闽东干旱概况及夏季人工增雨作业天气形势分析     

陈德汶  王金萍  林友爱  刘锐志  陈安芳 《气象科技》2005,(Z1)

对闽东干旱的成因和干旱的环流形势进行了探讨,着重分析了夏旱期间人工增雨作业的天气形势以及不同形势、不同云型下的降水情况。结果表明:闽东干旱的形成与大型环流形势、地理因素、土壤植被等有关,平均而言,沿海干旱明显多于内陆山区;夏季发生干旱的机率最大而且强度级别高,西太平洋副热带高压是致旱的主要天气系统;在夏季,台风型(T)、弱流场型(R)是进行人工增雨作业的优势天气型,Cb、Cu、Sc云是开展人工增雨作业比较适合的作业云。这些结果为夏旱期间开展人工增雨作业提供了理论依据。  相似文献   

Leaf area index retrieval based on canopy reflectance and vegetation index in eastern China     

JIANG Jianjun  CHEN Suozhong  CAO Shunxian  WU Hongan  ZHANG Li  ZHANG Hailong 《地理学报》2005,15(2):247-254

The aim of this paper is to investigate the feasibility of using Landsat TM data to retrieve leaf area index (LAI). To get a LAI retrieval model based ground reflectance and vegetation index, detailed field data were collected in the study area of eastern China, dominated by bamboo, tea plant and greengage. Plant canopy reflectance of Landsat TM wavelength bands has been inversed using software of 6S. LAI is an important ecological parameter. In this paper, atmospheric corrected Landsat TM imagery was utilized to calculate different vegetation indices (VI), such as simple ratio vegetation index (SR), shortwave infrared modified simple ratio (MSR), and normalized difference vegetation index (NDVI). Data of 53 samples of LAI were measured by LAI-2000 (LI-COR) in the study area. LAI was modeled based on different reflectances of bands and different vegetation indices from Landsat TM and LAI samples data. There are certainly correlations between LAI and the reflectance of Tm3, TM4, TM5 and TM7. The best model through analyzing the results is LAI = 1.2097*MSR + 0.4741 using the method of regression analysis. The result shows that the correlation coefficient R2 is 0.5157, and average accuracy is 85.75%. However, whether the model of this paper is suitable for application in subtropics needs to be verified in the future.  相似文献   

Efficient use of resources: urban waste ash and soil fertility on the Jos Plateau, Nigeria     

M W Pasquini  F Harris 《Area》2005,37(1):17-29

Waste disposal constitutes an acute problem in numerous African cities. One solution could lie in the recycling of the nutrient-rich waste into agriculture taking place in and around cities. Farmers involved in vegetable production around Jos, Nigeria, have developed a sophisticated soil fertility management strategy combining inorganic fertilizers, manure and urban waste ash. This paper: (1) investigates the socio-economic constraints linked to obtaining scarce organic inputs, particularly urban waste ash and the health hazards (particularly heavy metal contamination of soil and crops) caused by using this ash and (2) suggests ways to improve use of this important resource.  相似文献   

Ensemble prediction of regional droughts using climate inputs and the SVM–copula approach          下载免费PDF全文

Poulomi Ganguli  M. Janga Reddy 《水文研究》2014,28(19):4989-5009

In this study, the climate teleconnections with meteorological droughts are analysed and used to develop ensemble drought prediction models using a support vector machine (SVM)–copula approach over Western Rajasthan (India). The meteorological droughts are identified using the Standardized Precipitation Index (SPI). In the analysis of large‐scale climate forcing represented by climate indices such as El Niño Southern Oscillation, Indian Ocean Dipole Mode and Atlantic Multidecadal Oscillation on regional droughts, it is found that regional droughts exhibits interannual as well as interdecadal variability. On the basis of potential teleconnections between regional droughts and climate indices, SPI‐based drought forecasting models are developed with up to 3 months' lead time. As traditional statistical forecast models are unable to capture nonlinearity and nonstationarity associated with drought forecasts, a machine learning technique, namely, support vector regression (SVR), is adopted to forecast the drought index, and the copula method is used to model the joint distribution of observed and predicted drought index. The copula‐based conditional distribution of an observed drought index conditioned on predicted drought index is utilized to simulate ensembles of drought forecasts. Two variants of drought forecast models are developed, namely a single model for all the periods in a year and separate models for each of the four seasons in a year. The performance of developed models is validated for predicting drought time series for 10 years' data. Improvement in ensemble prediction of drought indices is observed for combined seasonal model over the single model without seasonal partitions. The results show that the proposed SVM–copula approach improves the drought prediction capability and provides estimation of uncertainty associated with drought predictions. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Likely effects of climate change on groundwater availability in a Mediterranean region of Southeastern Spain          下载免费PDF全文

