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1.
随机森林算法在全球干旱评估中的应用   总被引:2,自引:0,他引:2  
干旱是发生频率最高,造成社会、经济损失和生态破坏最严重、最广泛的自然灾害之一,因此对干旱进行可靠、有效的评估十分重要.本文以月平均降水、月平均温度、月最高温度、月最低温度、土壤湿度、蒸散发、NDVI、叶绿素荧光等作为解释变量,以基于SPI的干旱等级作为目标变量,采用随机森林算法,以2007-2012年的数据作为训练数据...  相似文献   

2.
Understanding streamflow changes in terms of trends and periodicities and relevant causes is the first step into scientific management of water resources in a changing environment. In this study, monthly streamflow variations were analyzed using Modified Mann-Kendall(MM-K) trend test and Continuous Wavelet Transform(CWT) methods at 9 hydrological stations in the Huaihe River Basin. It was found that: 1) streamflow mainly occurs during May to September, accounting for 70.4% of the annual total streamflowamount with Cv values between 0.16–0.85 and extremum ratio values between 1.70–23.90; 2) decreased streamflow can be observed in the Huaihe River Basin and significant decreased streamflow can be detected during April and May, which should be the results of precipitation change and increased irrigation demand; 3) significant periods of 2–4 yr were detected during the 1960 s, the 1980 s and the 2000 s. Different periods were found at stations concentrated within certain regions implying periods of streamflow were caused by different influencing factors for specific regions; 4) Pacific Decadal Oscillation(PDO) has the most significant impacts on monthly streamflow mainly during June. Besides, Southern Oscillation Index(SOI), North Atlantic Oscillation(NAO) and the Ni?o3.4 Sea Surface Temperature(Ni?o3.4) have impacts on monthly streamflow with three months lags, and was less significant in time lag of six months. Identification of critical climatic factors having impacts on streamflow changes can help to predict monthly streamflow changes using climatic factors as explanatory variables. These findings were well corroborated by results concerning impacts of El Nino-Southern Oscillation(ENSO) regimes on precipitation events across the Huaihe River Basin. The results of this study can provide theoretical background for basin-scale management of water resources and agricultural irrigation.  相似文献   

3.
Drought, as a recurring extreme climate event, affects the structure, function, and process of terrestrial ecosystems. Despite the increasing occurrence and intensity of the drought in the past decade in Southwestern China, the impacts of continuous drought events on vegetation in this region remain unclear. During 2001–2012, Southwestern China experienced the severe drought events from 2009 to 2011. Our aim is to characterize drought conditions in the Southwestern China and explore the impacts on the vegetation condition and terrestrial ecosystem productivity. The Standardized Precipitation Index(SPI) was used to characterize drought area and intensity and a light-use efficiency model was used to explore the effect of drought on the terrestrial ecosystem productivity with Moderate Resolution Imaging Spectrometer(MODIS) data. The SPI captured the major drought events in Southwestern China during the study period, indicated that the 12-year period of this study included both ‘normal' precipitation years and two severe drought events in 2009–2010 and 2011. Results showed that vegetation greenness(Normalized Difference Vegetation Index, NDVI and Enhanced Vegetation Index, EVI) both declined in 2009/2010 drought, but the 2011 drought resulted in less declines of vegetation greenness and productivity due to shorten drought duration and rising temperature. Meanwhile, it was about 5 months lapse between drought events and maximum declines in vegetation greenness for 2009/2010 drought events. In addition, forest, grassland and cropland revealed significant different ecosystem responses to drought. It indicated that grassland showed an early sensitivity to drought, while cropland was the most sensitive to water deficit and forest was more resilient to drought. This study suggests that it is necessary to detect the difference responses of ecosystem to drought in a regional area with satellite data and ecosystem model.  相似文献   

4.
In this paper, by using ocean surface temperature data (COADS), the study is made of the characteristics of the monthly and annual changes of the SST in the tropical western Pacific and Indian Oceans, which have important influences on the climate change of the whole globe and the relation between ENSO(E1 Nino-Southern Oscillation) and the Antarctic ice area is also discussed. The result indicates that in the tropical western Pacific and the Indian Oceans the change of Sea Surface Temperture (SST) is conspicuous both monthly and armaully, and shows different change tendency between them. This result may be due to different relation in the vibration period of SST between the two Oceans. The better corresponding relationship is obvious in the annual change of SST in the tropical Indian Ocean with the occurrence El Nino and LaNlra. The change of the SST in the tropical western Pacific and the tropical Indian Oceans has a close relation to the Antarctic ice area, especially to the ice areas in the eastern-south Pole and Ross Sea, and its notable correlative relationship appears in 16 months when the SST of the tropical western Pacific and the Indian Oceans lag back the Antarctic ice area.  相似文献   

