RAINFALL CHANGE AND ITS IMPLICATIONS FOR BELG HARVEST IN SOUTH WOLLO, ETHIOPIA

Most farmers in the Ethiopian highlands depend on rain‐fed agriculture. Some areas have the favourable situation of having two rainy seasons, Belg (February‐May) and the long rainy season Kiremt (June‐October), which is the case in some parts of South Wollo. Tef (Eragrostis tef) is the staple crop that farmers prefer to grow and the 90‐day variety is suitable for growing during the short rainy season. One out of eight Ethiopians lives in tef potential areas which have Belg rainfall. The aim in this study is to analyse rainfall variation in South Wollo, in particular the area east of the small town of Hayk, and to study its effect on the ability to grow tef during the Belg season. Results from interviews showed that a more difficult farming situation had emerged during the past 40 years, largely due to deterioration of physical resources such as rainfall. Rainfall is analysed by comparing daily rainfall data from four stations in two periods, 1963 to 1982 and 1984 to 2003, for changes in totals, seasonal distribution and variability. Coefficient of variance, rainy days, rainfall intensity and dry spells were analysed. Results from this study show that there have been minor rainfall changes but greater rainfall variability. During fieldwork key informants were asked if they were able to harvest tef during the past nine years, a period that has been used in a model of rainfall influence on tef cultivation during the Belg season. In both 20–year periods, farmers were able to grow tef every second year. In spite of a greater variability in rainfall the farmers proved their knowledge and flexibility and were able to harvest tef in the same number of years during both periods.     

青海高原近40 a降水变化特征及其对生态环境的影响

 利用青海省1961-2002年26个代表站逐日雨量资料和高原东部地区10个站的降水自记资料,分析了近40 a来降水量、雨日、雨强的气候变化特征。结果表明:青海高原近40 a来年降水量无明显的变化,但夏半年降水量呈减少趋势,冬半年降水量呈明显的增多趋势；夏半年降水量和雨日虽在减少,但降水强度在增大；夏半年降水量的减少主要是降水日数的减少造成的,而冬半年降水量的增加是由于雨日增多和每个降水日平均雨量的增大所造成；随着气候变暖,夏、秋季降水明显偏少,出现暖干化的气候趋势。     

Start, end and dry spells of the growing season in semi-arid southern Zimbabwe

Smallholder agriculture in semi-arid Zimbabwe is dependent on the seasonal characteristics of rainfall. The determination of start, end and length of the growing season, and the pattern of dry spells during the season is useful information for planning land preparation and planting activities. This study was designed to assess whether there has been any changes in the start, end and length of growing season and the pattern of 14 and 21 day dry spells during the season. Daily rainfall data were collected from five meteorological stations located in southern Zimbabwe. Results indicated that no significant changes in the start, end and subsequent length of growing season occurred over the past 50-74 years. There was no significant change in the number of wet days per season over the period reviewed. There is a high probability of 14 and 21 day dry spells during the peak rainfall months. The relationship between start and end of growing season is stronger as aridity increases. We conclude that growing seasons have not changed significantly over the past 50-74 years in southern Zimbabwe. As smallholder agriculture continues to be affected by dry spells and droughts, there is scope in exploring rainwater management technologies in rainfed cropping systems.     

近50年华北地区极端气候分析

Climate extremes for agriculture-pasture transitional zone, northem China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season for precipitation is May-September, i.e., the rainy season. For temperature is the hottest three months, i.e., June through August. Heavy rain events, defined as those with daily precipitation equal to or larger than 50 mm, show no significant secular trend. A jump-like change, however, is found occurring in about 1980. For the period 1980-1993, the frequency of heavy rain events is significantly lower than the previous periods. Simultaneously, the occurring time of heavy rains expanded, commencing about one month early and ending one month later. Long dry spells are defined as those with longer than 10 days without rainfall. The frequency of long dry spells displays a significant (at the 99% confidence level) trend at the value of 8.3% /10a. That may be one of the major causes of the frequent droughts emerging over northern China during the last decades. Extremely hot and low temperature events are defined as the uppermost 10% daily temperatures and the lowest 10% daily temperatures, respectively. There is a weak and non-significant upward trend in frequency of extremely high temperatures from the 1950s to the mid-1990s. But the number of hot events increases as much as twice since 1997. That coincides well with the sudden rise in mean summer temperature for the same period. Contrary to that, the fiequency of low temperature events have been decreasing steadily since the 1950s, with a significant linear trend of-15%/10a.     

