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1.
The hydrographic eastern Mediterranean Basin of Turkey is a drought sensitive area. The basin is an important agricultural area and it is necessary to determine the extent of extreme regional climatic changes as they occur in this basin. Pearson's correlation coefficient was used to show the correlation between standardized precipitation index(SPI) and standardized streamflow index(SSI) values on different time scales. Data from five meteorological stations and seven stream gauging stations in four sub-basins of the eastern Mediterranean Basin were analyzed over the period from 1967 to 2017. The correlation between SSI and SPI indicated that in response to meteorological drought, hydrological drought experiences a one-year delay then occurs in the following year. This is more evident at all stations from the mid-1990 s. The main factor causing hydrological drought is prolonged low precipitation or the presence of a particularly dry year. Results showed that over a long period(12 months), hydrological drought is longer and more severe in the upper part than the lower part of the sub-basins. According to SPI-12 values, an uninterrupted drought period is observed from 2002–2003 to 2008–2009. Results indicated that among the drought events, moderate drought is the most common on all timescales in all sub-basins during the past 51 years. Long-term dry periods with moderate and severe droughts are observed for up to 10 years or more since the late 1990 s, especially in the upper part of the sub-basins. As precipitation increases in late autumn and early winter, the stream flow also increases and thus the highest and most positive correlation values(0.26–0.54) are found in January. Correlation values(ranging between –0.11 and –0.01) are weaker and negative in summer and autumn due to low rainfall. This is more evident at all stations in September. The relation between hydrological and meteorological droughts is more evident, with the correlation values above 0.50 on longer timescales(12-and 24-months). The results presented in this study allow an understanding of the characteristics of drought events and are instructive for overcoming drought. This will facilitate the development of strategies for the appropriate management of water resources in the eastern Mediterranean Basin, which has a high agricultural potential.  相似文献   
2.
宁夏原州区生态移民村生境景观连接度变化及其驱动因素   总被引:1,自引:1,他引:0  
[目的]分析生态移民土地利用过程中生境景观连接度变化及其驱动因素,为生态移民的生态风险管理及移民可持续性提供科学依据。[方法]以宁夏原州区"十二五"时期4个生态移民村(丰泽、金轮、和润及泉港)为例,基于2016年高分影像数据,同时参考移民前谷歌地球2010年数据和第二次全国土地调查数据(2010年),经野外GPS校验,通过计算障碍影响指数和生境景观连接度指数,分析生态移民村土地利用生境景观分异。[结果]丰泽村和金轮村的生境景观连接度呈下降态势,和润村和泉港村呈上升态势。4个生态移民村的变化趋势明显,但极高连接度和高连接度比例很小。生态移民村生境景观变化驱动力主要为人为因素,建设用地占用耕地、园地普遍,其中泉港村与和润村建设用地面积年均增长率分别高达27.49%和21.28%,同时金轮村、和润村、泉港村无后备土地资源,生态压力突出。[结论] 4个生态移民村人口密度增大导致建设用地占用耕地明显,生态用地被分割,移民的非农活动比重大造成耕地撂荒,景观破碎化和孤岛化现象明显,生境景观呈现出不稳定状态,生态压力增加。  相似文献   
3.
[目的]研究特大暴雨条件下小流域沟道泥沙输移路径、泥沙连通程度及其影响因素,旨在探讨水库溃坝的原因,为沟道防洪措施的布设提供依据。[方法]以陕西省子洲县"7·26"暴雨条件下小流域沟道泥沙连通情况为例,选取面积相近、形状相异的清水沟和蛇家沟小流域,对沟道泥沙淤积情况进行现场调查,同时将沟道分为坝地沟段和自然沟段,选取流域面积与形状系数、沟道比降,以及淤地坝的类型与分布进行对比分析两个小流域沟道泥沙连通性的差异。[结果]在此次特大暴雨条件下,清水沟和蛇家沟的淤地坝大都呈现打开状态,由上游到下游清水沟泥沙连通性呈现较强的增长趋势,蛇家沟泥沙连通性则呈现先增长后减弱的趋势。整体上清水沟的泥沙连通性比蛇家沟的强,且清水沟流域的土壤侵蚀也较为严重。串联和混联坝系以及修建有卧管、竖井和排水渠的淤地坝防洪能力更强。[结论]流域面积、流域形状和沟道比降均影响着沟道泥沙的连通性,而淤地坝类型及分布是影响沟道泥沙连通性的主导因子。  相似文献   
4.
