全球干旱卫星监测计划

干旱是损失最严重的自然灾害之一,干旱监测已受到了广泛关注。目前,干旱的遥感监测取得了很好的进展,但是针对全球干旱的监测并未与基于气象数据的全球干旱信息系统实现有机结合。2007年以来,地球观测组织提倡实施全球干旱监测预警信息系统,以充分利用遥感的全球监测能力,而2008年发生的西方金融危机影响了全球干旱监测预警信息系统的建设。2011年全球20国集团农业部长确认的地球观测组织全球农业监测计划再次给全球干旱监测预警信息系统的建设带来了新的机会。美国已经用MODIS数据监测全球干旱以及干旱造成的作物减产分布,中国的风云卫星也具有全球干旱监测的潜力,国际社会应该努力推动建立集成遥感监测的全球干旱监测预警信息系统,为决策者及时提供干旱信息,以便积极应对可能发生的干旱,减轻干旱对国家社会经济的影响。

基于气候区的全球干旱形势分析

使用Mann-Kendall趋势检验方法对过去三十多年间全球陆地和各气候区的干旱变化进行了分析,得到了全球陆地和各气候区内的干旱变化情况。结果表明:在干旱发生影响范围上,湿润地区的影响范围更大,而在干旱发生的频率上,干旱半干旱地区的频率更高。同时,热带季风气候区、热带稀树草原气候区、沙漠气候区、湿润亚热带气候区和海洋性气候区干旱面积有显著变大趋势,全球陆地、湿润大陆性气候区、亚寒带气候区和苔原气候区干旱面积有显著变小趋势。文章又对过去三十多年间全球和各气候区的变干趋势和变湿趋势进行了研究,发现全球20%以上的陆地有显著变干趋势,20%以上的陆地有显著变湿趋势,其中热带季风气候区和热带稀树草原气候区有40%以上面积有显著变干趋势,亚寒带气候区和苔原气候区有40%以上面积有显著变湿趋势。

全球干旱在过去60年中变化甚微

由于气候变化,预计未来干旱的频次及强度均会增加,其主要归因于区域降水量减少和全球气候变暖所导致的蒸发量增加。20世纪末至21世纪初干旱变化趋势的评估结果显示,干旱加剧已波及全球;尤其是采用帕尔默干旱指数(Palmer Drought Severity Index,PDSI)的计算结果表明,自20世纪70年代以来全球湿度降低,干旱面积相应增加,其可部分归因于全球变暖。帕尔默干旱指数由月降水量和温度数据直接驱动一个简单的水量平衡模型计算得到,由于该方法的简单性,使其成为广泛应用于干旱评估的重要工具;但该方法过分简化,使其在气候变化背景下的干旱评估结果可能出现偏差。本研究发现,由于帕尔默干旱指数在计算中应用了一个简化的潜在蒸发模型,该模型仅考虑了温度变化驱动的响应,并没有完全、准确地反映近几十年全球变暖背景下的蒸发响应。所以,已有报道可能高估了全球干旱的加剧程度。对干旱的合理计算应该充分考虑能量、湿度、风速等因素作用的物理机制,综合考虑这些因素的影响。更加精准的预估结果则认为:在过去的60年,全球干旱变化不大。这一结果对我们如何解释全球变暖对水文循环及其极值的影响具有一定的指导意义,可能有助于解释为什么基于树木年轮数据的古气候干旱重建与近年来基于PDSI的干旱记录有所不同。

NASA研究发现全球干旱恢复期变长

NASA网站2017年8月15日报道,20世纪以来,陆地生态系统从干旱中恢复过来的时间越来越长,部分地区的生态系统尚未从一次干旱中恢复便又遭遇干旱。这或将成为一种新常态,可能导致树木死亡以及温室气体排放加剧。相关论文发表在Nature上。

夏季森林火灾的严重性及控制对策

近几年来 ,世界各地夏季森林火灾趋于严重 ,我国中高纬度林区也受到夏季森林火灾的危害 ,且有上升的趋势。夏季林火发生后 ,扑救困难 ,损失严重。作者对夏季森林火灾做了详实的调查 ,提出夏季火灾的特点 ,发生原因及其危害性 。

Future Changes of Drought and Flood Events in China under a Global Warming Scenario

This study investigates the impact of global warming on drought/flood patterns in China at the end of the 21st century based on the simulations of 22 global climate models and a regional climate model(RegCM3) under the SRES(Special Report on Emissions Scenarios) A1B scenario.The standardized precipitation index(SPI),which has well performance in monitoring the drought/flood characteristics(in terms of their intensity,duration,and spatial extent) in China,is used in this study.The projected results of 22 coupled models and the RegCM3 simulation are consistent.These models project a decrease in the frequency of droughts in most parts of northern China and a slight increase in the frequency in some parts of southern China.Considering China as a whole,the spatial extents of droughts are projected to be significantly reduced.In contrast,future flood events over most parts of China are projected to occur more frequently with stronger intensity and longer duration than those prevalent currently.Additionally,the spatial extents of flood events are projected to significantly increase.

