetation changes due to anthropogenic disturbance made the dominant contribution to GPP variations over China, while the dominant factor influencing ET changes differed by sub-region due to the joint effects of vegetation and climate; (3) temperature and precipitation positively affected ET, while wind speed, humidity, and solar radiation negatively contributed to ET in most parts of Mainland China. These findings may provide a workable, scientific reference for further ecological restoration decision-making processes in China. [ABSTRACT FROM AUTHOR]

The Northeast region of China and Huang Huai Hai (3H) region are vital maize production bases in northern China that are crucial for national food security. The absence of phenological data hinders a detailed assessment of the alignment between maize development stages and climatic resources. This study combines the authors' maize phenology data with climate suitability modeling to evaluate maize's climate suitability at different developmental stages in both regions. This study shows that during the maize growth cycle, the average temperature, precipitation, sunshine, and comprehensive climate suitability were 0.77, 0.49, 0.87, and 0.65, respectively, in the Northeast. In contrast, the average temperature, precipitation, sunshine, and comprehensive climate suitability in the 3H region were 0.98, 0.53, 0.73, and 0.70, respectively. Precipitation is a major factor influencing maize growth, with temperature and sunshine impacting growth differently across regions. Temperature significantly affects maize in the Northeast, while sunshine plays a greater role in the 3H region. The Northeast is suitable for drought-resistant maize varieties, and implementing a late harvest policy in Liaoning could enhance maize yield. The 3H region generally has favorable climatic conditions. Apart from certain parts of Henan needing drought-resistant varieties, areas with ample growing seasons can adopt long-duration varieties to maximize thermal resource utilization. Our results have important implications for optimizing maize planting strategies and enhancing regional resilience, aiming to assess meteorological factors' impact on maize growth in key production areas. [ABSTRACT FROM AUTHOR]

The Rolling Hilly Region of Northeast China (RHRNEC) is a critical grain production area in China, and soil erosion is a major problem in this region. To determine spatial and temporal changes in rainfall erosivity (RE) in the RHRNEC and generate information useful for soil and water conservation, agricultural management, and ecological protection efforts, a RE index consisting of nine erosivity indices based on normal and extreme precipitation was established. The normal RE index (NREI) comprised annual RE (ARE), wet season RE (WRE), dry season RE (DRE), typical wet-month RE (TWRE), and typical dry-month RE (TDRE), and the extreme RE index set (EREI) comprised maximum one-day RE (RE × 1 day), maximum five consecutive days RE (RE × 5 day), storm RE (RE50), and maximum continuous RE (CRE). ARE, WRE, and TWRE decreased at relative rates of 2.5%, 2.9%, and 4.1%, respectively. By comparison, DRE increased at a non-significant relative rate of 6.3%, and all extreme RE indices decreased at a non-significant rate relative to 1981–2015 mean values. The future trends for all RE indices were predicted to be opposite to historical trends. The future trends and historical trends of all indices exhibited opposite patterns. RE gradually increased from north to south, and WRE, DRE, and all extreme RE indices were significantly negatively correlated with longitude, latitude, and altitude (p < 0.05). ARE, WRE, and TWRE showed increasing trends in the north and south and decreasing trends in the center. The findings are useful for soil and water conservation, especially for agricultural management and ecological protection. [ABSTRACT FROM AUTHOR]

