黄土高原气象干旱和农业干旱特征及其相互关系研究

选择标准化降水指数（SPI）和植被状态指数（VCI）分别作为评价黄土高原气象干旱和农业干旱的指标,使用干旱频率和Sen斜率分析了黄土高原地区干旱的分布特征与变化趋势,并探讨了气象干旱与农业干旱的相关性。结果表明：① 黄土高原西部干旱频率总体上高于东部。气象干旱和农业干旱变化趋势在空间上表现有所不同,黄土高原西部、北部气象干旱呈不显著减缓趋势,东部和南部呈不显著加重趋势,但绝大部分地区的农业干旱呈减缓趋势,尤其是400 mm等降水量一线两侧区域。② 季节上,黄土高原夏季和秋季气象干旱频率较高,春季和冬季气象干旱频率相对较低。黄土高原农业干旱频率春季最高,夏季其次,VCI对农业干旱实时监测的适用性更强。③ 不同季节,农业干旱滞后气象干旱的时间长短不同,冬季滞后约2个月,春季滞后约1个月,夏季和秋季滞后少于1个月。黄土高原一熟制种植区的SPI-12值与VCI值具有较好的正相关性。研究结果可以为黄土高原的干旱监测和预警、干旱区划以及干旱灾害风险评估提供科学依据。     

长江荆南三口河系水位演变规律及对江湖水量交换关系的响应

为分析荆南三口河系水位演变规律与江湖水量交换关系。依据1956—2017年荆南三口、湖南四水、洞庭湖城陵矶站以及长江干流枝城站月平均水位及流量和该流域8个雨量站的降水数据,运用Mann-Kendall趋势检验法、回归分析、流量年特征值等方法研究了三口水位的时序演变特征及其与流量、降水、江湖水量交换、人类活动的关系。结果表明：① 与阶段一（1956—1966年）相比,阶段二（1967—1980年）、三（1981—2002年）、四（2003—2017年）河系年平均水位、年最高水位分别下降0.74 m、0.37 m,年最低水位上升0.07 m;② 在涨（4—5月）、丰（6—9月）、退（10—11月）、枯（12月—次年3月）四个水文节点上,最低水位降幅最大（-0.98 m）,平均水位次之（-0.78 m）,最高水位最小（0.55 m）,并将其降幅按水文节点排序依次为退水期（-0.95 m）>丰水期（-0.61 m）>涨水期（-0.21 m）>枯水期（0.15 m）;③ 河系水位变化与其流量变化有着较好的一致性（二者的相关系数r =0.65）,与降水量相关性较弱（r =-0.16）,但2002—2017年相对干旱的气候加剧了河系水位的下降。从总体上看,长江枝城来水量减少和以水利工程为代表的人类活动方式是导致荆南三口河系特征水位下降的主要驱动因素。     

1961—2015年雅鲁藏布江流域降雨侵蚀力

降雨是土壤侵蚀的主要动力,也是风水蚀复合区沙漠化的主要驱动力。研究降雨侵蚀力时空变化对雅鲁藏布江流域土壤侵蚀的监测、评估、预报和治理具有重要意义。利用1961—2015年雅鲁藏布江流域8个气象站日降雨量气象资料,采用趋势系数、气候倾向率、MK检验等研究方法对雅鲁藏布江流域降雨侵蚀力时空变化进行分析。结果表明:雅鲁藏布江流域年降雨侵蚀力平均值为758.1 MJ·mm·hm^-2·h^-1,变差系数Cv值为0.29,趋势系数r值为0.3140。空间分布呈现由东向西逐渐递减的特点,东部可达2 000 MJ·mm·hm^-2·h^-1以上,最西部仅为200MJ·mm·hm^-2·h^-1。雅鲁藏布江流域年降雨侵蚀力总体呈波动上升趋势,其中嘉黎和波密站年降雨侵蚀力上升趋势明显,日喀则、泽当站年降雨侵蚀力呈下降趋势。通过MK检验及滑动T检验得知,流域内年降雨侵蚀力在1982年发生突变,年侵蚀性降雨突变不显著。雅鲁藏布江流域年降雨侵蚀力与侵蚀性降雨相关性显著。     

