三种综合气象干旱指数在洞庭湖流域的适用性分析

结合洞庭湖流域水文气象特点,从不合理跳跃点、统计特征、区域干旱以及空间分布等方面综合分析了3种气象干旱指数在该流域的适用性及可靠性。评价结果表明：（1）NCC2CI与CInew指数均可较好解决传统CI指数评估中出现的不合理震荡、旱情加剧等不足，且该指数对长历时干旱表现较为敏感，对短历时干旱存在漏测的可能性；（2）对具有较大烈度特征的干旱事件，NCC2CI指数虽然能较好地监测出等级较高的干旱强度，但对极端干旱强度的特征表征有所不足；（3）干旱NCC2CI指数较好地延续了传统CI指数的统计特性以及空间分布特性，反映出的某时段较大降水对日后的影响时段为20~40 d，指数表征更加符合干旱发生的过程。而CInew指数反映的影响时段为45~70 d，且在空间分布上变化较大，应用可靠性相对较差。综合比较分析表明，NCC2CI指数在洞庭湖流域更具实用性，研究结果对其它类似流域干旱评估具有一定参考作用

APPLICABILITY OF THREE COMPREHENSIVE METEOROLOGICAL DROUGHT INDEXES IN DONGTING WATERSHED

The meteorological data from 19 meteorological stations of the Dongting watershed during 1961-2009 were chosen. NCC2CI and CInew are improved form of the traditional CI. NCC2CI is an improved form of the traditional CI in the accumulated rainfall weight, while the CInew is equivalent to change the SPI30 and M30, which are part of NCC2CI, into SPI90 and M90. The calculation principle of this three drought index is simple synthesis of the standard precipitation index and relative moisture index. This study investigates the applicability of three comprehensive meteorological drought indexes (traditional CI, NCC2CI, CInew) in the Dongting Lake basin, from the unreasonable jump point, the statistical characteristics, the process of site drought, the process of regional drought and spatial distribution, and so on. Results showed that CInew and NCC2CI could be good solution to the problems such as the unreasonable shocks, the unreasonable increased drought and other shortcomings of the traditional CI. The CInew index is more sensitive to NCC2CI and traditional CI in the monitoring of long duration drought, while there is more possibility to leak the short duration of drought. NCC2CI can better monitor short duration drought, and CInew is better in capturing the starting time of drought than CInew and NCC2CI index. For monitoring the large intensity feature drought, the NCC2CI index can better monitor the higher intensity drought but weakly monitor the extreme drought. NCC2CI index can inherit the distribution and spatial characteristics of the traditional CI index. NCC2CI shows that the influence period of a larger precipitation is 20-40 d, which is more consistent with the development process of drought; while the influence period of a larger precipitation, shown through CInew index, is 45-70 d. In addition, the CInew index has larger difference with the traditional CI index in the spatial distribution, so having a poor reliability 〖JP2〗on application. With a comprehensive comparative analysis, the NCC2CI index is more practical in the Dongting Lake watershed; the research results have a certain reference to other similar watershed on the assessment of drought. In addition，one thing to note is that the meteorological drought index evaluate drought is only based on the evaporation, rainfall and other meteorological information. However, the actual drought is often integrated decision by meteorological, soil moisture, water conservancy facilities and water applications. The comprehensive meteorological drought index can not distinguish the difference between the harm degrees which is caused by the same degree of less precipitation in the farming period and the slack period (i.e. winter). Therefore, the evaluation of drought only based on meteorological index may cause