Extreme climate events over northern China during the last 50 years

Climate extremes for agriculture-pasture transitional zone, northern China, are analyzed on the basis of daily mean temperature and precipitation observations for 31 stations in the period 1956-2001. Analysis season for precipitation is May-September, i.e., the rainy season. For temperature is the hottest three months, i.e., June through August. Heavy rain events, defined as those with daily precipitation equal to or larger than 50 mm, show no significant secular trend. A jump-like change, however, is found occurring in about 1980. For the period 1980-1993, the frequency of heavy rain events is significantly lower than the previous periods. Simultaneously, the occurring time of heavy rains expanded, commencing about one month early and ending one month later. Long dry spells are defined as those with longer than 10 days without rainfall. The frequency of long dry spells displays a significant (at the 99% confidence level) trend at the value of +8.3%/10a. That may be one of the major causes of the frequent droughts emerging over northern China during the last decades. Extremely hot and low temperature events are defined as the uppermost 10% daily temperatures and the lowest 10% daily temperatures, respectively. There is a weak and non-significant upward trend in frequency of extremely high temperatures from the 1950s to the mid-1990s. But the number of hot events increases as much as twice since 1997. That coincides well with the sudden rise in mean summer temperature for the same period. Contrary to that, the frequency of low temperature events have been decreasing steadily since the 1950s, with a significant linear trend of -15%/10a.     

近58a我国西北地区干期与湿期变化特征

利用西北地区1960—2017年68个站点逐日降雨气象数据,分别将日降雨小于（大于等于）0.1 mm和1 mm定义为旱日（湿日）,从干期和湿期变化特征的角度分析西北地区雨日年内分配变化。结果表明：西北地区东部年降雨量变化不明显,降雨频率下降,平均降雨强度增加;西北地区西部年降雨量、降雨频率和平均降雨强度均呈现增加趋势,平均降雨强度增加主要是由于降雨量增加速率快于降雨频率增加速率。结合干期和湿期变化特征,发现西北地区东部虽然干期旱日总数增加,但干期平均长度、干期次数和最长干期旱日数变化不明显,同时湿期湿日数和次数减少,说明西北地区东部在降雨量不变情况下,降雨更加集中。在西北地区西部,干期次数增加,但干期旱日总数、干期平均长度以及最长干期旱日数减少,湿期湿日数和湿期次数增加,湿期平均长度不变,西北地区西部在降雨量和降雨频率增加过程中,干期持续时间缩短,对该区域农业生产和生态环境有利。另外,使用不同阈值会影响特征值变化趋势大小及其显著性,甚至会得到相反的变化趋势,说明选择合理阈值对于研究降雨、干期以及湿期变化十分重要,需要结合区域气候特征进一步研究。     

1736-2010年华南前汛期始日变化

根据清代华南雨雪分寸记载的内容、特点,参照华南地区前汛期降水特征,提出了利用雨雪分寸记载重建华南前汛期开始时间的方法,重建了1736-1911 年福州与广州前汛期开始日期变化序列;并利用福州与广州（分别始于1953 和1952 年）逐日降水观测记录辨识了器测时期两地前汛期的逐年开始时间;据此分析了过去300 年华南前汛期开始日期的年-年代际变化特征。结果表明：1736-2010 年间,福州、广州两地前汛期开始时间平均为5 月第1 候;但存在显著的年际和年代际波动,其中重建时段（1736-1911 年）的主周期为2~3 年、准10 年和准40年,器测时段的主周期为2~3 年、准10 年和准22 年。在年际尺度,重建时段福州和广州前汛期开始时间最早的年份均为4 月第4 候,最晚的年份则分别为5 月第6 候和6 月第1 候;而器测时段两地前汛期开始时间的最早年、最晚年均为4 月第4 候和6 月第1 候。在年代际尺度,重建时段福州和广州相邻年代最大变幅分别为2.2 候和1.6 候;器测时段福州和广州相邻年代最大变幅则分别为2.5 候和2.4 候。     