Estimating trends of the Mediterranean Sea level changes from tide gauge and satellite altimetry data (1993-2015)

The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of studies based on tide gauges observations and satellite altimetry measurements. This study focuses on trend estimates from 18 high-quality tide gauge stations along the Mediterranean Sea coast. The seasonal Mann-Kendall test was run at a 5% significance level for each of the 18 stations for the period of 1993-2015 (satellite altimetry era). The results of this test indicate that the trends for 17 stations were statistically significant and showed an increase (no significant trend was observed only at one station). The rates of sea level change for the 17 stations that exhibit significant trends, estimated using seasonal Sen's approach, range after correction for Vertical Land Motion (VLM) from 1.48 to 8.72 mm/a for the period 1993-2015. Furthermore, the magnitude of change at the location of each tide gauge station was estimated using the satellite altimetry measurements. Thus, the results obtained agree with those from the tide-gauge data analysis.     

Precipitation,temperature and runoff analysis from 1950 to 2002 in the Yangtze basin,China / Analyse des précipitations,températures et débits de 1950 à 2002 dans le bassin du Yangtze,en Chine

Abstract

Abstract Monthly precipitation and temperature trends of 51 stations in the Yangtze basin from 1950–2002 were analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation and temperature data. Significant positive and negative trends at the 90, 95 and 99% significance levels were detected. The monthly mean temperature, precipitation, summer precipitation and monthly mean runoff at Yichang, Hankou and Datong stations were analysed. The results indicate that spatial distribution of precipitation and temperature trends is different. The middle and lower Yangtze basin is dominated by upward precipitation trend but by somewhat downward temperature trend; while downward precipitation trend and upward temperature trend occur in the upper Yangtze basin. This is because increasing precipitation leads to increasing cloud coverage and, hence, results in decreasing ground surface temperature. Average monthly precipitation and temperature analysis for the upper, middle and lower Yangtze basin, respectively, further corroborate this viewpoint. Analysis of precipitation trend for these three regions and of runoff trends for the Yichang, Hankou and Datong stations indicated that runoff trends respond well to the precipitation trends. Historical flood trend analysis also shows that floods in the middle and lower Yangtze basin are in upward trend. The above findings indicate that the middle and lower Yangtze basin is likely to face more serious flood disasters. The research results help in further understanding the influence of climatic changes on floods in the Yangtze basin, providing scientific background for the flood control activities in large catchments in Asia.     

Trend analysis of Climatic Research Unit temperature dataset for Gangotri glacier,India

The absence of continuous long term meteorological dataset has led to limited knowledge of glaciers’ response to climate change over Himalayas. This study presents an open source long term temperature dataset Climatic Research Unit (CRU) available since 1901 to study trend analysis of temperature (T_max, T_min and T_mean) for Gangotri basin in Himalayas. The study first establishes close agreement between CRU time series data and observed temperature dataset available from National Institute of Hydrology (NIH), Roorkee for a period of 11 years from 2005 to 2015 using standard anomaly, Wilcoxon Signed-Rank (WSR) and correlation tests. The close agreement of CRU with NIH data validate the use of CRU time series to study variation in meteorological parameter for hilly terrain of Himalayas. The second part includes application of different statistical tests such as Mann-Kendall (MK), Sen’s slope and CUSUM technique on CRU data to detect existence of any possible trends and identification of change points in T_max, T_min and T_mean on long term scale. On annual scale, significant increasing trends for T_mean and T_min were observed with no significant trend for T_max. On seasonal and monthly scale, T_max showed significant decreasing trend for monsoon season and increasing trend for winters while T_min show significant increasing trend for all months (except May) and seasons. CUSUM technique identified 8 change points from 3 annual time series with 2 for T_mean (1974 and 1999), 3 each for T_max (1941, 1975 and 1999) and T_min (1941, 1965 and 1999) respectively. Overall, significant increase in T_min with no significant trend for T_max has been identified over the study area.     

