| It is widely recognized that wetlands play an important role in the watershed hydrological cycle,influencing groundwater,low flows and floods,and can be used as a nature-based solution for improving basin hydrological resilience.However,how and to what extent wetlands affect basin hydrological processes has become a relevant issue for scientists as well as stakeholders and decision-makers.In recent years,climate change and anthropogenic activities have considerably decreased the wetland area and impaired eco-hydrological function of wetlands in the Nenjiang River Basin(NRB).These changes have altered hydrological processes and water balance,thus increasing flood and drought risks in the basin.In this study,we carried out a hydrological modeling study(integrated with wetland modules)in the Nenjiang River Basin in northeast China,where covered with abundant wetlands,to quantitatively assess how and to what extent wetlands can mitigate flows currently and historically.Moreover,the projected hydrological services provided by different wetland restoration scenarios were quantified.This study can provide a scientific basis for water resource managemnt and wetland ecological restoration,and strengthen the sustainable management of water resources in the NRB.The conclusions are as follows:(1)Integration of wetland modules into the watershed hydrological modelThe PHYSITEL/HYDROTEL modeling platform and prepared databases were used to build a hydrological model in the NRB following:(i)characterization of parameters for isolated and riparian wetlands using PHYSITEL;and(ii)integration of specific isolated wetland and riparian wetland modules into HYDROTEL,a distributed hydrological model;and(iii)evaluate the performance of the modeling platform with respect to the capacity of replicating various hydrograph characteristics in the NRB.To achieve this,two sets of simulations were performed(with presence or absence of wetland modules),and the added value was assessed at two river segments of the NRB,using four general goodness-of-fit indicators and 14 water flow criterias.Results indicate the following:(i)integration of specific wetland modules can increase the capacity of model to replicate basic hydrograph characteristics;and(ii)the modeling platform allows for the explicit assessment of the impact of wetlands on watershed hydrology.(2)Quantitative assessment on basin-scale hydrological services of existing wetlands in the Nenjiang River BasinThe validated HYDROTEL was used to simulate hydrological processes during 2011–2018 for quantitatively assessing the impact of wetlands with paired simulation scenarios in the NRB,namely with and without the wetland modules.Simulation results showed that wetlands exert a significant impact on basin hydrological processes by decreasing daily flow(acted on decreasing 11.47% of daily flow)and altering flow regimes(i.e.,magnitude,frequency,duration and time of flow events).The intensity(significant or not)and effect(mitigation or augment)of wetlands on daily flow temporally varied at daily,monthly,seasonal,and annual scales.Wetlands significantly attenuated flood in the NRB by the following:(i)decreased peak flow,mean flow and volume by 23.63%?10.94% and 9.50%,(ii)extended flood duration by 0.47%,and(ii)mitigated flood with different spatiotemporal intensity and effect(e.g.,during the rising and falling limbs,seasonal and annual scales;upstream/downstream wetlands).Moreover,upstream wetlands significantly supported baseflow while downstream wetlands showed faint effect on baseflow variation.(3)Quantitative assessment on hydrological services of historical wetland scenarios with consideration of dam's effect in the Nenjiang River BasinHydrological processes simulation with historical wetland scenarios showed that the wetland scenario in 1980 decreased daily flow and peak flow by 3.49% and 33.88%;while the wetland scenario in 2000 reduced daily flow and peak flow by 2.20% and 23.13%,respectively.These indicated a degenerative trend of hydrological services of wetlands in the NRB.In addition,the regulation of Nierji Reservoir altered intensity and effect of wetlands by diminishing the capacity of flow regulation and their beneficial effects(i.e.transformed from baseflow support to baseflow reduction).(4)Estimation of flow regulation services under the scenarios of future climate change and wetland restorationThe basin hydrological processes driven were simulated to estimate flow regulation services of current wetlands under future climate change scenarios(RCP4.5 and RCP8.5)in the NRB.Results showed that the current wetlands expect to decrease daily flow by 2.38% and 2.24%,and reduce annual maximum flow by 12.85% and 11.98% under RCP4.5 and RCP8.5 scenarios,respectively.Then three wetland restoration scenarios(with respect to wetland map in 1980?1990 and 2000)were prepared to examine how and to what extent wetland services can occur following area increase in the NRB.Results indicated that flow regulation services of wetlands could improve when more wetlands are restored.For 1980 wetland restoration scenarios,the regulation services on daily and annual maximum flow increased to 23.84 % and 19.61%(18.20 % and 21.87)under the RCP4.5(RCP8.5)scenario respectively,compared with the current wetland scenario.Through the above results and the concept of ecohydrology and nature-based solution,the adaptation water resources management for improving hydrological services of wetlands was proposed to provide solid references for the restoration of wetlands and integrated water resources management in the NRB. |
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