植被恢复工程对黄河中游12个典型流域水热平衡的影响研究

中国已成为全球植被迅速变绿贡献最大的国家,但植被变绿对水量平衡和能量收支平衡影响的相关研究有待加强。本文以植被恢复典型区域黄河中游12个流域为例,利用遥感植被指数NDVI和常规气象数据,基于布迪克假设和水热平衡指数（Water-Energy Ratio, WER）,分析了植被变绿的时空变化格局及其对水热平衡的影响。结果表明：① 傅抱璞模型中反映流域属性的参数w在12个流域的平均值为2.9,略大于模型的缺省值2.6。参数w与NDVI拟合的Pearson相关系数介于0.31~0.75,拟合性能较好。② 1982—2016年NDVI在12个流域均呈现显著增加趋势,尤其以植被恢复工程实施后更为显著（p<0.001）。相对1982—1999年,2000—2016年NDVI相对变化率在9.1%~17.5%之间,均值为12.9%,显著植被变绿已导致水热平衡向可利用水分减少、可利用能量增加方向转化。③ NDVI对WER变化的绝对贡献率达到77.5%,植被变绿已经成为黄河中游12个流域水热平衡变化的主导因素,其次为气候要素。植被的持续变绿带来了一些不利影响,植被恢复工程的生态效应研究有待进一步深入研究。

Quantitative assessment of the impact of the vegetation restoration project on water-energy balance in 12 typical basins of the middle Yellow River

China has become the country with the largest contribution to the rapid greening of vegetation in the world. However, the impact of vegetation greening on water and energy balance is still unknown in many aspects. In this study, 12 watersheds, located in the middle reaches of the Yellow River and represented as a typical area of vegetation restoration, were selected to study the impact of vegetation greening. Using the Normalized Difference Vegetation Index (NDVI) derived from the remote sensing and the conventional daily meteorological data (precipitation, temperature, wind speed, relative humid), based on the Budyko assumption theory and the Water-Energy Ratio (WER), this paper analyzes the spatiotemporal pattern of vegetation greening and its impact on the water and energy balance during 1982-2016. The results reveal that: (1) the parameter of w in the Fu′s model was evaluated in the 12 watersheds, and its mean value is approximately 2.9, slightly larger than the default value in the Fu′s model (w=2.6). The Pearson correlation coefficient between parameter w and NDVI ranges from 0.31 to 0.75, which indicated that their fitting performance is good and NDVI can be used to represent the impact of vegetation change on water and energy balance. (2) The NDVI in the 12 watersheds showed a significant increase trend during 1982-2016, especially after the implementation of vegetation restoration projects (1999) with a significant level of p<0.001. Compared with the period from 1982 to 1999, the relative change rate of NDVI from 2000 to 2016 was between 9.1% and 17.5%, with an average value of 12.9%. The significant vegetation greening has led to a conversion in the water and heat balance, with a decreasing trend in available water and an increasing trend in available energy. This may bring deteriorated impact to the fragile ecological environment in the middle reaches of the Yellow River. (3) The absolute contribution rate of NDVI to WER changes reached 77.5%. The greening of vegetation has become the domain factor in the changes in the water and energy balance of the 12 basins in the middle reaches of the Yellow River, followed by climate factors. We suggest that more attention should be given to water resource availability and ecological effects under the background of vegetation greening and climate change in further studies.