Study on the spatial-temporal differences and evolution of ecological security in the typical area of the Loess Plateau.

The development and utilization of energy in the Loess Plateau has caused a wide range of ecological security issues, and Yan'an has become a typical area for ecological security research on the Loess Plateau. Ecological security evaluation research can provide data support and scientific reference value for the sustainable development, which is of great significance to the overall social and economic development of the region. In this study, the pressure-state-response (PSR) model was used to establish the evaluation index system in the evaluation of ecological security in Yan'an region (YAR), then the fuzzy analytic hierarchy process (FAHP) was used to determine the internal index weight of each element, and finally the ecological security index value (ESI) was calculated. The GIS technology was used to simulate the distribution map of ecological security in YAR and then analyzed the temporal and spatial changes and evolution of ecological security in YAR. The results showed that from 1997 to 2016, the ecological security in the western part of Luochuan County and the eastern part of Yanchuan County was still very high, while the ecological security index was relatively low in the southern part of Huanglong County. The ecological security index of Baota District had increased significantly, from 1.85 in 1997 to 2.76 in 2016. The proportion of III and IV ecological security regions had increased significantly, and the ecological security of the entire YAR was generally in a good situation. This study could clarify the temporal and spatial characteristics of ecological security and provided some reference for the study of ecological security evolution in typical regions of the Loess Plateau.

Sunshine duration reconstruction in the southeastern Tibetan Plateau based on tree-ring width and its relationship to volcanic eruptions.

Sunshine is as essential as temperature and precipitation for tree growth, but sunshine duration reconstructions based on tree rings have not yet been conducted in China. In this study, we presented a 497-year sunshine duration reconstruction for the southeastern Tibetan Plateau using a width chronology of Abies forrestii from the central Hengduan Mountains. The reconstruction accounted for 53.5% of the variance in the observed sunshine during the period of 1961-2013 based on a stable and reliable linear regression. This reconstructed sunshine duration contained six sunny periods (1630-1656, 1665-1697, 1731-1781, 1793-1836, 1862-1895 and 1910-1992) and seven cloudy periods (1522-1629, 1657-1664, 1698-1730, 1782-1792, 1837-1861, 1896-1909 and 1993-2008) at a low-frequency scale. There was an increasing trend from the 16th century to the late 18th and early 19th centuries and a decreasing trend from the mid-19th to the early 21st centuries. Sunshine displayed inverse patterns to the local Palmer drought severity index on a multidecadal scale, indicating that this region likely experienced droughts under more sunshine conditions. The decrease in sunshine particularly in recent decades was mainly due to increasing atmospheric anthropogenic aerosols. In terms of the interannual variations in sunshine, weak sunshine years matched well with years of major volcanic eruptions. The significant cycles of the 2- to 7-year, 20.0-year and 35.2-year durations as well as the 60.2-year and 78.7-year durations related to the El-Niño Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation suggested that the variation in sunshine duration in the southeastern Tibetan Plateau was possibly affected by large-scale ocean-atmosphere circulations.

Recent enhancement of central Pacific El Niño variability relative to last eight centuries.

The far-reaching impacts of central Pacific El Niño events on global climate differ appreciably from those associated with eastern Pacific El Niño events. Central Pacific El Niño events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NIÑO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Niño4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Niño-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.