The changing characteristics of drought in China from 1982 to 2005

Drought is one of the most detrimental natural disasters. Studying the changing characteristics of drought is obviously of great importance to achieve the sustainable use of water resources at river basin scales. In this paper, the satellite-based Vegetation Condition Index (VCI) and Vegetation Health Index (VH) were firstly calculated by using NDVI and brightness of the Global Vegetation Index dataset derived from Advance Very High Resolution Radiometer for China in growing seasons over 1982–2005. Then, the long-term VCI and VH data were employed to study the variation of droughts in the ten basins covering the whole country. The linear trend of each pixel showed that most parts of China were getting wetter in growing seasons, and the drought areas defined by the number of drought pixels have decreased in most basins. The increasing trend of basin averaged values of VCI and VH also indicates the whole country was generally getting wetter. At last, to better understand the two remote sensing drought indices, the response of the growing-season VCI and VH was compared to that of the Palmer Drought Severity Index and 6-month Standard Precipitation Index. Significant spatial variability of the relationship between the VCI, VH, and the station-based meteorological drought indices was shown, and some more closely related areas were found. The study will be useful for water resources management for each basin in the future.     

1979-2014年东北地区雪深时空变化与大气环流的关系

基于被动微波遥感反演的雪深数据集（1979-2014年）,利用Mann-Kendall检验、R/S分析、相关分析和小波分析等方法研究了东北地区雪深时空变化特征及其与大气环流的关系。结果表明：1979-2014年,东北地区年均雪深总体呈减小趋势,减小速率为-0.084 cm·（10a）^-1。其中,春季雪深减小速率最大,为-0.19 cm·（10a）^-1（P<0.05）,其次是冬季[-0.17 cm·（10a）^-1],而秋季雪深减小速率最小,仅为-0.05 cm·（10a）^-1。空间上,平原区（东北平原和三江平原）与少部分高原区（呼伦贝尔高原西南部）年均雪深呈增大趋势,山地（大、小兴安岭和长白山）与高原大部（内蒙古高原）雪深呈减小趋势,而且雪深增大区域的面积和变化速率均小于雪深减小的地区。东北地区年均雪深变化的Hurst指数为0.85,表明雪深未来减小的持续性很强;同时雪深变化具有22 a的主周期。春秋季雪深变化与东亚槽强度及北半球极涡面积呈显著负相关性,而冬季雪深与北半球副高强度关系密切。     

基于RS和GIS的丹巴县植被盖度与地质灾害关系研究

植被盖度作为地表特征指数之一,其发育和分布特征受控于生态地质环境,而地质灾害又是生态地质环境不良作用的表现方式之一,二者存在一定联系。以地质灾害发育且危害严重的丹巴县为例,采用1999年和2006年二期卫星遥感数据,提取这二个时相的植被盖度图,以及1999年～2006年植被盖度变化图,采用地理信息系统技术,将地质灾害与二期的植被覆盖图进行叠加和统计分析。其结果表明,地质灾害主要分布在海拔较低,人类工程活动强烈的低植被覆盖和较低植被覆盖区域,且地质灾害在植被覆盖度减少的区域较之植被盖度不变和增加的区域,更加容易突发,研究结果与区内其它地质灾害工作成果吻合。     

The relationship between groundwater and natural vegetation in Qaidam Basin

To accurately evaluate ecological risks trigged by groundwater exploitation, it must be clarified the relationship between vegetation and groundwater. Based on remote sensing data sets MOD13Q1, groundwater table depth (WTD) and total dissolved solids (TDS), the relationship between groundwater and natural vegetation was analyzed statistically in the main plain areas of Qaidam Basin. The results indicate that natural vegetation is groundwater-dependent in areas where WTD is less than 5.5 m and TDS is less than 7.5 g/L. Aquatic vegetation, hygrophytic vegetation and hygrophytic saline-alkali tolerant vegetation are mainly distributed in areas with WTD <1.1 m. Salt-tolerant and mesophytic vegetation mainly occur in areas with WTD of 1.4-3.5 m, while the xerophytic vegetation isprimarily present in areas where WTD ranges from 1.4 m to 5.5 m. Natural vegetation does not necessarily depend on groundwater in areas with WTD >5.5 m. For natural vegetation, the most suitable water TDS is less than 1.5 g/L, the moderately suitable TDS is 1.5-5.0 g/L, the basically suitable TDS is 5.0-7.5 g/L, and the unsuitable TDS is more than 7.5 g/L.     

