基于GWR模型的陕西秦巴山区TRMM降水数据降尺度研究

应用TRMM降水数据,进行国内典型区域降尺度相关研究,可弥补应用气象站点数据研究带来的局限。以陕西秦巴山区为研究区,基于TRMM降水数据和NDVI数据,应用GWR模型和比例指数,获得GWR年、月降尺度数据并进行检验,最后分析地形对降尺度结果的影响。结果表明：获得的1 km分辨率的GWR降尺度降水数据,具有较强的细节表现能力;降尺度数据与实测降水数据年尺度上相关系数为0.88,月为0.93,相关性较好;与TRMM原始数据对比,降尺度结果降水值略小,整体低估降水;区内秦岭山地GWR降尺度结果精度变化幅度最小,相似地形条件下,海拔越高,GWR降尺度结果表现越好;采用GWR模型进行秦巴山区TRMM降水数据的降尺度研究,具有较强的适用性。     

Estimating the spatial and temporal impacts of climate change on rainfall reliability: An example in a Mediterranean agricultural region

Rainfall is the major driver of crop growth in Mediterranean agricultural regions and its spatial and temporal distributions determine yield potential. This study uses a long term spatial archive of rainfall observations for the Eyre Peninsula (South Australia) to estimate the spatial and temporal impacts of climate change on wheat yield. The three step process involved: (1) cluster analysis and statistical comparison to spatially distinguish heterogeneous “hazardscapes” (places that represent the physical susceptibility to hazards (Khan, 2012)); (2) using historical rainfall reliabilities to estimate the probability of receiving rainfall within a range of predefined thresholds and season for each hazardscape; (3) applying 2030 and 2070 climate change projections to determine the potential future impacts on rainfall. Nine hazardscapes were spatially differentiated each having temporally different historical seasonal rainfall reliabilities. Variations over space and time mean that the impacts of climate change will be spatially explicit. Projected rainfall reductions for 2030 showed marginal impact on hazardscapes with low seasonal reliabilities, primarily in winter and spring. The 2070 projections showed that some hazardscapes were unlikely to receive past rates of rainfall thus limiting the ongoing prospects of current and perhaps the potential adoption of alternative rain-fed land uses. Reductions in rainfall for hazardscapes with higher historical rainfall reliabilities will cause negative impacts on crop development. The ability to quantify the potential spatial and temporal impacts of climate change on seasonal trends will inform land managers' climate change mitigation and adaptation pathways.     

Falling water-levels in saline lakes of the central Rift Valley of Kenya: The case of Lake Elmenteita

Reasons why Lake Elmenteita and rivers flowing into it decreased in volume during 1958–1987 were investigated. The effects of changing climate, landcover and landuse were considered. The study suggested that falling lake water-levels are not due to climate change alone: landuse changes and river abstraction and damming may also be important. Long-term trends in rainfall and evaporation reveal various patterns: monthly evaporation has slightly decreased recently but with no effect on lake levels; rainfall has remained more or less constant in total amount, but monthly falls show increased variability. Although flows in rivers and streams are primarily determined by rainfall, other factors operate near the lake so discharge into the lake cannot be predicted from rainfall. Increased settlement and farming on former forested areas within the catchment and irrigation along rivers also indirectly affect discharge values. Additionally, accelerated soil erosion from farmed lands has led to a reduced lake volume following soil deposition in the lake. It is noted that landuse changes need to be carefully monitored because of their effect on lake levels.     

Preliminary Analysis of the Temporal Patterns of Heavy Rainfall across the Southeastern United States

This paper examines trends in heavy rainfall events across the southeastern United States over the past century. Time series of the number of annual storm events over a 76.2 mm threshold were used for analysis. Significant trends that had some spatial coherence were identified. Increasing trends were detected in a region extending from northeastern Texas to the Appalachians, with a weaker signal of decreasing events along the East Coast. These patterns may be linked to fluctuations in the strength and migration of the Bermuda High.     

Flooding 1990s along the Yangtze River, has it concern of global warming?

