Adapting Tea Production to Climate Change under Rapid Economic Development in China from 1987 to 2017

Abstract

Tea (Camellia sinensis L.), as one of the most important cash crops in China, plays an important role in increasing farmers’ incomes and guaranteeing a high quality of life. Tea production has been greatly influenced by both climate change and economic development in China. However, without a scientific understanding of the interaction mechanism of climate change and the impetus from rapid economic development on tea production practices in China, it is difficult to take adaptive actions to meet the climate change challenges for the tea industry. In this paper, we firstly assessed the potential impacts of climate change on tea climate suitability by empirical formula calculation using meteorological data; then, the effects from the additional climatic stress due to warming on tea production were detected with the annual statistical tea yield record on a municipal level. The contribution of socioeconomic development to the tea industry was evaluated with the comparison of the movement of China’s national economy’s and tea industry’s gravity center during the period of 1987–2017. Finally, a conceptual adaptation framework was built to demonstrate the interaction mechanisms between climate change, tea production, and the economic development. The results showed that there was a negative impact of climate change on tea production in mainland China, with the percentage of high tea climate suitability (>0.9) areas dropping by 45% to 32%, while opportunities of enlarging the tea cultivating area emerged in the north tea production region where the tea climate suitability increased. We found that the tea planting area expanded northwards from 33° N in 1987 to 35° N in 2017 to take advantage of the favorable climatic resources due to warming, and tea planting decreased at an altitude of 100–400 m while increasing to higher altitude of 400–2000 m to avoid hot temperature damage and seek the optimum environment in high mountainous areas for tea production. In addition, the tea production moved westward along the longitude, decreasing obviously at 117–121° E while increasing significantly at 98–104° E and 107–110° E. Meanwhile, the tea production gravity center showed a westward movement consistent with the national economic gravity center moving trend, which means that tea industry development was driven by multiple socioeconomic factors and climatic forcings. A conceptual framework was built in this paper, aiming to show a robust adaptation mechanism for the tea system to maximize the benefits and minimize the damages from the altered climatic resources under rapid economic development in mainland China. The results in this study would help deepen the understanding of the adaptation process and practices for tea production in mainland China.

1. Introduction

As the most popular global beverage, tea (Camellia sinensis L.) is widely planted in tropical and subtropical regions in more than 50 countries and regions all over the world [1]. In the past few decades, tea planting areas and production expanded greatly worldwide. The global tea harvest area and production reached 5.63 million ha and 7.34 million tonnes in 2017, increasing by 127% and 225% from 2.48 million ha and 2.26 million tonnes in 1987, respectively (www.fao.org/faostat, accessed on 15 January 2019). The increase of tea production in the world was mainly attributed to China, India, Kenya, Sri Lanka and Vietnam, and was mainly distributed in east Asia and central Africa. There has been a long history of tea planting due to favorable and diverse natural environments in China, tea cultivation can even be expanded beyond the northern subtropical zone. According to China’s climatic zoning and national tea regionalization scheme [2], tea cultivation zone can be divided into four regions (North Yangtze River Regions, South Yangtze River Region, Southern China Region, and Southwest China Regions) as shown in Figure 1. The topography of the Southern and Southwest China Regions features with mountainous terrains, while the North and South Yangtze River Regions are relatively flatter, and the temperature and precipitation for tea planting in the North Yangtze River Region is lower than the other three regions (Appendix A Figure A1). Tea production and planting areas in China was continuously rising from 1987 to 2017 (Figure 1a), but varied in different regions (Figure 1b–e). The proportion of tea output and area in each region in recent years increased in marginal production areas (North Yangtze River Region and Southwest China Region) but decreased in the original core production areas (South Yangtze River Region and Southern China Region), which may be related to climate condition and other non-climate factors. The years of 1987–2017 were not only a period of rapid development of tea production, but also a period of rapid changes of meteorological conditions, which influences on tea production cannot be ignored [3].

