新疆北部降水的气候分布特征及其对ENSO的响应

分析研究了新疆北部地区近50年(1951～2000年)全年各月降水的气候分布特征和各季降水的年际变化规律,重点揭示了北疆多雨季节(4～7月)及其各月降水量对赤道东太平洋的海温SST和南方涛动指数SOI的显著响应关系,并用前期SST和SOI作为预报因子,建立了北疆地区雨季降水量的预报方程.该方程可用于北疆地区雨季降水量的长期预报.     

1644年以来西太平洋暖池海温重建

利用西太平洋地区8个珊瑚代用资料序列重建了1644年以来3～7月平均西太平洋暖池区平均海表温度（SST）．统计分析表明高通滤波后的高频重建和原始值重建结果都有较高的可靠性．近360年来暖池SST存在明显长期趋势变化：1644～1825 AD有显著上升趋势（＋0．04℃／100a）,1826-1885AD呈显著下降（-0．24℃／100a）,1886～2006 AD有强烈上升趋势（＋0．28℃／100a）,其中20世纪50年代以来的增温达N＋0．67℃／100a,是过去360多年中最强的．暖池SST突出的周期包括年际尺度的～2．1,～2．3,～2．9,～3．6,～3．8a周期以及80．7a的低频周期．暖池SST与我国黄淮流域夏季降水变化有显著的相关性,重建时段（1880～1949 AD）SST与区域平均夏季降水量相关系数达到-0．44,与观测时段（1950～2005 AD）二者的相关（-0．46）接近．这种关系在近360年来的旱涝等级中也是显著的,1644～1949 AD区域平均旱涝等级与重建SST相关系数为-0．20,在年代际尺度上二者关系更为明显,低通滤波后的相关系数为-0．42．这说明近360多年来当暖池SST偏高（低）时,黄淮流域降水易偏少（多）．长时间序列的暖池SST重建结果,对分析历史时期我国东部旱涝气候变化机制提供了有用的信息．     

青藏高原湖泊纹层孢粉记录的过去2000年雨季时长和雨季降水时空变化

青藏高原雨季时长及雨季降水量的长尺度定量重建,是揭示高原西风、季风时空演变规律及其生态环境效应的关键,其中准确判断高原雨季的起止时间是研究难点.本文通过寻找降水拐点的方法确定了高原不同地点的雨季起、止时间,并计算了雨季时长和雨季降水量,建立了表土孢粉组合与雨季起止时间、雨季时长和雨季降水量的转换函数,重建了具有年纹层沉积特征的高原北部库赛湖区和中部江错湖区过去2000年来的雨季起止时间、雨季时长和雨季降水量变化.结果表明,过去2000以来,库赛湖区雨季降水序列记录了5次高降水时段:AD580～680、AD1000～1100、AD1200～1450、AD1550～1780、AD1920至今,其普遍对应雨季天数长的时段;江错湖区雨季降水序列记录了4次高降水时段:AD80～500、AD800～950、AD1250～1450、AD1780至今,其与雨季天数长的时段在AD1000以前对应良好,在AD1000后关系不明确.在空间上,高原雨季降水呈现出“南北同湿”、“南北同旱”、“南湿北旱”和“南旱北湿”四种模式,其中“南北同湿”可能与异常强盛的夏季风有关,“南北同旱”与弱西风和弱季风有关,“南湿北...     

青海湖流域圆柏年轮指示的近千年降水变化

根据采自青海湖流域天峻地区树木年轮样本,建立了该地1061a树木年轮年表序列.通过响应函数计算得出,该年表对青海湖区前一年年降水量反映敏感,由其重建了该地的年降水量序列,并应用交叉检验方法对校准方程进行了检验,证明重建方程稳定,重建的年降水变化比较可靠,具有一定的代表性.在10a时间尺度上年降水经历了11个偏多和偏少时段,其中6(7)个显著的偏少(多)时段分别是1001-1060、1131-1320、1411-1510、1691-1740、1811-1850年和1911-1940年(961-1000、1061-1110、1321-1410、1511-1650、1741-1790、1881-1910年和1941-2000年).平均约53a发生一次突变,13-14世纪是年降水的多变时期,12、17和20世纪是年降水的相对稳定时段.     

