Jing YUAN，Jianping XU，Lijuan SUN，Xiuzhen ZHANG，XiaoliWANG

1.Weifang Meteorological Bureau，Weifang 26101，China；2.Linqu Meteorological Bureau，Linqu 262600，China

1 Introduction

In recent years，the global warming has not stopped，and the impact of climate warming can not be ignored.The summary of policymakers in the First Working Group of the Fifth Assessment Report of Intergovernmental Panel on Climate Change（IPCC）［1］pointed out that over the past130 years，global temperatures have increased by 0.85℃，and the global warming degreemay exceed 1.5℃ in the21st century.The past climate trend of Weifang City was consistent with global climate trend，and over the past 30 years，the annual average temperature has increased by 0.5℃ every 10 years［2］.Wheat is the main food crop in Weifang City，and it is found that the climate change over the past 30 years has had an impact on the growth stage and yield of wheat［3-4］，so on the basis of analyzing future climate change trends，this paper analyzes its effects on the growth and yield of wheat，which can provide a scientific basis for reducing the climate change vulnerability and ensure the food security and rapid economic development in Weifang City.

2 Materials and methods

In this study，we use the climate scenario data from PRECIS［5］to analyze the future climate change trends.The future weather data from PRECIS are embedded into CERES-Wheat model［6］to simulate the wheat production during 2021-2050，and analyze future trends of the growth stage and yield of wheat in Weifang City during 2021-2050.

2.1 Introduction to climate models and climate scenariosPRECIS（Providing Regional Climate for Impacts Studies）is developed at the Hadley Centre at the UK Met Office，PRECIS is a regional climate modelling system designed to run on a Linux based PC.PRECIScan be applied to any area of the globe to generate detailed climate change projections.PRECIS is a regional climate model（RCM）ported to run on a Linux PC with a simple user interface，so that experiments can easily be set up over any region of the globe.PRECIS is designed for researchers（with a focus on developing countries）to constructhigh-resolution climate change scenarios for their region of interest.The horizontal resolution is 50km ×50km，and it is vertically divided into 19 layers.It has a friendly interface，and it can be setup in any region of the world for regional downscaling.Xu Yinlonget al.［7-10］verify the simulation capability of PRECISmodel in China and carry out the simulation verification at the site level［11］.This paper uses SRES A2and B2scenarios［12］.According to China's national conditions，it should pay equal attention to economic development and environmental protection in the future，which is closest to B2scenario（namely the regional sustainable scenario）.A2scenario considers the rapid population growth，greatly different from China's population growth，but as a hypothetical high-emission scenario，it can be used to assess the possible impact of climate change in the worst situation of development.

2.2 Crop modelCERES-Wheat model was a user-oriented crop growth simulation model developed by the United States for the actual production.It consists of three parts：input module of climate，soil，crop genetic parameters and crop cultivation and management；simulation module of main physiological processes；output and analysis module of simulation results.CERES-Wheat mode has been extensively verified at the site level in China［13-16］.

3 Results and analysis

3.1 The future climate trends in Weifang City

3.1.1 Temperature trend.As can be seen from Fig.1，under A2and B2scenarios，the temperature showed a rising trend inWeifang City during 2021-2050，and the increasing extent of temperature in A2is greater than in B2.Under A2scenario，the annu-al average temperature will rise by 0.9℃；under B2scenario，the annual average temperature will rise by 0.6℃.

From the inter-annual average temperature change（Table 1），the average temperature in the 2030swill be lower than in the period before and after the 2030s under A2and B2scenarios.Under A2scenario，the temperature at each stage shows an upward trend，and the temperature rise in the 2030s is slower than in the 2020s but the temperature sharply rises in the 2040s.Under B2scenario，the temperature shows a downward trend in the 2020s，and it rises in the following 20 years，and the temperature rise in the 2040s is faster than in the 2030s.

3.1.2 Precipitation trends.Under A2and B2scenarios，the precipitation shows an increasing trend in Weifang City over the next 30 years，and the precipitation in B2scenario is slightly more than in A2scenario（Fig.2）.Under A2scenario，the average annual precipitation increases by 17.9%inWeifang City over the next30 years；under B2scenario，the average annual precipitation increases by 21.3%.