There were a series of severe floods along the middle to lower reaches of the Yangtze River (Changjiang River) in China during the 1990s. The extensive summer (June, July and August) precipitation is mostly responsible for the flooding. The summer rainfall in the 1980s and the 1990s is much higher than that in the previous 3 decades. The means for 1990-1999 is +87.62 mm above normal, marked the 1990s the wettest decade since the 1950s. Six stations with a time span of 1880-1999 are selected to establish century -long rainfall series. This series also shows that the 1990s is the wettest decade during the last 120 years. In the wettest 12 years, four occurred in the 1990s (1991,1996,1998 and 1999). Both global and China’s temperature show there is a relative lower air temperature during the 1960-1970s, and a rapid warming in the 1980-1990s. Comparisons of rainfall between 1960-1979 and 1980-1999 show there are dramatic changes. In the cold period 1960-1979, the summer rainfall along the Yangtze River is 3.8 % to 4.7 % below the normal, during the warm period 1980-1999, over 8.4 % to 18.2 % of summer rainfall occurs. Over the whole eastern China, the summer rainfall shows opposite spatial patterns from the 1960-1970s to 1980-1990s. The consistent trend toward more rainfall with global warming is also presented by the greenhouse scenario modeling. A millennial Drought/flood Index for the middle to lower reaches of the Yangtze River showed that although the surplus summer rainfall in the 1990s is the severest during the past 150 years, it is not outstanding in the context of past millennium. Power spectra of the Drought/flood Index show significant interdecadal periods at 33.3 and 11.8 years. Thus, both the natural inter-decadal variations and the global warming may play important roles in the frequent floods witnessed during the last two decades.     

Flooding 1990s along the Yangtze River, has it concern of global warming?

1 IntroductionFloods occurring along the Yangtze River (Changjiang River) valley make up about 35.8 % of the floods over China[1]. Most noteworthily, a series of severe floods happened along the middle to lower Yangtze River and caused great damages during the past decade. The flood of 1991 afflicted 0.98 million hectares of farmland and resulted in 1,200 loss of life. Severe flood occurred again over this region in 1996. An extremely destructive flood emerged during the summer of 1998, wh…     

Empirical models of rain-spells characteristics – A case study of a Mediterranean-arid climatic transect

Environmental (geomorphological, hydrological and ecological) processes are controlled by rainfall, particularly in the Mediterranean, semi-arid and arid regions. Rainfall was analyzed using the concept of rain-spells, i.e., a period of successive rain days preceded and followed by at least one day without rainfall. Daily data from 13 stations along a climatic transect extending from the Judean Mountains with a Mediterranean climate to the Dead Sea arid region in Israel were studied. Rain-spell characteristics (number, yield and duration), based on these data, are presented for different rainfall thresholds, which might be used for different environmental processes such as rock weathering, soil organic matter dynamics, landslides, overland flow and floods and soil erosion. Three estimation models have been developed in order to predict the mean annual Number of Rain-Spells (NRS), mean Rain-Spell Yield (RSY), and mean Rain-Spell Duration (RSD) for the mean annual rainfall and for any given rainfall threshold. These models can be used for current climatic conditions and for scenarios in which the rainfall total changes.     

Preliminary Analysis of the Temporal Patterns of Heavy Rainfall across the Southeastern United States

This paper examines trends in heavy rainfall events across the southeastern United States over the past century. Time series of the number of annual storm events over a 76.2 mm threshold were used for analysis. Significant trends that had some spatial coherence were identified. Increasing trends were detected in a region extending from northeastern Texas to the Appalachians, with a weaker signal of decreasing events along the East Coast. These patterns may be linked to fluctuations in the strength and migration of the Bermuda High.     

Land degradation and climate change in South Africa

This paper considers the potential impact of future climate change on the nature and extent of land degradation in South Africa. The basis of the assessment is the comprehensive review published by the Department of Environmental Affairs and Tourism (DEA&T) as a contribution to the South African effort in respect of the United Nations Convention to Combat Desertification. The DEA&T report is founded on information collated from 34 workshops, one in each of the agricultural regions of South Africa, involving some 453 participants consisting mainly of agricultural extension officers and soil conservation technicians. This analysis reveals that land degradation is underpinned by poverty and its structural roots in colonial and apartheid political planning. Nevertheless, future climate change represents a key challenge to the developing economies of countries like South Africa. Regionally downscaled models predicting the nature and degree of rainfall changes in the future are used to assess the possible impact of future change on the South African land degradation situation. It is concluded that the most severely degraded areas of the country, including large areas of the former 'homeland' states, are likely to become even more susceptible under predicted climate change scenarios.     