云南破坏性地震与气象要素的关系

本文认为云南破坏性地震与降水和地面气温之间有着密切的关系。在雨季,震中位于发震前一月内降水分布高值中心附近,发震前半月内震中均有中雨以上的降水出现,且其中出现大～暴雨的概率为60%,发震前一月内震中降水量比同期多,年平均值偏高,震前半月内地面平均气温距平值的高值中心总是位于震中附近。而在干季则恰恰与此相反,即震中位于降水分布低值区,发震前后降水都很少,震中降水量比同期多年平均偏低,震前半月内地面平均气温距平值的高值中心总是位于震中下风方向约120km处。这些结果对提高震前短期预报水平具有现实意义。     

青藏高原雨季的客观监测方法及其近60年的变化趋势

本文通过对青藏高原降水季节演变特征的分析,选取日降水量和降水频率两个特征量来定义青藏高原各站点及全区的雨季,揭示了1961—2019年青藏高原雨季开始时间、结束时间、雨季长度和总雨量等的气候和变化特征.分析发现,青藏高原雨季的开始自东向西推进,而结束西早东晚,雨季持续时间自东向西缩短,雨季雨量东多西少.就青藏高原整体而言,雨季开始的平均日期在5月4日,结束的平均日期在10月15日,雨季平均持续163天,雨季雨量平均为413.2 mm.近60年,青藏高原雨季发生了显著变化,表现为开始时间提前、结束时间推迟、雨季延长、雨量增多.青藏高原各站点雨季的变化具有一定的区域性差异,主要表现为：高原雨季的开始整体提前,但是,高原东部边缘雨季开始提前的变化幅度相对较小;高原雨季的结束时间在南部和北部提前而在中部和东部推后;高原大部地区雨季雨量增多,但南部边缘等部分地区雨季雨量有所减少.     

大别山库区降水预报性能评估及应用对策

对降水预报进行性能评估及应用对策研究可以更好地发挥降水预报在水库调度中的决策支持作用.基于大别山库区近10 a汛期(2007—2016年5月1日—9月30日)24~168 h共7个预见期降水预报和地面降水观测资料,采用正确率、TS评分、概率统计、ROC曲线以及CTS等方法评估大别山库区降水预报性能,并以响洪甸水库为重点研究区域分析降水预报在水库调度中的应用对策.结果表明:1)大别山库区各量级的降水预报都有正预报技巧;24~72 h预见期降水预报的TS评分较高且空报率、漏报率也较低,具有较高的预报性能;但96 h及以上预见期降水预报性能明显下降,中雨以上量级空报率、漏报率较大,特别是对大暴雨及其以上量级的降水预报性能显著下降.2)大别山库区预报降水量级与实况降水量级基本符合,预报降水量级大于等于实况降水量级的概率超过75%;虽然降水预报量级上呈现出过度预报的现象,但降水过程预报对水库调度仍有较好的应用价值,应用时要考虑到降水预报量级可能存在偏差.3)转折性天气预报96 h及以上预见期CTS评分较低,但72 h以内预见期的性能明显改进,尤其是24 h预见期CTS评分也提高到了38.2%;水库调度可从长预见期的降水预报获取降水过程及其可能发生转折的信息,根据短预见期的降水预报进行调度方案调整.     

长江上游地区可利用降水量的气候特征

利用长江上游地区107个观测站1960-2008年气温、降水观测资料,采用陆面蒸发经验模型计算得到各观测站的月蒸发量,再根据水量平衡关系,得到可利用降水量,采用数理统计、REOF分析和M-K突变检验等方法,分析长江上游地区可利用降水量的气候变化特征.结果表明:长江上游可利用降水量季节变化显著,5-9月长江上游可利用降水...     

干旱与强震活动关系的研究实例

震前干旱与强烈地震之间的关系,已日益为地震界所重视.本文通过新疆柯坪——乌恰地区历年降水量与Ms6.0强震关系的研究发现,该地区Ms6.0地震大部分(85.7%)是在震前1——2年的干旱背景下发生的;震级随旱区面积大小而增减.运用鉴定震兆信息量R值方法,对该地区降水因子预报地震的预报效能进行评定,效果良好.本文还对1985年乌恰7.4级大震震前的降水异常特征进行了讨论. 研究表明,震前1——3年大面积的干旱与强烈地震的发生有着某种内在的联系.旱震关系,是强震中期综合预报的依据之一.      