Table 1 The average temperature anomaly and climate tendency rate in Weifang City during 2021-2050

From the inter-annual precipitation changes（Table 2），under A2and B2scenarios，the average precipitation at three stages is higher than at other stages，and the precipitation in the 2030s goes through the largest increase.Under A2scenario，during2021-2030，the precipitation shows an increasing trend，and during 2031-2040，2041-2050，the precipitation shows a decreasing trend.During 2031-2040，2041-2050，the precipitation falls more sharply.The precipitation trend under B2scenario is consistent with the precipitation trend under A2scenario，and the difference is that the precipitation during 2041-2050 falls much faster than during 2031-2040.

3.2 The impact of future climate change on the growthstage and yield of wheatAssuming wheat varieties and management mode remain unchanged，we input the meteorological data under A2and B2scenarios inWeifang City during2021-2050 into crop model，to simulate the future wheat growth and development and evaluate the impact of future climate change on the growth stage and yield of wheat.

Table 2 The precipitation anomaly percentage and climate tendency rate in Weifang City during 2021-2050

3.2.1 The impact on the growth stage.The changes in growth stage affect the biomass accumulation.In this study，by simulating the wheat growth under future climate change scenarios，we analyze the impact of climate change on the growth stage of wheat.By simulating the main growth stages（flowering and maturity）of wheat，it can be found that：（i）under A2and B2scenarios，the flowering and maturity stages of wheat inWeifang City during2021-2050 are earlier than usual（under A2scenario，flowering and maturity stages of wheat are 5，7 days earlier than usual，respectively；under B2scenario，flowering and maturity stages of wheat are3，5 days earlier than usual，respectively）；（ii）flowering and maturity stages under A2scenario are much earlier than under B2scenario，mainly because the temperature under A2scenario is higher than under B2scenario，and the higher the temperature，the shorter the phenophase duration of wheat.

Table 3 The flowering and maturity stages of wheat under different future climate scenarios

3.2.2 The impact on yield.Both A2and B2scenarios consider the change in the concentration of CO2，and the rising concentration of CO2has a fertilization effect on the growth of agricultural crops［17-19］，so when evaluating the impact of future climate change on wheat yield，this paper studies two cases（without considering CO2fertilization effect and considering CO2fertilization effect）（Table 4）.As can be seen from the simulation results，if we keep the existing variety and field management model and do not consider the CO2fertilization effecton wheat yield，then under A2and B2scenarios，the future wheat production in Weifang City shows a downward trend，and the magnitude under A2is larger than under B2.This is mainly due to the rising temperature which dominates the future climate trends，and the rising temperature will accelerate the growth of wheat，shorten the growth period，reduce the dry matter accumulation time，and lower the yield.When considering the CO2fertilization effect on wheat，the CO2fertilization effect partially offsets the negative impact of rising temperature，and the future wheat yield in Weifang City will be significantly increased.

Table4 The changes in wheat yield under the future climate change scenarios

4 Conclusions and discussions

（i）In the context of global climate change，the temperature and precipitation will increase inWeifang City in the future.The temperature will rise by 0.6-0.9℃ and the precipitation will increase by 17.9%-21.3%in 2050.（ii）The future climate change will advance the growth stages of wheat.In 2050，the flowering period of wheat in Weifang City will be advanced by 3 to 5 days and the maturity period will be advanced by 5 to 7 days.（iii）When considering the CO2fertilization effect，the future wheat yield will show an upward trend，an increase of 3.2%-5.4%；when we do not consider the CO2fertilization effect，the future wheat yield will show a downward trend，a decrease of 0.9%-1.7%.（iv）When this study considers the CO2fertilization effect to simulate the growth of wheat，it is assumed that the conditions of irrigation and fertilization for wheat are fully satisfied，and the other conditions are very suitable for growing wheat，but in the actual planting process，there are still great difficulties in fully achieving this ideal standard.Thus，when evaluating the impact of future climate change on wheat yield，the assessment of CO2fertilization effect is merely for reference.（v）The site selected in this study is irrigated arable land，so when using the crop model to simulate the wheat growth，it is assumed that the conditions of irrigation and fertilization for wheat are fully satisfied，and the impact of pests and diseases is not considered，but there are still some difficulties in achieving such conditions in real production，so the results in this paper are only for reference，and there is a need to perform specific analysis in the production.

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