Junhui YAN,Hui FU,Hongsheng ZHOU,Xinchuang XU

1.College of Urban and Environmental Sciences,Xinyang Normal University,Xinyang 464000,China;

2.College of Geography and Tourism,Chongqing Normal University,Chongqing 400047,China

3.Southern Henan center for mineral rock and gem-jade identification and processing,Xinyang Normal University,Xinyang 464000,China

4.The School of Resources Environment Science and Technology,Hubei University of Science and Technology,Xianning 437100,China

5.Key Laboratory of Land Surface Pattern and Simulation,Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences,Beijing 100101,China

Variations of Frost-free Period and Its Impact on Grain Yields in Henan Province during 1961-2013

Junhui YAN1*,Hui FU2,Hongsheng ZHOU1,3,Xinchuang XU4,5*

1.College of Urban and Environmental Sciences,Xinyang Normal University,Xinyang 464000,China;

2.College of Geography and Tourism,Chongqing Normal University,Chongqing 400047,China

3.Southern Henan center for mineral rock and gem-jade identification and processing,Xinyang Normal University,Xinyang 464000,China

4.The School of Resources Environment Science and Technology,Hubei University of Science and Technology,Xianning 437100,China

5.Key Laboratory of Land Surface Pattern and Simulation,Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences,Beijing 100101,China

The aim of this study was to investigate the responses of frost dates to global warming and its influences on grain yields.In this study,based on the frost date series defined by daily minimum ground temperature,the spatial and temporal characteristics of first frost date (FFD),last frost date (LFD)and frost-free period (FFP)were analyzed.The impact of extending FFP on major crop yields was also studied.The results were as follows:FFD showed a significantly delaying trend of 2.2 d/10 y,and LFD presented an advancing trend of 2.4 d/10 y.FFP extended at a rate of 4.5 d/10 y due to the later FFD and earlier LFD.The most obvious trend of FFD was in western Henan,while the most significant trend of LFD and FFP occurred in south central parts of the study area.However,in eastern region,the trends of FFD,LFD and FFP were not so obvious.Major crop yield showed a significant correlation with frost-free period for Henan during 1961-2013.The yields of grain,rice,wheat,and maize increased by 79.5,90.0,79.5 and 70.5 kg/hm2with FFP extending by one day.

Dailyminimum ground temperature;Frost-free period;Grain yield; Henan province;1961-2013

T he IPCC Fifth Assessment Report(AR5)pointed out that the globally averaged combined land and ocean surface temperature has increased by 0.85℃ [0.65℃to 1.06℃]over the period 1880 to 2012[1]. This warming trend has also been observed in China[2].Under this warming background,there isincreasing concern thatglobalwarming has brought key effects on ecological system,agriculturalenvironmentand crop yields[3].In China,the impacts of climate change on agriculture have been comprehensively reviewed[4].Using improved datasets of crop production by county,Tao et al.investigated climate trends during the growing period and their impacts on crop yields[5]. Li et al.found that natural disasters deeply influence the security of the crop’s production by analyzing the relationship between crop production and the influence factors[6].Frost-free period is an important index of heat in agriculture,which has an important impact on crop yield and quality[7]. The frost-free period lengthened during the past 50 years due to the later first frost date and the earlier last frost date[8-11].However,the quantitative relationship between this prolonged period and grain yield has not been as well understood.The study attempted to investigate the statistical relationship between frost-free period andyields of major crops(rice,wheat,and maize)in Henan province,using linear regression model.This study will help to improve the adaptability of agricultural system to climate change and ensure China’s food security.

Data and Methods

Data sources

Two types of data were used in this study,meteorological data and grain yield data of major crops.China monthly surface climate data from 1961-2013 are published every year by the Chinese Meteorological Administration (CMA).To obtain the starting and ending date of frost-free period in Henan province,the research downloaded daily minimum ground temperature data of 17 stations from the CMA website(http://cdc.cma.gov.cn) (Fig.1).The meteorological data were derived from instrumental measurements,and quality assurance checks were undertaken,including examining the data for completeness,reasonableness and accuracy.Major crop yield data were obtained from China Statistical Yearbook.

Methodology

Frost is a deposit of small white ice crystals formed on the ground or other surfaces when the temperature falls below freezing[12].It is difficult to obtain a continuous longer frost date series,due to the fact that frost observation data are usually missing in early years for some reason[13].Some researchers have defined frost dates by surface ground temperature and air temperature in precious studies[9,14-19]. However,Han et al.found that frost date defined by surface ground temperature was very close to first frost observation date[20].Hence,the research used daily minimum ground temperature to define frost dates.First frost date(FFD)is defined as the surface ground temperature falls below 0℃ for the first time in autumn,while last frost date (LFD)is defined as the surface ground temperature rises above 0℃for the first time in spring time.The period between FFD and LFD is defined as frost-free period (FFP).