TRMM多卫星降水分析资料揭示的青藏高原及其周边地区夏季降水日变化

本文在对比了TRMM多卫星降水分析TMPA(TRMM Multi-satellite Precipitation Analysis)资料和中国643个气象站观测降水量时空分布的基础上,采用2002~2006年夏季TMPA每小时降水量资料,用合成分析和谐波分析的方法研究了青藏高原及其周边地区夏季降水量和降水频率的日变化特征.分析结果表明,平均降水量和降水频率日变化谐波分析的标准振幅显示出青藏高原地区夏季降水具有显著的日变化特征,高原中部地区对流活动日变化最强,其次是高原西南方向的印度半岛地区.谐波分析的位相表明降水量和降水频率最大值出现的时间具有选择性,高原中部降水量最大值多集中在傍晚前后,高原以东的四川盆地通常在夜晚,尤其是在后半夜达到最大值,而长江上游和中下游地区对流活动则分别在上午和下午最为活跃.青藏高原以东地区降水量日变化的位相明显不同于其他陆地地区,也不同于高原中部,具有自西向东传播的信号,四川盆地的夜雨现象可能是高原地区对流活动日变化自西向东传播的结果.     

Detection of ENSO‐influence on the monthly precipitation in South Korea

During the latest several decades, there has been considerable interest in revealing the relationship between El Niño–southern oscillation (ENSO) and hydro‐meteorological variables. The oscillation is characterized by a simple index, the southern oscillation index (SOI). However, thus far, there is little evidence for the influence of ENSO in Korea and Japan. The influence of ENSO has also been studied in South Korea, but the estimated results are still qualitative and show an indirect relationship between ENSO and hydro‐meteorological variables. In this study we use simple approaches to reveal the quantitative and direct correlation between SOI and the monthly precipitation at five stations distributed over South Korea. The monthly precipitation data are transformed into nonexceedance probability time series because the data cannot be normally distributed by applying the usual transformations. The SOI is classified into five categories according to their values. Additionally, to detect the nonlinear relationship between categorized SOI and nonexceedance probability of the monthly precipitation, we use Kendall's τ, a nonparametric test. Significant correlations between the categorized SOI and the transformed precipitation are detected. Generally, the monthly precipitation is influenced by a La Niña event with a lag time of 4 months for southern coastal areas and a lag time of 5 months for middle to high regions in South Korea. Copyright © 2005 John Wiley & Sons, Ltd.     

Hydroclimatic teleconnection between global sea surface temperature and rainfall over India at subdivisional monthly scale

It is well established that sea surface temperature (SST) plays a significant role in the hydrologic cycle in which precipitation is the most important part. In this study, the influence of SST on Indian subdivisional monthly rainfall is investigated. Both spatial and temporal influences are investigated. The most influencing regions of sea surface are identified for different subdivisions and for different overlapping seasons in the year. The relative importance of SST, land surface temperature (LST) and ocean–land temperature contrast (OLTC) and their variation from subdivision to subdivision and from season to season are also studied. It is observed that LST does not show much similarity with rainfall series, but, in general, OLTC shows relatively higher influence in the pre‐monsoon and early monsoon periods, whereas SST plays a more important role in late‐ and post‐monsoon periods. The influence of OLTC is seen to be mostly confined to the Indian Ocean region, whereas the effect of SST indicates the climatic teleconnection between Indian regional rainfall and climate indices in Pacific and Atlantic Oceans. Copyright © 2006 John Wiley & Sons, Ltd.     

Interannual variability in western US precipitation

Low-frequency (interannual or longer period) climatic variability is of interest, because of its significance for the understanding and prediction of protracted climatic anomalies. Since precipitation is one of the key variables driving various hydrologic processes, it is useful to examine precipitation records to better understand long-term climate dynamics. Here, we use the multi-taper method of spectral analysis to analyze the monthly precipitation time series (both occurrence and amount) at a few stations along a meridional transect from Priest River, ID to Tucson, AZ. We also examine spectral coherence between monthly precipitation and widely used atmospheric indices, such as the central Northern Pacific (CNP) and southern oscillation index (SOI). This analysis reveals statistically significant ‘signals' in the time series in the 5–7 and 2–3 year bands. These interannual signals are consistent with those related to El-Niño southern oscillation (ENSO) and quasi-biennial variability identified by others.     