As a woody perennial plant, tea requires a hot and moist climate condition with temperatures ranging from 13–26 °C and a minimum annual precipitation of 1500–2000 mm, acidic soils, 0.5–10 degree slopes, and elevations below 2000 m [4,5]. Changes in climatic conditions would directly affect tea growth, quality, planting distribution, and even transactions [6,7]. In the past decades, the annual average temperature increase in China has exceeded 1 °C and the average annual rainy days decreased significantly, while the number of rainstorm days increased [8]. The annual precipitation decreased in Southeast China, but increased in North and Southwest China [9]. According to observations, there has been more extreme climate events in China due to climate change. The frequency and intensity of agro-meteorological disasters such as drought, cold, and hot temperature events have been enhanced. Almost all tea cultivation regions in China would be affected by drought, especially in summer, with high temperature stress [10]. It is estimated that 11–35% of the reduction in tea production is due to enhanced drought, resulting in fluctuations of tea price [11]. In 2011, a severe drought in Guiyang City led to the death of about 80% of young tea trees, resulting a direct economic loss of about 10 million CNY [12]. A devastating heatwave with a high temperature of over 40 °C, lasting for 20 days in the Zhejiang province, caused heat damage to about 138.6 × 10³ ha of tea gardens in 2013, which resulted in a direct economic loss of 1.31 billion CNY and 20% decrease in spring tea yield in the next year [13]. Cold damage has been also enhanced due to greater climate variability, which delays the picking date of spring tea and causes huge economic losses [14]. Evidence showed that tea plantations in the mid-latitude of China are more vulnerable to freezing damage, especially in the North Yangtze River Region [15]. Severe freezing disaster occurred in the Shandong province from 2010~2011, causing an 80% yield reduction of spring tea [16]. Furthermore, the tea yield and quality are greatly affected from the enhanced outbreak of pests and diseases due to climatic warming. Increasing temperatures advance the emergence of pests and diseases and increase the number of post generations [17]. Changes in meteorological conditions do not only affect the production of tea, but also adjust the suitable tea habitat, which has been represented with an index of tea climate suitability (TCS) [18,19]. There has been a couple of case studies on the TCS index in the typical tea production regions at the provincial level and even sub-provincial level such as the Fujian province [20], Zhejiang province [21], and Nanjing city [22], high suitability index means favorable climatic conditions and a suitable growth habitat for tea production.

Generally, tea production is affected by both climate conditions and socioeconomic developing level. The tea industry plays a notable role in rural development, poverty reduction, and food security in tea-producing regions [1]. High-quality, fresh tea leaf production can be the primary source of livelihood for smallholder tea farmers [23]. With rapid socioeconomic development, tea consumption is boosted corresponding to increasing of per capita income levels in China, tea production had been inevitably raised to narrow down the gap between supply and consumption demand. Gross domestic product (GDP) in China increased from 1.22 × 10⁶ million CNY in 1987 to 8.32 × 10⁷ million CNY in 2017 (http://data.stats.gov.cn, accessed on 15 October 2019), and it is shown an overall 8% of annual mean increase for the total tea consumption from 1997–2017, which enabled China to become the largest tea-consuming country in the world [1]. Now the economic development in China is being transformed into a new stage of low carbon emissions with the new principle, the “Two Mountains Theory” [24]. Understanding how tea production adapts to climate change and adjusts with the rapid economic growth in the past few decades would be helpful for the future sustainable development of the tea industry in China.

In this study, the tea climate suitability was taken as an index to assess the impact of climate change on Chinese tea production. The tea production amount at the municipal level across China during the period 1987–2017, archived from the statistical yearbook, was used to detect the spatiotemporal changes of tea planting areas. Then, the trajectories of gravity centers of tea production and China’s national GDP were compared to investigate the contribution from adaptations to both climate change and economic structure adjustment. Finally, a conceptual framework was built to demonstrate the adaptation mechanism of Chinese tea production with the drivers of climate change and rapid economic development.

2. Materials and Methods

2.1. Study Regions

There are totally 18 provinces in Chinese mainland in this study (Figure 2). Though Chongqing was split from the Sichuan province in 1997 to be set up as a municipality directly under Chinese Central Government, statistics of tea yield and planting area for Chongqing is still integrated into Sichuan province in this study for data consistency. The North Yangtze River Region is special, including whole provinces of Shandong and Henan, where the tea planting area expanded northwards due to warming during 1987–2017 to enable the tea production available in all municipalities in these two provinces. Longnan, the only tea-producing municipality in Gansu province, and three sub-provincial municipalities of Ankang, Hanzhong, and Shangluo in Shaanxi province are also included in the North Yangtze River Region. The correspondence of provinces of the other three Regions are presented in Figure 2.

2.2. Data Sources

The data used in this study can be categorized into three main types.

(1) The recorded tea production in municipal-level (sub-provincial) for 18 provinces during 1987–2017 was obtained from the Tea Database, Ministry of Agriculture, the People’s Republic of China (http://www.moa.gov.cn, accessed on 15 October 2019), and the economic data of provincial-level GDP in Chinese mainland was collected from the National Bureau of Statistics of China (http://data.stats.gov.cn, accessed on 15 October 2019), respectively.

(2) The administrative map was obtained from the National Geomatics Center of China (NGCC, http://ngcc.sbsm.gov.cn, accessed on 5 September 2019). The digital elevation model (DEM 90) data (Version 4.1) was downloaded from the CIAT-CSI SRTM website (http://srtm.csi.cgiar.org, accessed on 15 October 2019).

(3) The meteorological data was obtained from the National Meteorological Network Weather Stations under the China Meteorological Administration (CMA, http://cdc.cma.gov.cn, accessed on 15 October 2019), including maximum temperature, minimum temperature, solar radiation, precipitation, relative humidity, sunshine duration, and other factors for 18 provinces from 1987 to 2017.

2.3. Calculation of Tea Climate Suitability Index

The suitability index quantifies whether climate conditions are suitable for tea growth, which can be used to assess the potential impacts of climate change on tea production in mainland China. In this study, the suitability index was composed of climatic factors as shown in Appendix A

Table A1. Agricultural Index of Tea Growth.

