Dryness–Wetness Encounter Probabilities’ Analysis for Lake Ecological Water Replenishment Considering Non-Stationarity Effects

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.

Spatial and temporal changes in land and water resources on the northern slopes of the Tianshan mountains from the perspective of “production-living-ecological space”

“…In comparison, water used for ecological purposes accounts for only 5.3% of the total water consumption (Chen et al, 2019). The allocation of water resources is dominated by the economic development planning department, which pays more attention to production and domestic water and ignores ecological water (Hu et al, 2021;Lu et al, 2021;Xu et al, 2022). The misuse of water resources has worsened the ecological environment in fragile inland areas (Eaton et al, 2021).…”

Flood-Triggering Rainfall and Potential Losses—The Copula-Based Approach on the Example of the Upper Nysa Kłodzka River

“…The research fits into the trend of analyzing relationships between hydro-and meteorological variables in terms of synchronicity and asynchronicity, described also as, e.g., "synchronous-asynchronous encounter probability", "probability of synchronous or asynchronous occurrence", or "dryness-wetness/rich-poor encounter probability". Such an approach has been used in the analyses of the probability of the co-occurrence of precipitation [48][49][50], runoff and sediment load [51][52][53], the water level of a sea and coastal lakes [54], maximum or average annual discharge/runoff [55][56][57][58][59], precipitation and runoff [60][61][62], flood hazard [62] or water transfer projects [63]. The novelty of this research is its combining of the estimated economic flood losses and rainfall data within one copula-based model, which allows the formulation of spatio-temporal dependencies.…”