Quantitative assessment and spatial characteristic analysis of agricultural drought risk in China

Based on the natural disaster analysis theory, the spatial characteristics of agricultural drought risk in China were investigated at 10 × 10 km grid scale. It shows that agricultural drought risk in China has a clear southeast–northwest spatial pattern. High and very high risk mainly occur in the eastern part of Northeast Plain, the central of Inner Mongolian Plateau, the Loess Plateau, north Xinjiang, the north and south of Yangtze Plain, and Yunnan-Guizhou Plateau. Statistics also show that 19.5 % of the main crop planting area is exposed to low risk, 35.1 % of the area to moderate risk, 39.8 % of the area to high risk, and 5.6 % of the area to very high risk. Further investigation shows that 23 % of total wheat growing areas is located in high and very high risk class; corn and rice are 16 % and 14 % respectively. Comprehensive analysis shows that severely affected areas by drought in the history are mainly located in the high and very high risk areas.     

Spatial and temporal analysis of drought risk during the crop-growing season over northeast China

Northeast China as an important agricultural zone for commercial and economic crop in China suffered from increased drought risk that seriously threatened agricultural production and food security in recent decades. Based on precipitation datasets from 71 stations from 1960 to 2009 and on the reliable statistical methods of the Mann–Kendall test, Sen’s slope and the Standardized Precipitation Index, we analyzed the temporal and spatial variation of drought occurrence during the crop-growing season (from May to September) and summer (from June to August). The results showed that regional mean precipitation during the crop-growing season and summer over the last 40 years has decreased at the rate of ?1.72 and ?1.12 mm/year, respectively. According to timescale analysis of abrupt changes, there were two distinct time series (1965–1983 and 1996–2009) with decreasing precipitation trends at a 95 % confidence level. A comparison between the two time series of these two periods demonstrated that more frequent and more severe drought occurred during 1996–2009. Furthermore, drought risk in recent decades has become even more serious both in severity and in extent. Especially in the crop-growing season of 2001 and summer of 2007, over 25 % (2.0 × 10⁵ km²) of study area experienced severe drought (serious and extreme droughts). Our results highlight the urgent need for the development of effective drought adaptations for cropland over northeast China.     

Dynamic risk prediction based on discriminant analysis for maize drought disaster

This study presents a discriminant analysis-based method for prediction of agriculture drought disaster risk. We selected the Chaoyang city in the Northeast China as the study area. We employed multi-scale standard precipitation index (SPI) to reflect drought hazard. We used the yield losses to indicate the drought disaster risk, which was divided into no, low, or high drought risk. We used the multi-scale SPI and drought disaster risk as the input factors for the discriminant analysis-based risk prediction model. The results showed that the model’s prediction accuracy varied between 40 and 82.4 %. The accuracy of high drought disaster risk category was higher than low and no drought disaster risk category. The prediction accuracy of the milky maturity stage was highest. We use leave-one-out cross-validation method to validate the model’s accuracy. And the results showed that the model validation accuracy of high drought group could reach 70.6 % in milky maturity stage. This study showed discriminant analysis is an effective and operable method for disaster risk prediction. This model can provide timely information for decision makers to make effective measures for drought disaster management and to reduce the drought effects to yields at the minimum level.     

Characterization and evaluation of MODIS-derived Drought Severity Index (DSI) for monitoring the 2009/2010 drought over southwestern China