Agricultural Meteorological Elements	Suitable Growth Conditions	Survivable Conditions	Harmful Conditions
The annual average temperature/°C	15~25	13~15 or 25~35	<13 or >35
≥10 °C Active accumulated temperature	≥5000	3000~5000	<3000
Average annual extreme minimum temperature	≥−8	−10~−8	<−10
Annual precipitation/mm	≥1500	1000–1500	<1000
Monthly precipitation in tea growth period/mm	≥100	50~100	<50
Relative humidity/%	≥78	60~78	<60
Percentage of sunshine/%	<45	45~60	>60

. For tea production, the higher the percentage of sunshine, the lower the quality the tea leaves will be due to damages from strong direct radiation. The average temperature and accumulated temperature can represent the heat resources for tea growth in planting areas, while the minimum temperature may cause the freezing injury on tea brushes. With climate warming and precipitation varying, tea plants will suffer serious damages from enhanced drought, which will affect the germination of tea buds. Meanwhile, dryness due to lower relative humidity in the air will also affect the quality of tea.

The value range of the suitability index is [0, 1]. The calculation process is a unified quantitative analysis of various meteorological factors, which can measure and compare the suitable conditions for tea growth. The further and longer the meteorological index deviates from the suitable conditions, the more serious the harm to tea production will be. Therefore, according to the suitable growth index of tea plants, the climatic factors in Appendix A Table A1 are selected for calculation. The closer the suitability index is to 1, the higher the suitability it is. For the convenience of comparison, the suitability index >0.9 is regarded as high suitability in this study. These indicators can provide information about tea production response to climate through ecophysiological thresholds. The fuzzy mathematical analysis method was used to calculate the suitability index of tea. According to the climate factors of tea growth and the Cauchy distribution model, the membership function of main influencing climate factors can be obtained from the following formulae [20,22,25].

$${\mu }_T=\left\{\begin{array}{c}\frac{1}{1 + 0.04{\left(T - 25\right)}^2} T>25.0\\ 1 15.0\le T\le 25.0\\ \frac{1}{1 + 0.25{\left(T - 15\right)}^2} T<15.0\end{array}\right.$$

(1)

$${\mu }_{\sum T}=\left\{\begin{array}{c}1 \sum T\ge 5000\\ \frac{1}{1 + 0.004{\left(\frac{\sum T}{100} - 50\right)}^2} \sum T<5000\end{array}\right.$$

(2)

$${\mu }_{Tm}=\left\{\begin{array}{c}1 T_m\ge - 8.0\\ \frac{1}{1 + 0.11{\left(T_m + 8\right)}^2} T_m< - 8.0\end{array}\right.$$

(3)

$${\mu }_{YR}=\left\{\begin{array}{c}1 YR\ge 1500\\ \frac{1}{1 + 0.01{\left(\frac{YR}{100} - 15\right)}^2} YR<1500\end{array}\right.$$

(4)

$${\mu }_{MR}=\left\{\begin{array}{c}1 MR\ge 100\\ \frac{1}{1 + 4{\left(\frac{MR}{100} - 1\right)}^2} MR<100\end{array}\right.$$

(5)

$${\mu }_E=\left\{\begin{array}{c}1 E\ge 78\\ \frac{1}{1 + 0.028{\left(E - 78\right)}^2} E<78\end{array}\right.$$

(6)

$${\mu }_I=\left\{\begin{array}{c}1 I\ge 45\\ \frac{1}{1 + 0.01{\left(\frac{I}{100} - 45\right)}^2} I<45\end{array}\right.$$

(7)

$${\mu }_D=\left\{\begin{array}{c}1 D\le 0.7\\ \frac{1}{1 + 1.11{\left(D - 0.7\right)}^2} D>0.7\end{array}\right.$$

(8)

μ_T, μ_∑T, μ_Tm, μ_YR, μ_MR, μ_E, μ_I, μ_D, represent the membership function of average temperature (T/°C), active accumulated temperature over 10 °C (ΣT/°C), annual extreme minimum temperature (Tm/°C), annual precipitation (YR/mm), monthly precipitation in the growing season (MR/mm), relative humidity (E/%), sunshine percentage (I/%), and dryness (D), respectively (Appendix ATable A1). The membership degree of each element is calculated by the membership function, and then the relative distance ambiguity and climate suitability of tea growing in various places are calculated. The calculation formula is:

$$R_z=\sqrt{\frac{1}{N}\sum _{i=1}^N{\left(1 - {\mu }_{zi}\right)}^2}$$

(9)

$$M_z=1 - R_z$$

(10)

where μ_zi is the membership degree of the i-th climatic element at the station in Z province, N is the total number of study elements, Rz is the fuzzy degree of relative distance of the most suitable growth of tea trees in Z province, and Mz is the climate suitability of tea tree growth in Z province. Then, the climate adaptability is used to describe the suitability of tea growth in different regions. ArcGIS software (v.10, developed by Esri, Redlands, CA, USA) was used to spatially interpolate and reclassify the suitability index to achieve spatial processing.

