AimChanges in surface thaw onset in Arctic permafrost can regulate terrestrial ecosystem dynamics. Permafrost surface thaw onset has advanced significantly because of strong Arctic warming. However, surface thaw onset change effects on vegetation during the different growing season stages remain unclear.LocationArctic and subarctic permafrost region.Time Period1982-2016.Major Taxa StudiedArctic vegetation.MethodsThis study investigated surface thaw onset change effects on vegetation growth in the Arctic permafrost region by analysing the relationships between surface thaw onset dates and vegetation indices obtained via satellite remote sensing from 1982 to 2016.ResultsThe leaf area index (LAI) from April to June was negatively correlated (-0.16 area-averaged partial correlation coefficient) with surface-thawed dates in over 78.6% of the Arctic permafrost region, and the LAI from August to October was positively correlated (0.17 area-averaged partial correlation coefficient) with surface-thawed dates in over 79.9% of the Arctic permafrost region. These distinct relationships suggest that earlier thaw onset may have a positive effect on vegetation growth during the early stage of the growing season. However, earlier thaw onset can limit vegetation growth during the late stage of the growing season. The different relationships between surface thaw onset and LAI can be explained by moisture availability. This difference occurred because 67.3% of the Arctic permafrost region was more constrained by temperature during the early stage of the growing season, therefore, the earlier thaw onset alleviated this temperature constraint and benefited vegetation growth. During the late stage of the growing season, 47.7% of the Arctic permafrost region was more constrained by moisture.Main ConclusionsOur results suggest that surface thaw onset change effects on vegetation vary by period, and this difference requires careful consideration when predicting ecosystem changes in permafrost regions.

In order to investigate NPP and its stability at long time scales of nearly 100 years under future climate scenarios,the authors developed the dataset of Stability of Vegetation Net Primary Productivity and Climate Impacts in China in the Following Century using HadGEM2-ES data scenarios based on the Regional Climate Model RegCM4.6 and CMIP5.The dataset includes:(1)mean NPP values and their trends from 2006 to 2099 under RCP4.5 and RCP8.5 scenarios;(2)multi-year mean NPP stability values for the full(2006-2099),early(2006-2035),mid(2036-2065)and late(2066-2099)periods.The spatial resolution of the data is 0.1°.The dataset is archived in 17 data files with data size of 15.0 MB(Compressed into one file with 4.26 MB).One of the research results based on this dataset was published in Acta Geographica Sinica,Vol.78,No.3,2023.

Arctic permafrost surface freeze-thaw (FT) changes related to warming could regulate the magnitude of global warming by altering the terrestrial carbon cycle and energy balances. This study investigated the sensitivity of surface FT changes to warming over Arctic permafrost regions by analyzing long-term changes in surface FT phenology from satellite remote sensing and meteorological variables from the climate data for the period from 1979 to 2017. Averaging over the entire Arctic permafrost regions, spring thawed date apparently advanced by -2.05 days decade-1, whereas autumn frozen date showed weak delaying trend of 0.83 days decade-1, implying the lengthening of the thawed season. Dividing the regions by permafrost types, advancing trends of thawed dates in continuous and high ice content permafrost areas (-2.57 and -2.70 days decade-1) were stronger than those over the discontinuous and low ice content permafrost areas (-1.61 and -1.73 days decade-1). The difference in changes in spring thawed dates between the regions is attributed to the difference in absolute magnitude of warming trends (e.g., 0.72 degrees C decade- 1 for continuous vs. 0.44 degrees C decade- 1 for discontinuous). However, the temperature sensitivity over discontinuous (low ice content) permafrost areas was 23% (10%) stronger than that over continuous (high ice content) permafrost areas for thawed date. In case of autumn, delaying trends of frozen dates were smaller over continuous and high ice content areas (0.69 and 0.74 days decade-1) than those over discontinuous and low ice content areas (1.01 and 0.88 days decade-1). This is mainly explained by the difference in temperature sensitivity (e.g., 1.57 days degrees C- 1 for continuous vs. 2.18 days degrees C- 1 for discontinuous) to warming between the regions rather than the difference in the absolute warming trends between the regions (e.g., 0.91 degrees C decade- 1 for continuous vs. 0.51 degrees C decade- 1 for discontinuous). The stronger temperature sensitivity of discontinuous and low ice content permafrost could be related to the lower demand of latent heat for the phase change of ground ice (or water). Overall, our results suggest that discontinuous and low ice content permafrost are more vulnerable to atmospheric warming. In addition to the magnitude of warming, the sensitivity to warming also needs to be considered when predicting permafrost FT changes.