This article investigates whether the Moderate Resolution Imaging Spectroradiometer (MODIS)-derived global terrestrial Drought Severity Index (DSI) had the capability of detecting regional drought over subtropical southwestern China. Monthly, remotely sensed DSI data with 0.05° spatial resolution were used to characterize the extent, duration, and severity of drought from 2000 to 2010. We reported that southwestern China suffered from incipient to extreme droughts from November 2009 to March 2010 (referred to as the “drought period”). The area affected by drought occupied approximately 74 % of the total area of the study region, in which a moderate drought, severe drought, and an extreme drought accounted for 20, 12.7, and 13.2 % of the total area, respectively; particularly in March 2010, droughts of severe and extreme intensity covered the largest areas of drought, which were 16.1 and 18.6 %, respectively. Spatially, eastern Yunnan, western Guizhou, and Guangxi suffered from persistent droughts whose intensities ranged from mild to extreme during the drought period. Pearson’s correlation analyses were performed between DSI and the in situ meteorological station-based Standardized Precipitation Index (SPI) for validating the monitoring results of the DSI. The results showed that the DSI corresponded favorably with the time scales of the SPI; meanwhile, the DSI showed its highest correlation (mean: r = 0.58) with a three-month SPI. Furthermore, similar spatial patterns and temporal variations were found between the DSI and the three-month SPI, as well as the agro-meteorological drought observation data, when monitoring drought. Our analysis suggests that the DSI can be used for near-real-time drought monitoring with fine resolution across subtropical southwestern China, or other similar regions, based solely on MODIS-derived evapotranspiration/potential evapotranspiration and Normalized Difference Vegetation Index data.     

Assessing drought in the drylands of northeast Brazil under regional warming exceeding 4 °C

Natural Hazards - Historically, during periods of extreme drought, food security in the drylands of the semiarid region of Northeast Brazil (NEB) is under severe risk due to agricultural collapse....     

A composite index for drought hazard assessment using CPC rainfall time series data

Hazard analysis is the first step in any disaster management activity. Drought is a serious environmental hazard strongly limiting the agricultural production in the tropical countries like India. A comprehensive drought hazard map is useful for multiple perspectives such as agriculture, environment and hydrology. In this study, daily rainfall data of the Climate Prediction Centre during the south-west monsoon season (June–September) of 12 years, over India was analysed. Based on rainfall and rainy days, six indicators of drought were generated which were then synthesized into a composite index of drought hazard for every 10 × 10 km pixel. The weights for the composite index were generated through variance approach. The index has effectively captured the spatial variations in meteorological drought across India by showing a typical pattern with increasing hazardous area from east to west. The drought hazard map also shows considerable agreement with the climate classification map and the drought proneness map reported by other studies. Thus, the current study presents a simple and novel approach for drought hazard analysis, using the routinely available geospatial rainfall data products. The methodology can be extended to other geographies and disasters too. Use of time series data of longer period would improve the reliability of the composite drought hazard index.     

Analysis of extreme low-temperature events during the warm season in Northeast China

The trends of global warming are increasingly significant, especially in the middle and high latitude regions of the northern hemisphere, where the impact of climate change on extreme events is becoming more noticeable. Northeast China is located in a high latitude region and is sensitive to climate change. Extreme minimum temperatures causing cold damage during the warm season is a major type of agro-meteorological disaster in Northeast China, which causes serious reductions in crop yield. In this paper, we analyzed the temporal and spatial trends in the frequency of extreme minimum temperatures during the warm season (from May to September) during 1956–2005 in Northeast China. Abrupt climatic changes were identified using the Mann–Kendall test. The results show that the frequency of extreme minimum temperature days during the warm season in Northeast China decreases significantly from 1956 to 2005 with a background of climate warming. The highest number of extreme minimum temperature days occurred in the 1970s and 1980s, and there was an abrupt climatic change in 1993. The spatial analysis identified that the north and southeast of the region experienced a larger decrease in the number of extreme low temperature days than the west and south of the region. Rice, sorghum, corn, and soybeans are most vulnerable to cold damage. In severe low temperature years, the average crop yield was reduced by 15.2% in Northeast China.     

Assessing cadmium risk in wheat grain using soil threshold values

At present, the prior-established threshold values are widely used to classify contaminated agricultural soils with heavy metals under the cultivation of a variety of crops, without considering the different sensitivity of plants to heavy metals. Evaluation of the characteristics of cadmium transfer from a polluted calcareous soil to cultivated wheat crop and assessment of the efficiency of using the threshold values to reflect the soil pollution risk by cadmium in Zanjan Zinc Town area at the northwest of Iran were the goals of this study. Totally, 65 topsoil (0–20 cm) and corresponding wheat samples of an agricultural region in the proximity of a metallurgical factory were collected and analyzed for cadmium concentration. The results revealed that industrial activities strongly control cadmium distribution in the studied soils. Relatively high bioavailable cadmium contents (mean 0.77 mg kg^?1) were found in the soils, notwithstanding their alkalinity. It was observed that just 22.5% of the studied area around the Zinc Town is covered by polluted soils with the cadmium concentration exceeding the maximum permissible concentration of 5 mg kg^?1, whereas cadmium concentration in wheat grains of 19 sampled plants is higher than the threshold value of 0.2 mg kg^?1. Among these polluted plants, a total of eight samples were grown in areas classified as unpolluted soils with cadmium, based on the soil threshold value. It seems that this misclassification of polluted soils is mainly related to the crop sensitivity to heavy metals uptake from the soil which should be considered.     