2.4. Calculating Gravity Center

The gravity center calculation model expresses the characteristics of spatial distribution of geographical objects intuitively by calculating the barycenter of a certain attribute [26,27]. The trajectory of a gravity center in an agricultural system is one of the most important indicators reflecting the spatial distribution of crops. The calculation formula is as follows:

$${\mathrm{X}}_t=\frac{{\sum }_{i=1}^n\left(P_{i,t}\times X_i\right)}{{\sum }_{i=1}^n{P}_{i,t}}; {\mathrm{Y}}_t=\frac{{\sum }_{i=1}^n\left(P_{i,t}\times Y_i\right)}{{\sum }_{i=1}^n{P}_{i,t}}$$

(11)

where X_t and Y_t represent the longitude and latitude of tea production gravity center in year t, respectively. X_i and Y_i represent the coordinates of the geographical center of sub-region i (in our research this region is a tea production in municipal-level), P_i,t represents the tea production of sub-provincial municipality i in year t, and n represents the total number of tea production municipalities.

If the coordinates of the gravity center of tea planting in the k and k + m year are Pk(x_k,y_k) and Pk + m(x_k+m,y_k+m), and then the movement distance of the barycenter (d_m) is:

$$d_m=R\times \sqrt{{\left(x_{k + m} - x_k\right)}^2 + {\left(y_{k + m} - y_m\right)}^2}$$

(12)

The value of R is 111.13 km, which represents the coefficient of the transformation of the longitude and latitude coordinates of the earth spherical surface into a planar distance.

Meanwhile, the gravity center of the economy was also calculated by this method, where X_i and Y_i represent the geographical center of province i and P_i,t represents the GDP value in province i in year t, and n represents the total number of provinces in the Chinese mainland. The coordinates of the gravity center are imported to ArcGIS10 to draw the moving track, and the moving distance is calculated by Excel 2016.

3. Results

3.1. Changes of Tea Climate Suitability in China

Tea climate suitability can be used as a unified quantitative indicator of various climatic factors. It is shown a general decreasing trend of the tea climate suitability (Figure 3) on the Chinese mainland, which clearly indicates the negative impact of climate change on Chinese tea production. For the spatial distribution of the tea climate suitability, the proportion of high suitability land (>0.9) decreased by 14% from 45% in 2008–2017 to 32% in 1987–1997. The tea climate suitability degradation areas were mainly located in the Southern Yangtze River Region, the southern and eastern part of the Southern China Region, and the western part of Southwest China Region. Combined with the topography of China, we can see that the tea production was less degraded over the eastern part of the second step on the ladder of Chinese topography with averaging altitude between 1000 and 2000 m (Figure 1a, Appendix A Figure A1). This can be explained by the fact that climate change has less impact on tea production over these mountainous areas, while providing an opportunity vice versa for the upward expansion of tea planting. In contrast to the general degradation of tea climate suitability in the southern part of Chinese mainland, the increased suitability areas expanded obviously over the Northern Yangtze River Region, which could be attributable to climate warming, and would be favorable to the northward expansion of tea planting.

3.2. Adjustment of Tea Production

As shown in Section 3.1, the change of tea climate suitability provided the physical potential for tea planting, but tea production is comprehensively driven by climatic and non-climatic factors. To examine how the tea industry adjusted to climate change and the rapid economic development in recent decades, tea yield data at the municipal level (sub-provincial) from 1987 to 2017 were collected in the statistical yearbook, and the comparison of tea yield between 2017 and 1987 is shown in Figure 4a. According to Appendix A Table A1, the lowest suitable annual temperature for tea growth is 13 °C, so the comparison of the isotherm of 13 °C in 1987–1997 (purple dotted line) and 2008–2017 (green dotted line) is shown in Figure 4a to demonstrate the potential north boundary for tea planting. It can be seen from Figure 4a that the most intensive tea cultivation areas (with red dots) in 1987 were mainly located in Zhejiang and the South Anhui province at the latitude of 29–30° N; nevertheless, the tea production in 2017 (with blue dots) was greatly increased in the north side of the main tea production area of 1987, the intensive tea planting area expanded up to 32° N. Meanwhile, the increase in 23° N was mainly located in the southwest Yunnan and south Fujian regions, which could fit the characteristic of upward movement in Figure 4a. It can be seen that the changes of spatial distribution of tea planting showed two typical features. One feature is the northward shift of tea planting over the annual mean temperature of 13 °C in the Shandong, He’nan, and Shaanxi provinces, where the climate had not previously been favorable for tea plantings. The fact is that the northward expansion of tea cultivation in Shandong and Shaanxi provinces even surpassed the temperature limit of tea plants (Figure 4a). The another feature was an upward shift, centralized over the mountainous areas in the north and south edges of the Yun-Gui Plateau, the mid-east part of the second step on the ladder of Chinese topography, and the mountainous areas in the south of the middle reach of the Yangtze River and along the southeast coast near Taiwan (the topographic map is shown in Appendix A Figure A1). The northward and upward shifts of tea planting are primarily driven by dramatic increases in temperature.