The production of tea ( Camellia sinensis (L.) Kuntze), the world’s second most consumed beverage, is susceptible to extreme weather events. However, our understanding about the impacts of extreme temperatures and climate change on tea yields remains fairly limited. Here we quantify the historical and predict future fluctuations in tea yield caused by extreme temperatures in China, the largest tea producing country. We found that both heat and cold extremes were associated with significantly reduced tea yields. In the present climate, dominating cold extremes influence more than half of China’s tea production, with a maximum of 56.3% reduced annual production. In the near future, we predict positive net impacts of climate change on tea yield in all study regions at both the 1.5 °C and 2.0 °C global warming levels. Climate warming may diminish the negative impacts of cold extremes to 14%, especially at the current most affected northern tea growing regions (>28° N). However, new areas of yield reduction by intensified heat extremes will emerge, up to 14%–26% yield losses estimated at the Yangtze River (∼30° N) and southern China (<∼25° N) regions. Although the Paris Agreement targets limiting global warming to 1.5 °C, we expect up to 11%–24% heat-induced yield loss in Chongqing, Hunan, Anhui, and Zhejiang. Increasing heat extremes pose the most challenging changes for tea production in China. Therefore, addressing the regional difference of extreme temperature shifts is urgent for adapting tea production to climate change.

Monitoring and evaluating ecological quality and changes are crucial for policy formulation to guide ecosystem management and socioeconomic sustainable development. However, evaluation of ecological quality is still very challenging due to difficulties in determination of its associated indicators and weights. This paper proposes supporting, providing and regulating ecosystems services-based indicators to describe ecological quality, and applies a Projection Pursuit Model to eliminate redundant indicators and objectively determine weights for an ecological quality index (EQI) on a regional scale. Taking Jiangxi Province, China, as a demonstration area, the data for indicator measures were retrieved from satellite remote sensing and ecosystem modelling with a spatial resolution of 1 km for the three years 2005, 2010 and 2015. The results suggest that Normalized Difference Vegetation Index (NDVI) and water use efficiency (WUE) should be weighed higher and leaf area index (LAI) and Bowen ratio should be weighed lowest in the calculation of an EQI for Jiangxi Province. For 2015, the regional EQI was calculated to be 55.32 on a scale from 0 as the worst to 100 as the best, with higher values ascribed to the hills and mountains and the lower values existing near urban areas. The EQI increased from 52.26 in 2005 to 55.32 in 2015 with an increased area of good-and-above grade from 25.47% to 36.8% for the whole province. The changes in EQI could be attributed to a warmer and wetter climate trend playing a positive dominant effect, while urbanization and afforestation have negative and positive effects, respectively. This study demonstrates that it is feasible to evaluate ecological quality based on a comprehensive set of indicators and PPM-based weight determination, which could be further applied in regular ecological quality monitoring and evaluation on the regional, or even the national scale.

Wind stilling has been observed in many regions across the Northern Hemisphere; however, the related mechanisms are not well understood. Analyses of the wind speed variations in South Korea during 1993-2015 in this study reveal that the annual-mean surface wind speeds at rural stations have increased by up to 0.41 m s(-1) decade(-1), while those at urban stations have decreased by up to -0.63 m s(-1) decade(-1). The local wind speed variations are found to be negatively correlated with the population density at the corresponding observation sites. Gustiness analyses show the increase in local surface roughness due to urbanization can explain the observed negative wind speed trends at urban stations as the urbanization effect overwhelms the positive wind speed trend due to climate change. The observed negative wind speed trend in urban areas are not found in the regional climate model simulations in the Coordinated Regional Climate Downscaling Experiment-East Asia (CORDEX-EA) as these models do not take into account the impact of urbanization on wind variations during the period. This study suggests that urbanization can play an important role in the recent wind stilling in rapidly developing regions such as South Korea. Our results suggest that future climate projections in CORDEX-EA may overestimate wind speeds in urban areas, and that future regional climate projections need to consider the effects of urbanization for a more accurate projection of wind speeds.

Different roof materials are deployed for mitigating the urban heat, which significantly affects our life. However, the performance of specific roof materials could be influenced by the background climate. To evaluate the effectiveness of roof materials on temperature reductions in a subtropical monsoon climate region, this study performs field experiments using four different roof materials (gray and white surfaces, solar panel, and grass surface) from December 2017 to July 2018. The results show that the white surface reduced the average daily surface temperature by 3.37 °C. This cooling effect increased with the increase in surface albedo and incoming solar radiation. However, the average cooling effect of the grass surface was much lower (0.43 °C). This is attributable to the low soil moisture, which was influenced by the monsoon, thereby indicating that irrigation is required to improve the thermal performance of grass roofs even in humid regions. The solar panel reduced the daily surface temperature by 0.59 °C but exerted strong warming (7.36 °C) during midday and cooling effects (4.03 °C) during midnight because of its low albedo, low emissivity, and low heat capacity. Our results suggest that, for the roof treatments explored here, white roofs are more effective for mitigating urban heat in a subtropical monsoon climate under the present climatic conditions and especially for drier climates predicted for the future, while grass roofs are not a sustainable method as they require irrigation to achieve a cooling effect and solar panels may heat the urban atmosphere.