Thermodynamic Effects on Particle Movement:Wind Tunnel Simulation Results

Sand/dust storms are some of the main hazards in arid and semi-arid zones. These storms also influence global environmental changes. By field observations, empirical statistics, and numerical simulations, pioneer researchers on these natural events have concluded the existence of a positive relationship between thermodynamic effects and sand/dust storms. Thermodynamic effects induce an unsteady stratified atmosphere to influence the process of these storms. However, studies on the relationship of thermodynamic effects with particles (i.e., sand and dust) are limited. In this article, wind tunnel with heating was used to simulate the quantitative relationship between thermodynamic effects and particle movement on different surfaces. Compared with the cold state, the threshold wind velocity of particles is found to be significantly decrease under the hot state. The largest decrease percentage exceedes 9% on fine and coarse sand surfaces. The wind velocity also has a three-power function in the sand transport rate under the hot state with increased sand transport. Thermodynamic effects are stronger on loose surfaces and fine particles, but weaker on compacted surfaces and coarse particles.

How Large Precipitation Changes over Global Monsoon Regions by CMIP5 Models?

Future changes in precipitation over global monsoon domains and their adjacent dry regions are investigated using present-day climate simulations(1986–2005)and future climate simulations under the Representative Concentration Pathways(RCP4.5)scenario by the Coupled Model Intercomparison Project Phase 5(CMIP5)models.In the present-day climate simulations,high reproducibility of the extents of global monsoon domains and dry regions is observed from the multi-model ensemble(MME)result;the associated local summer precipitation variation and its interannual variability are also successfully reproduced.In the future,the global monsoon domains are projected to be expanded,while the dry regions are expected to initially increase and then decrease.The summer precipitation and its variability show significant increases over most global monsoon domains and obvious decreases over their adjacent dry regions.These results indicate that currently wet regions will become wetter and dry areas will be dryer under global warming conditions.Further analysis indicates that changes in summer precipitation over global monsoon and dry regions can be interpreted as moisture convergence changes associated with changes in horizontal moisture transport.

Climate Change and Water Resources： Strategies and Practices for Improved Water Management in Arid Countries

Assessment report of the Intergovernmental Panel on Climate Change （IPCC） highlighted the complex linkages between climate change and water. The likely warmer climate induced by the climate change is set to alter hydrological cycle and the shifting pattern of the rainfall would affect the spatial and temporal distribution of runoff, soil moisture, and surface and groundwater reserves. Therefore, there is an urgent need to assess the impacts of climate change on water and devise adaptation measures including management structures and processes by which one can deal with this challenge. The paper highlights with the global overview of climate change impacts on water in the arid region, supported and substantiated through scientific evidence drawn from IPCC reports and other relevant documents. This paper provides an overview of water resource management challenges including transboundary geopolitical concerns documented across the world and emphasizes the importance of an integrated framework for adaptive policy making. Further, it examines the viable water resource management options for various sectors and regions and showcases some of the international best practices in adaptation and mitigation. The paper also explains the complementary role of traditional knowledge in coping with climate change risks and uncertainties and the need for a balanced view in designing adaptation and mitigation strategies.

Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland

Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and87Sr/86Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.

Spatiotemporal precipitation variations in the arid Central Asia in the context of global warming

This study analyzed the temporal precipitation variations in the arid Central Asia （ACA） and their regional differences during 1930-2009 using monthly gridded precipitation from the Climatic Research Unit （CRU）. Our results showed that the annual precipitation in this westerly circulation dominated arid region is generally increasing during the past 80 years, with an apparent increasing trend （0.7 mm/10 a） in winter. The precipitation variations in ACA also differ regionally, which can be divided into five distinct subregions （Ⅰ West Kazakhstan region, Ⅱ East Kazakhstan region, ⅢCentral Asia Plains region, Ⅳ Kyrgyzstan region, and V Iran Plateau region）. The annual precipitation falls fairly even on all seasons in the two northern subregions （regions Ⅰ and Ⅱ, approximately north of 45°N）, whereas the annual precipitation is falling mainly on winter and spring （accounting for up to 80% of the annual total precipitation） in the three southern subregions. The annual precipitation is increasing on all subregions except the southwestern ACA （subregion Ⅴ） during the past 80 years. A significant increase in precipitation appeared in subregions Ⅰ and Ⅲ. The long-term trends in annual precipitation in all subregions are determined mainly by trends in winter precipitation. Additionally, the precipitation in ACA has significant interannual variations. The 2-3-year cycle is identified in all subregions, while the 5-6-year cycle is also found in the three southern subregions. Besides the inter-annual variations, there were 3-4 episodic precipitation variations in all subregions, with the latest episodic change that started in the mid- to late 1970s. The precipitations in most of the study regions are fast increasing since the late 1970s. Overall, the responses of ACA precipitation to global warming are complicated. The variations of westerly circulation are likely the major factors that influence the precipitation variations in the study region.