Besides the northward shift in latitude and the upward shift in altitude, we can see that there is also an overall westward shift of tea planting distribution in longitude for the tea production adjustment during 1987–2017. A dissection on the shifts of tea cultivation in different directions in the past decades (Figure 4b–d) would be helpful for in-depth scientific understanding of the adjustment mechanism hidden in tea production adaptation practice. The results showed that the distribution of tea yield proportion along longitudes of around 98–104° E and 107–110° E in 2017 more obviously increased than in 1987, where the terrains corresponded to the east edge of the Tibetan Plateau (the first step on the ladder of Chinese topography, averaging over 4000 m) and the middle-east part of the second step on the ladder of Chinese topography, respectively. However, the opposite deceasing trend appeared around 117–121° E, where had been the intensive tea planting area in 1987 (Figure 4b).

The tea yield proportion increased obviously from 1987 to 2017 along 22–26° N and 31–34° N, corresponding with the upwards shift and northward shift of tea planting, respectively. A decreasing trend can be seen around 28–30° N, overlapping along with the longitude 117–110° E, which means that the proportion in the original intensive tea planting area decreased (Figure 4c). In the national level, it can be seen that the northward expansion of tea planting coincided with the westward movement trend, which was furthermore related with the upward shift of tea planting. In the perspective of altitude dimension, the proportion of tea yield in 2017 deceased sharply around the elevation of 300 m, but increased in the altitude from 500 m up to 2000 m (Figure 4d). The upward shift of tea planting is autonomous adaptation practices to avoid heat temperature damage due to global warming.

3.3. The Trajectory of Gravity Center of Tea Production

From the above analysis it is shown a general westward movement trend of tea industry combining the joint three-dimensional shift of tea cultivation, climate warming is an important driving force to the westward trend, while non-climatic drivers such as land use policies are also responsible for the development of the tea industry [28,29,30]. A typical example is that the tea production decreased in the Jiangsu province in the South Yangtze River Region, which was opposite to the northward movement associated with the provinces in the same latitude such as the Henan, Hubei, and Shaanxi provinces (Figure 4a). The reason for this phenomenon can be attributed to China’s land use policy. Jiangsu is believed to be the “flattest” province in China, where the arable land is prohibited to be used for tea production because of the strict 1.8 billion Mu Arable Land Red Line (http://www.gov.cn/gongbao/content/2006, accessed on 12 January 2020) to ensure the cropland for cereal food production. More mountainous land in west China would avail potential expansion of tea cultivation due to warming. To investigate the relation between tea production and economic development, the movement of the geographical gravity centers for tea planting and economic development were drawn through the calculation method in Section 2.4.

The movement of the geographical gravity centers of tea production and economic development were drawn in Figure 5b,c. From 1987 to 2017, there was an obvious westward movement for tea industry. The tea production gravity center moved westward by about 280 km over the past three decades (see Appendix A

Table A2. Moving Distance of Tea Production Gravity Center in China from 1987 to 2017.

Year	Spatial Position of Tea Production		Distance (km)
	East Longitude	North Latitude
1987	113°17′03.52″	28°24′06.00″	-
1988	113°21′52.62″	28°19′21.87″	12.51
1989	113°10′31.73″	28°15′07.38″	22.44
1990	113°10′02.36″	28°14′37.39″	1.30
1991	113°4′53.34″	28°13′38.82″	9.71
1992	113°4′43.85″	28°9′40.36″	7.37
1993	112°56′36.96″	28°8′01.25″	15.34
1994	112°39′42.56″	28°1′37.34″	33.48
1995	112°45′23.94″	27°56′27.06″	14.24
1996	112°44′38.83″	27°58′00.18″	3.19
1997	112°53′41.46″	27°58′03.27″	16.75
1998	112°53′00.53″	28°0′55.50″	5.46
1999	112°59′12.66″	28°3′44.52″	12.62
2000	112°52′00.42″	28°1′57.33″	13.75
2001	112°53′12.43″	28°2′18.89″	2.32
2002	113°1′43.64″	28°5′31.74″	16.87
2003	112°51′08.81″	28°8′19.83″	20.27
2004	112°40′17.37″	28°11′04.47″	20.74
2005	112°27′35.45″	28°9′28.57″	23.71
2006	112°14′01.82″	28°9′15.92″	25.12
2007	111°59′10.60″	28°8′30.38″	27.55
2008	112°1′41.99″	28°14′06.59″	11.38
2009	111°57′13.38″	28°15′41.89″	8.80
2010	111°39′23.72″	28°16′50.57″	33.09
2011	111°29′41.20″	28°14′29.78″	18.50
2012	111°18′27.81″	28°14′54.92″	20.80
2013	111°10′25.60″	28°12′28.34″	15.56
2014	111°3′11.62″	28°12′53.44″	13.42
2015	111°0′07.99″	28°11′04.27″	6.59
2016	110°47′03.52″	28°12′54.10″	24.45
2017	110°43′01.70″	28°10′23.05″	8.80

), driven not only by climatic warming, but mainly by non-climatic factors such as the increasing per capita income with the rapid economic development in mainland China in the past decades. From the comparison of the movement of gravity center of tea production and economy it is demonstrated that the tea industry is increasing positively correlated with economic development (Figure 5d, Appendix A Table A2 and

Table A3. Moving Distance of Economy Gravity Center in China from 1987 to 2017.

