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Abstract: Extreme climate events often cause catastrophic damage to nature and human society. Therefore, regional assessments in various climates and geographic regions are needed for understanding the uncertainties of the change trends for extreme climate events. The objective of this study was to assess the spatial distribution and temporal trends of extreme precipitation and temperature events on the Loess Plateau of China during 1961–2007. Nine indicators (pq90, px5d, pint, pxcdd, pnl9, txq90, tnq10, tnfd, txhw90) were chosen to quantify extreme climate events, the Mann-Kendall method and linear trend analysis were used to test the change in trend and the magnitude, and inverse distance weighted interpolation was used to interpolate the spatial patterns. Results showed that most extreme climate indicators were spatially distributed with obvious gradients from the southeast to the northwest. Heavy rainfall threshold (pq90), greatest 5-day total rainfall (px5d), heavy rainfall days (pnl9) and cold-night threshold (tnq10) decreased from the southeast to the northwest, while simple daily rainfall intensity (pint), longest dry period (pxcdd) and number of frost days (tnfd) increased from the southeast to the northwest. Most stations had monotonic trends in extreme indicators during 1961–2007. However, the number of stations with significant trends varied greatly. Precipitation-based indicators showed more mixed patterns of change and few stations had significant trends. However, temperature-based indicators had more uniform changes and most stations had significant trends. Hot-day threshold (txq90) and cold-night threshold (tnq10), and the longest heatwave (txhw90) tended to increase while the number of frost days decreased since the 1960s on the Loess Plateau. Overall, extreme precipitation events did not change significantly; however, extreme temperature events became more severe and frequent. The results implied that extreme climate events on the Loess Plateau will continue to have adverse impacts, and adaptive measures should be considered for future ecological construction and agriculturally sustainable development. [Copyright &y& Elsevier]

Abstract: There is a growing interest in using soil microbial parameters as indicators of soil quality changes after revegetation of disturbed soils. This study investigated the changes in different soil microbial parameters as well as physico-chemical parameters as affected by vegetation rehabilitation of soil in the Loess plateau of China subjected to natural succession after enclosure. The results showed that the soil nutrients tend to be concentrated in the soil surface layer, especially the soil organic C, total N and alkali extractable N with soil organic C being doubled (up to 20gkg−1) after 50 years of revegetation. Soil enzyme activities and microbial biomass C (Cmic) and N (Nmic) increased with rehabilitation time up to 23 years. After 23 years, soil Cmic and Nmic and enzyme activities remained stable. Enzyme activities increased rapidly during the early stage of revegetation, about 15–20 years after enclosure. Soil Cmic and Nmic also increased about 20% faster up to 23 years since enclosure in the 0–20-cm soil layer. Soil basal respiration (BR) in the 23 years site was higher than in other sites, indicating high microbial activity in this site. These findings demonstrated significant impacts of natural vegetation succession in overgrazed grassland on the properties of the surface soils, including the soil nutrients, organic matter, soil microbial biomass, respiration, and enzyme activities. [Copyright &y& Elsevier]