Hurricane wind risk in Louisiana

A statistical procedure for estimating the risk of strong winds from hurricanes, known as the Hurricane Risk Calculator, is demonstrated and applied to several major cities in Louisiana. The procedure provides an estimate of wind risk over different length periods and can be applied to any location experiencing this hazard. Results show that an area 100 km around the city of New Orleans can expect to see hurricane winds blowing at 49 ms^?1 (44.3–53.7) [90 % confidence interval (CI)] or stronger, on average, once every 20 years. In comparison, for the same time period, the capital city of Baton Rouge and the surrounding area can expect to see hurricane winds of 43 ms^?1 (38.2–47.8) (90 % CI) or stronger. Hurricane track direction is also analyzed at the cities of interest. For Morgan City, Lafayette, Lake Charles, and Alexandria, tropical cyclones with winds at least 18 ms^?1 travel from the southeast to northwest. New Orleans and Baton Rouge tropical cyclones have a greater tendency to turn toward the east while within 100 km of the city, historically giving them a southwesterly approach. Tropical cyclones within 350 km off the south-central Louisiana coast occur most often in September, and the most extreme of these events are becoming stronger through time as shown with quantile regression.     

Assessment on agricultural drought vulnerability in the Yellow River basin based on a fuzzy clustering iterative model

Drought is one of the major natural disasters occurring in China and causes severe impacts on agricultural production and food security. Therefore, agricultural drought vulnerability assessment has an important significance for reducing regional agricultural drought losses and drought disaster risks. In view of agricultural drought vulnerability assessment with the characteristics of multiple factors and uncertainty, we applied the fuzzy comprehensive evaluation framework to agricultural drought vulnerability model. The agricultural drought vulnerability assessment model was constructed based on the multi-layer and multi-index fuzzy clustering iterative method, which can better reveal the drought vulnerability (including sensitivity and adaptation capacity). Furthermore, the cycle iterative algorithm was used to obtain the optimal index weight vector of a given accuracy by setting the objective function. It provides a new approach to weight determination of agricultural drought vulnerability assessment. In this study, agricultural drought vulnerability of 65 cities (as well as leagues and states) in the Yellow River basin was investigated using a fuzzy clustering iterative model and visualized by using GIS technique. The results showed clear differences and regularities among the spatial distribution of agricultural drought vulnerability of different regions. A large number of the regions in the basin consisted of those exhibiting high to very high vulnerability and were mainly distributed throughout Qinghai, Gansu, northern Shaanxi, and southern Shanxi, accounting for 46 % of the total assessment units. However, the regions exhibiting very high vulnerability were not significantly affected by droughts. Most of the regions exhibiting moderate vulnerability (21.5 % of the assessment units) were mainly concentrated among agricultural irrigation areas, where agriculture is highly sensitive to droughts, and drought occurrence in these regions will likely cause heavy losses in the future. The regions exhibiting slight to low vulnerability were relatively concentrated, accounting for 32.3 % of the assessment units, and were mainly distributed in the plains of the lower reaches of the Yellow River, where the economy was rather well developed and the agricultural production conditions were relatively stronger.     

