Is Bulgaria becoming warmer and drier?

This article attempts to analyse the current climatic variations based on air temperature and precipitation data from 18 stations for the 1916–1993 period. No substantial changes have been established in the annual air temperatures, averaged over the whole country's area, but there is evidence of late fall cooling and winter warming in the recent decade. A marked drought set in during 1982–1993, which in SW Bulgaria which reached a record level for the last 100 years both in terms of its duration and intensity. Climatolgical patterns contributing to these observations are discussed.     

River runoff changes and recent climatic fluctuations in Bulgaria

Some estimates of global climatic change in the next 100 years suggest a general warming and rainfall decrease on the Balkan Peninsula. Our studies suggest that in Bulgaria climatic changes have already started. Because water resources to a great extent depend upon climate dynamics, this paper develops the linkage of climatic fluctuations and water resources using time-series analysis of climatic parameters and some river runoff characteristics and their correlation. One of the main conclusions, based on the results, is that climatic change manifested in the last 15 years has significantly influenced river runoff. A study of the recent prolonged drought and the influence of changes on water resources and human activity begins with characterizing climate-hydrology linkages. The results of this study point to several problems of regional and local importance.     

Book reviews

Under thhe drought conditions that have occurred in Bulgaria during the last decade, agricultural use of non-conventional water may be an important resource. This is a specific case of simultaneous purification and utilisation by soil ecological systems. However, using non-conventional quality water presents a number of ecological and health risks and poses problems connected with soil and surface and ground water contaminated and with producing crops of acceptable quality. Bulgaria's municipal, industrial, and rural wastewater reclamation and reuse, in addition to other non conventional water resources as sea water, drainage water and mineralised groundwater, may be a reliable source even in drought years and thus is capable of replacing potable used in agriculture. This paper reviews the work of the authors and their colleagues in assessing the irrigation potentials of waste water in Bulgaria.     

西北旱区潜在蒸散发的气候敏感性及其干旱特征研究

潜在蒸散量（PET）是干旱监测评价的重要指标,分析影响潜在蒸散发的气候敏感因子对揭示气候变化的水文响应机理尤为重要。常采用的局部敏感性方法不适用于非线性模型且难以评估各气象因子间的相互作用。对此,基于1964—2018年西北旱区内163个气象站的监测数据,通过Penman-Monteith公式,采用Sobol全局敏感性方法分析了西北旱区潜在蒸散发的气候敏感因子,计算得到了自校准帕默尔干旱指数（scPDSI）,进而分析了区域干旱的时空演变特征。结果表明:1964—2018年西北旱区年均潜在蒸散量为1157.8 mm,高值出现在新疆东部与内蒙古西部地区,低值出现在青海南部地区。1993年为转折点,西北旱区潜在蒸散发受气温、日照时数、风速、相对湿度等多种因素综合影响由显著下降的趋势转变为显著上升,且在夏季最为明显。在1964—1993年,净辐射、风速与相对湿度的变化对潜在蒸散发的影响较大;在1994—2018年,风速与相对湿度的变化对潜在蒸散发的影响较大。scPDSI的时空分布表明新疆北部、青海中部以及甘肃境内的干旱有缓解的趋势;而黄河流域西南部干旱呈现加重趋势,将加剧区域水资源紧张,威胁生态安全。     

Possibilities for water conservation in Bulgaria

The drought during the last 10 years in Bulgaria caused the interruption of water supply to more than 70% of the population of the country. Investigations on recent water demand showed that the role of water losses and irrational use so considerable that existing water resources became inqdequate. Bringing new water to existing supply systems is connected with considerable investments, time, and controversy. Water conservation could solve some water supply problems by providing more reasonable water consumption and additional time for development of new resources. In this paper the possibilities for reducing water use in Bulgaria and the need for developing a national conservation program are discussed. An analysis of the variables which effect water use is performed. The reasons for the water losses and using more than the necessary water quantities are discussed. Developing of water-use efficiency standards for plumbing fixtures and conservation-oriented water rates and measures are proposed.     

Understanding the impact of droughts in the Yarmouk Basin,Jordan: monitoring droughts through meteorological and hydrological drought indices

This article assesses drought status in the Yarmouk Basin (YB), in northern Jordan, using the Standardized Precipitation Index (SPI), the Standardized Water-Level Index (SWI), and the Percent Departure from Normal rainfall (PDNimd) during the years 1993–2014. The results showed that the YB suffers from frequent and irregular periods of drought as variations in drought intensity and frequency have been observed. The SPI results revealed that the highest drought magnitude of ??2.34 appeared at Nuaimeh rainfall station in 1991. This station has also experienced severe drought particularly in years 1995, 1999, 2005, and 2012 with SPI values ranging from ??1.51 to ??1.59. Some other rainfall stations such as Baqura, Ibbin, Khanasiri, Kharja, Mafraq police, Ramtha, Turra, and Umm Qais have also suffered several periods of drought mostly in 1993. The SWI results show the highest extreme drought events in 2001 in Souf well while other extreme drought periods were observed at Wadi Elyabis well in 1994 and at Mafraq well in 1995. As compared to SPI maps, our SWI maps reflect severe and extreme drought events in most years, negatively impacting the groundwater levels in the study area.     