大凌河流域上游水资源变化趋势及成因研究

R/S和Mann-Kendall都是用来研究径流和降雨变化的常用方法,R/S方法可以揭示序列的水文特征和变异点,但不能说明研究对象未来的变化趋势;Mann-Kendall可以检验水文序列趋势和变化的程度,但不能预测水文时间序列未来的趋势特征。针对R/S和Mann-Kendall法在水文变化趋势分析中的优点和不足,提出了二者相结合的水文变化趋势特征分析,并将其应用于大凌河流域上游的水资源变化趋势分析中。研究表明,R/S和Mann-Kendall综合分析法较好地揭示了降水和径流的变异点,也揭示出降水变化趋势不明显,径流呈现较为显著的下降趋势。本文对径流和降水不对称的相应关系及其成因进行了分析,得出流域内大量的水利工程截留和人类活动取用水成为径流显著下降的主要驱动因素。     

Trend estimation and univariate forecast of the sunspot numbers: Development and comparison of ARMA, ARIMA and Autoregressive Neural Network models

In the present study, a prominent 11-year cycle, supported by the pattern of the autocorrelation function and measures of Euclidean distances, in the mean annual sunspot number time series has been observed by considering the sunspot series for the duration of 1749 to 2007. The trend in the yearly sunspot series, which is found to be non-normally distributed, is examined through the Mann-Kendall non-parametric test. A statistically significant increasing trend is observed in the sunspot series in annual duration. The results indicate that the performance of the autoregressive neural network-based model is much better than the autoregressive moving average and autoregressive integrated moving average-based models for the univariate forecast of the yearly mean sunspot numbers.     

Trend analysis of water discharge and sediment load during the past three decades of development in the Langat basin,Malaysia

Abstract

In this study, the trends of water discharge and sediment load from three hydrometric stations over the past 25 years of development in the state of Selangor, Peninsular Malaysia, were analysed using the Mann-Kendall and Pettitt tests. Landscape metrics for establishing the relationship between land-use changes and trends of hydrological time series were calculated. The hydrological trends were also studied in terms of rainfall variations and manmade features. The results indicate upward trends in water discharge in the Hulu Langat sub-basin and in sediment load in the Semenyih sub-basin. These increasing trends were mainly caused by rapid changes in land use. Upward trends of hydrological series in the Hulu Langat sub-basin matched its rainfall pattern. In the Lui sub-basin, however, trends of hydrological series, and variations in rainfall and land use were not statistically significant.

Editor Z.W. Kundzewicz; Associate editor K. Hamed

Citation Memarian, H., Balasundram, S.K., Talib, J.B., Sood, A.M., and Abbaspour, K.C., 2012. Trend analysis of water discharge and sediment load during the past three decades of development in the Langat basin, Malaysia. Hydrological Sciences Journal, 57 (6), 1207–1222.     

Spatio-temporal trends of precipitation,its aggressiveness and concentration,along the Pacific coast of South America (36–49°S)

ABSTRACT

Precipitation is the most critical climatic element that directly affects the availability of water resources. The objective of this study was to describe and discuss spatio-temporal patterns of annual precipitation, its aggressiveness, and its concentration along the southwest coast of South America (36°–49°S) from 1930 to 2006. An annual and multi-decadal analysis was applied to 107 sampling stations distributed throughout this region, using the Mann-Kendall test (MK), and the Sampling Uncertainty Analysis (SUA) coupled with Gumbel probability density function (SUA-Gumbel). The analysis revealed positive but not significant trends in annual precipitation and aggressiveness for the region between 36° and 44°S, at least during the last 50 years of the analysed period. However, a significant decrease in annual precipitation and aggressiveness was observed between 44° and 49°S during the same period. The annual concentration of precipitation became slightly more seasonal in the last 50 years within the entire study area.