Year	Spatial Position of Tea Production		Distance (km)
	East Longitude	North Latitude
1987	113°17′03.52″	28°24′06.00″	-
1988	113°21′52.62″	28°19′21.87″	12.51
1989	113°10′31.73″	28°15′07.38″	22.44
1990	113°10′02.36″	28°14′37.39″	1.30
1991	113°4′53.34″	28°13′38.82″	9.71
1992	113°4′43.85″	28°9′40.36″	7.37
1993	112°56′36.96″	28°8′01.25″	15.34
1994	112°39′42.56″	28°1′37.34″	33.48
1995	112°45′23.94″	27°56′27.06″	14.24
1996	112°44′38.83″	27°58′00.18″	3.19
1997	112°53′41.46″	27°58′03.27″	16.75
1998	112°53′00.53″	28°0′55.50″	5.46
1999	112°59′12.66″	28°3′44.52″	12.62
2000	112°52′00.42″	28°1′57.33″	13.75
2001	112°53′12.43″	28°2′18.89″	2.32
2002	113°1′43.64″	28°5′31.74″	16.87
2003	112°51′08.81″	28°8′19.83″	20.27
2004	112°40′17.37″	28°11′04.47″	20.74
2005	112°27′35.45″	28°9′28.57″	23.71
2006	112°14′01.82″	28°9′15.92″	25.12
2007	111°59′10.60″	28°8′30.38″	27.55
2008	112°1′41.99″	28°14′06.59″	11.38
2009	111°57′13.38″	28°15′41.89″	8.80
2010	111°39′23.72″	28°16′50.57″	33.09
2011	111°29′41.20″	28°14′29.78″	18.50
2012	111°18′27.81″	28°14′54.92″	20.80
2013	111°10′25.60″	28°12′28.34″	15.56
2014	111°3′11.62″	28°12′53.44″	13.42
2015	111°0′07.99″	28°11′04.27″	6.59
2016	110°47′03.52″	28°12′54.10″	24.45
2017	110°43′01.70″	28°10′23.05″	8.80

). An interesting fact is that there is a similar counterclockwise rotation for the tea gravity center and economy gravity center (Figure 5b,c); the tea gravity center was moving westward directly from 2002 while the movement of economy gravity center turns westward from 2003. This implies that the growth of tea production contributes to the economic development to some extent. The southward movement of the economic gravity center turned westward, somewhat corresponding to the westward shift of tea production. Meanwhile, the tea industry development was incorporated into the 12th and 13th Five-Year National Plans as special agricultural products (http://www.gov.cn, accessed on 12 January 2020). These plans could promote the development of the tea industry at the national level, especially encouraging the green tea industry towards western China to promote the local economic development. The synergy effects in poverty alleviation and tea industry development should be an initiative for the westward shift of tea production as well.

4. Discussion

Agriculture in China has been being under additional stresses of climate change, which profoundly impacts agricultural production, especially in the suitable growth environment and distribution of crop planting areas [31]. Climate change has resulted in the adjustments on crop growth duration and planting structure, the northward shifts of planting regions, and more severe plant diseases and insect pests. To adapt to climate change, measures such as the optimization of agricultural arrangement, adjustment of planting structure, expansion of thermophilic crops, and development of water-saving agriculture have been taken [32], there would be opportunities in marginal areas for regional cropping availability due to the shifts of potential planting boundaries [33,34]. Huang [35] mapped the suitable tea cultivation areas according to annual mean air temperature, accumulated temperatures above 10 °C, and mean annual precipitation, the results showed that the most suitable regions for tea planting in 1982 were located in the central and southern parts of China, and the northern boundary was mainly located in southern Shaanxi, He’nan, and Shandong provinces. This is quite similar to the results of the period 1987–1997 in this study. With the average temperature increasing, especially the consecutive increasing of the minimum temperature, the tea producing areas gradually expand to the north and high-altitude areas [36]. Several researches showed that suitability has changed dramatically at the regional level. Zhao et al. [37] revealed that the tea climatic suitability was improved in Tai’an, Shandong Province, the climate risk of tea production reduced and the phenology has been prolonged due to climate warming in 1977–2007. However, the suitability in the Eastern Fujian Province deteriorated, especially along the coastal zones, where the climatic conditions had been favorite for tea production in the past [20]. Jin et al. [21] found that the climate suitability of tea in Zhejiang province had obvious time-varying characteristics from 1971 to 2007. However, the results from Han et al. [38] showed that the late spring frost damage since 2003, especially in 2008, 2010, and 2013, had been greatly enhanced to cause huge economic losses, which could be explained as the decline of the suitability of tea growth due to the greater climate change-induced temperature variability. The above research on the suitable areas for tea production were based on a single index or limited to the province or even at sub-province level, lacking of the overall comparison for the whole production area with multidimensional climatic factors. In this study, the tea climate suitability in the Chinese mainland decreased in original tea production regions from 1987 to 2017, and the suitable tea planting area expanded northwards and upwards, even surpassing the former temperature limit (Figure 3a). The Shandong province is a typical example, where there were 6 tea-producing municipalities in the Shandong province in 1987, mainly located in the southern part of the province; while in 2017 there had been 12 municipalities recorded for tea producing already, clearly showing a new tea producing areas expansion to high altitudes and high latitudes (Appendix A Figure A2). Zhao et al. [39] found that the tea suitable area in the future climate condition will expand to the north and west of China, corresponding to the current trend of our results in this study.