Understanding spatial population structure and biocomplexity is critical for determining a species’ resilience to environmental and anthropogenic perturbations. However, integrated population models (IPMs) used to develop management advice for harvested populations have been slow to incorporate spatial dynamics. Therefore, limited research has been devoted to understanding the reliability of movement parameter estimation in spatial population models, especially for spatially dynamic marine fish populations. We implemented a spatial simulation–estimation framework that emulated a generic marine fish metapopulation to explore the impact of ontogenetic movement and climate‐induced distributional shifts between two populations. The robustness of spatially stratified IPMs was explored across a range of movement parametrizations, including ignoring connectivity or estimating movement with various levels of complexity. Ignoring connectivity was detrimental to accurate estimation of population‐specific biomass, while implementing spatial IPMs with intermediate levels of complexity (e.g. estimating movement in two‐year and two‐age blocks) performed best when no a priori information about underlying movement was available. One‐way distributional shifts mimicking climate‐induced poleward migrations presented the greatest estimation difficulties, but the incorporation of auxiliary information on connectivity (e.g. tag‐recapture data) reduced bias. The continued development of spatially stratified modelling approaches should allow harvested resources to be better utilized without increased risk. Additionally, expanded collection and incorporation of unique spatially explicit data will enhance the robustness of IPMs in the future.  相似文献   
5.
6.
自然保护区是保护物种栖息地的重要基础,但频繁的人类活动干扰导致自然保护区内生物栖息地斑块破碎化的问题依然存在,景观连接度定量评价对于保护区生物栖息地保护具有重要作用。以纳板河自然保护区为例,基于图论的指数方法利用2014年和2018年高空间分辨率遥感数据,对保护区栖息地的景观连接度指数的变化及其驱动力因素进行分析。结果表明:1)2014—2018年的景观连接度指数中整体性连接度指数(IIC)、概率连接度指数(PC)都呈现下降趋势,IIC和PC指数分别下降0.29和0.53,指示保护区内栖息地破碎化加剧;2)最大斑块的重要性指数从85.14减少到84.19,重要性前十的斑块时空变化表明了自然保护区栖息地斑块面积不断减小,中部、中西部地区破碎化显著;3)土地利用变化对保护区景观连接度产生重要影响,其中橡胶林、耕地、水库、茶园4类土地利用增加是栖息地破碎化的驱动力因素。研究结果可为纳板河自然保护区栖息地保护管理提供科学依据。  相似文献   
7.
以文峪河流域为研究对象,分析流域2000—2018年景观格局数量动态的面积、转移及速度特征。从斑块类型尺度与景观尺度2个层面选取景观指数分析流域近18年的景观格局动态,并在流域尺度上沿城市—林区梯度线分析沿线景观格局指数的梯度分布,基于数量统计模型对景观格局动态驱动力进行研究。结果表明,流域耕地、林地、草地面积有所减少,向其余地类支出面积,水域、建设用地、未利用地面积增加,向其余地类吸收面积,不同地类土地转移、变化速度情况不同。不同景观类型的格局动态不同,流域整体景观破碎化程度增加,连通性下降、景观规则度下降、景观核心面积下降,不同景观指数的梯度分布特征不同。自然驱动因子、社会驱动因子对流域景观格局变化均具有驱动作用,文峪河流域的景观动态在过去18年间经历了快速、复杂的变化,社会经济驱动因子是景观格局演变的主要驱动力量,经济与人口发展、产业结构及工业化进程是文峪河流域景观格局演变的重要驱动力量。  相似文献   
8.