The relationship between land surface temperature and land use/land cover in Guangzhou,China

The integration of remote sensing, geographic information system, landscape ecology and statistical analysis methods was applied to study the urban thermal environment in Guangzhou. Normalized Difference Vegetation Index (NDVI), Normalized Difference Build-up Index (NDBI), Normalized Difference Barren Index (NDBaI) and Modified Normalized Difference Water Index (MNDWI) were used to analyze the relationships between land surface temperature (LST) and land use/land cover (LULC) qualitatively. The result revealed that, most urban built-up lands were located in the middle part, and high LST areas mostly and were in the middle and southern parts. Therefore, the urbanization and thermal environment in the middle and southern parts need to be determined. Land surface temperature increased with the density of urban built-up and barren land, but decreased with vegetation cover. The relationship between MNDWI and LST was found to be negative, which implied that pure water would decrease the surface temperature and the polluted water would increase the surface temperature. A multiple regression between LST and each indices as well as the elevation was created to elevate the urban thermal environment, which showed that NDVI, NDBI, NDBaI, MNDWI were effective indicators for quantifying LULC impacts on LST.     

Investigating relationship between drought severity in Botswana and ENSO

Natural Hazards - The objective, accurate and rapid quantification of agricultural drought is the key component of effective drought planning and management mechanism. The present study proposed a...     

Correlation analysis between drought indices and terrestrial water storage from 2002 to 2015 in China

Drought monitoring is a key topic in environmental monitoring and assessment although there is still a need to determine the correlation between drought monitoring indices and remote sensing products. We analyzed the correlation between the self-calibrating Palmer Drought Severity Index (sc_PDSI), the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index (SPEI) and terrestrial water storage monitored through the Gravity Recovery and Climate Experiment (GRACE) on a monthly timescale from 2002 to 2015 in China. As a consequence of anomalies in the soil water budget, the highly significant correlation between the sc_PDSI and the GRACE satellite-observed terrestrial water storage suggested that these two datasets are the most suitable for use in monitoring droughts. In comparing the three drought indices, the sc_PDSI was introduced as a means of drought monitoring in the Yangtze, Pearl, Huaihe, Southeast and Songhua River Basins, whereas the SPEI was found to be more applicable to other major river basins, such as the Inland River Basin. These diverse spatial behaviors are caused by the differences between the hydrological droughts characterized by these three drought indices.     

新疆博格达山分段及深浅构造转换关系

研究表明 ,天山及邻区自中生代以来一直处于热衰减状态 ,博格达山新生代再造山具有“冷隆升”性 ,盆山边界断裂多限于上地壳内 ,而非直通中地壳低速体甚至上地幔的“深大断裂”。造山带内的韧性剪切带是在古生代形成的 ,而不是再造山期的断裂 ,它对造山带隆升及盆山耦合无贡献 ,博格达山的隆升为复式背斜构造所支持。博格达山与准东的关系为背斜北翼与盆地平缓基底构成的挠曲构造 ,而不是被深大断裂分隔的断块。博格达山具有独特鲜明的分段性 ,造山带的两个弧形构造与新生代再生前陆盆地构成独特的“斜方对称”分布样式。以板条观点为指导 ,从盆山单元的平面配置关系和深浅构造转换关系入手 ,探讨了博格达山板内造山阶段的几何学和运动学分段性的成因 ,构建了盆山耦合模式     

Analysing the relationship between drought and soil erosion using vegetation health index and RUSLE models in Godavari middle sub-basin,India