我国东北地区冬季降水和东亚冬季风的关系研究

利用1961-2011年我国东北地区(包括黑龙江、吉林、辽宁、内蒙古东部)的冬季降水资料,分析了东北地区冬季降水量的时空分布和冬季降水日数的时空分布,对比分析了东亚冬季风对我国东北地区冬季降水的影响. 结果表明：东北地区冬季降水量和降水日数分布有明显的区域差异,以内蒙古东南部、辽宁西北部、吉林西部、黑龙江西南部为低值中心,外围辽宁东部,吉林南部,黑龙江东部、中北部、北部,内蒙古东北部等地区为高值区;冬季降水量年际变化呈增加的线性趋势,1980年代中期以后冬季降水量的高值和低值都有明显的增大;年降雪日数年际变化呈线性增加趋势. 1948-2011年东亚冬季风强度指数的结果表明,东亚冬季风呈明显的线性减弱趋势,弱东亚季风主要集中在20世纪80年代中期以后,除内蒙古东南部等少数区域外,我国东北大部分地区的冬季降水量都和东亚冬季风呈负相关. 对应地,东北地区冬季降水量增大,年际变化的幅度变化增大,降水日数增量较小,这可能与东北地区冬季极端降水天气和干旱天气增加有关. 在东亚范围内,我国东北地区冬季降水多年200 hPa U风增强、500 hPa高压减弱、850 hPa东海南风增强,冬季降水少年则相反.     

Risk assessment to China’s agricultural drought disaster in county unit

China faces drought disaster risk under the changing climate. Risk analysis is a suitable approach in order to design ex-ante measure able to anticipate effects of drought on agricultural production. In this article, with the support of historic drought disaster data from 583 agro-meteorological observations (1991–2009), a risk analysis method based on information diffusion theory was applied to create a new drought risk analysis model, and the risk of China’s agriculture drought disaster was evaluated on higher spatial resolution of county unit. The results show that in more than three hundred counties of China, risk probability was biyearly or annually when Drought Affected Index (DAI) was over 5%. When DAI was up to 40%, more than one hundred counties were prone to drought disaster annually or once every 5 years. This showed that the impact of drought disaster on China’s agriculture, whether in frequency or intensity, was large. With the different level of DAI, China’s agricultural drought risk pattern showed variable pattern characteristics. When DAI was low, the distribution of county agricultural drought risk in China presented the East–West pattern of differentiation, and high risk mainly lied in the eastern, low risk mainly in the western. On the other hand, when DAI was high, the distribution of county risk appeared a pattern of high in center, and the north areas higher than the south, increased gradually from southwest to northeast. Drought risk presents a clear zonal differentiation that may be result from stepped topography, different precipitation and hazard-affected bodies. Spread of high value area of drought risk in northern may be related to the southeast monsoon and ecological degradation in northern Ecotone.     

1961-2009年西北地区基于SPI指数的干旱时空变化特征

利用西北五省区137个测站的1961-2009年逐月降水量资料计算标准化降水指数(SPI), 统计了逐月、春末夏初、初夏、夏季及秋季的干旱、重旱、特旱的频率及面积率, 分析其时空变化特征.结果表明: 新疆北部、青海的中部及甘肃河西是西北地区干旱频率较高的区域, 干旱频率在15个月以上, 新疆南部除个别月份干旱发生频率较高外, 总体干旱发生频率较低;干旱发生区域随月份有由南到北、由西向东变化的趋势;除新疆、青海、及甘肃个别区域重旱频率超过5月外, 其他区域基本上都在5月以下;新疆南部重旱频率仍然较低;夏季发生范围高于其他季节;新疆北部、甘肃河西是特旱的高发区. 不同等级的月及季节干旱面积率其逐年变化具有相似的特征, 西北干旱面积率的变化总体上可以分为3个阶段: 1961-1980年干旱面积率比较高, 平均在35%左右;1981-1990年为转折期, 干旱面积率下降到15%左右;而1991-2009年为稳定期, 干旱面积率变化不大.全球气候变暖导致西北地区降水量、冰川融水量、河川径流量增加和湖泊水位上升、面积扩大, 是1987年以来干旱面积率下降的原因.     