Drought and floods affect the growth and yield of maize, affecting food security. Therefore, it is crucial to assess maize's drought and waterlogging status in various growth stages. We used phenological and daily meteorological data and spatial analysis to identify the drought and waterlogging conditions of spring maize in Northeast China in eight growth stages. We calculated the crop water surplus/deficit index and used the national standard for maize drought and waterlogging. The results indicate a significant decreasing trend of effective precipitation in Northeast China. The maize's water requirements changed during the growing period. The ranking of the daily water requirements of maize from high to low in the different growth stages was the flowering stage to the silking stage (6.9 mm/d), the tasseling stage to the flowering stage (6.1 mm/d), the jointing stage to the tasseling stage (4.9 mm/d), the seven-leaf stage to the jointing stage (3.4 mm/d), the silking stage to the harvesting stage (2.0 mm/d), the emergence stage to the three-leaf stage (1.4 mm/d), the three-leaf stage to the seven-leaf stage (1.3 mm/d), and the sowing stage to the emergence stage (1.2 mm/d). Drought occurred primarily in the early growth and development stage, and the most severe drought conditions were observed in the sowing to emergence stages and the emergence to the three-leaf stages in most areas in Northeast China. Waterlogging occurred predominantly in the flowering to the silking stages and the silking to the maturity stages in southeast Liaoning and parts of Jilin. Inner Mongolia had the lowest soil moisture conditions and was unsuitable for maize growth, followed by Heilongjiang, Jilin, and Liaoning. The dominant meteorological factors affecting the drought and waterlogging status of maize in different growth stages were precipitation and wind speed, followed by the minimum temperature, relative humidity, sunshine hours, and maximum temperature. The average temperature did not influence the drought and waterlogging status. The results provide a basis for selecting drought-resistant varieties and preventing waterlogging. [ABSTRACT FROM AUTHOR]

High temperature oxidation is considered to play an essential role in the thickness debit effect on the creep rupture life of Ni-based single crystal (SC) superalloys. In order to clarify thickness effects, thin-walled specimens of different thickness (t = 0.1, 0.3, 1.0 mm) were prepared. Cyclic and isothermal oxidation tests of a high-Al Ni-based SC superalloy IC21 were carried out at 900 °C and 1100 °C in order to study the thickness effects on the oxidation behavior and consequent microstructural degradation. Thin-walled specimens of S01-N exhibited a good oxidation resistance when the protective scale-forming elements were enough in the matrix. Specimen thickness tuned the oxidation kinetics by changing the spallation behavior but had few influences on the thermodynamics. The easier stress relief via creep deformation in thin specimens is the main reason behind this phenomenon. Moreover, the obvious temperature effects on the multilayer oxide scales caused the different thickness-related spallation behaviors. Weaker microstructural degradation appeared and was further mitigated by reduced specimen thickness. Sufficient Al content is considered to be indispensable for the formation of protective α-Al2O3 scale with less degradation of matrix during the high temperature oxidation of thin-walled Ni-based SC superalloy castings. [ABSTRACT FROM AUTHOR]

With the complexity of the structure of aero-engine turbine blades, the blade wall thickness continues to decrease. It is found that when the blade wall thickness decreases to a certain extent, its mechanical properties will decline significantly. It is extremely important to study this phenomenon of a significant decline in mechanical properties caused by wall thickness. In this paper, the creep behavior of a second-generation Ni3Al-based single crystal superalloy with different wall thicknesses and [001] orientation at 980 °C/220 MPa has been studied and compared with the creep life of Φ4 round bar. The experimental results show that the second orientation and the surface affected zone are not the main reasons for the reduction of the life of thin-walled samples under this experimental condition. By analyzing the fracture morphology and deformed microstructure of thin-walled samples with different thicknesses, it is found that the thickness debit effect of the single crystal alloy occurs since the effective stress area of the alloy changes due to internal defects and surface affected zone during the creep process. For thicker samples, the creep life of the alloy can be extended by making the samples undergo certain plastic deformation through better plastic deformation coordination ability, while for thinner samples, the plastic coordination ability is poor, and the ability to extend the creep life through plastic deformation is also weaker when the effective stress area of the alloy changes, which leads to the thinner samples being more prone to fracture. [ABSTRACT FROM AUTHOR]