It analyzed the long-term frost trends by calculating the regression coefficients using simple linear regression model.The coefficient k was computed as follows:

Note that assuming the linear regression y=kx+b,predictor(x)is the year,and the predictant (y)is frost date anomaly with the reference period of 1961-1990.It analyzed the spatial characteristics of FFD,LFD and FFP by plotting the trend coefficients on map using ArcGIS software.

Results

The temporal variations of FFD, LFD and FFP

Fig.2 presents the regional interannual variations of FFD,LFD andFFP during 1961-2013.FFD shows a significantly delaying trend while LFD indicates a significantly advancing trend.The FFP extends during the past 53 years due to the later first frost date and the earlier last frost date.The trend coefficients of FFD,LFD and FFP are 0.22,0.24,and 0.45 d/y,respectively.Meaning that FFD is postponed for 11.5 days and LFD is advanced for 12.9 days during the past 53 years.As a result,FFP lengthens for 23.6 days during the past 53 years. It is worth noting that the inter-annual variation of LFD is a little larger than that of FFD,and the inter-annual variation of FFP is much larger than that of LFD.

On decadal timescales,FFD changed little before 2000.However,it delayed markedly since the 21stcentury.FFD of 2001-2010 is postponed for 9 days compared to 1961-1970 mean. Unlike FFD,LFD was obvious ahead of time since 1980s,especially after 2000.Mean LFD of 2001-2010 is advanced for 13 days than that of 1961-1970.FFP has almost no obvious trend in the 1960s and 1970s.It began to extend since 1980s,especially after 2000.Mean FFP of 2001-2010 has prolonged for 22 days than 1961-1970 (Table 1).

The spatial variations of FFD,LFD and FFP

Fig.3 shows the spatial trend map of FFD,LFD and FFP.In all stations except Gushi,FFD shows a significantly delaying trend during the past 53 years.But the magnitude varies from region to region.The largest delaying trend occurs in the western region of Henan Province,with the maximum value occurring in Lushi(with a trend of 4.0 d/10 y).However,in eastern region,the delaying trend is not obvious,with the minimum delaying trend locating in Shangqiu (with a trend of 1.1 d/10 y).In Gushi,however, FFD is slightly advanced during the period 1961-2013 (at a rate of-0.3 d/10 y).Unlike FFD,LFD in all stations presents a significantly advancing trend.These trends are ranging from 1.2 to 4.6 d/10 y,with the maximum trend occurring in Zhumadian and minimum trend locating in Gushi.The most obvious trend occurs in south central region.But in eastern region, the trend is not so obvious.

Due to the later FFD and earlier LFD,FFP shows an extending trend in Henan province.The magnitude is ranged from 2.3 to 38.3 days during the past 53 years.The most obvious trend occurs in south central region. However,in eastern region,the trend is not so obvious.Our results are consistent with previous studies[8-11],although there are some minor differences.For instance,the amplitude of changing trend varies in different studies.These differences may be due to the following reasons.On the one hand,data source used to define FFD and LFD are different.On the otherhand,different study area and reference period may be the causes of these differences.

Table 1 Decadal change of FFD,LFD and FFP

Table 2 Linear regression between FFP and grain yield

The relationship between frost-free period and grain yield

The impactsoffroston major crops have been studied previously[20-25],but these studies mainly focused on the abnormal frost events and its influence on agriculture. The relationship between frost-free period and grain yield is not clear.To answer this question,the research established regression equations using FFP as predictors and crop yields as predictant.

The major crop yields show a significant correlation,ranging from 0.53 to 0.61,with frost-free period(Table 2). All equations passed the 99%confidence level.The value of F statistic is high,considering that the 95th percentile of its distribution under the null hypothesis of no real relationship is about 4.02.So using these equations, the quantitatively relationship can be investigated between the extendingFFP and crop yields.The regression coefficient between gain yield and FFP is 5.33,representing that gain yield increases by 79.5 kg/hm2when FFP extends by one day.Of the 3 major crops,rice yield is the most sensitive to FFP,which increases by 90 kg/hm2with FFP extends by one day.Wheat and maize yields increase by 79.5 kg/hm2and 70.5 kg/hm2,respectively, when FFP extends by a single day.

