Framework for comprehensive assessment of ecological water conveyance based on long-term evolution forecast of riparian forests in arid floodplains: synergistic consideration of flood inundation and groundwater

Ecological water conveyance (EWC) is a crucial measure to address ecological degradation in arid regions. To scientifically formulate ecological water conveyance pattern (WCP), and provide a basis for ecological flow management of reservoirs, this study proposes a framework to assess the effect of EWC, and applied it to the Irtysh River basin as a case study. Following the framework, we first developed a calculation method to assess the evolution of the reproduction and growth of riparian forests caused by hydrological variations. Additionally, simulations of surface water and groundwater conditions under different scenarios of water resources development were conducted based on hydrodynamic and groundwater models. The study further predicted the longterm evolution of riparian forest reproduction and growth based on the simulation results. The results indicated that when EWC was not carried out (reservoirs operating according to the designed rules), after 30 years, floodplain flood (FF) inundation area decreased by 47%, duration shortened by 73%, and groundwater levels in 80% of the region declined by 1.5-2 m, causing severe and moderate impacts on the reproduction and growth of riparian forests, respectively. Alternatively, adopting EWC (reservoirs operating according to ecological rules) led to a 24% decrease in FF inundation area, a 63% reduction in its duration, and a groundwater level decline of 0.5-1 m in 87% of the region, and these changes caused severe impacts on riparian forest reproduction, while growth remained unaffected. These findings indicate that the current EWC effectively safeguards the growth of riparian forests but fall short of mitigating the impacts of water conservancy project construction and operation on the reproduction of riparian forests. Given the current trajectory, riparian forests are anticipated to undergo a gradual decline. Consequently, a sustainable EWC should ensure that the water volume discharged into the region exceeds 53% of the natural inflow and urgently requires measures to extend the duration of FF inundation. This study can provide new insights for the early evaluation, comparison and optimization of various WCPs before their implementation.