Detailed traits are required for early warning and prediction of crop-related meteorological hazards. Currently, data sets describing maize phenological traits in Northeast China are few and incomplete, resulting in poor spatial interpolation results that do not accurately reflect the spatial distributions and temporal development patterns of maize phenology in the region. In this study, a maize-phenology data set is produced containing nine phenological stages and phenological stage maps based on three sets of in situ maize-phenology data from three different sources. First, the relationship between each phenological stage and date of the previous stage, longitude, latitude, and altitude, is uncovered using a multiple stepwise regression method. Then, the spatial variation of each phenological stage using ArcGIS is explored. Finally, a maize phenological stage data set and a phenological stage atlas are established for the average state of 2010–2020 in Northeast China. The data set was validated using phenological data from agricultural weather stations run by the China Meteorological Administration. The validated data set can be used for various purposes, including real-time warning and prediction of maize-related meteorological hazards. [ABSTRACT FROM AUTHOR]

In superalloys, topologically close–packed (TCP) phases, which contain refractory elements, usually significantly influence the mechanical properties. The current work investigates the structure and composition of the TCP phase in an Al–Mo–rich Ni–based single crystal superalloy. It is shown that after 40 h of thermal exposure, a large number of strip–like TCP phases are formed, which are enriched in Mo and Re. The structure of the TCP phase is identified as the tetragonal σ phase with the lattice parameter a being 0.93 nm and c being 0.50 nm. During the creep process, the single crystal tilts obviously and leads to orientation variation from <1 1 0> direction. Two groups of dislocations are observed in the deformed sample. One group contains straight dislocation lines and another group contains dislocation networks. The interaction between TCP phase and dislocation in the single crystal superalloy is studied to reveal the effect of the TCP phase on the deformation behavior. During creep, the σ phase hinders the dislocation movement, which may contribute to the propagation of the cracks and the final fracture. [ABSTRACT FROM AUTHOR]

Since the beginning of the global precipitation measurement (GPM) era, the global satellite mapping of precipitation (GSMaP) products underwent a major upgrade on January 2017, when the newest Version 4 (V4) GSMaP products were formally released. In this study, for the first time ever, the error characteristics of the successive Version 3 (V3) and V4 GSMaP products were evaluated at multiple temporal and spatial scales by comparing them to the China daily Precipitation Analysis Products from March 2014 to February 2017. The GSMaP products include the V3 and V4 standard products (MVK_V3 and MVK_V4), the gauge-adjusted standard products (GAU_V3 and GAU_V4), and the V3 near-real-time product (NRT_V3). Both versions of the gauge-adjusted datasets exhibit improvements over their corresponding unadjusted counterparts. With regard to the three-year daily mean precipitation, both gauge-adjusted products have similar spatial precipitation patterns, and the GAU_V4 provides higher precipitation estimates than the GAU_V3 over China. The MVK_V4 generally outperforms the MVK_V3 over the high-altitude Qinghai-Tibetan plateau, the deserts, and the moist southern regions. Elsewhere, the MVK_V4 has a lower performance than the MVK_V3. Based on the seasonal statistics, the V4 GSMaP products are superior to the V3 GSMaP products over China in the winter and the MVK_V4 provides higher precipitation estimates than the MVK_V3 in most areas of China (except for the Qinghai-Tibetan plateau and the deserts) in spring, summer, and autumn. The daily statistics show that the MVK_V4 significantly corrects for the precipitation bias of the MVK_V3 in the western, arid, and high-altitude regions. [ABSTRACT FROM AUTHOR]

