水利工程对年楚河流域农业水资源利用效率和作物生产力的影响

水库是水资源调配的主要举措之一,影响着流域生态水文过程和农业生产。满拉水库作为"西藏第一坝",其兴建与运行对青藏高原的水资源管理与农业发展都具有重要意义。该研究以满拉水库所在的年楚河流域为例,结合SWAT水文模型与遥感影像,分析了满拉水库蓄水量变化。基于农田水量平衡原理,利用植被界面过程模型（Vegetation Interface Processes,VIP）模型估算了水库调度下流域耕地总初级生产力（Gross Primary Productivity,GPP）的变化。采用岭回归定量分析了人类活动（水库灌溉）、气候因子（气温、降水、辐射）以及大气CO2浓度对流域GPP变化的影响。结果表明：1）自满拉水库修建以来,年楚河径流量减少3.78×109 m3/a,其中,66%的水量经由水库调蓄补给灌溉。2）2000-2019年,流域内耕地多年平均GPP在143～852 gC/(m2·a)之间,90%以上耕地的GPP呈上升趋势,平均上升速率为5.3 gC/(m2·a2),其中67%以上的区域上升趋势显著（P<0.05）。3）灌溉量增加和大气CO2浓度上升对耕地GPP上升的贡献率分别为43.9%和25.1%,是GPP增加的主导因素。满拉水库的修建不仅显著改变了流域的生态水文过程,更提高了下游农业灌溉水平和作物生产潜力,研究结果对年楚河流域水资源配置及农业规划具有科学参考价值。

Impacts of water conservancy projects on agricultural water use efficiency and crop productivity in the Nianchu River Basin of China

Abstract: Water conservancy engineering has been one of the most important human activities to impact the hydrological process in the watershed. Among them, the agricultural reservoirs for irrigation can change the various hydrological elements in the watershed, even the water resources utilization and agricultural production. The Manla Reservoir (known as "The first dam in Tibet") has also posed a great challenge to water resources management and agricultural development in the Qinghai-Tibet Plateau. Taking the Nianchu River near the Manla Reservoir as an example, this study aims to determine the optimal parameters using the Soil and Water Assessment Tool (SWAT). The runoff was predicted after the construction of the reservoir using the data before construction. The normalized difference water index (MNDWI) was combined with the inflow, outflow, and water storage of the reservoir after the SWAT simulation. A Vegetation Interface Processes (VIP) model was used to calculate the cultivated land Gross Primary Productivity (GPP) in the reservoir dispatch scenario using the farmland water balance. The ridge regression was selected to quantify the effects of human activities on the GPP, such as the reservoir irrigation and major climatic factors (Carbon dioxide concentration, Air temperature, Precipitation, and Solar radiation). The results show that: 1) The runoff decreased 3.78×109 m3 after the construction of the Manla Reservoir, according to the simulation of the SWAT model. Among them, 2.5×109 m3 of water was transported through the Manla reservoir for irrigation per year. The utilization rate of runoff increased from 10.3% to 25% in agriculture in the basin. The runoff was reduced by 1.28×109 m3/a, due to the impoundment of the reservoir, of which the direct effect of the Manla Reservoir was 0.65×109 m3/a. 2) The average annual GPP of cultivated land was between 143-852 gC/(m2·a) in the VIP model. The average annual GPP of cultivated land increased by 5.3 gC/(m2·a2). The GPP of more than 90% of the cultivated land areas showed an upward trend during the operation of the reservoir (2000-2019), of which more than 67% was a significant upward trend. There was a changing trend in the spatiotemporal scale for the carbon dioxide concentration, air temperature, and radiation during the operation of the reservoir, indicating an excellent agreement with the GPP. But, there was negatively correlated between the precipitation and GPP. 3) The operation of the Manla Reservoir greatly contributed to the deployment of water resources. The GPP increase was attributed to the irrigation and CO2 concentration, according to the ridge regression model. The average relative contributions were 43.9% and 25.1%, respectively, which were much higher than those of all climatic factors. The relative contributions of air temperature, radiation, and precipitation were only 14.7%, 6.9%, and -5.1%, respectively. Consequently, there was some impact of the construction and operation of the Manla Reservoir on the eco-hydrological elements (runoff, and evaporation) in the basin. The relative contributions of Manla reservoirs were quantitatively analyzed to improve the irrigation level and crop production. The finding can provide a strong reference for the decision-making on water resources allocation and agricultural irrigation instruction.