石林巴江流域近40年气温和降水变化的初步研究

利用数理统计方法分析了石林巴江流域中部近40年（1964-2001年）的气温和降雨量的年、季节和月变化。本区气温的增温速率是0．2℃／10a，与昆明市区增温率相近，低于同期全国增温速率；雨季（夏季）增温幅度大于旱季（冬季）。在过去40年中，年降雨量增加总量约为40mm，雨季降雨量略有降低，而旱季降雨量略有增强，全年第一次降雨强度和全年日最大降雨量也略有增加，但每年连续不降雨天数增加约1．9天。降雨量变化的波动性比气温变化的波动性强。气温、降雨量在1960s、1970s、1980s和1990s表现出不同的变化趋势。     

华北平原降水的长期趋势分析(英文)

The North China Plain (NCP) is the most important food grain producing area in China and has suffered from serious water shortages. To capture variation water availability, it is necessary to have an analysis of changing trends in precipitation. This study, based on daily precipitation data from 47 representative stations in NCP records passed the homogeneity test, analyzed the trend and amplitude of variation in monthly, seasonal and annual precipitation, annual maximum continuous no-rain days, annual rain days, rainfall intensity, and rainfall extremes from 1960 to 2007, using the MannKendall (M-K) test and Sen’s slope estimator. It was found that monthly precipitation in winter had a significant increasing trend in most parts, while monthly precipitation in July to September showed a decreasing trend in some parts of NCP. No significant changing trend was found for the annual, dry and wet season precipitation and rainfall extremes in the majority of NCP.A significant decreasing trend was detected for the maximum no-rain duration and annual rain days in the major part of NCP. It was concluded that the changing trend of precipitation in NCP had an apparent seasonal and regional pattern, i.e., precipitation showed an obvious increasing trend in winter, but a decreasing trend in the rainy season (July to September), and the changing trend was more apparent in the northern part than in the southern and middle parts. This implies that with global warming, seasonal variation of precipitation in NCP tends to decline with an increasing of precipitation in winter season, and a decreasing in rainy season, particularly in the sub-humid northern part.     

西南地区干旱的变化特征及其与大气环流的关系

选用1962—2017年（10月~次年5月）西南地区（四川、贵州、云南和重庆市）90 个地面气象观测台站的逐日降水和日平均气温实测气象要素资料,运用综合气象干旱指数[WTBX](CI)[WTBZ]统计出西南地区累计干旱日数和频次,并分析两者近56 a来的时空变化特征,再挑选其高、低值年进行大气环流形势讨论,最后制作差值图（均为高值年减低值年）与相关场构造的图进行比较。研究结果表明：累计干旱日数和频次均呈逐渐降低的趋势;两者的年代距平在20世纪60年代~80年代同为正,而在20世纪90年代同为负,其后21世纪初两者距平则相反;累计干旱日数具有5 a和9 a的年际周期变化,12 a的年代际周期,干旱频次具有8 a左右的年际周期和20 a的年代际周期;两者均在四川西部地区和云南中北部为大值中心,云南西部、重庆和贵州中东部为小值中心;高、中和低层的环流形势也缺少水汽和系统抬升等配置关系。     

近60年昆明市气候变化特征分析

利用线性倾向率、Mann-Kendall非参数检验、滑动T检验(MTT法)和小波分析等数理统计分析方法,分析昆明市近60 a气候变化趋势和气候突变特征。结果显示:近60 a昆明市气候变化呈气温升高、降水量略微减少的暖干化趋势;气温上升率0.24℃/10 a,降水量下降率3.89 mm/10 a;干季增温强于雨季,而雨季降雨量下降趋势明显;2001~2010年是近60 a来昆明气温最高、降水量最少的10 a;昆明市气温变化包含5~10、10~15 a左右周期,其降水量变化有10~15 a左右的周期变化特征。     

Quantifying precipitation extremes and their relationships with large-scale climate oscillations in a tropical country,Singapore: 1980–2018

