Drylands are home to more than 38% of the world's population and are one of the most sensitive areas to climate change and human activities. This review describes recent progress in dryland climate change research. Recent findings indicate that the long‐term trend of the aridity index (AI) is mainly attributable to increased greenhouse gas emissions, while anthropogenic aerosols exert small effects but alter its attributions. Atmosphere‐land interactions determine the intensity of regional response. The largest warming during the last 100 years was observed over drylands and accounted for more than half of the continental warming. The global pattern and interdecadal variability of aridity changes are modulated by oceanic oscillations. The different phases of those oceanic oscillations induce significant changes in land‐sea and north‐south thermal contrasts, which affect the intensity of the westerlies and planetary waves and the blocking frequency, thereby altering global changes in temperature and precipitation. During 1948–2008, the drylands in the Americas became wetter due to enhanced westerlies, whereas the drylands in the Eastern Hemisphere became drier because of the weakened East Asian summer monsoon. Drylands as defined by the AI have expanded over the last 60 years and are projected to expand in the 21st century. The largest expansion of drylands has occurred in semiarid regions since the early 1960s. Dryland expansion will lead to reduced carbon sequestration and enhanced regional warming. The increasing aridity, enhanced warming, and rapidly growing population will exacerbate the risk of land degradation and desertification in the near future in developing countries.

Abstract. Dicarboxylic acids (C 2 -C 10 ), metals, elemental carbon (EC), organic carbon (OC), and stable isotopic compositions of total carbon (TC) and total nitrogen (TN) were determined for PM 10 samples collected at three urban and one suburban sites of Baoji, an inland city of China, during winter and spring 2008. Oxalic acid (C 2 ) was the dominant diacid, followed by succinic (C 4 ) and malonic (C 3 ) acids. Total diacids in the urban and suburban areas were 1546 ± 203 and 1728 ± 495 ng m −3 during winter and 1236 ± 335 and 1028 ± 193 ng m −3 during spring. EC in the urban and the suburban atmospheres were 17±3.8 and 8.0± 2.1 µg m −3 during winter and 20 ± 5.9 and 7.1 ± 2.7 µg m −3 during spring, while OC at the urban and suburban sites were 74 ± 14 and 51 ± 7.9 µg m −3 in winter and 51 ± 20 and 23 ± 6.1 µg m −3 in spring. Secondary organic carbon (SOC) accounted for 38 ± 16% of OC in winter and 28 ± 18% of OC in spring, suggesting an enhanced photochemical production of secondary organic aerosols in winter under an inversion layer development. Total metal elements in winter and spring were 34 ± 10 and 61 ± 27 µg m −3 in the urban air and 18 ± 7 and 32 ± 23 µg m −3 in the suburban air. A linear correlation (r 2 > 0.8 in winter and r 2 > 0.6 in spring) was found between primary organic carbon (POC) and Ca 2+ /Fe, together with a strong dependence of pH value of sample extracts on water-soluble inorganic carbon, suggesting fugitive dust as an important source of the airborne particles. Polycyclic aromatic hydrocarbons (PAHs), sulfate, and Pb in the Correspondence to: G. Wang (wanggh@ieecas.cn) samples well correlated each other (r 2 > 0.6) in winter, indicating an importance of emissions from coal burning for house heating. Stable carbon isotope compositions of TC (δ 13 C) became higher with an increase in the concentration ratios of C 2 /OC due to aerosol aging. In contrast, nitrogen isotope compositions of TN (δ 15 N) became lower with an increases in the mass ratios of NH + 4 /PM 10 and NO − 3 /PM 10 , which is possibly caused by an enhanced adsorption and/or condensation of gaseous NH 3 and HNO 3 onto particles.

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The methylenation of β-lactones 5 with dimethyltitanocene provides a versatile, reliable, and highly chemoselective entry to 2-methyleneoxetanes 7. The conversion proceeds selectively in the presence of alkenes, unprotected alcohols, and a variety of other carbonyl moieties. A study of conditions for the optimization of this reaction is delineated. In addition, the first X-ray structure of a 2-methyleneoxetane, which shows its similarity to related β-lactones, is reported. Reactivity studies of 2-methyleneoxetanes are presented in which it is demonstrated that these compounds are attacked at C-4 with a nucleophile; then, subsequently, the resultant enolate reacted with an electrophile. An interesting dichotomy of reactivity was observed when methyleneoxetane 7c was treated with electrophiles. Reaction of 7c with acetic acid gave acetoxyoxetane 19. When 7c was exposed to bromine, dibromoketone 20 resulted.

The regional hydrology and ecosystems of the Hexi Corridor region of northwestern China have changed over the last half century under the driving force of intense human activity and regional climate changes. Streamflow issuing from mountains in the eastern section of the Corridor by way of the Shiyang River has decreased significantly. Annual mountain outflow from the Heihe and Shule Rivers in the central and western portions of the Corridor, respectively, have tended to increase; however, their downstream discharge has decreased sharply. These lower reaches clearly display anthropogenic hydrological features. Water salinization and pollution have worsened. Presently, up to 208 km of river courses exhibit the poorest water pollution grades of IV and V. Overall, the forested area in the south Qilian Mountain region has decreased by 16.5% in the last 50 years, but has recently begun to show a gradual increase. However, natural desert forests in the northern portion of the Hexi Corridor have continued in a trend of degradation and rapid disappearance, with 3431 km 2 lost in Minqin and Ejin counties alone. Grasslands have been progressively degraded and their area decreased such that grasslands in the Hexi Corridor region only cover 46.86% of their former area. Desertification has been exacerbated and the grasslands' stock capacity reduced. In the Hexi Corridor region desertification has proceeded swiftly over the last 50 years, reaching, in the early 1980s, a maximum annual rate of 2.15% of total initial grassland area. However, from the late 1980s through the 1990s their desertification rate has dropped significantly. A unified watershed-scale plan for water use and management in different regions of the Hexi Corridor, considering water demands for economic development as well as ecosystem maintenance and remediation, must be implemented. The improved and ultimate sustainability of regional development for the Hexi Corridor is linked to following ecological criteria in exploiting land resources, and to systematically protect ecosystem function, allowing for sound ecosystem development.