5.
半干旱区旱情监测指数应用分析   总被引:1,自引:0,他引:1  
本文利用MODIS地表温度数据(Ts)和增强型植被指数EVI构建Ts和EVI(Enhanced Vegetation Index)空间。同时分别获取2002年3月8日,4月2日、4月13日、6月12日的温度植被干旱指数TVDI,以其为旱情指标对黄河三花间(三门峡-花园口区间)区域旱情进行了监测;结合气象站点数据及表观热惯量对TVDI进行评价,TVDI与热惯量相关系数R2达到0.7,并分析了土地利用和高程对TVDI的影响。结果表明:土地利用影响着TVDI值的分布;三花间(三门峡-花园口区间)区域250m以上高程和TVDI关系显著。以Ts和EVI构建的TVDI适用于半干旱区的旱情监测。  相似文献   

6.
1 Introduction TheMadden JulianOscillation (MJO)isastrongatmosphericconvection phenomenonoccurringovertheEasternIndianOceanandtheTropicalWesternPacific,usuallyinregionswithseasurfacetempera tures (SSTs)over 2 9℃ .Theeastwardmovingofalarge scalecirculat…  相似文献   

7.
Long-range precipitation forecasts are useful when managing water supplies.Oceanicatmospheric oscillations have been shown to influence precipitation.Due to a longer cycle of some of the oscillations,a short instrumental record is a limitation in using them for long-range precipitation forecasts.The influence of oscillations over precipitation is observable within paleoclimate reconstructions;however,there have been no attempts to utilize these reconstructions in precipitation forecasting.A data-driven model,KStar,is used for obtaining long-range precipitation forecasts by extending the period of record through the use of reconstructions of oscillations.KStar is a nearest neighbor algorithm with an entropy-based distance function.Oceanic-atmospheric oscillation reconstructions include the El Nino-Southern Oscillation(ENSO),the Pacific Decadal Oscillation(PDO),the North Atlantic Oscillation(NAO),and the Atlantic Multi-decadal Oscillation(AMO).Precipitation is forecasted for 20 climate divisions in the western United States.A 10-year moving average is applied to aid in the identification of oscillation phases.A lead time approach is used to simulate a one-year forecast,with a 10-fold cross-validation technique to test the models.Reconstructions are used from 1658-1899,while the observed record is used from 1900-2007.The model is evaluated using mean absolute error(MAE),root mean squared error(RMSE),RMSE-observations standard deviation ratio(RSR),Pearson’s correlation coefficient(R),NashSutcliffe coefficient of efficiency(NSE),and linear error in probability space(LEPS) skill score(SK).The role of individual and coupled oscillations is evaluated by dropping oscillations in the model.The results indicate ’good’ precipitation estimates using the KStar model.This modeling technique is expected to be useful for long-term water resources planning and management.  相似文献   

8.
Empirical orthogonal function (EOF) analysis reveals a co-variability of Sea surface temperatures (SSTs) in the Southern Hemisphere (0°-60°S). In the South Indian and Atlantic Oceans, there is a subtropical dipole pattern slanted in the southwest- north-east direction. In the South Pacific Ocean, a meridional tripole structure emerges, whose middle pole co-varies with the dipoles in the South Indian and Atlantic Oceans and is used in this study to track subtropical Pacific variability. The South Indian and Atlantic Ocean dipoles and the subtropical Pacific variability are phase-locked in austral summer. On the inter-decadal time scales, the dipoles in the South Indian and Atlantic Oceans weaken in amplitude after 1979/1980. No such weakening is found in the subtropical South Pacific Ocean. Interestingly, despite the reduced amplitude, the correlation of the Indian Ocean and Atlantic dipoles with El Nio and Southern Oscillation (ENSO) are enhanced after 1979/1980. The same increase in correlation is found for subtropical South Pacific variability after 1979/1980. These inter-decadal modulations imply that the Southern Hemisphere participates in part of the climate shift in the late 1970s. The correlation between Southern Hemisphere SST and ENSO reduces after 2000.  相似文献   