灌丛沙堆是旱区灌丛植被水文过程的快通道,也是调节土壤水分平衡的关键点。以荒漠草原退化人工柠条林为研究对象,通过人工沙埋的方式改变灌丛沙堆大小与形态,在连续监测分析基础上(2012—2016年),探讨了人工沙埋干预下灌丛沙堆土壤水文过程与水文效应的动态响应。结果表明:与对照相比,(1)沙埋干预并未显著改变表层0—10cm主要的水文物理指标,但是显著提高了5—10cm土壤水分入渗速率,同时0—5cm初渗率显著降低;(2)沙埋干预明显提高了降水后表层0—5cm土壤的即时持水性,同时降水后表层土壤水分含量衰减过程呈现出很强的季节性变化;(3)2012—2016年生长季末沙埋处理的0—100cm土壤相对储水率分别为11.3%,-6.5%,4.5%,4.3%,15.7%,这种效应集中在0—60cm,对照处理下层土壤(60—100cm)水分含量的波动性更强。总体而言,沙埋干预对表层土壤水文物理特性无显著影响,但是显著提高了5—10cm土层水分入渗性能并降低了0—5cm初渗率;但是这种局部入渗性能的加强并未提高水分补给深度,上下层间水文联系反而弱化。沙埋干预的长期水文效应及其作为旱化成龄人工林适应性管理措施的适宜性还有待进一步的跟踪监测与分析。  相似文献   
9.
To examine the role of longitudinal connectivity on the spatial and temporal dynamics of mountain whitefish (Prosopium williamsoni), we quantified movement and population dynamics following installation of the Landsburg Dam fishway, Cedar River, WA, USA. Mountain whitefish is widely distributed, poorly studied and not the focus of restoration. Before the fishway, mountain whitefish were not observed above the dam. Here, we focus on snorkel counts collected at reach and mesohabitat (e.g. pools) scales over 11 summers on the 20‐km above‐dam segment following restoration. A camera within the ladder provided number, size and movement timing, thereby informing on behaviour and recolonisation. Segment‐scale abundance increased following fish passage reaching an asymptote in 7 years, and mountain whitefish were detected throughout the main stem in 10 years. Annual movement through the ladder increased over time and was positively correlated with instream abundance and discharge, but negatively correlated with water temperature. About 60% of fish movements occurred in spring and early summer, potentially for foraging opportunities. Reach‐scale abundance peaked between 7 and 10 km from the dam; deep, cool (~10.6 to 11.6°C) conditions characterised these reaches. At the mesohabitat scale, mountain whitefish detection increased with depth and velocity after accounting for distance from the dam. Our results show how restoring longitudinal connectivity allowed this nontarget species to colonise newly available habitat. Their response supports the critical roles of longitudinal connectivity and environmental conditions, that manifest at different spatial scales, in dictating how freshwater fish respond to habitat disturbance.  相似文献   
10.
A recent population hypothesis for Antarctic silverfish (Pleuragramma antarctica), a critical forage species, argued that interactions between life history and circulation associated with glacial trough systems drive circumpolar distributions over the continental shelf. In the Ross Sea, aggregations of eggs and larvae occur under fast ice in Terra Nova Bay, and the hypothesis predicted that dispersing larvae encounter outflow along the western side of Drygalski Trough. The outflow advects larvae towards the shelf‐break, and mixing with trough inflow facilitates return toward the inner shelf. To examine the hypothesis, we compared samples of P. antarctica collected near Coulman Island in the outflow, along Crary Bank in the inflow, and a third set taken over the rest of the Ross Sea. We ruled out misidentification using an innovative genetic validation. Silverfish larvae comprised 99.5% of the catch, and the highest population densities were found in Drygalski Trough. The results provided no evidence to reject the population hypothesis. Abundance indices, back‐calculated hatching dates, length distributions and growth were congruent with a unified early life history in the western Ross Sea, constrained by cryopelagic early stages in Terra Nova Bay. By contrast, a sample in the Bay of Whales revealed much smaller larvae, suggesting either a geographically separate population in the eastern Ross Sea, or westward connectivity with larvae spawned nearby by fish sourced from troughs upstream in the Amundsen Sea. These results illustrate how hypotheses that integrate population structure with life history can provide precise spatial predictions for subsequent testing.  相似文献   
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