Drought is a natural phenomenon posing severe implications for soil, groundwater and agricultural yield. It has been recognized as one of the most pervasive global change drivers to affect the soil. Soil being a weakly renewable resource takes a long time to form, but it takes no time to degrade. However, the response of soil to drought conditions as soil loss is not manifested in the existing literature. Thus, this study makes a concerted effort to analyze the relationship between drought conditions and soil erosion in the middle sub-basin of the Godavari River in India. MODIS remote sensing data was utilized for driving drought indices during 2000–2019. Firstly, we constricted Temperature condition index (TCI) and Vegetation Condition Index (VCI) from Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI) derived from MODIS data. TCI and VCI were then integrated to determine the Vegetation Health Index (VHI). Revised Universal Soil Loss Equation (RUSLE) was utilized for estimating soil loss. The relationship between drought condition and vegetation was ascertained using the Pearson correlation. Most of the northern and southern watersheds experienced severe drought condition in the sub-basin during 2000–2019. The mean frequency of the drought occurrence was 7.95 months. The average soil erosion in the sub-basin was estimated to be 9.88 t ha^?1 year^?1. A positive relationship was observed between drought indices and soil erosion values (r value being 0.35). However, wide variations were observed in the distribution of spatial correlation. Among various factors, the slope length and steepness were found to be the main drivers of soil erosion in the sub-basin. Thus, the study calls for policy measures to lessen the impact of drought and soil erosion.     

Spatial and temporal of variations of alpine vegetation cover in the source regions of the Yangtze and Yellow Rivers of the Tibetan Plateau from 1982 to 2001

Spatial and temporal variations in alpine vegetation cover have been analyzed between 1982 and 2001 in the source regions of the Yangtze and Yellow Rivers on the Tibetan Plateau. The analysis was done using a calibrated-NDVI (Normalized Difference Vegetative Index) temporal series from NOAA-AVHRR images. The spatial and temporal resolutions of images are 8 km and 10 days, respectively. In general, there was no significant trend in alpine vegetation over this time period, although it continued to degrade severely in certain local areas around Zhaling and Eling Lakes, in areas north of these lakes, along the northern foot of Bayankala Mountain in the headwaters of the Yellow River, in small areas in the Geladandong region, in a few places between TuoTuohe and WuDaoliang, and in the QuMalai and Zhiduo belts in the headwaters of the Yangtze River. Degradation behaves as vegetation coverage reduced, soil was uncovered in local areas, and over-ground biomass decreased in grassland. The extent of degradation ranges from 0 to 20%. Areas of 3×3 pixels centered on Wudaoliang, TuoTuohe, QuMalai, MaDuo, and DaRi meteorological stations were selected for statistical analysis. The authors obtained simple correlations between air temperature, precipitation, ground temperature and NDVI in these areas and constructed multivariate statistical models, including and excluding the effect of ground temperature. The results show that vegetation cover is sensitive to variations in temperature, and especially in the ground temperature at depths of ∼40 cm. Permafrost is distributed widely in the study area. The resulting freezing and thawing are related to ground temperature change, and also affect the soil moisture content. Thus, degradation of permafrost directly influences alpine vegetation growth in the study area.     

Modifications in vegetation cover and surface albedo during rapid urbanization: a case study from South China

The green vegetation fraction (GVF) and surface albedo are important land surface parameters often used for validation of climate and land surface models that are influenced largely by environmental gradients and human activities. In this study, fine resolution GVF and albedo values derived from Landsat Thematic Mapper/Enhanced Thematic Mapper Plus images from 1990 to 2000 were used to examine the relationship of both GVF and albedo values to the spatial gradients of parameters related to dramatic urbanization in the Greater Guangzhou metropolitan area, Guangdong Province, in South China. Moderate resolution GVF and albedo datasets derived from the MODIS Collection 5 product were used to analyze the seasonal variation of GVF and albedo with rapid urban expansion from 2001 to 2007. The results show that the shortwave albedo had a clear declining trend from the urban center to natural land in 1990. However, no obvious trend in shortwave albedo change was observed along urban–rural gradients caused by the expansion of low-albedo urban buildings and more heterogeneous land cover patterns in 2000. A threshold of GVF (~0.21) was estimated for determining the change of albedo associated with vegetation fraction. Vegetation cover modified by urban expansion changed surface reflectance and influenced the surface energy balance. It is suggested that a large portion of energy absorbed in an urban area is likely to be converted to thermal energy that heating up is near the surface and emitted as longwave radiation.     

