Response Of Hydrological Drought To Meteorological Drought And The Impact Of A Large Reservoir

As one of the most extreme hydrological events,hydrological drought is associated with deficiencies in streamflow,groundwater,and water supply of lakes or reservoirs,which will last continuously after the end of meteorological drought.The evolution of hydrological drought is not only related to climate change,but also closely related to the physical mechanism of social system.Exploring the response of hydrological drought to meteorological drought under the influence of large reservoirs helps further understand the causes,characteristics of drought and enrich the theory of droughts,which is crucial for early warning of hydrological drought depended on weather forecast.This study took Jinjiang River basin in the southeast coastal region of China as an example,where Shilong hydrological station is influences by a large reservoir(Shanmei),and the Anxi hydrological station is not,and used comparison method to understand the response changes/differences of hydrological drought to meteorological drought under the impact of a large reservoir.This paper has been studied from three aspects.Firstly,based on monthly data of streamflow and precipitation and historical drought records from 1960 to 2010,the Standardized Precipitation(SPI)and Standardized Streamflow Index(SSI)series(representing meteorological drought and hydrological drought,respectively)were each calculated.And run theory was then used to identify the characteristics of meteorological and hydrological drought,including duration and magnitude.The relationship between the drought events and historical drought records was evaluated to analysis the regional applicability of multi time scales of SPI and SSI.Then the Mann-Kendall non-parametric test,Wavelet analysis,Pearson correlation coefficients and Difference Curve-Rank test method etc.were applied to explore the evolution of time series of hydrological drought responds to evolution of time series of meteorological drought under the influence of large reservoir(Shanmei reservoir).Secondly,the Pearson correlation coefficients(PCC),Cross-wavelet transform(XWT)and a comparison method were used to reveal the detailed correlations between the evolution of hydrological drought and climate indices(ENSO,PDO,NAO and AMO)at different coherence circles.Finally,the relationship between the characteristics of hydrological drought and meteorological drought were established by a non-linear function model at the Anxi station,and also at the Shilong station which reflects the periods of natural-influence and reservoir-influence,respectively.Then the response of hydrological droughts to meteorological droughts with impact of large reservoir was discussed and the concept of threshold that meteorological drought evolved into hydrological drought was proposed.Results indicated that:(1)Based on the assessment,SPI and SSI indices can effectively reflect the duration and magnitude of drought in Jinjiang River basin.(2)Meteorological and hydrological drought have the tendency of decreasing during recent several decades.Monthly SSI has a statistically significantly decreasing trend in November to next year February and noticeably increasing trend in May to July in Shilong hydrological station under the influence of Shanmei reservoir regulation.(3)the occurrence frequency of hydrological drought has obvious characteristics of inter generational variations.There were three significant periodic variations at scales of 6-7a,11-12a and 20-21a for annual scales of SSI(SSI12)series and they are almost consistent of the same scales of SPI,but have not been synchronous since the 1980s at the Shilong hydrological station because of Shanmei reservoir regulation influences,especially the periodic variations at scales of 20-21a.(4)The correlations between SSI and ENSO or PDO are more obvious than the other two climate indices,NAO,AMO.Moreover,the effect of El Nino was more obvious than that of LA Nino.There exist apparent intra-annual(12-48 months)and inter-decadal(128-256 months)common oscillation circles between SSI and ENSO.Meanwhile,there is an unequal lag time(1.47-1.80 months)between the coherence circles of SSI with ENSO.(5)The regulation functions of the large reservoir with respect to streamflow changed the correlations between SSI and climate indices.The correlations at Shilong station were weaker than those at Anxi station.A stronger common oscillation circle of 64-128 months between SSI and PDO during 2000-2008 and 64-96 months between SSI and NAO during 2004-2008 existed at Anxi station,but the correlations between SSI and PDO or NAO did not show any significant common oscillation circles during the same time period at Shilong station.(6)there is a clear non-linear(three parameters of the Logarithm function)relationship with which hydrological drought responds to meteorological drought,and the threshold within which hydrological drought starts to respond to meteorological drought can be obtained according to the non-linear function model;(7)the operational activities of the Shanmei reservoir have significantly reduced the duration and magnitude of hydrological drought at the Shilong station compared to the natural-influence period,which,in turn,altered the relationship between the hydrological drought and meteorological drought and shortened the propagation processes of drought from meteorological to hydrological.