Regional sea-surface temperatures explain spatial and temporal variation of summer precipitation in the source region of the Yellow River

ABSTRACT

The summer precipitation (June–September) in the source region of the Yellow River accounts for about 70% of the annual total, playing an important role in water availability. This study divided the source region of the Yellow River into homogeneous zones based on precipitation variability using cluster analysis. Summer precipitation trends and teleconnections with global sea-surface temperatures (SST) and the Southern Oscillation Index (SOI) from 1961 to 2010 were investigated by Mann-Kendall test and Pearson product-moment correlation analysis. The results show that the northwest part (Zone 1) had a non-significantly increasing trend, and the middle and southeast parts (zones 2 and 3) that receive the most precipitation displayed a statistically significant decreasing trend for summer precipitation. The summer precipitation in the whole region showed statistically significant negative correlations with the central Pacific SST for 0–4 month lag and with the Southern Indian and Atlantic oceans SST for 5–8 month lag. Analyses of sub-regions reveal intricate and complex correlations with different SST areas that further explain the summer precipitation variability. The SOI had significant positive correlations, mainly for 0–2 months lag, with summer precipitation in the source region of the Yellow River. It is seen that El Niño Southern Oscillation (ENSO) events have an influence on summer precipitation, and the predominant negative correlations indicate that higher SST in equatorial Pacific areas corresponding to El Niño coincides with less summer precipitation in the source region of the Yellow River.

Editor Z.W. Kundzewicz; Associate editor D. Gerten     

Trends in rainfall and runoff in the Blue Nile Basin: 1964–2003

Most of the water from the Nile originates in Ethiopia but there is no agreement on how land degradation or climate change affects the future flow in downstream countries. The objective of this paper is to improve the understanding of future conditions by analysing historical trends. During the period 1964–2003, the average monthly basin‐wide precipitation and monthly discharge data were collected and analysed statistically for two stations in the upper 30% of the Blue Nile Basin and monthly and 10‐day discharge data of one station at the Sudan–Ethiopia border. A rainfall–runoff model examined the causes for observed trends. The results show that, while there was no significant trend in the seasonal and annual basin‐wide average rainfall, significant increases in discharge during the long rainy season (June to September) were observed at all three stations. In the upper Blue Nile, the short rainy season flow (March to May) increased, while the dry season flow (October to February) stayed the same. At the Sudan border, the dry season flow decreased significantly with no change in the short rainy season flow. The difference in response was likely due to the construction of weir in the 1990s at the Lake Tana outlet that affected the upper Blue Nile discharge significantly but affected less than 10% of the discharge at the Sudan border. The rainfall–runoff model reproduced the observed trends, assuming that an additional 10% of the hillsides were eroded in the 40‐year time span and generated overland flow instead of interflow and base flow. Models concerning future trends in the Nile cannot assume that the landscape runoff processes will remain static. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of El Niño and La Niña effects and the impact of Atlantic sea surface temperatures (SSTs), on precipitation in Nigeria from 1950 to 1992

Monthly precipitation data from meteorological stations in Nigeria are analysed from 1950 to 1992, in relation to sea surface temperatures (SSTs) in the tropical Pacific and Atlantic Oceans. The analyses have shed some light on understanding the variability of rainfall anomalies observed in Nigeria for this period. The correlation values between rainfall anomaly indices (RAI) and different meteorological indices are not all significant. Thus, the analyses show some indication that rainfall in Nigeria is associated with El Niño-related circulation and rainfall anomalies. The low correlations between RAI and SST in the Pacific confirm low correlations between rainfall and southern oscillation indices (SOI). SST correlations in the tropical Atlantic suggest that warm surface water in this part of the Atlantic moves the Inter Tropical Convergence Zone (ITCZ) southward and away from the SouthEast of Nigeria, indicating less rainfall, while, in SouthWest of Nigeria, the warm surface waters in this part of the Atlantic are likely to be responsible for a more northern position of the ITCZ, which produces more rainfall. The lower correlation in Northern Nigeria may be attributed to its continentality, away from the influence of the sea surface conditions in the Gulf of Guinea and the tropical Atlantic. The drought, or rainfall, cycles in Northern Nigeria are more closely connected to the land surface conditions in the nearby Sahel region.     