Impact of spate irrigation of flood waters on agricultural drought and groundwater recharge: case of Sidi Bouzid plain,Central Tunisia

In Sidi Bouzid plain, rainfall alone is insufficient to satisfy crop water requirements. Within this framework, and in order to improve water resources in the region, the Tunisian State adopted non-conventional water mobilization techniques, among which artificial spate irrigation. The objective of the study is to evaluate the impact of spate irrigation of flood water on the mitigation of agricultural drought and the enhancement of groundwater recharge. Annual and monthly rainfall data as well as flood water volumes were monitored. The study focused on the groundwater drawdown monitoring. Results showed a high flood water contribution to crop water requirements that exceeded rainfall. This water prevented drought in the spate perimeters. The groundwater drawdown was found to fluctuate over time, with an average decreasing rate of 0.4 to 0.5 m/year. Groundwater recharge was found to be highly correlated with flood water contribution through spate irrigation (R ² = 84 %). Out of the spate zone, a high decrease in the groundwater level was noted. The lowest rate of 1 m/year was that of the farthest piezometer from the spate perimeters. This is influenced by the excessive pumping out of the spate zone. In 1980, groundwater flew from the west to the east. In 2015, the flow movement from the east to the center of the plain did not change due to the presence of the spate perimeters. Nevertheless, excessive pumping around sabkhas changed the flow directions at the outlet zone. A variation in groundwater salinity was observed in both space and time. In 1975, salinity was very low. The outlet zone was the most affected where the drawdown reached several meters, causing saltwater intrusion from the surrounding sabkhas.     

近40年中国平均气候与极值气候变化的概述

随着中国气象局对近50年来逐日气象观测资料的释放,人们从不同的角度对中国平均气候和极端气候的分布特征有了更多的了解.从目前研究的结果来看,这些认识需要有一个集成,即需要有一个总体的归纳和解释.通过中国近40年来的温度极值和降水极值事件的分析认识到全球增暖和区域环流异常决定着气候极值事件的分布格局.与全球增暖相联系的是:我国微量降水在空间上表现为一致的减少趋势,我国北方寒潮事件显著减少,冷夜和冷日的减少与暖夜和暖日的增多并存,以及极端强降水有增多的趋势.与东亚季风气流和西风带气流异常对应的我国有效降水在区域分布上发生了显著变化,东部季风区中的"北涝南旱"从1970年代末转型为"南涝北旱",与华南的偏干一起形成了东部季风区降水从华南、长江到华北的"-、 、-"异常分布型,但华南在1991年出现了转湿的突变;东北和西北先后从1983年和1987年前后转为暖湿气候.极端温度和极端降水趋势的空间分布与平均温度和平均降水趋势的空间分布一致.     

Risk analysis and influencing factors of drought and flood disasters in China

The risk analysis of flood and drought disasters and the study of their influencing factors enhance our understanding of the temporal and spatial variation law of disasters and help identify the main factors affecting disasters. This paper uses the provincial administrative region of China as the research area. The proportion of the disaster area represents the degree of the disaster. The statistical distribution of the proportions was optimized from 10 alternative distributions based on a KS test, and the disaster risk was analyzed. Thirty-five indicators were selected from nature, agriculture and the social economy as alternative factors. The main factors affecting flood and drought disasters were selected by Pearson, Spearman and Kendall correlation coefficient test. The results demonstrated that the distribution of floods and drought is right-skewed, and the gamma distribution is the best statistical distribution for fitting disasters. In terms of time, the risk of flood and drought disasters in all regions showed a downward trend. Economic development and the enhancement of the ability to resist disasters were the main reasons for the change in disasters. Spatially, the areas with high drought risk were mainly distributed in Northeast and North China, and the areas with high flood risk were mainly distributed in the south, especially in Hubei, Hunan, Jiangxi and Anhui. The distribution of floods and drought disasters was consistent with the distribution characteristics of precipitation and water resources in China. Among the natural factors, precipitation was the main factor causing changes in floods and drought disasters. Among the agricultural and socioeconomic factors, the indicators reflecting the disaster resistance ability and regional economic development level were closely related to flood and drought disasters. The research results have reference significance for disaster classification, disaster formation mechanisms and flood and drought resistance.