Soil erosion has become a significant environmental problem that threatens ecosystems globally. The risks posed by soil erosion, the trends in the spatial distribution in soil erosion, and the status, intensity, and conservation priority level in the middle reaches of the Yellow River Basin were identified from 1978 to 2010. This study employed a multi-criteria evaluation method integrated with GIS and multi-source remote sensing data including land use, slope gradient and vegetation fractional coverage (VFC). The erosion status in the study region improved from 1978 to 2010; areas of extremely severe, more severe, and severe soil erosion decreased from 0.05%, 0.94%, and 11.25% in 1978 to 0.04%, 0.81%, and 10.28% in 1998, respectively, and to 0.03%, 0.59%, and 6.87% in 2010, respectively. Compared to the period from 1978 to 1998, the area classed as improvement grade erosion increased by about 47,210.18 km2 from 1998 to 2010, while the area classed as deterioration grade erosion decreased by about 17,738.29 km². Almost all severe erosion regions fall in the 1st and 2nd conservation priority levels, which areas accounted for 3.86% and 1.11% of the study area in the two periods, respectively. This study identified regions where soil erosion control is required and the results provide a reference for policymakers to implement soil conservation measures in the future. [ABSTRACT FROM AUTHOR]

The Integrated Multi-satellitE Retrievals for Global Precipitation Measurement Final Run (IMERGF) product has now been upgraded to Version 4 (V4), which has been available since March 2017. Therefore, it is desirable to evaluate the characteristic differences between the V4 and the previous V3 products. A comprehensive performance evaluation of the errors of the successive V3 and V4 IMERGF products is performed with a comparison of the China daily Precipitation Analysis Products (CPAP) from March 2014 to February 2015. The version 6 Global Satellite Mapping of Precipitation (GSMaP) research product (which is another Global Precipitation Measurement (GPM) based precipitation product) is also used as a comparison in this study. Overall, the IMERGF-V4 product does not exhibit the anticipated improvement for China compared to the IMERGF-V3 product. An analysis of the metrics of annual daily average precipitation over China for the IMERGF-V3 and IMERGF-V4 products indicates a decrease of the relative bias (RB) from 3.70% to -7.18%, a decrease of the correlation coefficient (CC) from 0.91 to 0.89, an increase of the fractional standard error (FSE) from 0.49 to 0.56, and an increase of the root-mean-square error (RMSE) from 0.63 mm to 0.72 mm. Compared to the IMERGF-V3 product, the IMERGF-V4 product exhibits a significant underestimation of precipitation in the Qinghai-Tibetan plateau with a much lower RB of -60.91% (-58.19%, -65.30%, and -63.74%) based on the annual (summer, autumn, and winter) daily average precipitation and an even worse performance during winter (-72.33% of RB). In comparison, the GSMaP product outperforms the IMERGF-V3 and IMERGF-V4 products and has the smallest RMSE (0.47 mm/day), highest CC (0.95), lowest FSE (0.37), and best performance of the RB (-2.39%) in terms of annual daily precipitation over China. However, the GSMaP product underestimates the precipitation more than the IMERGF-V3 product for the arid XJ region. [ABSTRACT FROM AUTHOR]

The sediment load on the Chinese Loess Plateau has decreased sharply in recent years. Therefore, it is critical to determine the effects of anthropogenic and climatic factors on the reduction in sediment load. The Huangfuchuan River is the primary tributary in the sediment-rich region of the Loess Plateau in China. This study identified a significant reduction in the sediment load in the Huangfuchuan River basin. The accumulative anomaly method was used to determine the change in annual sediment load from 1960 to 2010. The mean annual sediment load in the Huangfuchuan River was 0.564 × 10 t from 1960 to 1979 (Period I), and it decreased to 0.379 × 10 t between 1980 and 1996 (Period II) and to 0.100 × 10 t between 1997 and 2010 (Period III). Instead of conventional ways, a method that coupled a dynamic water balance model and a back-propagation artificial neural network was employed to separate the contributions of climate variability and human activities on the reduction in sediment load. The results showed that compared to the sediment load in Period I, human activities were responsible for 64.32 and 71.55% of the reductions in sediment load in Periods II and III, respectively, while climatic effects accounted for 35.68 and 28.45% of the reductions in Periods II and III, respectively. The construction of check dams was the main human activity that resulted in the sediment reduction between Periods I and II and accounted for 35.51% of the decrease. Vegetation restoration due to the implementation of the 'Grain-to-Green' program was the dominant cause of the reduction in sediment between Periods II and III and caused more than 40.00% of the decrease. The increase of water consumption by humans also contributed the reduction in sediment between Periods II and III in the Huangfuchuan River basin. [ABSTRACT FROM AUTHOR]