Extreme precipitation indices (EPIs) were defined to quantify the precipitation extremes in Singapore, a typical tropical country situated near the equator. The paper investigated the spatial and temporal variability of precipitation extremes based on seventeen EPIs using non-parametric Mann-Kendall test and Sen’s slope, and further explored the linear and nonlinear relationships between precipitation extremes and four large-scale global climate oscillations using correlation and wavelet analysis, during the period of 1980–2018 in Singapore. The results indicated that the trends of precipitation extremes varied for different EPIs, regions and stations. Increasing trends dominated thirteen out of seventeen EPIs. The trends of EPIs were scattered and irregularly distributed. The cross-correlation analysis between different EPIs demonstrated that annual total precipitation on wet days (PRCPTOT) was strongly correlated with other EPIs. The result of composite analysis indicated that El Niño Southern Oscillation (ENSO) exerted stronger impacts on southwest monsoon season (SMS) precipitation than PRCPTOT and northeast monsoon season (NMS) precipitation. The SMS precipitation composite suggested that ENSO created more influence on dry spells than wet spells. The linear and nonlinear relationships revealed that all climate oscillations were negatively correlated with precipitation. The wavelet coherence and phase differences were consistent with the results of correlation analysis, indicating possible prediction of precipitation extremes using climate oscillations as potential predictors.     

Daily precipitation changes in the semi-arid region over northern China

The semi-arid area in northern China is an agro-pastoral transition zone. The environment there is sensitive to climate variation, particularly to precipitation change. Daily precipitation records of 30-gauge stations from May to September during 1956–2000 are analysed in this study. The precipitation amounts show only slightly decreasing trends; however, some aspects of the rainfall characteristics display significant changes. Compared to the 1950s, rainy days have been reduced by about 8 days in the 1990s. Significant change is observed in the number of days when there is light rain (<10 mm day⁻¹). The days with light rain also show a significant tendency toward a stronger intensity, whereas those days with moderate and above moderate rains do not. At the same time, the long duration precipitation (3days) event is found to decrease remarkably with a linear trend of −5.6% per 10 years. In contrast, the frequency of long dry spells (10 consecutive days without rainfall) is becoming more frequent at a rate of 7.2% per 10 years. Taking 30 stations as a whole the maximum daily rainfall displays no evident trend. But the median of the maximums shows a step-like drop beginning in 1979 and the low values are notable until the early 1990s. This is coincident with the large-scale climate regime shift over East Asia, probably suggesting a response of regional daily precipitation extremes due to the change of the East Asian summer monsoon system.     

全球低纬高原地区气候特征的初步研究

提出了全球１０大低纬高原和２０个著名春城的概念,给出了３５个有代表性的低纬高原气象站资料,通过分析气温和降水变化,得到低纬高原气候的共同特征是气温年较差小,四季如春,气温日较差大,一天分四季,降水适中,干湿季分明。主要气候类型是热带草原气候和高原型季风气候     

500 Years of rainfall variability and extreme hydrological events in southeastern Spain drylands

The semiarid SE fringe of the Iberian Peninsula is considered one of the most sensitive to extreme floods and droughts in the western Mediterranean area. The controlling climatic mechanisms are nevertheless difficult to predict and model. A combined documentary-sedimentary-instrumental 500 years comprehensive register of climatic data (rainfall and flooding) was collated for analysing the decadal to centennial scale hydrological response. Wet years are closely linked to the presence of autumn (SON) positive anomalies (e.g. early 18th century). However, continuous, decadal wet periods seem to correspond in time to both autumn and spring (MAM) positive rainfall anomaly years (e.g. 1570/90, 1830/40, 1870/1900). High frequencies of large floods were registered during the late Medieval Warm Period (AD 950–1200), and during some decades of the Little Ice Age with an average of 0.22 floods/year (1440–1490, 1520–1570, 1600–1740, 1770–1800, 1820–1840, 1870–1900), but flood frequency decreased in the 20th Century (1945–1973; 0.14 floods/year). During wet phases (e.g. late 19th century), large floods occurred during all seasons, whereas a predominantly autumn extreme flooding (>70%) is linked to a rainfall patterns with higher inter-annual variability (e.g. 1945–1973). The recurrence of dry phases is higher since early 17th century, and the frequency of continuous wetter phases lower than the ones with marked annual variability. This results in a trend with less frequent high magnitude catastrophic floods. This study confirms a shift from autumn rainfall maxima towards winter since the early 1990's. The tendency towards longer dry periods and increased inter-annual variability (with 1–3 years maximum wet spells) and a changing seasonal rainfall distribution are thought to be key in modelling projections for this specific arid Mediterranean region.     

