Effects Of Climate Seasonality Index Andstarting Month Of Water Year On Catchment Water Balance Estimation In Budyko-Fu Model

The catchment coupled water-energy process is influenced by climate and underlying surface changes and evapotranspiration is one of the most important links in it.Budyko theory has been widely used in recent years,among which Budyko-Fu equation was more famous.Jinghe River catchment is located in the middle of the Loess Plateau.It is one of the most serious areas of soil erosion on the Loess Plateau.In recent years,vegetation coverage has increased significantly in this area,resulting in climate and underlying surface changes.Then the catchment coupled water-energy process will change accordingly.Based on these,this study used the meteorological,hydrological and vegetation data in Jinghe River catchment during 1981-2011,explored the influencing factors of parameter?under the Budyko-Fu model,and analysed the relationship between parameter?and three climate seasonality indexes?SI1,SI2,SAI?to improve the semi-empirical equation of parameter?.Among which SI1—considering the monthly precipitation departure in a year,SI2—considering the amplitude difference between seasonal variations of precipitation?P?and potential evapotranspiration?ET₀?by sinusoidal simulation,and SAI—considering the time-phase differences between seasonal variations of P and ET₀ on the basis of SI2.SAI was also different from SAI1 and SAI2 in terms of annual value or multi-year mean value when calculating the phase of P and ET₀ seasonality.On this basis,the water year,which can minimize the influence of soil water storage change??W?on interannual scale,was discussed,and the starting months corresponding to the higher estimation accuracy of annual actual evapotranspiration?ET?and annual streamflow?R?are proposed respectively.It is hoped that this paper can provide a reference for the improvement of the semi-empirical equation of parameter?,and provide a basis for more accurate estimation of the annual actual evapotranspiration in catchments.It can also protect the ecological environment of the Jinghe River catchment,and the Eco-economic System will achieve sustainable development.The main results of this study are as follows:?1?There was no obvious change-point in P,while the ET₀ had a change-point at 1993 during1981-2011.The average annual P and ET₀ in the whole catchment were 496.0 mm and 1044.8mm,respectively.The monthly variations of P and ET₀ were simulated by sinusoidal method,and the average annual relative amplitudes of them were 1.11 and 0.68 respectively,which indicated that the variation and fluctuation of P were greater in this period.The climate seasonality index?SI2?used sinusoidal curve to simulate seasonal variation of P and ET₀,and the average annual SI2 and aridity index???were 0.45 and 2.21 respectively,showing a slight upward trend,indicated that the difference of seasonal fluctuation of P and ET₀ in this catchment was slightly increased.On interannual scale,the spatial variations of P and ET₀ had no significant effect on the parameter?.However,the normalized difference vegetation index?NDVI?and SI2 were significantly correlated with parameter?.On this basis,a semi-empirical equation of the parameter?in Jinghe River catchment was given.The difference between calculated?and measured?was significant after 2000,which may be due to the interference of other factors.?2?Among the three climate seasonality indexes,the correlation between SI2 and parameter?was better.If the phases of P and ET₀ in this catchment was determined by average annual data to calculate the climate seasonality index SAI2,which was better than SI2.Accordingly,the semi-empirical equation of parameter?given by SAI2 and NDVI had a higher determination coefficient,reaching 0.746.Applying it to Budyko-Fu model can improve the estimation accuracy of annual runoff in catchments,which shows that the average annual phase can more accurately describe the catchment seasonal characteristics when calculating the SAI.?3?The relationship between annual precipitation and average annual NDVI or the average NDVI in growing season was better from June to May.Moreover,the relationship between parameter?and NDVI in same period from June to May was also best.Based on the analysis of the two aspects,it was concluded that the calculation of evapotranspiration using water balance equation start from June should be closer to the evapotranspiration under steady flow condition,that is minimized?W.Therefore,it was considered that from June to May is a water year in Jinghe River catchment.