To control soil erosion and restore the degraded environment in the Loess Plateau, a large number of measures related to soil and water conservation have been employed that have profoundly affected catchment properties. This study constructed three indicators to characterize changes to the catchment slope, proposed both a method for a regression analysis of adjacent images and a sequence model, and applied multisource remotely sensed images and GIS spatial clustering analysis technologies to extract thematic information and comprehensively analyze the catchment change characteristics. The results indicate that the catchment slope properties changed significantly. At catchment scale, the average values of ARC, DVC and ART were 6.43%, 25.57% and 4.30%, respectively. There were six clustering types of catchment slope property changes. The maximum and minimum of the average similarities of the clustering types were 0.992 and 0.935. Each slope control measures had a distinct effect on catchment slope; the dominating factor of each clustering type was identified as: Type 1: D-VC, Type 2: D-VCLU, Type 3: D-LUVC, Type 4: D-TAVC, Type 5: D-TAC and Type 6: D-MFC. Type 5 and Type 1 covered the largest areas, respectively occupying 37.28% and 31.01%. Catchment slope property changes also had distinct types that depended on their geomorphological conditions. These findings provide a useful basis from which to further study catchment slope hydrological and soil erosion processes. [ABSTRACT FROM AUTHOR]

The objective of this study is to quantitatively evaluate Tropical Rainfall Measuring Mission (TRMM) data with rain gauge data and further to use this TRMM data to drive a Distributed Time-Variant Gain Model (DTVGM) to perform hydrological simulations in the semi-humid Weihe River catchment in China. Before the simulations, a comparison with a 10-year (2001-2010) daily rain gauge data set reveals that, at daily time step, TRMM rainfall data are better at capturing rain occurrence and mean values than rainfall extremes. On a monthly time scale, good linear relationships between TRMM and rain gauge rainfall data are found, with determination coefficients R varying between 0.78 and 0.89 for the individual stations. Subsequent simulation results of seven years (2001-2007) of data on daily hydrological processes confirm that the DTVGM when calibrated by rain gauge data performs better than when calibrated by TRMM data, but the performance of the simulation driven by TRMM data is better than that driven by gauge data on a monthly time scale. The results thus suggest that TRMM rainfall data are more suitable for monthly streamflow simulation in the study area, and that, when the effects of recalibration and the results for water balance components are also taken into account, the TRMM 3B42-V7 product has the potential to perform well in similar basins. [ABSTRACT FROM AUTHOR]

In areas with topographic heterogeneity, land use change is spatially variable and influenced by climate, soil properties, and topography. To better understand this variability in the high-sediment region of the Loess Plateau in which soil loss is most severe and sediment diameter is larger than in other regions of the plateau, this study builds some indicators to identify the characteristics of land use change and then analyze the spatial variability as it is affected by climate, soil property, and topography. We build two indicators, a land use change intensity index and a vegetation change index, to characterize the intensity of land use change, and the degree of vegetation restoration, respectively. Based on a subsection mean method, the two indicators are then used to assess the spatial variability of land use change affected by climatic, edaphic, and topographic elements. The results indicate that: 1) Land use changed significantly in the period 1998-2010. The total area experiencing land use change was 42,302 km, accounting for 22.57%of the study area. High-coverage grassland, other woodland, and forest increased significantly, while low-coverage grassland and farmland decreased in 2010 compared with 1998. 2) Land use change occurred primarily west of the Yellow River, between 35 and 38 degrees north latitude. The four transformation types, including (a) low-coverage grassland to medium-coverage grassland, (b) medium-coverage grassland to high-coverage grassland, (c) farmland to other woodland, and (d) farmland to medium-coverage grassland, were the primary types of land use change, together constituting 60% of the area experiencing land use change. 3) The spatial variability of land use change was significantly affected by properties of dryness/wetness, soil conditions and slope gradient. In general, land use changed dramatically in semi-arid regions, remained relatively stable in arid regions, changed significantly in clay-rich soil, remained relatively stable in clay-poor soil, changed dramatically in steeper slopes, and remained relatively stable in tablelands and low-lying regions. The increase in vegetation coincided with increasing changes in land use for each physical element. These findings allow for an evaluation of the effect of the Grain to Green Program, and are applicable to the design of soil and water conservation projects on the Loess Plateau of China. [ABSTRACT FROM AUTHOR]