Variation of Dry Days Since Last Rain (DDSLR) as a measure of dryness along a Mediterranean – Arid transect

Dry periods between rainstorms control the soil moisture conditions, and are the antecedent conditions for various geomorphological, hydrological and ecological processes. An annual distribution of dry condition, based on the Dry Days Since Last Rain (DDSLR) approach is presented, showing the duration and timing of dry periods for various daily rainfall thresholds and probabilities.Daily rainfall data from five stations along a climatic transect in Israel, extending from the Judean Mountains, which have a Mediterranean climate, to the Dead Sea arid region were studied. The results show that DDSLR values increased with increasing aridity. At a 0.1 mm rainfall threshold, the DDSLR values were similar along this transect. However, at higher daily thresholds, differences among different locations along the transect, become more noticeable.     

Decrease in snowfall/rainfall ratio in the Tibetan Plateau from 1961 to 2013

On the basis of two gridded datasets of daily precipitation and temperature with a spatial resolution of 0.5°×0.5°, and meteorological station data released by the National Meteorological Information Center (NMIC) during 1961–2013, the spatial and temporal variations of total amount of precipitation, amount of rainfall, amount of snowfall and snowfall/rainfall ratio (S/R) in the Tibetan Plateau (TP) are analyzed using Sen’s slope, the Mann–Kendall mutation test, Inverse Distance Weighting (IDW) and the Morlet wavelet. Total amount of precipitation and amount of rainfall generally show statistically significant increasing trends of 0.6 mm·a^–1 and 1.3 mm·a^–1, respectively, while amount of snowfall and S/R have significant decreasing trends of–0.6 mm·a^–1 and–0.5% a^–1, respectively. In most regions, due to significant increasing trends in total amount of precipitation and amount of rainfall, and significant decreasing trends in amount of snowfall, S/R shows a decreasing trend in the TP. Abrupt changes in total amount of precipitation, amount of rainfall, amount of snowfall and S/R are detected for 2005, 2004, 1996 and 1998, respectively. Total amount of precipitation, amount of rainfall, amount of snowfall and S/R are concentrated in cycles of approximately 5 years, 10 years, 16 years and 20 years, respectively. The trend magnitudes for total amount of precipitation and amount of rainfall all show decreasing-to-increasing trends with elevation, while amount of snowfall and S/R show decreasing trends.     

Implications of climate,land-use and land-cover changes for pastoralism in eastern Sudan

This study examines the changes in climate and land-use/land-cover (LULC) along the livestock seasonal migration routes in El Gedaref region (eastern Sudan). Analysis of temperature, rainfall and aridity index (ratio of rainfall to reference evapotranspiration) data during 1941–2009 shows significant warming of the climate, increasing rainfall variability and seasonality, and intensifying aridity conditions during the start and end of the wet season. The somewhat recent enhancement of the overall (annual) rainfall has reflected only in the mid wet season and were caused by few very wet days, indicating increased rainfall concentration and possible risk of soil erosion. Such climatic alterations and variability have inherent implications for land-use and land-cover over the region. LULC changes were investigated using multi-temporal satellite imagery from three sites along the livestock routes. The major trends were drastic conversions of natural vegetation areas into large-scale mechanized agricultural land. This resulted in a progressive loss and degradation of grazing area in the entire region. Overall, the documented LULC changes may cause an irreversible loss of biodiversity and a depletion of other ecological services provided by natural vegetation. The results of this study provide useful information when seeking to resolve complex land-management issues.     

