东江流域蓝绿水资源演变特征及驱动机制研究

(2) 评估了流域水安全状况。流域蓝水短缺程度为低蓝水短缺（22.4%），绿水短缺程度为低绿水短缺（41.4%），超过80%的区域人均可用水量超过1700 m3 capita-1 a-1。流域蓝水短缺度以0.3% a-1的速率缓慢上升，绿水短缺度以-0.04% a-1的速率显著下降。流域年尺度上发生蓝绿水短缺的风险较小，但年内发生了中度蓝绿水短缺，蓝水短缺峰值多出现在10月到次年3月且下游发生蓝水短缺频率大于其他区域，而全流域均在5-9月发生中度绿水短缺。

(3) 探究了蓝绿水资源和蓝绿水分配对气候变化和土地利用变化的响应机制。降水（潜在蒸散发）每增加10%，流域蓝水增加12.8%（减少21%），绿水流减少0.04%（增加4.2%），绿水储增加1.2%（减少5.2%）。降水量、潜在蒸散发和极端降水量是影响绿水系数的主要气象因子，其对绿水系数变化的相对贡献分别为57.5%、11%和31.4%。土地利用转换改变了流域蓝绿水时空分布，每10%的耕地-林地（耕地-建设用地、林地-建设用地、林地-耕地），蓝水减少0.3%（蓝水增加0.26%、0.3%、0.3%），绿水流增加2%（绿水流减少1.6%、3%、1.7%），绿水储增加1.2%（绿水储减少1.2%、1.5%、0.6%），绿水系数增加0.8%（减少0.69%、1.3%、1.2%）。基于Budyko水热耦合平衡框架定量分析了绿水流和径流对下垫面因子的响应，气候季节性、降水季节性、植被总覆盖度、树冠覆盖度和矮植被覆盖度对流域绿水流和径流变化的平均相对贡献分别为：6.8、14.1、5.6、11.5、11.1%和2.9、6.6、2.4、5、5.5%。树冠覆盖度增加导致径流减少和绿水流增加效应与矮植被覆盖度减少导致径流增加和绿水流减小效应相互抵消。

(4) 探究了气候和土地利用变化对蓝绿水及其短缺度的耦合驱动效应。蓝绿水对气候和土地利用变化的响应存在显著差异，气候变化对东江流域蓝水、绿水流和绿水储变化相对贡献分别为88.01%、88.54%和39.44%。降水量和人口数量变化对蓝水短缺变化的相对贡献分别为57.7%和42.3%。气候和土地利用变化对绿水短缺的相对贡献分别为96.7%和3.3%。子流域尺度上蓝绿水对土地利用变化更为敏感，将蓝绿水变化整合到流域尺度可能会导致土地利用的影响被相互抵消。气候和土地利用对东江流域蓝水和绿水储的耦合驱动效应为叠加效应，对绿水流和绿水短缺的耦合驱动机制为负协同效应。

(5) 预测了东江流域未来2022-2100年气候、蓝绿水变化和2050年土地利用变化。SSP126和SSP585情景下流域降水量年内分布相较于基准期（1970-2017年）更加集中，两种情景下降水量较基准期分别增加112.9和133.1mm，日最高气温升高2.1和3.2℃，日最低气温升高1.2和2.2℃。SSP126情景下，近未来（远未来）蓝水量相较于基准期减少5.6%（增加0.8%），绿水流增加14.6%（18.7%），绿水储减少8%（8.4%）；SSP585情景下，近未来（远未来）蓝水相较于基准期减少5.8%（增加6.2%），绿水流增加9.1（13.8%），绿水储减少5.8（9.8%）。

总体而言，本研究科学认识了东江流域历史和未来水热状况演变和土地利用变化下蓝绿水资源演变特征，评估了流域水资源安全状况，可以为流域蓝绿水资源综合规划管理和上下游蓝绿水资源优化配置提供理论依据；利用多种方法量化了气候变化和土地利用变化对蓝绿水及其短缺度的影响，揭示蓝绿水、蓝绿水分配和蓝绿水短缺变化对气候变化和土地利用变化的响应机制，对于进一步认识蓝绿水演变规律具有重要意义。

(2) The water security status of the basin was evaluated. The degree of blue water shortage in the basin was low (22.4%), and the degree of green water shortage was also low (41.4%). Over 80% of the region had a per capita available water volume of more than 1700 m3 capita-1 a-1. The degree of blue water shortage in the basin slowly increased at a rate of 0.3% a-1, while the degree of green water shortage significantly decreased at a rate of -0.04% a-1. The risk of blue and green water shortage at an annual scale was relatively low in the basin, but moderate blue and green water shortages occurred during the year. The peak of blue water shortage occurred from October to March of the following year, and the downstream area had a higher frequency of blue water shortage than other regions. Moderate green water shortage occurred throughout the basin from May to September.