1928年至1929年中国东部的严重干旱

1928~1929年夏季, 中国北方(34°~45°N, 106°~122°E)和华南(20°~30°N, 106°~122°E)地区遭受了严重的干旱, 此次旱灾是中国近代十大灾荒之一。由于早期观测资料缺乏, 数值模拟成为研究此次旱灾形成机制的重要手段。本研究诊断分析了挪威地球系统模式(NorESM1-F)过去千年试验中1928年和1929年的模拟。结果表明: 模拟的1928年与1929年夏季中国东部季风区旱涝空间分布与历史记录重建非常相似; 即1928年夏季, 降雨集中在长江与黄河之间, 而1929年夏季, 降雨集中在长江中下游; 其他地区降雨偏少。重建和观测资料证实NorESM1-F能够较好地模拟中高纬海表面温度异常; 同时, 模拟结果显示, 这两年夏季北大西洋高纬地区以及北美西海岸的海表面温度偏高是造成这两年干旱的控制因素之一。它激发出影响东亚夏季降水的遥相关波列。1928年夏季, 明显的正位相欧亚遥相关, 导致东亚大槽加深、西太平洋副热带高压南撤、东亚夏季风减弱, 并最终导致1928年夏季降水异常减少; 而1929年夏季, 中纬度的丝绸之路遥相关波列(SRP)使200hPa南亚高压加强东伸、中国东部沿海地区出现正位势高度异常、西太平洋副热带高压西伸, 导致长江流域降雨增多, 中国北方和华南地区降雨减少。

     

Spatial and temporal pattern of precipitation and drought in Gansu Province, Northwest China

Drought is one of the most harmful natural hazards in Gansu Province in Northwest China. The changes of precipitation affect the severity of drought. In order to recognize the trend of precipitation and understand the effect of rainfall change on water resources management and drought severity, Mann–Kendall test was used. Standardized Precipitation Index (SPI) was calculated to reconstruct the drought at different time scales and analyze the frequency of drought occurrence in the recent 50 years. The results show that the SPI is applicable in Gansu Province. The number of severe droughts differs among regions: it is more obvious as a 3-month drought in the Yellow River Basin and the Yangtze River Basin than in the Inland River Basin, and other droughts at 6-, 9-, and 12-month time scales have the same effect in the three regions. Mann–Kendall test results show that there is an upward trend in the summer periods and a downward trend in the autumn-winter-spring intervals ranging from 10.5 mm/10 years to −37.4 mm/10 years, which affect the local water resources management, droughts mitigation, and agriculture decision making. This situation poses challenges for future study.     

The roles of community assets in mitigating the impact of drought on grain yields in Northwest China

As an arid and semiarid region in that is frequently hit by drought, Northwest China is ecologically vulnerable. Faced with drought and other extreme events, policy makers have given top priority to the formulation and implementation of adaptation policies. This paper investigates the roles of community assets, including community social capital and access to public services, in mitigating the impact of drought in Northwest China. Based on a micro-level dataset of individual households and villages from two provinces, we find a major effect of community assets on grain yields, after controlling for other influences. Our econometric analyses show that the severity of drought in the study areas significantly reduces grain yields. The negative impact of drought, however, can be significantly mitigated in villages with better community assets. Several policies, including enhancing investments in communities’ infrastructure and providing public services related to drought, are recommended to both improve local adaptive capacity to drought and reduce poverty in the drought-prone areas.     