Hassane Moutahir  Pau Bellot  Robert Monjo  Juan Bellot  Miguel Garcia  Issam Touhami 《水文研究》2017,31(1):161-176

Groundwater resources are typically the main fresh water source in arid and semi‐arid regions. Natural recharge of aquifers is mainly based on precipitation; however, only heavy precipitation events (HPEs) are expected to produce appreciable aquifer recharge in these environments. In this work, we used daily precipitation and monthly water level time series from different locations over a Mediterranean region of Southeastern Spain to identify the critical threshold value to define HPEs that lead to appreciable aquifer recharge in this region. Wavelet and trend analyses were used to study the changes in the temporal distribution of the chosen HPEs (≥20 mm day^?1) over the observed period 1953–2012 and its projected evolution by using 18 downscaled climate projections over the projected period 2040–2099. The used precipitation time series were grouped in 10 clusters according to similarities between them assessed by using Pearson correlations. Results showed that the critical HPE threshold for the study area is 20 mm day^?1. Wavelet analysis showed that observed significant seasonal and annual peaks in global wavelet spectrum in the first sub‐period (1953–1982) are no longer significant in the second sub‐period (1983–2012) in the major part of the ten clusters. This change is because of the reduction of the mean HPEs number, which showed a negative trend over the observed period in nine clusters and was significant in five of them. However, the mean size of HPEs showed a positive trend in six clusters. A similar tendency of change is expected over the projected period. The expected reduction of the mean HPEs number is two times higher under the high climate scenario (RCP8.5) than under the moderate scenario (RCP4.5). The mean size of these events is expected to increase under the two scenarios. The groundwater availability will be affected by the reduction of HPE number which will increase the length of no aquifer recharge periods (NARP) accentuating the groundwater drought in the region. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

A new standardized Palmer drought index for hydro‐meteorological use          下载免费PDF全文

Mingwei Ma  Liliang Ren  Fei Yuan  Shanhu Jiang  Yi Liu  Hao Kong  Luyan Gong 《水文研究》2014,28(23):5645-5661

Accepting the concept of standardization introduced by the standardized precipitation index, similar methodologies have been developed to construct some other standardized drought indices such as the standardized precipitation evapotranspiration index (SPEI). In this study, the authors provided deep insight into the SPEI and recognized potential deficiencies/limitations in relating to the climatic water balance it used. By coupling another well‐known Palmer drought severity index (PDSI), we proposed a new standardized Palmer drought index (SPDI) through a moisture departure probabilistic approach, which allows multi‐scalar calculation for accurate temporal and spatial comparison of the hydro‐meteorological conditions of different locations. Using datasets of monthly precipitation, temperature and soil available water capacity, the moisture deficit/surplus was calculated at multiple temporal scales, and a couple of techniques were adopted to adjust corresponding time series to a generalized extreme value distribution out of several candidates. Results of the historical records (1900–2012) for diverse climates by multiple indices showed that the SPDI was highly consistent and correlated with the SPEI and self‐calibrated PDSI at most analysed time scales. Furthermore, a simple experiment of hypothetical temperature and/or precipitation change scenarios also verified the effectiveness of this newly derived SPDI in response to climate change impacts. Being more robust and preferable in spatial consistency and comparability as well as combining the simplicity of calculation with sufficient accounting of the physical nature of water supply and demand relating to droughts, the SPDI is promising to serve as a competent reference and an alternative for drought assessment and monitoring. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Impact of climate indicators on continental‐scale potential groundwater recharge in Africa          下载免费PDF全文

Paolo Nasta  John B. Gates  Yoshihide Wada 《水文研究》2016,30(19):3420-3433

In the last decades, human activity has been contributing to climate change that is closely associated with an increase in temperatures, increase in evaporation, intensification of extreme dry and wet rainfall events, and widespread melting of snow and ice. Understanding the intricate linkage between climate warming and the hydrological cycle is crucial for sustainable management of groundwater resources, especially in a vulnerable continent like Africa. This study investigates the relationship between climate‐change drivers and potential groundwater recharge (PGR) patterns across Africa for a long‐term record (1960–2010). Water‐balance components were simulated by using the PCR‐GLOBWB model and were reproduced in both gridded maps and latitudinal trends that vary in space with minima on the Tropics and maxima around the Equator. Statistical correlations between temperature, storm occurrences, drought, and PGR were examined in six climatic regions of Africa. Surprisingly, different effects of climate‐change controls on PGR were detected as a function of latitude in the last three decades (1980–2010). Temporal trends observed in the Northern Hemisphere of Africa reveal that the increase in temperature is significantly correlated to the decline of PGR, especially in the Northern Equatorial Africa. The climate indicators considered in this study were unable to explain the alarming negative trend of PGR observed in the Sahelian region, even though the Standardized Precipitation‐Evapotranspiration Index (SPEI) values report a 15% drought stress. On the other hand, increases in temperature have not been detected in the Southern Hemisphere of Africa, where increasing frequency of storm occurrences determine a rise of PGR, particularly in southern Africa. Time analysis highlights a strong seasonality effect, while PGR is in‐phase with rainfall patterns in the summer (Northern Hemisphere) and winter (Southern Hemisphere) and out‐of‐phase during the fall season. This study helps to elucidate the mechanism of the processes influencing groundwater resources in six climatic zones of Africa, even though modelling results need to be validated more extensively with direct measurements in future studies. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

