Hydrological Simulation And Runoff Response Analysis Based On SWAT Model

As the largest tributary of the Yellow River, Weihe River rising in the hydrologic cycle due to the impact of climate change, great changes have taken place in recent years on the depth and breadth of hydro logical situation. Guanzhong section of Weihe River has a long history of farming civilization, human activities penetrated into every aspect of the regional hydrologic cycle.Taking Guanzhong section of Weihe River as the research object, analyses the change characteristics and the reason of hydro logical cycle elements, adopts the distributed hydrological model SWAT, simulate the runoff change, analyses the effects of meteorological factors and land cover factor on runoff, respectively.Made the following main conclusions:1. Some features of the changecharacteristics and influencing factors of hydrological cycle elements were explored and revealed quantitatively as below:(DSolar radiation can influence the surface evaporation capacity profoundly, so as to change the process of water balance.Research showed that the study area presented downtrend in solar radiation, Lapse rate, for about1986MJ/(m3·a), showed the tendency of the "dark". At the same time, analyzed the main parameters of meteorological elements quantitatively, which showed that the sunshine was the important factor influenced the solar radiation.②Precipitation was the most active factor in the process of water cycle in nature, a lot of element of hydrological cycle had the important role which could’t be ignored.Quantitative analysis of the precipitation frequency in the study area showed:the annual precipitation and strong rainfall frequency had high correlation, and the correlation of annual precipitation frequency was lower.③Potential evaporation participated in the material migration and energy conversion of the hydrologic cycle. Quantitative analysis showed that the potential evaporation presented the tendency of decrease in study area from1955to2012, linear trend rate was9.16mm/10a. The average temperature in the corresponding time series presented the increasing trend, linear tendency rate was0.39℃/10a, which showed the "evaporation paradox" phenomenon. The results showed that themeteorological elements which had most significant effection on potential evaporation as follows:the average wind speed, sunshine time, diurnal range.④Actual evaporation in the research of the hydrologic cycle response to climate change had the important instruction meaning.The study found that the actual evaporation showed a trend of decline from1980to2012, which had good linear relation with the precipitation;the actual evaporation was controlled by precipitation.⑤Runoff was a state of surface water taking into account of precipitation and evaporation, which had obvious response to changes in rainfall and evaporation. On the monthly scale, runoff fitted by gaussian function showed a trend of normal distribution. On the yearly scale, runoff presented a declining trend. Based on hydro logical frequency analysis of P-Ⅲ Pearson curve, found that the Cv value was between0.4to0.8.2. Constructed a distributed hydrological model SWAT, simulated the runoff in the study area on the monthly and yearly scale, and drew the conclusion that the simulation on the monthly scale was better than the simulation on the yearly scale. Distinguished the effects of climate change and human activities on runoff quantitatively, and the research results showed that the impact of climate change on runoff accounted for30-40%, and the influence of human activities on runoff accounted for60-70%.3. Aiming at the effects of climate factors on runoff, using runoff sensitivity evaluation method which based on climate elasticity coefficient, the drought index and Budyko curve, sensitivity of runoff was evaluated for quantitative in the Guanzhong section of Weihe River. Methods of runoff sensitivity evaluation based on Climate elasticity coefficient, drought index and Budyko curve made the consistent conclusions that the most sensitive factor was rainfall. Sensitivity analysis based on the elasticity coefficient showed that climate elasticity coefficient of runoff to precipitation was0.035to2.84, that is, precipitation change10%will cause the runoff change about0.35%-35%. Sensitivity analysis based on the drought index showed that the drought index change10%, namely the change rate of potential evaporation and precipitation ratio is10%, will cause runoff change about14%to25%. Sensitivity analysis based on Budyko curve showed that the precipitation change about10%will cause runoff change about17%, the increase10%of potential evaporation will cause6%of runoff amount.4. Aiming at the effects of land use cover change on runoff, on the basis of the SWAT model, basin boundary made by the model as the study area, considering the runoff response under different land use cover scene, divided into different levels of runoff sensitivity partition. By setting the scene type, simulated the runoff of different land use cover through the distributed hydrological model. Simulation results showed that the influence of different land use scenarios on runoff was significant differences:the cultivated land cover situation (S3)> grass cover scene (S2)> forest land cover situation(S1)> the optimal combination cover scene (S4).5.According to evaluation results of runoff response to land use, considering river system, land use cover and factors such as rainfall, based on watershed response unit partitioned by SWAT model. According to runoff response degree in Guanzhong section of Weihe River basin, study area was divided into five areas:extremely sensitive area, highly sensitive area, moderate sensitive area, the sensitive area and general sensitive area.