黄土高原典型半干旱区水热变化及其土壤水分响应

利用黄土高原典型半干旱代表区68 a(1937-2004年)降水、气温资料和34 a(1971-2004年)土壤湿度资料,研究黄土高原半干旱区水热变化及土壤水分响应。结果表明:黄土高原半干旱区在近70 a中气温以下降为主,3-6月降水存在显著增多趋势,气温、降水倾向具有明显时段差异。干旱年份或少雨时段长周期振荡加强、短周期衰减;相对冷的时期气温振荡周期明显,反之不明显。干旱是该地区土壤的基本气候特征,生长期土壤水分波动式下降,蓄水期土壤水分波动式上升,总体上以下降为主,20世纪70年代中后期土壤水分较好,80年代土壤水分较差,90年代末到21世纪初转好。土壤水分对短期降水变化、降水气温气候变化及短周期振荡都存在明显响应。     

黑河流域春季降水空间分异性特征及其与黑河流量的相关分析

利用黑河流域13个气象站建站至2012年3—5月降水量资料和黑河莺落峡水文站流量资料,分析了黑河流域春季降水的基本气候特征;通过EOF、REOF、Morlet小波变换等方法,对黑河流域春季降水的时空特性进行了研究;用Mann-Kendall检验法检验黑河流域春季降水序列是否存在突变现象.结果表明:黑河流域春季降水空间分布极不均匀,其空间分布特征是南部为多雨区、北部为少雨区.黑河流域春季降水在第一空间尺度上为全区一致,在第二空间尺度上可分为2个自然气候区,在第三空间尺度上可分为3个自然气候区.从年代际变化来看,21世纪最初10年是近半个世纪来降水最多的10年,20世纪70年代是降水最少的10年;黑河流域春季降水的年际变率十分显著,降水最多的年份是最少年份的6倍多.1961—2012年间河西走廊春季降水发生了明显的突变:2001年出现了一次趋于增多的突变.最显著的周期是4年的短周期、14年和22年的长周期.黑河流域春季各月降水与黑河流量均呈正相关,尤其是春季各月降水滞后1个月的相关和5月份降水的同期相关性显著;春季气温与黑河流量也均呈正相关,特别是春季各月气温的同期相关和3月气温滞后1个月的相关性显著,说明黑河流量的增加取决于前期降水量的增加和同期气候的明显变暖.     

西沙群岛和涠洲岛气候变化特征 及其与近岸陆地的对比

采用1959―2014年中国西沙站和涠洲岛站及其临近陆地台站的基本气象观测资料,分析了2个海岛的气候变化特征及其与近岸陆地的差异。结果表明：1）近56年西沙和涠洲岛及近岸陆地气温变化均呈上升趋势,西沙增暖速率（0.19℃/10 a）大于涠洲岛（0.104℃/10 a）。显著的差异出现在近10年,西沙持续增暖（0.38℃/10 a）,而涠洲岛气温却呈下降趋势（-0.48℃/10 a）。从季节变化上,2个海岛都有春季越来越暖、冬季越来越冷的趋势。与周围陆地的气温相比,2个海岛的气温均高于近海陆地,但增温速率却小于近岸陆地。2）分析近56年降水量的变化,发现海岛降水量、降水强度和降水天数均小于陆地。受冬、夏季风转换的控制,海岛及近岸陆地有旱季、雨季的划分,且近半个世纪以来降水量波动大、变化趋势不显著,但伴随降水天数的减少,降水强度呈显著增长趋势。对比2个海岛近10年的降水变化特征,发现西沙站的旱季有越来越旱的趋势,涠洲岛及近岸陆地无论旱季、雨季降水量都有增加的趋势,表现为湿润化的趋势。     

1766～1911年黄河中游汛期水情变化特征研究

根据1766～1911年万锦滩汛期涨水情况的历史文献记录,重建研究时段内黄河三门峡断面逐年汛期流量R(109m3/a)和汛期开始时间T(侯尺度),其平均水平分别为径流量R=51.06×109m3/a,汛期开始时间T平均情况为7月上旬(7月第2个侯),对应于梅雨结束平均日期。研究时段内,1840 s前流量平,汛期开始时间总体较稳定;1840～1850 s流量普遍偏丰,汛期到来偏晚;1860 s开始流量减少,汛期提前,此阶段持续约40 a左右,是近300 a中黄河中游产流微弱持续最长的1个时期。