Conclusions

In this paper,the research defined frost dates by using daily minimum ground temperature.And then the research analyzed the temporal and spatialcharacteristics offirstfrost date,last frost date and frost-free period during the past 53 years.The research also investigated the influence of the extending FFP on major crop yields.The main conclusions are summarized as follows:

During the past 53 years,FFD showed a significantly delaying trend, and LFD showed an advancing trend. FFP lengthed due to the later FFD and earlier LFD.The trend coefficients of FFD,LFD and FFP are 0.217,0.244 and 0.445 d/y,respectively.

There existed some minor differences in the trend of FFD,LFD and FFP on decadal time scales.FFD obviously delayed since the 21thcentury, while LFD was obviously ahead of time since 1980s.FFP has almost no obvious trend in the 1960s and 1970s. It began to extend since 1980s,especially after 2010.

The trend of FFD,LFD and FFP at all stations is consistent,but the magnitude varies in different stations. The most obvious trend of FFD is in eastern region.And the most obvious trend of LFD and FFP occurs in south central region.However,in eastern region,the trend of FFD,LFD and FFP is not so obvious.

The major crop yields show a significant correlation,ranging from 0.53 to 0.61 with frost-free period.The yields of grain,wheat,rice,and maize increase by 79.5,79.5,90,and 70.5 kg/hm2when FFP extends by one day.

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Responsible editor:Xiaoxue WANG

Responsible proofreader:Xiaoyan WU

1961～2013年河南省無霜期變化及其對糧食產(chǎn)量的影響

閆軍輝1*，傅輝2，周紅升1,3，徐新創(chuàng)4,5*
（1.信陽師范學(xué)院城市與環(huán)境科學(xué)學(xué)院，信陽464000；2.重慶師范大學(xué)地理與旅游學(xué)院，重慶 400047；3.信陽師范學(xué)院豫南巖礦寶玉石鑒定及加工中心,河南信陽464000；4.湖北科技學(xué)院資源環(huán)境科學(xué)與工程學(xué)院，湖北咸寧437100；5.中國科學(xué)院地理科學(xué)與資源研究所陸地表層格局與模擬院重點實驗室，北京100101）

該文的目的是研究無霜期變化對全球變暖的響應(yīng)及其對糧食產(chǎn)量的影響。利用1961～2013年河南省17個測站均一化的逐日地面0 cm最低氣溫資料，根據(jù)霜凍氣候指標計算了各站逐年的初、終霜日期，在此基礎(chǔ)上分析了過去53年河南省初、終霜日期和無霜期的時空變化特征，并探討了無霜期的變化對糧食產(chǎn)量的影響。結(jié)果表明：①近53年來，河南省平均初霜日期以2.2 d/10 y的速率顯著推遲，平均終霜日期以2.4 d/10 y的速率顯著提前，受此影響無霜期以4.5 d/10 y的速率延長；②就空間變化而言，初霜期推遲最為明顯的地區(qū)位于河南西部地區(qū)，中、南部平原地區(qū)終霜期提前最為明顯。東部地區(qū)初、終霜日期和無霜期變化趨勢不明顯；③1961～2013年河南省無霜期的變化與主要糧食產(chǎn)量呈顯著正相關(guān)，無霜期每提前1 d，糧食總產(chǎn)量、稻谷、小麥和玉米分別提高79.5、90.0、79.5和70.5 kg/hm2。

日最低 0 cm地溫；無霜期；糧食產(chǎn)量；河南??；1961～2013年

中國科學(xué)院戰(zhàn)略性先導(dǎo)科技專項項目（XDA05090101，XDA05090104)；全球變化研究國家重大科學(xué)研究計劃項目(2010CB950101,2012CB955403)；科技基礎(chǔ)性工作專項項目(2011FY120300)；信陽師范學(xué)院博士科研啟動基金(0201403)；國家自然科學(xué)基金項目(41271124，41101549)。

閆軍輝（1983-），男，河北定州人，博士，講師，主要研究方向為全球變化，E-mail：yanjh2015@126.com。*通訊作者。

2015-06-02

修回日期 2015-08-14

Funded by"Strategic Priority Research Program"of the Chinese Academy of Sciences (XDA05090101, XDA05090104); China GlobalChange Research Program (2010CB950101,2012CB955403);Basic Research Project of the Ministry of Science and Technology (2011FY120300);Doctor Foundation of Xinyang Normal University (0201403);National Natural Science Foundation of China(41271124,41101549).

*Corresponding author.E-mail:yanjh2015@126.com

Received:June 2,2015 Accepted:August 14,2015