Climate Change Projections And Impacts On Water Resources Over Hongshui River Basin,China

Climate change adversely affects the global hydrological cycle.This research study aims to investigate the potential impacts of climate change and the combined impacts of climate change and climate anomalies on the hydrology and water resources management for the Hongshui River Basin（HRB）,China,for the 21^st century.The hydrological characteristics of the Hongshui River Basin are complex and influenced by a range of factors,growing population in the Hongshui River Basin has placed increasing demands on the region’s water resources,making it important to implement sustainable water management practices and strategies to ensure that the needs of the people and the environment are met.To fill this gap,hydroclimatic trend,and periodicity during the second half of the 20^th century and 21^st century was investigated to identify significant changes in time and space over the study area.Precipitation trends have been analyzed in annual and seasonal rainfall over Hongshui River Basin using Global Climate Models（GCMs）under CMIP5 and CMIP6 projects for better understanding.Global Climate Models（GCMs）with all four emission scenarios（RCP-2.6,RCP-4.5,RCP-6.0,and RCP-8.5）from CMIP5 and four SSPs（SSP1-2.6,SSP2-4.5,SSP3-7.0,and SSP5-8.5）were statistically downscaled using Bias Correction Special Disaggregation（BCSD）applied for bias correction via Climate Change Toolkit（CCT）.The non-Parametric Mann-Kendall test was applied for statistical significance trend analysis.The relationship between climate change and its impact on streamflow and water yield was explored by applying the widely used ARC-SWAT（Soil and Water Assessment Tool）.Observed hydrological and Global Circulation Models（GCMs）data,with input from Land Use Land Cover（LULC）developed by the European Space Agency（1995,2005,2015）,USGS（2001-2010）,and Global Land Cover（GLC 2000）,was fed into the model to run simulations.The model was calibrated（1991-1997）and validated（1998-2001）using SUFI-2（Sequential Uncertainty Fitting Algorithm）in SWAT-CUP.Climatic variability and quantification of climate change impacts on hydrological parameters are persistently uncertain.A climate elasticity approach was applied to evaluate the relative contribution of climate variability to the streamflow.Remote Sensed Evapotranspiration（RSET）using GRACE（Gravity Recovery and Climate Experiment）data was incorporated into the Soil and Water Assessment Tool（SWAT）model with hydrological parameters based on the multi-model ensemble mean of earth system models from the sixth phase of the Coupled Model Intercomparison Project（CMIP6）across the basin.Furthermore,a new approach of integrating two models（SWAT-WEAP）was applied,the Soil and Water Assessment Tool（SWAT）for future climate prediction and Water Evaluation and Planning（WEAP）for the simulation of water supply and demand in the basin to evaluate the impacts of climate change and socio-economic scenarios,which plays a vital role in the life of inhabitants at the downstream of the He chi and Laibin cities.The foremost research conclusions were given as follows:（1）Declining trend was observed over the basin for the past 50 years with the MK test（Z）value of-0.71 and Sen’s slope Q value of-1.063.Historical GCMs precipitation detected decreasing trends with average Sen’s slope magnitude（Q）-1.09 apart from Noer ESM1-M,a slight increase with（Q）value of 0.77.The future trends will likely be positive for annual rainfall except for Noer ESM1-M.Significant positive trends were observed in monsoon and winter,while pre-monsoon and post-monsoon seasons will likely slightly decline.（2）SWAT model calibration and validation indicated a good match between measured and simulated monthly stream flows as depicted by values of R²,NSE,PBIAS,KGE,and RSR as 0.86,0.83,8.72,0.86,0.40 during calibration（1991–1997）and 0.84,0.81,14.27,0.81,0.43 during validation（1998–2001）,respectively.（3）The ensemble of GCMs members from CMIP6 predicted a 2°C increase in annual mean temperature.The average changes in long-term future scenarios suggest that streamflow will rise by 4.2%under SSP-1.26,6.2%under SSP-2.45,8.45%under SSP-3.70,and 9.5%under SSP-5.85.（4）The relative contribution of climate change in streamflow variability is11%using the climate elasticity approach over.In response to an increase in potential precipitation,hydrological simulations produce moderate to high increases in total water availability.The available water resources would be sufficient to meet the current needs shortly.Domestic water is sufficient for the two cities（He Chi and Laibin）till2050.Conclusively,water resources can meet the demand under socio-economic,low,and medium climate change emission scenarios;however,the basin will observe water shortage under high climate change emission scenarios.Most modelling ensemble members provide promising findings for future water resources management techniques,despite the uncertainty in hydrological variable projections.The study proposed that to ensure the sustainability of water resources,better long-term management policies must be implemented in the basin and accomplish downstream water needs in the future.