Research On The Effects Of Climate Change On Farmland Drainage Modulus

Calculation of design drainage modulus is of great significance for the safety of farmland and reducing water logging loss.The effects of climate change on farmland drainage modulus and if the current drainage modulus need revise have been controversial.Take a closed farmland area in Ninghe District of Tianjin City as an example,based on field test and simulation analysis,the runoff generation mechanism of plain area and the influence of climate change on farmland drainage modulus were discussed.The main research contents and achievements are as follows:(1)Lay rain gauge,soil moisture content analyser,flowmeter and water level gauge in the study area.Then collect necessary hydrological data and convert the soil thickness of soil moisture content and groundwater level variation into water thickness.Through two observation test years in 2016-2017,five rainfall processes have happened,of which four rainfall events were used for model calibration,and one event was used for model verification.(2)In order to solve the limited problem of observational samples,on the basis of field observation test,a three-source infiltration excess and saturated excess coupled runoff yield model which took the total runoff depth,soil water content and the relative variation of groundwater level as evaluation indexes was established.Based on total runoff depth and the sample of Latin hypercube sampling,mutual information and partial rank correlation coefficient was used to analyze parameter sensitivity.Choosing dynamic neural network to calibrate the model parameter automatically then manual trial and error was tested with the sensitivity analysis results and soil water content and the relative variation of groundwater level,finally,reasonable model parameters were obtained.The results show that the infiltration excess and saturated excess coupled runoff yield model is applicable for plain farmland area in Tianjin.(3)By analyzing the trend and transilience of precipitation and evaporation data in 1960-2015,it was found that precipitation reduced significantly in summer,the annual maximum one daily rainfall aberrance point is 1989;evaporation had no obvious change,considered the first water resources evaluation,took 1980 as the dividing point.On this basis,three climate scenarios were set up,which were time analogy method,scenario hypothesis method and comparison with previous drainage results.(4)The results of the three methods are consistent.In the same underlying surface conditions,rainfall is positively correlated with the drainage modulus,evaporation is negatively correlated with the drainage modulus,compared with the 2003 "water logging control manual",24 h design surface rainfall and design drainage modulus both decrease,when reappearing period is small,the effect of rainfall on drainage modulus is very small,with the increase of reappearing period,the reductions of design drainage modulus are also increased,the relationship between the design drainage modulus and the reappearing period is logarithm form.But in general,effects of climate change on the design drainage modulus are not large,and the current drainage modulus doesn't need to be revised.