Impact Of Climate Change On Volume Capture Ratio Of Annual Rainfall Of Low Impact Development Facilities

As a sensitive and fragile country to climate change,China has been experiencing a series of climate and environmental changes in the past 100 years.The change of rainfall pattern,frequency and intensity of extreme rainfall events will directly affect urban water security.The implementation of sponge city is committed to solving all kinds of urban water problems,among which the construction of low-impact development rainwater system is an important way to achieve the construction of sponge city.Low-impact development facility design is based on the history of the law of can reflect long-term rainfall long sequence of daily rainfall data in combination with a variety of factors affecting calculated results of an "optimal" in the context of climate change,climate change,global scale and regional scale will interfere with the original law of rainfall in different extent,which may affect the low-impact development facilities the actual control effect.In order to improve the climate resilience of low-impact development facilities,it is important to predict future rainfall trends.Global climate model(GCM)is the most effective method to simulate and predict global large-scale climate change.With the release of the latest CMIP5 mode,the model's ability to simulate rainfall in China has been greatly improved.The prediction of rainfall change trend based on the output of global climate models under different future climate scenarios has been widely used at home and abroad.However,the research on the application of the prediction results in the planning of low-impact development facilities is very limited at the present stage.In this paper,the simulation effects of 10 CMIP5 models on rainfall in China were compared and analyzed,and the model with better simulation ability was selected for revision.The revised integrated model was used to predict future rainfall changes with China's daily rainfall data in the case of RCP4.5 and RCP8.5,and the climate model prediction results were introduced to assist in planning the scale of low-impact development facilities.In the future,the total runoff control rate of different years and the corresponding designed rainfall distribution will be calculated.In order to quantitatively assess the impact of climate change on the volume capture ratio of annual rainfall of low-impact development facilities,and to identify the climatically sensitive regions in China,so as to provide strong support for China's urban rainwater system to cope with future climate change.Through this study,the following conclusions can be drawn:(1)CMIP5 model is an important tool for large-scale climate change simulation and prediction.In order to eliminate the local uncertainty caused by a single mode to a large extent,on the basis of the simulation capability evaluation of a single CMIP5 model,the optimal selection model is selected,and then the set average of the selected CMIP5 models is carried out.The 10 selected models were evaluated on time scale and spatial scale.In terms of time scale,the selected 10 models can roughly simulate the trend of rainfall change over time in each station and the seasonal variation characteristics of rainfall in different regions of China in summer and winter.In terms of spatial scale,the simulated rainfall value of themodel for most areas in China is higher than the historical observation value of weather stations.This deviation is especially evident in the northwest and the qinghai-tibet plateau.The rainfall of south China,northern Xinjiang and parts of central and eastern China is less simulated by the model.Different models have great differences in rainfall simulation ability,and 5 models with good simulation ability were finally selected,namely: CMCC-CM ?CNRM-CM5?CSIRO-Mk3-6-0?IPSL-CM5A-MR and NorESM-M.(2)In the case of RCP4.5 and RCP8.5,the multi-mode integrated rainfall prediction results(2006-2040)are similar to the spatial distribution of the multi-mode integrated simulation results.The deviation of the model in the simulation results still exists in the scenario prediction results.The statistical downscaling model of unitary linear regression is applied to the result of multimode integration for downscaling correction.This method can effectively reduce the uncertainty of multi-mode prediction.The model was used to modify the integrated daily rainfall prediction data under different future scenarios(RCP4.5 and RCP8.5).The results of integrated downscaling data have been able to accurately predict the increasing geospatial distribution pattern of China's rainfall from the northwest inland to the southeast coast.The average annual rainfall of most Chinese cities will increase slightly in the next 30 years.The increment of rainfall change in northern China is between 0 and 10%,while the rainfall in southern China tends to decrease,and the range of change rate is generally between-6% and 0.There is little difference in rainfall variation in different scenarios in the early 21 st century.(3)By statistical analysis of the historical measured and future predicted daily rainfall data of 166 meteorological stations,the designed regional distribution of rainfall across the country was obtained.The results show that the overall trend of regional distribution is similar,and the change range is relatively large,which is gradually weakened from the southeast coast to the northwest inland direction.In some provinces(Guangdong,Guangxi,Henan,Sichuan,etc.),the designed rainfall increases with the annual runoff total control rate.(4)In the early 21 st century,most cities in China had little difference in rainfall structure under the future scenario of RCP4.5 and RCP8.5,so the difference in designed rainfall under the two emission scenarios was basically controlled within-5~5mm.Part of the south China,north China,there are large differences in the situation.(5)China's northwest,southwest,northeast and north of east China are less affected by climate change.The difference between future scenario and historical measured design rainfall is between-2mm and 2mm under 85% volume capture ratio of annual rainfall.Low Impact Development facilities in these areas are less affected by climate change.The scale of facilities based on historical long series daily rainfall data can play a good role and reach a relatively optimal state in the early period of the 21 st century in the future.Therefore,for Low Impact Development facilities in cities in climate-insensitive areas,the scale of LID facilities can be accurately determined according to the relatively short rainfall sequence.(6)The climate sensitive areas of China's low-impact development facilities are mainly distributed in north China,central China,south China and south China.The sensitivity ishigher in the Beijing,Tianjin,Hebei region,Inner Mongolia region,Hainan province,Guangdong province and Guangxi province.The low-impact development facilities in the Beijing,Tianjin,Hebei region and Inner Mongolia region in the highly sensitive region may not be able to achieve the desired control effect due to climate change.Under 85% volume capture ratio of annual rainfall,the designed rainfall in this region is significantly larger in future scenarios to varying degrees,with an deviation range of 2~8mm.This deviation was more pronounced in the case of RCP 8.5.The scale of facilities based on historical data may not meet the actual control requirements of catchment areas.Therefore,when determining the design rainfall of these regions,the future rainfall change rule should be predicted.Considering longer time series rainfall data combined with future scenarios and appropriately increasing the design scale of urban low-impact development facilities to improve their climate resilience.Low-impact development facilities in cities in high-sensitive regions such as Hainan,Guangdong and Guangxi provinces may be wasted due to climate change.Under85% volume capture ratio of annual rainfall,the designed rainfall in this region is significantly smaller in future scenarios to different degrees,and the error is basically between-10~-2mm.The larger deviation basically appeared in the case of RCP8.5.Therefore,when determining the scale of facilities in these areas,it is necessary to predict the change law of rainfall and reduce the design scale of urban low-impact development facilities to improve economics.It should be noted that the increase or decrease of the scale of low-impact development facilities in cities in high-sensitive areas should be based on the more detailed characteristics of rainfall spatial changes to determine the criteria for the design of rainfall according to local conditions,and the factors affecting the actual project implementation effect should be considered at the same time.