| The increase in drought events that may be caused by global warming and climate anomalies will certainly have a serious impact on water resources security and food resources security.In this paper,the study area was Shaanxi Province and the meteorological data spans from 1960 to 2015.In this study,the time-varying trend of climatic factors closely related to drought was investigated using Ensemble Empirical Mode Decomposition(EEMD).The drought duration and drought severity were extracted from Standardized Precipitation Evapotranspiration Index(SPEI)based on run theory.Each drought characteristic index was evaluated for its distribution by comparing different marginal distributions.Then,the joint distribution of the 2 indices was established based on their correlation and further analyzed the linkage between the joint return period of drought events and crop drought losses.Finally,the influence of drought conditions on the function of the ecosystem was analyzed based on the climatic conditions and the relationship between precipitation and runoff and discussed the effects of drought events that caused changes in precipitation and runoff on the ecosystem policy.The main conclusions are as follows:(1)Different climatic factors in Shaanxi Province have relatively stable interannual and interdecadal periods on different time scales in the same time period.Based on the EEMD decomposition method,it is able to extract real and reliable climate change signals and characterize the nonlinear change characteristics of different climatic factors.It is of great significance to improve the cognition of the actual evolution rules in the process of climate factor change.(2)During the period of 1960-2015,the overall frequency of drought in Shaanxi Province decreased from south to north,and the frequent drought areas mainly concentrated in northern Shaanxi.In the past 56 years,Shaanxi province has been dominated by light drought events,followed by middle drought events and severe drought events.(3)There is a strong correlation between drought duration and drought intensity in different climatic regions of Shaanxi Province.The fitted empirical marginal distribution function and joint distribution function both have a high degree of fitness with the theoretical distribution function.The return periods of different grades of drought events in northern Shaanxi and Guanzhong regions showed a decreasing trend as a whole;while the frequency of drought events in southern Shaanxi had a slight decrease.When the characteristics of the drought event extracted in this study are close to the actual drought characteristics,the error range between the theoretical return period and the actual return period is mostly between 0.1-0.3 years.(4)Protracted drought could affect runoff generation and cause changes in the rainfall-runoff relationship.When we compared the annual average precipitation in separate watersheds and analyzed their drought characteristics,we concluded that this situation is likely to occur when the drought duration is not less than 6 years and the drought severity is equal to or greater than 0.55.(5)The Frank copula function can be used as the optimal joint distribution function of drought duration and severity in Shaanxi Loess Plateau.The spatial distribution characteristics of drought recurrence also further indicate the spatial heterogeneity of different watershed characteristics in Shaanxi Loess Plateau.The management of the Loess Plateau ecosystem in Shaanxi needs to pay more attention to the effects of multi-year drought events.Vegetation restoration in each river basin should be adapted to local conditions. |
PDF Full Text Request