A rain on snow climatology and temporal analysis for the eastern United States

ABSTRACT

Rain-on-snow (ROS) has the potential to produce devastating floods by enhancing runoff from snowmelt. Although a common phenomenon across the eastern United States, little research has focused on ROS in this region. This study used a gridded observational snow dataset from 1960–2009 to establish a comprehensive seasonal climatology of ROS for this region. Additionally, different rain and snow thresholds were compared while considering temporal trends in ROS occurrence at four grid cells representing individual locations. Results show most ROS events occur in MAM (March-April-May). ROS events identified with rainfall >1 cm are more frequent near the east coast and events identified with >1 cm snow loss are more common in higher latitudes and/or elevations. Decreasing trends in DJF (December-January-February) ROS events were identified near the coastal areas, with increasing trends in the northern portion of the domain. Significant decreasing trends in MAM ROS are likewise present on a regional scale. Factors playing a role in snowpack depth and rainfall, such as movement of storm tracks in this region, should be considered with future work to discern mechanisms causing the changes in ROS frequency.     

1960-2007年红河流域强降水事件频次和强度变化及其影响

利用中国境内红河流域23个气象站点1960-2007年的逐日降水数据,分析流域强降水事件频次和强度的变化特征及其相关影响。结果表明:①强降水频次和强度在空间上表现出由东南向西北逐渐递减的趋势,流域下游的河口-金平-绿春-江城一带为高值区,上游的巍山-南涧-弥渡一带则为低值区。②强降水频次和强度的变化趋势存在空间差异,趋势增加的站点大多分布在李仙江上游、元江中上游和藤条江流域,趋势减少的站点大多分布在李仙江下游、元江下游和盘龙河流域。③从流域整体来看,在α=0.05的显著性水平下,近48年来强降水频次和强度没有明显的上升趋势,频次和强度的趋势变化幅度分别为0.26 days/10a和0.18 mm·day^-1/10a;研究时段内频次和强度在时间变化上没有显著突变点。④基于相关统计数据分析强降水变化的影响,表明近20年间强降水频次和强度的增加,增大了局部地区滑坡泥石流、洪涝灾害的风险,河流泥沙含量也随之增加。     

Climatic change and rainfall patterns: Effects on semi-arid plant communities of the Iberian Southeast

The structure and functioning of semi-arid ecosystems are strongly influenced by precipitation patterns. Water availability in such environments is highly pulsed, and discrete rainfall events interspersed with drought periods are important components of the annual water supply. Plant communities do not only respond to rainfall quantity, but also to variations in time, so that relatively small changes in rainfall frequency (i.e., pulsed inputs) may have strong effects on communities. Within the Mediterranean basin, climate change models forecast a decrease in mean annual precipitation and more extreme events (i.e., less rainy days and longer drought periods between events), along with seasonal changes. However, little is known on the consequences of these future precipitation changes on plant communities, especially in semi-arid environments. Here, we summarize the few experiments that have manipulated rainfall patterns in arid and semi-arid areas worldwide, and introduce the first results of a pioneer, long-term rainfall exclusion in the semi-arid southeast region of the Iberian Peninsula. The experiment is not only manipulating the amount of rainfall, but also its frequency and seasonal distribution in a grassland-shrubland in the Tabernas desert (Almería, Spain). This work monitored the effect of precipitation changes on different ecosystem processes for five years, at the species and community level, concluding that this plant community (as other communities studied in the same area) exhibited great resilience to changes in rainfall availability, likely caused by plant adaptation to large intra- and inter-annual precipitation variability.     

The projected population of Russia in 2005

Two alternative projections of future population trends in Russia are presented up to the year 2005. The projections were prepared by the Center for Economic Analysis, an official body of the Government of the Russian Federation. Both alternatives show a projected decline in total population size from the 1992 population, varying from 9.6 million to 16.8 million fewer people in 2005.     