Drought monitoring is challenging, but it is required for improving agricultural production, protecting the ecological environment, and reducing economic losses in drought-prone regions such as the Mongolian Plateau (MP). This study is a systematic analysis of the spatiotemporal changes in the characteristics of drought events (drought duration, severity, intensity, frequency, peak, and starting season) at the sub-regional scale between 1959 and 2018 based on the run theory and using the gridded self-calibrating Palmer Drought Severity Index (scPDSI) dataset. Principal component analysis and Varimax rotation and the Mann–Kendall trend and Sen's slope were used for the sub-regional division and drought trend analysis, respectively. In addition, wavelet analysis was employed to analyze drought periodicity and determine the influence of large-scale climate indices on regional drought variation. The study results indicate clear differences in the spatial patterns of drought characteristics in the MP. The northern part suffered from droughts with longer duration and higher severity, whereas more drought events with shorter duration and less severity occurred in the southern part. Most of the MP experienced a relatively wet trend in 1996–2018 compared to the period of 1959–1995. The frequency of spring drought events showed an increasing trend in 1996–2018, unlike in 1959–1995. Some drought events simultaneously affected two or several sub-regions. The wavelet analysis results indicated that the drought periodicity in the MP was 10–64 months. The Arctic Oscillation (Pacific Decadal Oscillation) was significantly correlated with drought in the southern (northern) part. [ABSTRACT FROM AUTHOR]

This study simultaneously analyzed and evaluated the meteorological drought-monitoring utility of the following four satellite-based, quantitative precipitation estimation (QPE) products: the Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis 3B43V7 (TRMM-3B43), the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS), the Climate Prediction Center Morphing Technique gauge-satellite blended product (CMORPH-BLD), and the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR). Data from 2000 to 2016 was used at global scale. The global Climate Research Unit (CRU) Version 4.02 was used as reference data to assess QPE products. The Standardized Precipitation Evapotranspiration Index (SPEI) drought index was chosen as an example to evaluate the drought utility of four QPE products. The results indicate that CHIRPS has the best performance in Europe, Oceania, and Africa; the PERSIANN-CDR has the best performance in North America, South America, and Asia; the CMORPH-BLD has the worst statistical indices in all continents. Although four QPE products showed satisfactory performance for most of the world according to SPEI statistics, poor drought monitoring ability occurred in Southeast Asia, Central Africa, the Tibetan plateau, the Himalayas, and Amazonia. The PERSIANN-CDR achieves the best performance of the four QPE products in most regions except for Africa; CHIRPS and TRMM-3B43 have comparable performances. According to the spatial probability of detection (POD) and false alarm ratio (FAR) of the SPEI, more than 50% of all drought events cannot be accurately identified by QPE products in regions with sparse gauge distribution. In other regions, such as the southeastern USA, southeastern China, and South Africa, QPE products capture more than 75% of drought events. Temporally, all datasets (except for CMORPH-BLD) can detect all typical drought events, namely, in the southeastern US in 2007, western Europe in 2003, Kenya in 2006, and Central Asia in 2008. The study concludes that CHIRPS and TRMM-3B43 can be used as near-real-time drought monitoring techniques whereas PERSIANN-CDR might be more suitable for long-term historical drought analysis. [ABSTRACT FROM AUTHOR]