Contemporary runoff trends in some highland stream basins in Bulgaria

Hydrological changes in four stream basins situated on the northern slopes of the Stara Planina range (North Bulgaria) and in the Rodopi massif (South Bulgaria) have been investigated during the 1951–1989 time period. Parallel analysis of runoff and precipitation mean annual values have been made, calculating the respective annual ratios compared to the mean of the entire range mean value. Curves of runoff and precipitation frequencies have been developed and analyzed. This investigation establishes that during the 1980s a consistent trend towards significant humidity reduction has occurred. Mean annual deviation values of the last decade compared to the entire period mean annual figure amount to 5–20% and 10–25% for the precipitation and runoff, respectively, with humidity reduction of greater amplitude in the North Bulgarian stream basins. Annual Mean deviations are due to significant moisture reduction during the warm half of the year in North Bulgaria and in the cold half in South Bulgaria. Both regions reflect zonal differences caused by climatic patterns of European if not planetary scale.     

Dry years and their relationship to crop production in Sri Lanka

Drought is a distinct agroclimatological hazard with far reaching consequences upon crop production. Among them, famines are regarded the most serious effects of climatological drought. Although there is no doubt about the principally valid relationship between drought and production losses it seems more problematic how this relationship can be proved statistically. In this paper annual rainfall data and production figures of the three major crops of Sri Lanka, rice (paddy), tea and rubber, are correlated, but only partially a true relationship between dry years and production losses could be observed. Reason for this may be the moderate degree of annual drought. From the results shown, the question arises how agricultural drought can be defined and how the climatic effects upon crop production can be studied satisfactorily.     

Forest tree responses to extreme drought and some biotic events: Towards a selection according to hazard tolerance?

The aim of this paper is to illustrate how some extreme events could affect forest ecosystems. Forest tree response can be analysed using dendroecological methods, as tree-ring widths are strongly controlled by climatic or biotic events. Years with such events induce similar tree responses and are called pointer years. They can result from extreme climatic events like frost, a heat wave, spring water logging, drought or insect damage… Forest tree species showed contrasting responses to climatic hazards, depending on their sensitivity to water shortage or temperature hardening, as illustrated from our dendrochronological database. For foresters, a drought or a pest disease is an extreme event if visible and durable symptoms are induced (leaf discolouration, leaf loss, perennial organs mortality, tree dieback and mortality). These symptoms here are shown, lagging one or several years behind a climatic or biotic event, from forest decline cases in progress since the 2003 drought or attributed to previous severe droughts or defoliations in France. Tree growth or vitality recovery is illustrated, and the functional interpretation of the long lasting memory of trees is discussed. A coupled approach linking dendrochronology and ecophysiology helps in discussing vulnerability of forest stands, and suggests management advices in order to mitigate extreme drought and cope with selective mortality.     

A comprehensive approach to drought and desertification in Northern Nigeria

Drought has been a recurring feature of the arid and semi-arid areas of Nigeria. This paper reviews the extent, severity, and consequences of drought and desertification in Nigeria with particular emphasis on the northern part of the country. The haphazard manner in which these environmental hazards have been tackled is examined and a systematic approach for the formulation of a national policy is proposed. It is recommended that a detailed formulation and implementation of the proposed policy plan is imperative to mitigate the often devastating impacts of drought and desertification in the very prone areas of Nigeria. Until such is done, some areas of Nigeria will always be vulnerable to the whims of an inevitable climatic hazard of drought and associated land degradation in the form of desertification.     