Different roof materials are deployed for mitigating the urban heat, which significantly affects our life. However, the answer to the question of which roof material has the best cooling performance in urban areas remains uncertain. We need to compare different roof materials together under a certain climate condition to find geographically appropriate mitigation strategies. This study performs field experiments using four different roof materials (gray, white, and grass surfaces, and rooftop solar panel) to evaluate their effectiveness on temperature reductions in a subtropical monsoon climate region from December 2017 to July 2018. The results show that the white surface reduced the average daily surface temperature by 3.37 °C. This cooling effect increased with the increase in surface albedo and incoming solar radiation. On the other hand, the average cooling effect of the grass surface was much lower (0.43 °C). This is attributable to the low soil moisture, which was influenced by the monsoon, thereby indicating that the adoption of grass roofs requires consideration of the availability of water resources even in humid regions. The solar panel reduced the daily surface temperature by 0.59 °C but exerted strong warming effect (7.36 °C) during midday and cooling effect (4.03 °C) during midnight because of its low albedo, low emissivity, and low heat capacity. Our results suggest that the grass roof with a native plant species is still not comparable with the white roof for mitigating urban heat in a subtropical monsoon climate under the present climatic conditions and especially for drier climates predicted for the future, and rooftop solar panels may heat the urban atmosphere by their warm surface during daytime.

To meet the growing demand for food, land is being managed to be more productive using agricultural intensification practices, such as the use of irrigation. Understanding the specific environmental impacts of irrigation is a critical part of using it as a sustainable way to provide food security. However, our knowledge of irrigation effects on climate is still limited to daytime effects. This is a critical issue to define the effects of irrigation on warming related to greenhouse gases (GHGs). This study shows that irrigation led to an increasing temperature (0.002 degrees C year(-1)) by enhancing nighttime warming (0.009 degrees C year(-1)) more than daytime cooling (-0.007 degrees C year(-1)) during the dry season from 1961-2004 over the North China Plain (NCP), which is one of largest irrigated areas in the world. By implementing irrigation processes in regional climate model simulations, the consistent warming effect of irrigation on nighttime temperatures over the NCP was shown to match observations. The intensive nocturnal warming is attributed to energy storage in the wetter soil during the daytime, which contributed to the nighttime surface warming. Our results suggest that irrigation could locally amplify the warming related to GHGs, and this effect should be taken into account in future climate change projections.

For embankments in permafrost regions, the soil properties and the upper boundary conditions are stochastic because of complex geological processes and changeable atmospheric environment. These stochastic parameters lead to the fact that conventional deterministic temperature field of embankment become stochastic. In order to estimate the influence of stochastic parameters on random temperature field for embankment in permafrost regions, a series of simulated tests are conducted in this study. We consider the soil properties as random fields and the upper boundary conditions as stochastic processes. Taking the variability of each stochastic parameter into account individually or concurrently, the corresponding random temperature fields are investigated by Neumann stochastic finite element method. The results show that both of the standard deviation under the embankment and the boundary increase with time when considering the stochastic effect of soil properties and boundary conditions. Stochastic boundary conditions and soil properties play a different role in random temperature field of embankment at different times. Each stochastic parameter has a different effect on random temperature field. These results can improve our understanding of the influence of stochastic parameters on random temperature field for embankment in permafrost regions.

The air pollution characteristics during the Spring Festival in Lanzhou were investigated.Measurements for particles in the size range 0.5 to 20 μm were taken using a TSI particle sizer from 25th January to 18th February,2011 in urban Lanzhou.Elevated particle concentrations were observed from 3rd to 8th February,2011 due to the firework burning.The result showed that the most affected periods by fireworks burning were 00:00~01:00 and 21:00~22:00 on 3rd February 2011.During 00:00~01:00 on 3rd February,the average particle number,surface area and volume concentrations in the size range 0.5~20μm were(310.3±97.2)/cm3,(1061.6±396.0)μm2/cm3and(409.9±176.0) μm3/cm3,respectively,which were 6.10,7.72 and 9.93 times higher than that in normal days during the Spring Festival.The firework emissions affected particle concentration in different sizes with different extent.For number and volume concentrations,the most affected size range was 0.542~1.382μm and 3.278~8.354μm,respectively,while for surface area concentrations,the most affected size range were 0.542~1.981μm and 3.278~8.354μm.The volume median diameters for particle volume size distributions in normal days appeared most frequently around 0.85μm and 5.50μm,while that affected by fireworks appeared most frequently around 0.93μm and 5.50μm,indicating the growth of accumulation particles during fireworks burning.