     

西北地区东部季节干旱的时空变化特征分析

干旱作为我国西北地区东部影响最大的气象灾害, 可引起农业减产、水资源短缺、土地荒漠化和生态环境恶化等严重问题.在国家新一轮西部大开发战略实施之初, 在全球气候变暖背景下, 有必要对干旱发展的最新特征和演变趋势进行详细分析研究, 为加强防旱、抗旱,促进经济发展提供科学决策依据和参考.采用国家干旱标准综合干旱指数(CI指数), 利用西北地区东部74个气象代表站逐日气温、降水资料, 分析了西北地区东部不同级别干旱日数在各个季节的时空分布和变化趋势. 结果表明: 在气候变暖背景下, 西北地区东部从长期趋势看, 春、夏、秋季干旱呈加剧趋势, 冬季干旱呈减轻趋势. 21世纪以来春、夏季干旱进一步加剧, 尤其是夏季加剧更显著, 而秋、冬季干旱出现了减弱的新趋势. 在西北地区东部主降水期3-11月重-特旱加剧趋势比轻-中旱加剧显著, 南部干旱化趋势比北部更加明显. 尤其是宁夏同心地区春旱加剧非常显著, 已成为西北地区东部重-特旱最严重的地区.对于干旱发展的这一新动态, 必须引起有关部门的高度重视, 采取科学、有效手段加强防旱、抗旱.     

Storm surges in the Singapore Strait due to winds in the South China Sea

Among the semi-enclosed basins of the world ocean, the South China Sea (SCS) is unique in its configuration as it lies under the main southwest-northeast pathway of the seasonal monsoons. The northeast (NE) monsoon (November–February) and southwest (SW) monsoon (June–August) dominate the large-scale sea level dynamics of the SCS. Sunda Shelf at the southwest part of SCS tends to amplify Sea Level Anomalies (SLAs) generated by winds over the sea. The entire region, bounded by Gulf of Thailand on the north, Karimata Strait on the south, east cost of Peninsular Malaysia on the west, and break of Sunda Shelf on the east, could experience positive or negative SLAs depending on the wind direction and speed. Strong sea level surges during NE monsoon, if coincide with spring tide, usually lead to coastal floods in the region. To understand the phenomena, we analyzed the wind-driven sea level anomalies focusing on Singapore Strait (SS), laying at the most southwest point of the region. An analysis of Tanjong Pagar tide gauge data in the SS, as well as satellite altimetry and reanalyzed wind in the region, reveals that the wind over central part of SCS is arguably the most important factor determining the observed variability of SLAs at hourly to monthly scales. Climatological SLAs in SS are found to be positive, and of the order of 30 cm during NE monsoon, but negative, and of the order of 20 cm during SW monsoon. The largest anomalies are associated with intensified winds during NE monsoon, with historical highs exceeding 50 cm. At the hourly and daily time-scales, SLA magnitude is correlated with the NE wind speed over central part of SCS with an average time lag of 36–42 h. An exact solution is derived by approximating the elongated SCS shape with one-dimensional two-step channel. The solution is utilized to derive simple model connecting SLAs in SS with the wind speeds over central part of SCS. Due to delay of sea level anomaly in SS with respect to the remote source at SCS, the simplified solutions could be used for storm surge forecast, with a lead time exceeding 1 day.     

Potential predictability of wet/dry spells transitions during extreme monsoon years: optimism for dynamical extended range prediction

The duration and extreme fluctuations of prolonged wet or dry spells associated with intraseasonal variability during extreme monsoon have devastating impacts on agrarian-based economy over Indian subcontinent. This study examines the potential predictability limit of intraseasonal transitions between rainy to non-rainy phases (i.e., active to break phases) or vice versa over central Indian region during extreme monsoon using very high-resolution (0.25° × 0.25°) daily rainfall datasets. The present study reveals that the transitions from both active to break and break to active conditions are more predictable by ~8 days during the weak monsoon (WM) years compared to the strong monsoon (SM) years. Such asymmetric behavior in the limit of predictability could be linked to the distinct differences in the large-scale seasonal mean background instability during SM and WM years. The achievability of such predictability is further evaluated in a state-of-the-art climate model, the climate forecast system (CFSv2). It is demonstrated that the observed asymmetry in predictability limit could be reproducible in the CFSv2 model, irrespective of its spatial resolution. This study provides impetus for useful dynamical prediction of wet/dry spells at extended range during the extreme monsoon years.