9.
Climatic extremes such as drought have becoming a severe climate-related problem in many regions all over the world that can induce anomalies in vegetation condition. Growth and CO2 uptake by plants are constrained to a large extent by drought. Therefore, it is important to understand the spatial and temporal responses of vegetation to drought across the various land cover types and different regions. Leaf area index (LAI) derived from Global Land Surface Satellite (GLASS) data was used to evaluate the response of vegetation to drought occurrence across Yunnan Province, China (2001–2010). The meteorological drought was assessed based on Standardized Precipitation Index (SPI) values. Pearson’s correlation coefficients between LAI and SPI were examined across several timescales within six sub-regions of the Yunnan. Further, the drought-prone area was identified based on LAI anomaly values. Lag and cumulative effects of lack of precipitation on vegetation were evident, with significant correlations found using 3-, 6-, 9- and 12-month timescale. We found 9-month timescale has higher correlations compared to another timescale. Approximately 29.4% of Yunnan’s area was classified as drought-prone area, based on the LAI anomaly values. Most of this drought-prone area was distributed in the mountainous region of Yunnan. From the research, it is evident that GLASS LAI can be effectively used as an indicator for assessing drought conditions and it provide valuable information for drought risk defense and preparedness.  相似文献   

10.
基于随机森林的遥感干旱监测模型的构建   总被引:1,自引:0,他引:1  
利用遥感数据进行大面积旱情监测是现有干旱监测的重要方法之一,然而传统的遥感干旱监测方法主要侧重于对土壤湿度或植被状况等单一干旱响应因子进行监测,对综合多因子的干旱监测研究较为有限。随机森林是一种机器学习方法,具有学习过程快速、运算速度快、稳定性好、预测精度高的优点,近年来被应用于生态环境等多个领域。本文利用2001-2010年4-9月的MODIS数据提取的植被状态指数(VCI)、温度状态指数(TCI)和土地覆盖类型(LC),TRMM降水资料计算的TRMM-Z指数及SRTM-DEM、土壤有效含水量(AWC)等多个遥感及土壤资料提取的干旱因子为自变量,以气象站点的综合气象干旱指数(CI)为因变量,利用随机森林模型构建遥感干旱监测模型,并以河南省为研究区进行了评价和分析。该模型在2009-2010年的监测值和实测CI值的具有显著的相关性,并且二者干旱等级的一致率为81%。在2001-2010年4-9月间,模型监测值与气象站点的标准降水蒸散发指数(SPEI)总体干旱等级一致率为74.9%,较为一致,其中9月的模型结果与SPEI的干旱等级一致率最高,达到82.4%,空评估率和漏评估率最低;与10 cm土壤相对湿度的相关系数在0.475-0.639之间,达到极显著水平。河南省2011年4-6月干旱事件同样验证了本文构建的模型旱情监测结果,说明本模型能较好地就应用于监测区域旱情监测。  相似文献   

11.
The Simple Ocean Data Assimilation (SODA) package is used to better understand the variabilities of surface current transport in the Tropical Pacific Ocean from 1950 to 1999. Seasonal variation, internnual and decadal variability analyses are conducted on the three major surface currents of the Tropical Pacific Ocean: the North Equatorial Current (NEC), the North Equatorial Countecurrent (NECC), and the South Equatorial Current (SEC). The transport of SEC is quite larger than those of NEC and NECC. The SEC has two maximums in February and August. The NEC has a small annual variation. The NECC has a maximum in October and is very weak in March and April. All currents have remarkable interannual and decadal variabilities. The variabilities of the NEC and the SEC related to the winds over them well, but the relationship between the NECC and the wind over it is not close. Analysis related to El Niño-Southern Oscillation (ENSO) suggests that before El Niño (La Niña) the SEC is weaker (stronger) and the NECC is stronger (weaker), after El Niño (La Niña) the SEC is stronger (weaker) and the SEC is weaker (stronger). There is no notable relationship between the NEC and ENSO.  相似文献   

