Abstract
Ecological water replenishment (EWR) via interbasin water transfer projects has been regarded as a critical solution to reducing the risk of lake shrinkage and wetland degradation. The hydrological conditions of EWR water sources do not change synchronously, which may have an impact on the transferable water. Based on the GAMLSS model and the multivariate Copula model, this work presents a research approach for EWR via interbasin water transfer projects that can capture the non-stationarity of the runoff series and the frequency of dryness–wetness encounters, as well as speculates on various scenarios throughout the project operation phase. We present a case study on the Baiyangdian Lake, acting as the largest freshwater wetland in North China, which has suffered from severe degradation during the past decades and deserves thorough ecological restoration. The GAMLSS model was used to examine the non-stationarity characteristics of EWR water sources including the Danjiangkou Reservoir (DJK), the Huayuankou reach of the Yellow River (HYK), and upstream reservoirs (UR). The multivariate Copula model was implemented to evaluate the synchronous–asynchronous characteristics for hydrological probabilities for the multiple water sources. Results show that 1) significant non-stationarity has been detected for all water sources. Particularly, a significant decreasing trend has been found in UR and HYK. 2) The non-stationary model with time as the explanatory variable is more suitable for the runoff series of DJK, HYK, and UR. Under the non-stationary framework, the wet–dry classification of runoff series is completely changed. 3) Whether the bivariate or trivariate combination types, the asynchronous probability among the three water resources is over 0.6 except DJK-HYK, which indicates the complementary relationship. Multiple water resources are necessary for EWR. What is more, during a dry year of UR, the conditional probability that both DJK and HYK are in a dry year is 0.234. To alleviate the problem of not having enough water, some additional water resources and an acceptable EWR plan are required.
Highlights
Understanding the hydrological synchronization of numerous water sources is critical for the ecological water replenishment (EWR), as the EWR measures are heavily reliant on the hydrological conditions of water sources
We present a case study on the Baiyangdian Lake, acting as the largest freshwater wetland in North China, which has suffered from severe degradation during the past decades and deserves thorough ecological restoration
Non-stationary frequency analysis is modeled with time as the explanatory variable using GAMLSS
Summary
With the rapid increase in the human population and social progress, development has generated significant economic and social benefits, but these benefits often come at high costs. Several wetland restoration measures, such as ecological water replenishment, restoring natural waterways, recreating the natural river, establishing habitats, and returning cropland to wetland, are recognized (Xin, 2014; Wu et al, 2020). Among these measures, the ecological water replenishment (EWR) has been widely applied in restoring ecology and hydrological conditions across various climatic and geophysical regions (Onuoha, 2008; Weigang et al, 2018), such as the Baiyangdian wetland (Ding et al, 2019), the Boluo Lake (Huang et al, 2021), and the Chagan Lake (Zhang et al, 2017). When water sources for EWR become diverse, the hydrological conditions of the water sources can hardly have a consistent change and made the EWR more complicated. A comprehensive analysis on the hydrological conditions of multiple water sources is suggested in aiding the formation of water diversion schemes (Zhang et al, 2017; Yan et al, 2018)
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