At present, the distribution of many terrestrial organisms is also changing to a higher latitude or altitude in response to climate warming [40,41,42,43]. However, as perennial evergreen woody plants, the poor dispersal ability of tea trees is hardly coupled with the pace of climate change, so human intervention is needed for tea species to track their environmental optimum present under climate conditions [44,45]. From 1987 to 2017, the tea production and planting area has increased in Chinese mainland (Figure 1a and Figure 4a) with three obvious characteristics of upward, northward, and westward movements, which can be influenced by the socioeconomic factors and the environment [46]. While few studies that have linked the movement of tea production gravity center with the economy and other social factors, Xiao et al. [47] found that the tea gravity center shifted westward in national level from 2009 to 2014, which was due to the combined actions of governance, product structure optimization, and the added value of tea products. Lin et al. [48] found that the gravity center of tea production in Sichuan Province expanded to the southwest due to the change of local natural resources, brands, and the supporting policies from 1990 to 2015. It is shown an obvious feature of westward movement by the comparison of tea yield distribution in 2017 vs. 1987. The updated trajectory results in this paper showed that there was a similar counter-clockwise rotation for the economy and tea production gravity centers from 1987 to 2017, which indicated that there should be a spatial correlation between them. Meanwhile, some favorable policies have been implemented to promote the development of tea industry to the west [49], such as Regional Layout Planning of Featured Agricultural Products (2006–2015) and Regional Layout Planning of Featured Agricultural Products (2013–2020) (http://www.moa.gov.cn/nybgb/2007, accessed on 12 October 2021 and http://www.moa.gov.cn/nybgb/2014, accessed on 12 October 2021). Those plans pointed out that the provinces of Sichuan (including Chongqing municipality in this study) and Guizhou were advantageous areas for developing green tea, and it was planned to create several famous brands of specialty beverages in central and western China by 2020, so as to improve the certification of localized products. It is worth noting that since the publication of these favorable policies in 2007, the tea industry had developed rapidly in central and western China. For the shifting of tea production, economic conditions are the main driving factors of tea production movement under the favorable policies and climate conditions. When the three pillars (policy, economy, and climate) are set up, farmers would prioritize tea production because of the high add value of tea products.

Adaptation is simply the process of adjusting to the actual or expected climate and its effects, with the sole aim of moderating or avoiding harm or exploiting beneficial opportunities [8]. The adaptation mechanism of Chinese tea production systems could be summarized as a conceptual framework in Figure 6. It can be seen that the tea production system is an interface of the climate system and economic system, which is driven with the additional stresses due to climate change and pulled by the demand from the rapid economic development in China. The potential geographical distribution of tea production has been initially shaped by climate suitability, thus showing three typical features of a northward shift, upward shift, and westward movement driven with climatic- and social-economic factors. It could be an opportunity for the tea industry to maximize the utilization of climatic resources due to the expansion of the northern boundary of tea planting, and avoid the damages of hot temperature due to the upward expansion of tea planting to high-altitude mountains areas. The high yield and quality tea products would be available to meet the demand from Chinese consumers. Meanwhile, with the impetus from economic development, innovative technology packages have been applied on tea production to address the enhanced climate-related disasters and take conditional advantages of warming. For example, technology packages have been developed to address the climate change challenges, including asexual reproduction to increase the climate adaptability of tea, the integration of intercropping and covering, water-saving irrigation systems, shading, drought-resistant water-retaining agents, and deep ploughing to diminish the damage of drought and hot temperature; combination of covering, smoking, spraying water, and anti-freezing fan to prevent the tea from frost damage. The interference behavior measures, like LED narrow-wave insecticidal lamps, yellow insect-infected plates, sex pheromones, and the natural enemies of pests as well were used for pest and disease control. High-tech technologies, such as big data and the Internet of Things, have been adopted for comprehensive solutions to climate change issues [50,51,52,53,54,55]. The adjustment of the tea production system in China is not only to adapt to climate change, but also to meet the increased demand on tea consumption, which would inevitably lead to more greenhouse gas emissions to aggravate climate warming in turn, the economic development in China would be in climate-resilient low-carbon pathways. The favorable ecological environment in east China is favorable for developing the green tea industry. China’s national plan for 2007–2020 had been made to promote agricultural products with geographical indications (http://www.moa.gov.cn/, accessed on 12 October 2021). In this policy document, the Southwest Yunnan province had been planned as a geographical indication production region for Pu’er tea, and some areas of the Yunnan province and Guangxi province are planned as the geographical indications production regions for black tea to promote local economic development. The farmers’ income has been greatly increased due to the optimization of agricultural structure according to the changed climate. In Guizhou province alone, it is estimated that 560,000 people have got rid of poverty by the development of the tea industry (http://www.guizhou.gov.cn/zwgk/zcfg, accessed on 12 October 2021). However, due to the limit of the method, it is difficult to qualify the influence of policy on the tea industry, and the research on the interactions of tea industry and economic system is still in the preliminary stage. Especially under the condition of future climate change, the in-depth study of policy and tea production needs to be strengthened.