12.
Tropical Atlantic climate change is relevant to the variation of Atlantic meridional overturning circulation (AMOC) through different physical processes. Previous coupled climate model simulation suggested a dipole-like SST structure cooling over the North Atlantic and warming over the South Tropical Atlantic in response to the slowdown of the AMOC. Using an ocean-only global ocean model here, an attempt was made to separate the total influence of various AMOC change scenarios into an oceanic-induced component and an atmospheric-induced component. In contrast with previous freshwater-hosing experiments with coupled climate models, the ocean-only modeling presented here shows a surface warming in the whole tropical Atlantic region and the oceanic-induced processes may play an important role in the SST change in the equatorial south Atlantic. Our result shows that the warming is partly governed by oceanic process through the mechanism of oceanic gateway change, which operates in the regime where freshwater forcing is strong, exceeding 0.3 Sv. Strong AMOC change is required for the gateway mechanism to work in our model because only when the AMOC is sufficiently weak, the North Brazil Undercurrent can flow equatorward, carrying warm and salty north Atlantic subtropical gyre water into the equatorial zone. This threshold is likely to be model-dependent. An improved understanding of these issues may have help with abrupt climate change prediction later.  相似文献   

13.
在全球气候变暖的大背景下,干旱事件发生越来越频繁,严重危害我国的粮食生产安全。构建准确的干旱监测模型不仅能够及时地反映出干旱事件的发生,同时可以为地方政府制定减灾保产措施提供科学支撑和保障。传统的气象干旱监测方法因为缺乏对植被本身需水状态和土壤供水信息的考虑旱情判定结果往往比实际情况偏重,而遥感监测指标大多只考虑了植被或土壤等单方面因素具有局限性,目前已有的综合干旱监测模型大多以气象指标为因变量,一方面需要数据资料较多参数复杂,另一方面模型准确度依赖于气象指标对当地农业干旱的响应能力,而同一气象指标在不同区域适应性存在差异,因此同样存在局限性。本文以河南省的冬小麦为研究对象,利用2001-2011年的EOS-MODIS数据产品以及气象站点监测数据,计算了标准化降水蒸散指数SPEI、植被状态指数VCI、温度状态指数TCI、温度植被状态指数TVDI,同时结合河南省农业气象灾害旬报对冬小麦受灾的记录,构建了基于决策树的定性农业干旱监测模型。测试集结果表明,模型综合了大气异常信息、植被状态信息以及土壤水分信息,优于单个指标的监测结果。另外,基于此模型监测了河南省2009年4-5月的干旱事件,结果与实情相符,能够较好地反映农业旱情的发生和空间演变情况。  相似文献   

14.
We analyzed the temporal and spatial variation, and interannual variability of the North Pacific meridional overturning circulation using an empirical orthogonal function method, and calculated mass transport using Simple Ocean Data Assimilation Data from 1958–2008. The meridional streamfunction field in the North Pacific tilts N-S; the Tropical Cell (TC), Subtropical Cell (STC), and Deep Tropical Cell (DTC) may be in phase on an annual time scale; the TC and the STC are out of phase on an interannual time scale, but the interannual variability of the DTC is complex. The TC and STC interannual variability is associated with ENSO (El Niño-Southern Oscillation). The TC northward, southward, upward, and downward transports all weaken in El Niños and strengthen in La Niñas. The STC northward and southward transports are out of phase, while the STC northward and downward transports are in phase. Sea-surface water that reaches the middle latitude and is subducted may not completely return to the tropics. The zonal wind anomalies over the central North Pacific, which control Ekman transport, and the east-west slope of the sea level may be major factors causing the TC northward and southward transport interannual variability and the STC northward and southward transports on the interannual time scale. The DTC northward and southward transports decrease during strong El Niños and increase during strong La Niñas. DTC upward and downward transports are not strongly correlated with the Niño-3 index and may not be completely controlled by ENSO.  相似文献   

15.
【Title】
There are knowledge gaps in our understanding of vegetation responses to multi-scale climate-related variables in tropical/subtropical mountainous islands in the Asia-Pacific region. Therefore, this study investigated inter-annual vegetation dynamics and regular/irregular climate patterns in Taiwan. We applied principal component analysis (PCA) on 11 years (2001~2011) of high-dimensional monthly photosynthetically active vegetation cover (PV) derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and investigated the relationships between spatiotemporal patterns of the eigenvectors and loadings of each component through time and multi-scale climate-related variations. Results showed that the first five components contributed to 96.4% of the total variance. The first component (PC1, explaining 94.5% of variance) loadings, as expected, were significantly correlated with the temporal dynamics of the PV (r = 0.94), which was mainly governed by regional climate. The temporal loadings of PC2 and PC3 (0.8% and 0.6% of variance, respectively) were significantly correlated with the temporal dynamics of the PV of forests (r = 0.72) and the farmlands (r = 0.80), respectively. The low-order components (PC4 and PC5, 0.3% and 0.2% of variance, respectively) were closely related to the occurrence of drought (r = 0.49) and to irregular ENSO associated climate anomalies (r = -0.54), respectively. Pronounced correlations were also observed between PC5 and the Southern Oscillation Index (SOI) with one to three months of time lags (r = -0.35 ~ -0.43, respectively), revealing biophysical memory effects on the time-series pattern of the vegetation through ENSO-related rainfall patterns. Our findings reveal that the sensitivity of the ecosystems in this tropical/subtropical mountainous island may not only be regulated by regional climate and human activities but also be susceptible to large-scale climate anomalies which are crucial and comparable to previous large scale analyses. This study demonstrates that PCA can be an effective tool for analyzing seasonal and inter-annual variability of vegetation dynamics across this tropical/subtropical mountainous islandin the Pacific Ocean, which provides an opportunity to forecast the responses and feedbacks of terrestrial environments to future climate scenarios.  相似文献   

