Driving Mechanism And Quantitative Assessment Of Drought In Luanhe River Basin Under Changing Environment

The Luanhe River basin undertakes the important task of supplying water to Tianjin and Tangshan cities.Due to the intense influence of changing environment,extreme drought disasters occurred more and more frequently in the Luanhe River basin.Consequently the related regions have been facing a series of serious problem with respect to water resources.The non-stationaries existing in hydrologic time series lead traditional methods of stationary drought analysis have been questioned in recent years.This paper mainly aims at discussing the inconsistent drought problem in drought research field,and attempts to provide new concepts and references to solving the problem.Taking the Luanhe River basin as study area,the recognition of drought driving mechanism and quantitative assessment of drought events were conducted in this research.A Copula-based Joint Deficit Precipitation Index(JPDI)was introduced,which is able to assess the drought events more roundly and objectively.The Standardized Precipitation Index(SPI)with different time scales and the JPDI were both used to describe the drought condition at a multi-scale in the Luanhe River basin.Drought evaluation results indicate that there were three sub-regions with distinct drought evolution.Droughts happened in the southeastern sub-region were more severe and frequent.The frequency and duration of drought events both tend to increase.Considering the evolutions of meteorological drought and hydrology drought,the driving pattern of drought in the Luanhe River basin was obtained by using the precipitation-runoff double accumulation curve method combined with the genetic analysis.The evaluation indicators based on drought indices were proposed to verify the driving pattern.Results imply that the variation of meteorological drought during 1959~2011,as well as the hydrology drought change before 1980,was mainly affected by climate change.However,the hydrology drought evolution after 1980 was the result of the effect of both climate change and human activity.Based on the drought driving pattern in the basin,Climate-change Index(CI)and Human-induced Index(HI)were put forward,using for representing the impact factors of the drought non-stationarity caused by climate change and human activity.The CI indicators were chose from different climate oscillations indices,and the HI indicator was designed based on SWAT model simulation.The CI and HI indicators can meet the needs of research on inconsistent drought problems.In order to identify meteorological drought under non-stationary condition,non-stationary models with time and CI indicators as covariates respectively were used for constructing the time-dependent Standardized Precipitation Index(SPIt)and Nonstationary Standardized Precipitation Index(NSPI).The performances of the SPIt,the NSPI and the traditional SPI were compared when modeling the historical drought events in the study area.The NSPI considers the impact of climate changes,showing better applicability for the Luan River basin than the other two.The drought severity described by the NSPI was characterized by dynamic,capable of responding to climate change.According to the assessment results based on NSPI,in recent years,especially after 2000,the frequency,duration and severity of meteorological drought all have an obvious increase tendency.For every drought feature,the gravity center tends to transfer from southeast to middle.A non-stationary model using CI and HI indicators as covariates was developed for fitting streamflow series,and then adopted to calculate the Non-stationary Standardized Streamflow Index(NSSI).The NSSI incorporates non-stationary influences in regard to climate variation and human activities,improving its ability to adapt the changing environment.Modeling results of historical drought in the Liuhe sub-basin indicated that the NSSI with dynamic characteristic is more applicable in the non-stationary context than the traditional drought index.The temporal pattern of hydrology drought in the sub-basin was obtained by using the NSSI.Results imply that the more severe and longer-lasing hydrological drought occurred frequently after 2000,leading to serious impacts on regional natural environment and social economy.