5. Conclusions

Climate change is a multi-dimensional challenge for the tea industry. In this study, the potential impacts of climate change on tea climate suitability in mainland China were calculated with empirical formula using meteorological data in China mainland. Then the features of adjustment of tea production were analyzed with the tea yield record at the municipal level, which could be believed as a comprehensive adaptation to climate change under rapid economic development. Finally, a conceptual framework has been built to dissect the adaptation mechanism on the interactions among additional climatic stress, the adjustment of tea production, and economic development. New scientific understandings were obtained from the above analysis.

• Generally, there were negative impacts of climate change on tea production in Chinese mainland. An obvious feature of the changes of tea climate suitability is that the high suitable index >0.9 decreased from 45% to 32% in the Chinese mainland, corresponding with the proportion of tea production area deceasing from 49% to 33% in the South Yangtze River Region, and from 18% to 12% in the Southern China Region, respectively.
• Tea climate suitability increased in the north part of the tea production area, which is conductive to the northward expansion of tea planting. Typically, such as in the Shandong province, the north boundary of tea planting expanded from 33° N in 1987 to 35° N in 2017 to take advantage of altered climatic resources due to warming, corresponding with the proportion of tea production yield increase from 1.8% to 5.8%, and tea planting area expansion from 4.8% to 9.6% in Northern Yangtze River Region, respectively.
• A special feature of upward expansion of tea production can be seen, the vertical distribution of tea planting decreased at 100–400 m while increased in the altitude of 400–2000+ m from 1987 to 2017. The tea planting area expansion is mainly concentrated in the north and south edges of the Yun-Gui Plateau and mid-east part of the second ladder of Chinese topography, which can be imagined as seeking the optimum environment on high mountainous areas to avoid the harm on tea growth from hot temperatures.
• A westward shift is presented for the distribution of the tea yield proportion along longitude, decreasing obviously at 117–121° E while increasing significantly at 98–104° E and 107–110° E from 1987 to 2017. Meanwhile, there had been a westward movement of the tea production gravity center, consistent with the economic gravity moving trend and corresponding with the proportion of tea production yield increasing from 23% to 31%, and area expansion from 25.9% to 45.3% in the Southwest Region, respectively. The westward shift could be explained with the red line policy of arable land in eastern China, and the national planning of optimizing the agricultural structure and promoting green economic development in western China, as well as the demand for high-quality tea to be produced in the western mountainous regions to avoid hot temperature damage on the tea quality.
• A conceptual framework is built in this paper to enrich the understanding of the comprehensive interactions among the three systems of tea, climate, and economy. It is clearly demonstrated that the adjustment of the tea system is to optimize the utilization of altered climatic resources due to warming, and to avoid the damage from enhanced climatic hazards, and finally meet Chinese demand on high-quality livelihood with the economic development.

The investigation for the tea system to adapt to climate change with the meanwhile rapid economic development in this paper is still preliminary. We firstly calculated the tea climate suitability index for the potential impacts of climate change using the empirical formula, then the annual statistical tea yield record at the municipal level was employed to detect the effects from the additional climatic stress due to warming. In reality, the recorded adjustment was driven not only by climate change but also socioeconomic factors, so the temporal and spatial features of the tea system’s adjustment could be believed as a qualitative inference rather than the quantitative attribution analysis. In the conceptual framework of the adaptation mechanism for tea system in Chinese mainland, only policy and technology were considered as socioeconomic factors to drive tea system adjustment. Actually, the institutional capacity would be very important as well for the tea industry development, so the scientific understanding in the conceptual framework is still a very preliminary one. More in-depth investigation should be done to reveal the adaptation mechanism of the tea industry in China. Concrete scientific understanding on adaptation mechanism would be helpful for tea producers to effectively take advantages and avoid disadvantages due to climate change.