16.
The nature decadal variability of the equatorial Pacific subsurface temperature is examined in the control simulation with the Geophysical Fluid Dynamics Laboratory coupled model CM2.1.The dominant mode of the subsurface temperature variations in the equator Pacific features a 20-40 year period and is North-South asymmetric about the equator.Decadal variations of the thermocline are most pronounced in the southwest of the Tropical Pacific.Decadal variation of the north-south asymmetric Sea Surface wind in the tropical Pacific,especially in the South Pacific Convergence,is the dominant mechanism of the nature decadal variation of the subsurface temperature in the equatorial Pacific.  相似文献   

17.
本文首先分析了北大西洋涛动的自身振动及其对欧亚地区冬季气温的影响,而后又对北大西洋涛动与500hpa西风指数变异之联系作了探讨。结果发现:北大西洋涛动存在着较显著的9年变化周期,其强弱变化对欧亚大范围冬季气温具有一定程度的影响,尤其是对大西涛动与同期和前期5月及10月特定区域500hpa西风指数关系密切。  相似文献   

18.
干旱遥感监测方法及其应用发展(可下载全文)   总被引:3,自引:0,他引:3  
 干旱是世界上影响范围最广和造成社会经济损失最严重的一种自然灾害。本文从干旱遥感监测的不同角度出发,总结了目前干旱遥感监测的主要方法、应用状况及优缺点。主要包括针对裸土地表类型的热惯量法、微波法,针对植被覆盖地表类型的可见光、近红外、短波红外等波段反射率数据的归一化植被指数法、距平指数法、条件植被指数法、归一化差值水分指数、归一化干旱指数、植被供水指数等,以及热红外遥感数据的温度植被干旱指数、温度条件指数、作物缺水指数、水分亏缺指数等。最后,提出了加强干旱遥感监测技术研究的建议,同时指出将可见光和微波相结合的指数模型的研究是干旱遥感监测可能的发展方向。  相似文献   

19.
The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.  相似文献   

20.
The neon flying squid(Ommastrephes bartramii) is a short-lived opportunistic species widely distributed in subtropical and temperate waters in the North Pacific Ocean. The life cycle of O. bartramii from planktonic eggs to nektonic adults is closely linked to oceanographic conditions. The fluctuations in O. bartramii abundance and distribution tend to increase and widen continuously due to the heavy influences of ocean-climate events on various spatio-temporal scales. In this study, we reviewed the interaction between O. bartramii and oceanography variability in the North Pacific with respect to large-scale climatic-oceanic phenomena including El Ni?o, La Ni?a, Kuroshio, Oyashio and Pacific Decadal Oscillation(PDO), as well as regional environmental variables such as sea surface temperature(SST), sea surface height(SSH), sea surface salinity(SSS), chlorophyll-a(Chl-a) concentration, and plankton density. The population dynamics of O. bartramii is mediated mainly by meso- and large-scale climatic-oceanic events(e.g., Kuroshio and Oyashio Currents) rather than other local environmental conditions(e.g., SST and Chl-a concentration), because all of the oceanographic influences are imposed on the context of large-scale climate changes(e.g., PDO). An unstructured-grid finitevolume coastal ocean model coupled with an individual-based model is proposed to simulate relevant physical-biological oceanographic processes for identifying ocean-climate influence and predicting O. bartramii distribution and abundance in the North Pacific. Future research needs to be focused on improving the knowledge about early life history of O. bartramii and evaluating the relationship between marine physical environment and two separate passive drifting life stages of O. bartramii including free-floating eggs and planktonic paralarvae.  相似文献   

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