Temporal and spatial variations in hydro-climatic extremes in the Lake Victoria basin

A study was carried out to investigate variability in long term hydro-climatic extremes in the Lake Victoria basin, East Africa. The study aimed at determining whether the long term historical changes in frequency and magnitude of hydro-climatic extremes are statistically significant, to give more light on the differentiation of climate variability from climate change. Long term extremes for 22 rainfall and 10 river flow gauge stations were examined. The hydro-climatic extremes were aggregated at levels from daily, decadal, to monthly scales defined for two wet seasons in the area, the long rainy season extending from March to May (MAM) and the short rainy season extending from October to December (OND), and time slices of 10 years using a sliding window approach. An empirical statistical technique based on Quantile Perturbation Method (QPM) was used. Quantile perturbations that represent empirical changes for precipitation and river flow extremes were derived. Significant decreasing trends in precipitation were observed in the 1930s, 1970s and 1980s, while significant increasing trends were common in the 1960s, late 1980s, and 1990s to the most recent years (2000–2006). In general, significant trends were dominant in the OND compared to MAM season for precipitation and river flow extremes. Results indicated further that there are differences in geographic location of significant trends in the hydro-climatic variables investigated implying that impacts are not spatially coherent. Areas with significant trends appeared to be concentrated in the North to North eastern parts compared to those in the southern parts of the basin.     

Trends of precipitation in Beijiang River Basin,Guangdong Province,China

An analysis of spatial and temporal trends of precipitation in Beijiang River basin, Guangdong Province, China during 1959–2003 was performed using 17 time series (including monthly, annual, wet season, dry season, early flood period and late flood period totals) both on station based and sub‐basin based data sets. Two nonparametric methods (Mann–Kendall and Sen's T) were used for data analysis. The results showed that (1) downward trends of temporal distribution were mostly detected during the early flood period, especially in May, while upward trends were observed in July and the dry season; (2) downward trends of spatial distribution were mostly detected in the southern Beijiang River basin, while upward trends were observed north of this area. Our results indicated a delayed rainy season and a northward trend of the precipitation belt compared to recent years. Copyright © 2007 John Wiley & Sons, Ltd.     

Hydro-climatic trends in the Abay/Upper Blue Nile basin,Ethiopia

Trends of the three hydro-meteorological variables precipitation, temperature and stream flow, represented by 13, 12, and 9 gauging stations, respectively, within the Abay/Upper Blue Nile basin have been studied to support water management in the region. The Trends were evaluated over different time periods depending on data availability at the stations. The statistical Mann–Kendall and Pettitt tests have been used to assess trends and change points respectively. The tests have been applied to mean annual, monthly, seasonal, 1- and 7-days annual minimum and maximum values for streamflow, while mean annual, monthly and seasonal timescales were applied to meteorological variables. The results are heterogeneous and depict statistically significant increasing/decreasing trends. Besides, it showed significant abrupt change of point upward/downward shift for streamflow and temperature time series. However, precipitation time series did not show any statistically significant trends in mean annual and seasonal scales across the examined stations.Increasing trends in temperature at different weather stations for the mean annual, rainy, dry and small rainy seasons are apparent. The mean temperature at Bahir Dar – typical station in the Lake Tana sub basin, has been increasing at the rate of about 0.5 °C/decade, 0.3 °C/decade in rainy season (June–September), 0.6 °C/decade in small rainy season (March–May), and 0.6 °C/decade in dry season (October–February). Other stations in the Abay/Upper Blue Nile show comparable results. Overall it is found that trends and change point times varied considerably across the stations and catchment to catchment. Identified significant trends can help to make better planning decisions for water management. However, the cause attributes to the observed changes in hydro-meteorological variables need further research. In particular the combined effects of land use/land cover change and climate variability on streamflow of Abay/Blue Nile basin and its tributaries needs to be understood better.