(3) The response mechanisms of blue and green water resources and their distribution to climate and land use changes were explored. For every 10% increase in precipitation (potential evapotranspiration), the blue water in the basin increased by 12.8% (decreased by 21%), the green water flow decreased by 0.04% (increased by 4.2%), and the green water storage increased by 1.2% (decreased by 5.2%). Precipitation, potential evapotranspiration, and extreme precipitation were the main meteorological factors affecting the green water coefficient, with relative contributions of 57.5%, 11%, and 31.4%, respectively. Land use conversion changed the spatial and temporal distribution of blue and green water in the basin. For every 10% increase in cropland-forest land (cropland-construction land, forest land-construction land, and forest land-cropland), the blue water decreased by 0.3% (increased by 0.26%, 0.3%, and 0.3%), the green water flow increased by 2% (decreased by 1.6%, 3%, and 1.7%), the green water storage increased by 1.2% (decreased by 1.2%, 1.5%, and 0.6%), and the green water coefficient increased by 0.8% (decreased by 0.69%, 1.3%, and 1.2%). Based on the Budyko water-heat coupling equilibrium framework, the response of green water flow and runoff to underlying surface factors was quantitatively analyzed. The average relative contributions of climatic seasonality, precipitation seasonality, total vegetation cover, tree canopy cover, and shrub cover to changes in green water flow and runoff in the basin were 6.8%, 14.1%, 5.6%, 11.5%, 11.1%, and 2.9%, 6.6%, 2.4%, 5%, and 5.5%, respectively. The effect of increasing tree canopy cover on reducing runoff and increasing green water flow was offset by the effect of decreasing shrub cover on increasing runoff and decreasing green water flow.

(4) The coupling driving effects of climate and land use changes on blue and green water and their shortage were explored. The response of blue and green water to climate and land use changes differed significantly. Climate change had a relative contribution of 88.01%, 88.54%, and 39.44% to the change in blue water, green water flow, and green water storage, respectively, in the Dongjiang River Basin. Changes in precipitation and population had relative contributions of 57.7% and 42.3%, respectively, to changes in blue water shortage. Climate and land use changes had relative contributions of 96.7% and 3.3%, respectively, to changes in green water shortage. Blue and green water were more sensitive to land use changes at the sub-basin scale, and integrating the changes in blue and green water at the basin scale may result in the effects of land use being offset. The coupling driving effects of climate and land use on blue water and green water storage were additive, while their effects on green water flow and green water shortage were negatively synergistic.

(5) The future changes in climate, blue and green water, and land use in the Dongjiang River Basin from 2022 to 2100 were predicted. The distribution of basin precipitation during the year was more concentrated under the SSP126 and SSP585 scenarios compared to the baseline period (1970-2017), with an increase in precipitation of 112.9 and 133.1 mm, respectively, under the two scenarios. The maximum daily temperature increased by 2.1 and 3.2°C, and the minimum daily temperature increased by 1.2 and 2.2°C, respectively. Under the SSP126 scenario, blue water decreased by 5.6% (increased by 0.8%) compared to the baseline period in the near future (distant future), while green water flow increased by 14.6% (18.7%), and green water storage decreased by 8% (8.4%). Under the SSP585 scenario, blue water decreased by 5.8% (increased by 6.2%) compared to the baseline period in the near future (distant future), while green water flow increased by 9.1% (13.8%), and green water storage decreased by 5.8% (9.8%).

Overall, this study scientifically understood the water and heat conditions and evolution characteristics of blue and green water resources under land use change in the Dongjiang River Basin, evaluated the water resource security status of the basin, and provided a theoretical basis for the comprehensive planning and management of blue and green water resources in the basin and the optimization of upstream and downstream blue and green water resource allocation. The study also quantified the impact of climate and land use changes on blue and green water and their shortage, revealed the response mechanisms of changes in blue and green water, distribution, and shortage to climate and land use changes, and had significant implications for further understanding the evolution laws of blue and green water.