近50年华北区域性气象干旱事件的特征分析

本文利用区域性极端事件客观识别法(OITREE),进行了1961—2010年华北地区区域性气象干旱事件的识别,确定了该方法中相应的参数组并识别得到100次事件,并对排名前15位的事件与文献记载情况逐一进行对比检验。结果表明OITREE方法对华北地区区域性气象干旱具有良好的识别能力。100次华北地区区域性气象干旱事件分为10次极端事件、20次重度事件、40次中等事件和30次轻度事件,其中1998年9月至1999年5月秋冬春连旱是华北地区强度最强的干旱事件。事件的持续时间一般在17~120 d、最大影响面积集中在(70~105)×10~4km^2之间,干旱事件具有较明显的季节特征,3—7和10—11月是事件的两个高发时段;华北南部为干旱多发区,其中河北、河南和山东三省交界为强度中心区域。重度(含)及以上的干旱事件可分为全境型、东部型、南部型、西部型、中部型和零散型6种分布类型,其中全境型出现机率最高。近50年华北地区区域性干旱事件频次、累积综合强度总体呈上升趋势,其主要原因可能是降水量减少所致,同时气温显著升高也起到了明显的推动作用。

陕西区域性气象干旱事件及变化特征

以陕西省为例,探讨了区域性气象干旱事件的识别和综合评估方法。采用陕西省96个国家级气象站1961-2013年逐日降水量和平均气温资料,计算了各站逐日综合气象干旱指数CI值,在此基础上定义了区域性气象干旱事件,并构建了以事件的极端强度、累积强度、累积面积、最大面积和持续时间5个指标的区域气象干旱事件综合评估模型,确定了区域气象干旱事件综合强度等级划分标准。历史干旱事件验证表明,采用的建模方法和评估等级划分合理。分析表明：陕西区域性气象干旱事件的持续时间以10~20 d为主,最长可达218 d。区域性干旱事件主要出现在春夏季。近53 a区域干旱事件频次呈弱的增加趋势,累积日数呈增多趋势,但年际差异大,阶段性特征显著。20世纪90年代持续性干旱事件频繁,强度强。干旱事件地域分布特征显示关中为陕西干旱事件发生的高频、高强中心区域。

1960-2010年中国西南地区区域性气象干旱事件的特征分析

利用区域性极端事件客观识别法(Objective Identification Technique for Regional Extreme Events,OITREE)和1960-2010年中国西南地区(四川、云南、贵州省和重庆市)101个站综合气象干旱指数(CI)进行区域性气象干旱事件识别研究,确定了相应的()ITREE方法参数组,并识别得出87次中国西南地区区域性气象干旱事件,其中9次达到极端强度,而2009年9月一2010年4月发生的特大干旱是中国西南地区近50年最严重的区域性气象干旱事件。进一步分析表明,中国西南地区区域性气象干旱事件的持续时间一般为10—80 d,最长可达231 d;11—4月是西南地区的旱季。云南和四川南部是西南干旱的频发和强度中心地区;强的(极端及重度)干旱事件可分为5种分布类型,其中南部型出现机会最多。过去50年西南地区区域性气象干旱事件频次显著增多,强度有所增强,其主要原因可能是该地区降水量显著减少所致,而气温升高也起到了推波助澜的作用。

大清河流域气象干旱时空演化和联合概率分析

为了评估大清河流域整体气象干旱状况,采用该流域1961—2015年逐日气象数据,基于CI干旱指数和面积阈值法识别区域气象干旱事件,提取历时、干旱面积等指标,分析研究区域气象干旱时空变化特征,并基于Copula函数进行多维干旱特征变量的联合概率分析和重现期计算。结果表明:研究区各地干旱频率相差不大;区域气象干旱程度总体有减轻趋势;冬旱发生的频数最多,春旱多于秋旱,跨季节连旱(尤其是冬春连旱和春夏连旱)较为常见;三维干旱特征变量联合概率能够全面地反映干旱极限特征,在工程设计、水资源决策中安全性更高。

Impact of Meteorological Drought on Streamflow Drought in Jinghe River Basin of China

Under global climate change, drought has become one of the most serious natural hazards, affecting the ecological environment and human life. Drought can be categorized as meteorological, agricultural, hydrological or socio-economic drought. Among the different categories of drought, hydrological drought, especially streamflow drought, has been given more attention by local governments, researchers and the public in recent years. Identifying the occurrence of streamflow drought and issuing early warning can provide timely information for effective water resources management. In this study, streamflow drought is detected by using the Standardized Runoff Index, whereas meteorological drought is detected by the Standardized Precipitation Index. Comparative analyses of frequency, magnitude, onset and duration are conducted to identify the impact of meteorological drought on streamflow drought. This study focuses on the Jinghe River Basin in Northwest China, mainly providing the following findings. 1) Eleven meteorological droughts and six streamflow droughts were indicated during 1970 and 1990 after pooling using Inter-event time and volume Criterion method. 2) Streamflow drought in the Jinghe River Basin lagged meteorological drought for about 127 days. 3) The frequency of streamflow drought in Jinghe River Basin was less than meteorological drought. However, the average duration of streamflow drought is longer. 4) The magnitude of streamflow drought is greater than meteorological drought. These results not only play an important theoretical role in understanding relationships between different drought categories, but also have practical implications for streamflow drought mitigation and regional water resources management.

Regional applicability of seven meteorological drought indices in China

The definition of a drought index is the foundation of drought research.However,because of the complexity of drought,there is no a unified drought index appropriate for different drought types and objects at the same time.Therefore,it is crucial to determine the regional applicability of various drought indices.Using terrestrial water storage obtained from the Gravity Recovery And Climate Experiment,and the observed soil moisture and streamflow in China,we evaluated the regional applicability of seven meteorological drought indices:the Palmer Drought Severity Index(PDSI),modified PDSI(PDSI_CN) based on observations in China,self-calibrating PDSI(scPDSI),Surface Wetness Index(SWI),Standardized Precipitation Index(SPI),Standardized Precipitation Evapotranspiration Index(SPEI),and soil moisture simulations conducted using the community land model driven by observed atmospheric forcing(CLM3.5/ObsFC).The results showed that the scPDSI is most appropriate for China.However,it should be noted that the scPDSI reduces the value range slightly compared with the PDSI and PDSI_CN;thus,the classification of dry and wet conditions should be adjusted accordingly.Some problems might exist when using the PDSI and PDSI_CN in humid and arid areas because of the unsuitability of empiricalparameters.The SPI and SPEI are more appropriate for humid areas than arid and semiarid areas.This is because contributions of temperature variation to drought are neglected in the SPI,but overestimated in the SPEI,when potential evapotranspiration is estimated by the Thornthwaite method in these areas.Consequently,the SPI and SPEI tend to induce wetter and drier results,respectively.The CLM3.5/ObsFC is suitable for China before 2000,but not for arid and semiarid areas after 2000.Consistent with other drought indices,the SWI shows similar interannual and decadal change characteristics in detecting annual dry/wet variations.Although the long-term trends of drought areas in China detected by these seven drought indices during 1961-2013 are consistent,obvious differences exist among the values of drought areas,which might be attributable to the definitions of the drought indices in addition to climatic change.