基于温度植被干旱指数的电网输电线路走廊干旱分析     

孙洋杰  唐华林 《测绘与空间地理信息》2016,(10):94-97

以湖北省输电线路走廊地区作为研究区,利用2013年1~9月MODIS卫星影像数据,处理得到月尺度的归一化植被指数(Normalized Differential Vegetation Index,NDVI)与地表温度(Land Surface Temperature,LST)数据,构建NDVI-Ts特征空间,计算得到温度植被干旱指数(Temperature Vegetation Dryness Index,TVDI),用TVDI监测结果分析湖北省输电线路走廊区域2013年干旱时空分布情况。结果表明,湖北省输电线路走廊地区TVDI和土壤含水量之间存在显著的负相关,相关系数达到0.525(p0.05),由MODIS卫星影像计算得到TVDI影像可以有效表明湖北省输电线路走廊地区的土壤含水情况。  相似文献   

中国北方地区秋季植被变化及对气候变化的响应研究     

安佑志  高炜  高志强  施润和 《测绘与空间地理信息》2016,(11)

基于1982~2006年的AVHRR GIMMS NDVI数据,使用一元线性回归和分段线性回归等方法,通过对中国北方地区植被变化及其与气候因子的关系研究,揭示该地区近25年来在不同时段的植被变化趋势及对气候变化的响应规律,从而为该地区的生态环境变化研究提供理论依据。研究结果表明:1)中国北方地区秋季植被在25年时间内整体呈上升趋势。秋季NDVI在秋季温度断点之前以上升趋势为主,秋季NDVI在秋季温度断点之后仍以上升趋势为主,但上升趋势有所放缓。2)通过分段线性回归方法和相关分析研究得出中国北方地区秋季温度是秋季NDVI变化的主要驱动力。在秋季温度断点之后,秋季温度仍呈上升趋势而降水呈显著减少的面积增多,从而在温度和降水双重影响下的干旱胁迫导致植被下降;当秋季温度下降而秋季降水增多时干旱发生概率变小,从而使秋季NDVI呈上升趋势。  相似文献   

Occurrence,durée et intensité des précipitations simulées par deux modèles régionaux canadiens du climat sur la région du Maghreb     

Mariem Jelassi  Philippe Gachon  René Laprise 《大气与海洋》2016,54(5):469-497

[Translated by the editorial staff] Simulating the precipitation regime of Northern Africa is challenging for regional climate models, particularly because of the strong spatial and temporal variability of rain events in the region. In this study we evaluate simulations conducted with two recent versions of regional climate models (RCM) developed in Canada: the CRCM5 and CanRCM4. Both are also used in the COordinated Regional Climate Downscaling EXperiment (CORDEX)-Africa. The assessment is based on the occurrence, duration, and intensity indices of daily precipitation in Maghreb during the fall and spring seasons from 1998 to 2008. We also examine the links between the North-Atlantic Oscillation (NAO) index, weather systems, and the precipitation regime over the region. During the rainy season (September to February), the CRCM5 reproduces the frequency and intensity of extreme precipitation adequately, as well as the occurrence of days with rain, while the CanRCM4 underestimates precipitation extremes. The study of links between weather systems and the precipitation regime shows that, along the Atlantic coast, precipitation (occurrence, intensity, and wet sequences) increases significantly with storm frequency in the fall. In winter, these links grow stronger going east, from the Atlantic coast to the Mediterranean coast. The negative phases of the NAO index are statistically associated with the increase in rain intensity, extremes, and accumulation along the Atlantic coast in the fall. However, the link weakens in winter over these regions and strengthens along the Mediterranean coast as the precipitation frequency rises during negative phases of the NAO. Both RCMs generally reproduce the links between the NAO and the precipitation regime well, regardless of location.  相似文献