Search

The periodicities of the climate change have long been explored by researchers not only because they reflect the inherent characteristics of the climate systems, but also because they are the foundations of climate-change predictability. This paper reports the periodicities of the hydroclimate variations reconstructed from a lacustrine sequence at Tiancun section (TC section) in the Luoyang Basin within the Central Plains of China and the sequence covers the first half of the Holocene. Our reconstruction shows that the hydroclimate variations at the TC section during the period from ∼10,135 and ∼ 5890 cal. yr BP were well corresponding with the effective soil moisture variations recorded by the stalagmite δ13C sequence at the Magou Cave. This corresponding relationship suggests that when the effective soil moisture increases (i.e., more negative δ13C values), the ratio of evaporation over precipitation in the paleolake at the TC section decreased, resulting in lower CaCO 3 content. It also suggests that when the effective soil moisture increases, more inflowing water entered the paleolake, resulting in coarser sediments. Our reconstruction also shows that the hydroclimate variations or lake level variations in the Luoyang Basin were characterized by millennial-scale quasi-periodicities that were most likely paced by the changes in ITCZ (Inter-tropical Convergent Zone) position and also by alterations in ENSO-like phase. And, both (ITCZ and ENSO) were most likely regulated by the solar activity. Our further analysis shows that the hydroclimate in the Luoyang Basin also experienced centennial-scale variations. Specifically, the grain size data express the following cycles: 692-year, 538-year, 217-year, 170-year and 123-year, all at the 99% confidence level. And, the CaCO 3 content data express the following cycles: 202-year, 184-year, 169-year and 85-year, all at the 99% confidence level. These cycles are approximately coincident with the widely-reported solar-activity cycles. • This paper reports the periodicities of the hydroclimate variations reconstructed from a lacustrine sequence in the Central Plains of China and the sequence covers the first half of the Holocene. • The hydroclimate variations were primarily paced by changes in ITCZ position and also by alterations in ENSO-like phase. And, both (ITCZ and ENSO) were most likely regulated by solar activity. • The centennial-scale hydroclimate variations were approximately coincident with the widely-reported solar-activity cycles. [ABSTRACT FROM AUTHOR]

Ecological research on the Qinghai–Tibet Plateau (QTP) has become a hotspot in recent years, and a great number of related research papers have been published. Here, a bibliometrics method was utilized to analyze 4315 papers from the Web of Science published from 1990 to 2019, and a comprehensive overview based on metrics, including the publication growth, first author' institutions and countries, research areas, international cooperation, high-impact journals and papers, and research hotspots and topics, is presented. The results revealed the following: (1) The number of published papers has grown exponentially, with China and India being the main research countries. However, China and the USA have the greatest weights in country cooperation. The Chinese Academy of Sciences has a relatively strong influence and plays the leading role in institutional cooperation. Wang Shiping, Zhang Zhenhua, Luo Caiyun, and seven other authors are highly influential. GLOBAL CHANGE BIOLOGY is the scientific journal that has published the greatest number of papers on the subject, and 'Environmental Sciences & Ecology' is the key research area; (2) Grazing, Precipitation, Soil moisture, Aboveground biomass, and Temperature are the top five core keywords. The research hotspots were mainly ecosystem services, biodiversity research, forest protection, and ecological adaptation under the background of climate change; and (3) Both new and old research topics appear in the periods 1990–1999, 2000–2009, 2010–2014, and 2015–2019, but all the periods focused on the impacts of rising temperature on natural elements, such as soil, forests, rivers, and lakes. Many recent also focused on the harmonious coexistence of human beings and nature. On the basis of these findings, some research suggestions and agendas are proposed for future research on the QTP. This is the first visualization and analysis of the hotspots and trends in ecological research on the QTP. • The method based on bibliometrics and text mining is effective in the discovery of natural science topics. • Research hotspots are focused on research around ecosystem services, biodiversity research, forest protection and ecological adaptation under the background of climate change. • More and more studies have paid attention to the harmonious coexistence of human beings and nature in recent years. • This is the first visualization and analysis of the hotspots and new trends in ecological research on the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

• A long series of highly accurate soil moisture data was combined. • SWDI was improved and extended to the monthly scaled drought index. • Temporal features of SWDI were characterized in four geographical regions. • The relationship among drought indexes (SPI, SWDI and VCI) was explored. Drought monitoring and assessment are of great importance due to the costly damage caused by drought. Datasets, drought indexes and drought relationships are three critical areas of drought research. Satellite-retrieved soil moisture (SM) products derived from the European Space Agency Climate Change Initiative (ESA CCI) show application potential in drought monitoring. However, the products are missing certain data in some areas. The model-assimilated SM product derived from the Global Land Data Assimilation System (GLDAS) was used to supplement these missing data. The main goals of this paper are to characterize agricultural drought after the utility and applicability of the combined SM product and the monthly scaled soil water deficit index (SWDI) have been evaluated and to investigate the relationships among meteorological, agricultural and vegetation droughts. First, we provided a long series of highly accurate SM products through simple calculations. The drought index, SWDI, was extended to a monthly scale for long-term drought analysis by using the combined SM product. The probability of detection (POD) between the SWDI and in situ drought records performed fairly well. Half of the 566 stations had PODs higher than 0.9, and one-third of these stations had POD values equal to 1. Through correlation analysis and grey incidence analysis (GIA) between the standardized precipitation index (SPI) and SWDI, we found that the propagation time from meteorological drought to agricultural drought was shorter under drier conditions than wetter conditions, and at the regional scale, the response time ranged from 1 month to 2.5 months. Correlation analysis between the SWDI and vegetation condition index (VCI) indicated that there was no delay effect from agricultural to vegetation drought on a monthly scale in most parts of China except in several provinces distributed in the South; additionally, there was a significant time lag in forests, while grassland and agriculture were more inclined to have no time lag or the response time was less than 1 month. [ABSTRACT FROM AUTHOR]