Stream Temperature Response To The Climate Change And Human Activity

As the major driver of the river ecological system,the stream temperature has great influence on the health of the river ecological system,and its change can threaten the survival and fecundity of the aquatic organism.In addition,the stream temperature change also can cause adverse effect on the agricultural irrigation,industrial water and domestic water.As a matter of fact,the climate change and human activity have effect on the stream temperature,so researching the specific change of stream temperature under the influence of climate change and human activity in this paper has great importance.Two empirical models(the linear regression model and the artificial neural network model)and a physically based model are adopted in this paper to simulate the stream temperature.The artificial neural network model and the physically based model are used to predict the change of stream temperature under the influence of climate change and human activity.Specifically,the temperatures of surface flow and base flow are considered separately;the VIC model is integrated to provide inputs for the artificial neural network model and the physically based model;three scenarios,climate change,human activity,climate change and human activity existing simultaneously,were set.Models and scenarios mentioned above were applied to the EEL river basin.Results and conclusions of the applications of models and scenarios are as follow:(1)The VIC hyrological model perfomances well in the selected basin,the EEL river basin,which proves that the modle is suitable to simulated the surface flow and base flow so as to provid exact inputs for the artificial neural network model and the physically based model.The artificial neural network model and the physically based model are all suitable used to simulate the stream temperature among the selected basin.The performance of the artificial neural network model is much better than that of the linear regression model;the physically based model performs much better than the linear regression model on the simulation of relative maximum and minimum values.Besides,compared with the physically based model,the artificial neural network model performs better on the aspects of simulation and prediction because of the lower requirement of model input.When predicting the impact of human activity on stream temperature,the predicted results of the artificial neural network model is more close to the real change,as a results that the predicted results of the physically based model is relatively small.And the weaker capacity of the physically based model on the aspects of simulation and prediction is because the model requires more inputs,including the river terrain data and energy data,which are hard to achieve leading the accuracy of them are low.(2)Under the influence of climate change,the stream temperature among the basin increases.During the end 21th century and under the emission scenario RCP 8.5,the stream temperature increase values in summer predicted by the artificial neural network model and the physically based model are 1.22-2.49? and 1.96-3.27?respectively;0.58-3.77? and 1.55-3.58? respectively in winter.On time scale,the air temperature is the major influence factor on stream temperature change.The more air temperature increase,the more stream temperature increase.In spatial scale,the base flow proportion and stream flow are the major influence factors on stream temperature changes.During the end 21th century and under the emission scenario RCP 8.5,the base flow proportion is the major influence factor on summer stream temperature,and the stream flow is the major influence factor on winter stream temperature;Under the influence of human activity,the stream temperature increases because of the irrigation,and the increase value differs under different irrigation schedules.Within irrigation intensities,the stream temperature under the high irrigation intensity increases bigger than that under the low irrigation intensity;within pumped stream flow components,the stream temperature when the base flow pumped increases larger than that when the surface flow pumped;Under the simultaneous influence of climate change and human activity,the stream temperature increase values on each pumping sites are bigger 1? than that under the soly influence of the human activity,and the increase value is not the simple additive value of the increase of air temperature and the increase of stream temperature caused by the human activity,but smaller than it.(3)The climate change and human activity(irrigation)all can aggravate the increase of the stream temperature and bring negative influence on the health of river ecology.To mitigate the influence of the climate change on stream temperature,the emission concentration of carbon dioxide should be controlled,so as to control the increase of the air temperature;to mitigate the influence of the irrigation on stream temperature,the irrigation schedule that pumping the surface flow as possible under the low irrigation intensity is recommended.