基于高分辨率格点数据的1961-2013年青藏高原雪雨比变化

基于国家气象信息中心发布的1961-2013年全国0.5° × 0.5°逐日降水量和日平均气温格点数据集以及气象站点日降水量和日平均气温实测资料,采用森斜率,M-K突变分析,IDW空间插值以及小波分析等方法,对近53年来青藏高原的降水量,降雨量,降雪量以及雪雨比的时空变化,突变和周期等特征进行了分析.结果表明:① 从时间尺度上看,青藏高原的降水量和降雨量总体呈增加趋势,增加幅度分别为0.6 mm·a^-1(p < 0.05)和1.3 mm·a^-1(p < 0.001);而降雪量和雪雨比均呈下降趋势,下降幅度分别为0.6 mm·a^-1(p < 0.01)和0.5% a^-1(p < 0.001).② 从空间分布上看,青藏高原的大部分地区降水量和降雨量呈增加趋势,而降雪量却呈现减少趋势.因此,雪雨比在青藏高原相应呈现减少趋势.③ 突变和周期分析表明,青藏高原降水量,降雨量,降雪量和雪雨比的突变时间分别出现在2005,2004,1996和1998年左右,而周期变化集中为5年,10年,16年,20年左右.④ 青藏高原降水量倾向率和降雨量倾向率均随海拔的升高呈现出先降低后升高的变化趋势,降雪量倾向率随海拔的升高而降低,雪雨比倾向率随海拔的升高呈微弱的下降趋势.     

关于全球冷暖和亚,非夏季风区干湿变迁之联系的一个述评

基于近年来的多种资料分析结果，讨论了不同时间尺度上全球热状况这于中国东部和其它低纬亚非夏季风影响区干湿变迁的宏观控制作用。指出：在丰年以上时间尺度上，全球暖而夏季风强从而导致有关区域多雨偏湿，全球冷则夏季风区域多偏干；但较短时间尺度上的全球性冷暖波动往往不足以使各地的夏季风系统和干湿状况产生一致响应。     

Climate and surface properties: hydrological response of small arid and semi-arid watersheds

A positive relationship between annual rainfall and geomorphic processes (runoff and erosion rates) and environmental factors (water regime, soil and vegetation cover) is often assumed for arid and semi-arid areas with an annual rainfall in the range of 100–300 mm. This assumption disregards the fact that changes along a climatic gradient, at desert margins, are not limited to purely climatic factors. They are often accompanied by a parallel change in surface properties; especially the relative extent of rocky or soil covered surfaces that differ greatly in their response to rainfall. This raises the issue whether the change in surface properties along a climatic gradient enhances the assumed positive effects of rainfall increase or limits it. The hypothesis advanced in this paper is that runoff generation and rate in arid and semi-arid areas are primarily controlled by surface properties rather than by the absolute amounts of storm and annual rain amounts. Hydrological data collected at two instrumented watersheds, located one in an arid rocky area, and the second in a semi-arid soil covered area, support this hypothesis. The implications of data obtained for runoff generation and flow continuity under changing climatic conditions are analyzed. They point to the fact that the same regional climatic change may have different, and even opposite effects, on the hydrological response of different adjoining surface units. This response is expected to be strongly controlled by the specific local surface conditions that prevailed in the area prior to the climatic change.     

Monitoring ecosystem dynamics in northwestern Ethiopia using NDVI and climate variables to assess long term trends in dryland vegetation variability

Dryland ecosystems are highly vulnerable to environmental changes. Monitoring is vital in order to evaluate their response to fluctuating rainfall and temperature patterns for long-term ecosystem safeguarding. Monitoring of long term changes of normalized difference vegetation index (NDVI) and climate variables are fundamental for better understanding of change trajectories in dryland ecosystem, and to ascertain their potential interaction with anthropogenic drivers. In this study, we identify determinant factors of dryland changes by using MODIS NDVI, precipitation and temperature data for Breaks for Additive Seasonal and Trend (BFAST) and Mann Kendall test statistic. BFAST predicts iteratively time and number of changes within a time series data to depict the size and direction of changes. Analysis of NDVI, precipitation and temperature time series data showed substantial changes during the study period of 2000–2014. There is a reduction trend in vegetation showed by the decline in NDVI, with significant breakpoints till 2009 and recovery afterwards, without a significant change in annual trends of precipitation (α < 0.05) for the same study period. Furthermore 2 positive climate trends were founded: a) a significant positive trend on long term annual rainfall during the main rainy seasons and; 2) a significant (α < 0.05) annual increment of the long term mean minimum and mean maximum temperature of 0.03 °C/year and 0.04 °C/year, respectively. This assessment showed that climate variables cannot be considered as the main factors in explaining the observed patterns of vegetation dynamics. Seasonal and interannual precipitation changes have a lower weight as driving factors for the reduction in vegetation trends. Hence, the decline in vegetation productivity of the region can be attributed to the increasing pressure of human activities.