Investigation of hydrological drought using Cumulative Standardized Precipitation Index (SPI 30) in the eastern Mediterranean region (Damascus,Syria)

The Eastern Mediterranean region has been exposed to drought episodes, which have been occurring more frequently during the last decades. The objective of the present paper is to study the precipitation regime of the Damascus (Mazzeh) meteoric station by analysing drought characteristics using the Standardized Precipitation Index (SPI) and comparing this with the drought in Cyprus. The cumulative drought conceptis proposed to characterize long-term hydrologic drought, which affects the shallow groundwater productivity in terms of quantity and quality. Gamma probability distribution was fitted to the long-term annual precipitation in Damascus from 1918–1919 to 2007–2008 (n = 90 years). Generally, a decreasing trend of 17% to the mean annual rainfall of Damascus and 13% to the mean annual rainfall of Cyprus was estimated between 1970 and 2000. The SPI identifies three major extended drought periods: (1) 9 years of severe drought (1954–1963) with an average 20% precipitation deficit per year compared to the mean. (2) 8 years of severe drought (1983–1991) with a 27% deficit per year on average. (3) 9 years of extreme drought (1993–2002) with a 31% deficit per year on average. The cumulative standardized precipitation index (SPI 30) demonstrates positive values for the first period and is indicative of having no effect on the global water balance. SPI 30 exhibits sensitive equilibrium with near zero values / a near zero value (±1.5) for the second period. For the third period, however, the SPI 30 decreases below ?10 indicating an extreme hydrological drought that has negative consequences on the recent groundwater recharge. It is required to develop and implement a sustainable groundwater management strategy to reduce long-terms drought risks. Generally, the SPI 30 in Cyprus is parallel to that in Damascus with a 3–5 year delay. Thus, the central zone of the Eastern Mediterranean region is facing big challenges and has been suffering from three decades of moderate to severe hydrological drought (SPI 30=?5 to ?10) causing a severe decrease in springs discharges of the region. Therefore, in order to reduce the climate change effects on water resources, it is necessary to adopt a sustainable proactive management plan during the frequent severe droughts.     

Drought in Bulgaria and atmospheric synoptic conditions over Europe

Drought in Bulgaria is analyzed from the multiple viewpoints of statistical occurrence, spatial patterns, and synoptic conditions. A new index of drought, the SD (spatial-dryness) index, characterizes drought by both intensity and spatial extent. The occurrence of the SD index is analyzed using global gridded data sets. Examination of transitional probabilities of multiple months and years with drought occurrence suggests persistence is sufficiently frequent to be important for climate-related environmental planning. Finally, it is shown that specific seasonal synoptic patterns are associated with wet and dry conditions in Bulgaria. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于水库群预报调度的黄河流域干旱应对系统

为有效应对日益严重的流域干旱问题,有必要开展面向干旱全过程的黄河流域干旱应对系统研究。基于干旱演变过程设计了干旱指数,通过天气预报模型、回归分析等进行干旱、需水与径流预报;设置多年调节水库旱限水位,实现水资源年际补偿;识别洪水和泥沙分期特征,采用分期汛限水位增加洪水资源利用量;建立了梯级水库群协同优化调度模型,调配抗旱水源。算例结果显示:黄河流域干旱应对系统能够平衡年际间的干旱损失以避免重度破坏,与实际情况相比,在重旱的2014年增加抗旱水源22.40亿m^3。建立的干旱应对系统已应用于黄河流域抗旱实践,提升了流域应对干旱的水资源调控能力。     

洞庭湖区第四纪气候变化的初步探讨

探讨了洞庭湖区第四纪以来的气候变化，初步得出以下规律：更新世气候变化剧烈，气候组合暖湿（温湿）与冷干；全新世气候转为温凉，主要气候组合为温湿与凉干；历史时期气候主要仍温湿与凉干交替，但15 世纪以来出现短暂的温干与凉温期；15世纪以来，气候波动频繁，有愈来愈不稳定的趋向，进入20世纪，旱涝灾害更加。在全球变暖的背景下，预计该区未来气候趋向于暖湿，但不排除暖干的可能性。     

广西北海市海水入侵状况分析

北海市海水入侵，主要出现在在市区北部海城区海角大道至四川路北段沿海岸。１９８９年初海水入侵到海角大道是Ｓ３１井一带，总的趋势是向南、东扩展；至１９９３年３月，海水入侵面积已超过３ｋｍ＾２，地下水Ｃｌ＾－最大含量约为入侵前的２０倍。１９９３年夏季双来，海水入侵范围略有缩小。自１９９４年年底起，在市区南侧侨港镇一带沿海，又出现海水从是海岸信侵的迹象。     

中国中纬度地带气候暖干化对水资源的影响

中纬度中国,主要指35°N至50°N之间的半湿润至干旱荒漠地带,占中国面积的60%以上,自上世纪末小冰期结束以来,具有鲜明的波动性的增暖和变干趋势,特别是60年代以来更为剧烈。在其影响下,冰川与湖泊萎缩,地表径流减少,地下水位下降,水质恶化,干旱频率和旱灾的严重性都在增加。 在全球变暖的大趋势下,干旱化在近期可能还会继续。但如CO₂及其它微量气体的温室效应导致下世纪升温2℃或更多.重现全新世暖期情景,则中纬度中国会变得湿润起来。而在气候剧变的过渡时期,水旱灾害会进一步增加。     

