基于历史参照系的三江源区径流调节功能及变化评估

以20世纪70年代植被类型图作为参照生态系统，采用径流量和径流系数作为径流调节功能的表征指标，建立了基于历史参照系的三江源区径流调节功能评估模型，以参照系径流系数与实际径流系数的比值作为径流系数质量指数，分析了2000-2017年三江源区生态系统径流调节功能参照值、现状值及变化量的时空变化规律。结果表明：2000-2017年，三江源区多年平均径流量为495.15亿m³，地表径流量为96.64亿m³，参照系条件下多年平均径流量为468.37亿m³，地表径流量为68.60亿m³。相比参照系，三江源区生态系统的径流蓄纳能力降低，总径流量和地表径流量均明显增加。空间上，基于参照系和实际生态系统的多年平均径流量表现为东南高西北低的空间分布特征，地表径流量则呈西部高东部低的空间分布特征。从时间变化看，实际径流和参照系径流的差别率在4%-9%之间，实际地表径流和参照系地表径流的差别率在22%-58%之间。径流系数质量指数得分显示，2000-2017年，三江源区径流系数质量指数平均得分为98.63，地表径流系数质量指数平均得分为96.98，两者均呈现先降低后增加的趋势，地表径流系数质量指数变化更为明显。2000-2017年，各县（镇）径流系数和地表径流系数质量指数得分具有较大差别，但各县（镇）得分变化均不明显，变化率分别在-1.95%-0.71%和-0.35%-1.90%之间。通过建立基于历史生态系统的评估参照系，定量评估了三江源区参照系和实际条件下的径流变化过程，实现了不同时间、不同区域生态系统径流调节功能的可比较，可对量化生态系统恢复进程提供支撑。

Assessment of runoff regulation function and its change in the Three Headwater Region based on a historical reference system

By taking the vegetation map in the 1970s a reference ecosystem and using runoff volume and runoff coefficient as the characteristic indexes of ecosystem runoff regulation function, a runoff regulation function evaluation model based on the SWAT (Soil & Water Assessment Tool) model and a historical reference system was established. Then, the temporal and spatial variation characteristics of runoff regulation function in the Three Headwater Region from 2000 to 2017 were analyzed. Besides, the ratio of the reference runoff coefficient to the actual runoff coefficient was used as the runoff coefficient quality index to describe the deviations of the actual ecosystem from the reference system, for further analysis of the variation characteristics of runoff deviations between the reference ecosystem and the actual ecosystem. Results showed that, between 2000 and 2017, the perennial average runoff and surface runoff were 495.15×10⁸ m³ and 96.64×10⁸ m³, and the perennial average reference runoff and surface runoff were 468.37×10⁸ m³ and 68.60×10⁸ m³. Compared with the reference ecosystem, the runoff storage capacity of ecosystem decreased, resulting in higher runoff and surface runoff. Spatially, the runoff was high in the southeast and low in the northwest, but surface runoff was high in the west and low in the east whether under the reference or actual ecosystems. In terms of the interannual change, we found a visible increase of runoff, especially surface runoff under the actual ecosystem. The difference rate between the actual runoff and the reference runoff ranged from 4% to 9%, and it showed a more pronounced deviation of 22% to 58% of surface runoff. Fro the runoff coefficient quality index score, the average score of runoff coefficient quality index was 98.63, and the average score of surface runoff coefficient quality index was 96.98 in 2000-2017 in the Three Headwater Region. Generally, both scores showed a trend of first decreasing and then increasing, indicating a process of degradation and then recovery during this period, and the change of surface runoff coefficient quality index was more obvious. The scores of runoff coefficient quality index and surface runoff coefficient quality index varied greatly among regions, but the interannual changes were small, with a change of -1.95% to 0.71%, and a change of -0.35% to 1.90%. By analyzing the temporal and spatial variation characteristics of runoff regulation function based on a historical reference system, the comparison of runoff regulation functions in different ecosystems at different times and in different regions was realized, which could provide support for quantifying the process of ecosystem restoration.