古陆块及其边缘与铀成矿的关系

古陆块及其边缘是重要的铀成矿区域,统计资料表明,中国有约47%的铀矿床分布于古陆块及其边缘。针对上述现象,笔者进行了一系列资料调研,初步总结了古陆块及其边缘与铀成矿的关系。一方面,古陆块是最古老的成熟地壳,其岩石铀含量高,可以为铀成矿提供物质来源;另一方面,古陆块边缘壳幔物质循环显著,岩浆及热液活动频繁。这些有利因素使古陆块及其边缘成了铀矿集中区,并且在一定程度上控制着铀矿床的时空分布。     

福建省植被与地质灾害关系初探

根据福建省县(市)地质灾害调查与区划已入库的资料,通过对地质灾害类型与植被类型关系的统计分析和局部林地的植被雨水截留率和土体径流路径的研究,表明了植被对于水文效应和土体性质的改良作用,从而揭示了植被对于防治地质灾害作用机理,同时指出植被对阻止各类地质灾害的发生还有许多积极作用及局限性,植被作用于滑坡的各种参数并不是一成不变的,需要根据当地树种、土壤、气候等综合因素判定。     

京津风沙源区2000—2015年植被覆盖状况的区域差异研究

植被覆盖状况是监测与表征区域生态建设成效的重要指标。以往研究注重区域植被覆盖状况的整体变化分析,对长时期区域内部植被覆盖变化及其差异研究较少。文中基于京津风沙源区遥感影像数据,采用GIS空间分析技术,重点评估了2000—2015年植被覆盖度的年际变化及其区域差异。研究结果表明,2000—2015年京津风沙源区植被覆盖度变化为35%~45%,且随年份变化呈波动增加趋势,年均增速为0.4%(P<0.05),生态治理取得明显植被恢复成效。8个治理分区植被覆盖均有所增加,但区域差异明显,晋北山地丘陵亚区和燕山丘陵山地水源保护亚区植被覆盖度年均增速超过0.6%,浑善达克沙地亚区与荒漠草原亚区植被覆盖度年均增速不及0.2%,这与区域地表组成和气候背景有关。从地市来看,北京、天津和承德植被覆盖度较高,但朔州和张家口植被覆盖度增速明显,而乌兰察布和包头植被覆盖度年均增速低于0.1%。相比2000年,2015年京津风沙源区有51%的区域植被覆盖度增加,49%区域植被覆盖度未变或降低,主要集中在京津风沙源区的中部和西部县市(旗),未来生态治理过程中应加以重点关注。     

Characterizing land condition variability in Northern China from 1982 to 2011

For the last three decades, Northern China has been considered as one of the most sensitive areas regarding global environmental change. The integration of AVHRR GIMMS and MODIS NDVI data (1982–2011), of which for the overlapping period of 2000–2006 show good consistency, were used for characterizing land condition variability. The trends of standardized annually ΣNDVI, temperature, precipitation and PDSI were obtained using a linear regression model. The results showed that Northern China has a general increase in greenness for the period 1982–2011 (a = 0.05). Also, annually ΣNDVI is significantly correlated with temperature and precipitation data at the regional scale (p < 0.05), implying that temperature and precipitation are the dominant limiting factors for vegetation growth. Since the greening is not uniform, factors other than temperature and precipitation may contribute to greening in some areas, while the grassland and cropland ecosystem are becoming increasingly vulnerable to drought. The results of trend analysis indicate that greenness seems to be evident in most of the study areas.     

Comprehensive analysis of relationship between vegetation attributes and soil erosion on hillslopes in the Loess Plateau of China

In soil and water conservation research, vegetation is considered to be a primary factor affecting soil erosion. Many studies focus on the relationship between soil erosion and a given attribute of vegetation. Few studies have attempted a comprehensive analysis of vegetation attributes. Thus, the aim of this study is to explain the relationship between vegetation and soil erosion in detail. We studied 104 vegetation plots and 104 soil samples in the Yangjuangou catchment, Loess Plateau, Shaanxi Province, China. According to a correlation analysis of the vegetation attributes and soil ¹³⁷Cs inventories, vegetation cover exerts a positive effect on soil erosion. In addition, vegetation aggregation increases with increasing soil loss. During this period of study, plant diversity can have different relationships with soil erosion according to the vegetation pattern. When vegetation distribution is relatively homogeneous, plant cover decreases with increasing diversity, and the soil loss increases. When vegetation pattern distributes between homogeneous and heterogeneous, the relationship between vegetation diversity and soil erosion is not obvious. When vegetation distribution is in a heterogeneous pattern, cover increases with increasing diversity, and soil loss decreases.