Vulnerability of Bulgarian agriculture to drought and climate variability with focus on rainfed maize systems

Bulgarian agriculture is affected by droughts and, likely, by climate change. Thus, aiming at assessing its vulnerability, this study includes a general characterization of climate variability in eight selected locations, both in northern and southern Bulgaria. Trend tests were applied to monthly precipitation, maximum and minimum temperature and to the Standardized Precipitation Index with two-month time step (SPI-2) relative to the period of 1951–2004. Negative trends were identified for precipitation and SPI-2 at various locations, mainly in the Thrace Plain, indicating that dryness is likely to be increasing in Bulgaria. The vulnerability of rainfed maize systems to drought was studied using the previously calibrated WinISAREG model and the Stewart’s yield model to compute both the relative yield decrease (RYD) due to water stress and the corresponding net irrigation required to overcome those losses. Results identified a strong relation between SPI-2 for July–August (SPI-2_July–Aug) and RYD. Results also show that yield losses are higher when the soils have a smaller soil water holding capacity. For the various regions under study, thresholds for RYD were defined considering the related economic impacts and the influence of soil characteristics on the vulnerability of the rainfed maize systems. Finally, to support drought risk management, SPI-2_July–Aug thresholds were developed to be used as indicators of the economic risk of rainfed maize for various climate regions and soil groups in Bulgaria.     

Drought analysis and its implication in sustainable water resource management in Barind area,Bangladesh

The study analyzes drought using Standardized Precipitation Index (SPI) and Mann-Kendall (MK) Trend Test in the context of the impacts of drought on groundwater table (GWT) during the period 1971-2011 in the Barind area, Bangladesh. The area experienced twelve moderate to extreme agricultural droughts in the years 1972, 1975, 1979, 1982, 1986, 1989, 1992, 1994, 2003, 2005, 2009 and 2010. Some of them coincide with El Niño events. Hydrological drought also occurred almost in the same years. However, relationship between all drought events and El Niño is not clear. Southern and central parts of the area frequently suffer from hydrological drought, northern part is affected by agricultural drought. Trends in SPI values indicate that the area has an insignificant trend towards drought, and numbers of mild and moderate drought are increasing. GWT depth shows strong correlation with rainy season SPI values such that GWT regaining corresponds with rising SPI values and vice versa. However, 2000 onwards, GWT depth is continuously increasing even with positive SPI values. This is due to over-exploitation of groundwater and changes in cropping patterns. Agricultural practice in Barind area based on groundwater irrigation is vulnerable to drought. Hence, adaptation measures to minimize effects of drought on groundwater ought to be taken.     

Extreme events as drivers of early human behaviour in Africa? The case for variability,not catastrophic drought

Extreme Late Quaternary climatic events, sometimes of considerable continental extent, are being proposed as major contributors to ancestral human behaviour, particularly migration, in Africa. Most recently, a catastrophic drought in the Afro‐Asian monsoon region has been proposed for 16 000–17 000 years ago, driven by global impacts of the Heinrich event 1 (H1), with potentially significant consequences for Palaeolithic cultures. We provide a new analysis of the assertion and find, on examination of a wide set of palaeoenvironmental records, that the scale and extent of the proposed drought is not supported. While some parts of the African tropics, close to the equator, do appear dry at this time, data for the tropics as a whole suggest markedly variable terrestrial conditions, with some environmental systems experiencing very positive hydrological excursions during H1. We contend that in the quest for evidence of climate drivers of ancestral human behaviour, the variability associated with spatially and temporally complex climatic conditions is a significant factor in itself. Copyright © 2011 John Wiley & Sons, Ltd.     

论气候变暖背景下干旱和干旱灾害风险特征与管理策略简

The drought is a most severe natural disaster worldwide, which leads to great risk in human being. The drought disaster and risk have more prominent because of obvious climatic warming in the last hundred years. At present, the understanding of the internal laws of the occurrence of drought and drought risk is not comprehensive, and the recognition of the characteristics of the drought and drought risk under climatic warming is obscure. In this paper, we summarized systematically the domestic and overseas research progress of the drought and drought disaster risk, introduced the principle of the drought disaster transfer process and the essential features of drought disaster, analyzed synthetically the main characteristics and interactions among the key factors of the drought disaster risk, discussed the effect of climatic warming on drought and drought disaster risk, and probed into the basic requirement of drought disaster risk management. Above all, we provide the main protective measurements of the drought disaster and the main strategy of drought disaster risk management.