Variation Characteristics of Heat Resources in Liaoning Province, China in Recent 60 Years and Their Impact on Meteorological Services

To study the temporal and spatial changes of heat resources to serve agricultural production and economic development. The climate data from 1958 to 2017 were selected, and the temporal and spatial changes of heat resources in Liaoning, China were analyzed by using the method of climate diagnosis and analysis. The results show that: the southern coastal area of Liaoning has the most heat resources, the northwestern hilly area and the eastern mountainous area the least, and the central plain area in the middle distribution pattern; compared with 1958-1980, 1981-2017 ≥0˚C, ≥10˚C accumulated temperature, etc. The value line is advanced 100-160km northward. The accumulated temperature of ≥0˚C and ≥10˚C in Liaoning experienced abrupt changes in climate in 1993 and 1994, and the climate abrupt change in the southern coastal area was earlier than that in the inland. , the increase in the northwestern hilly area and the eastern mountainous area is less than that in the central plain area and the southern coastal area. The study on the impact on meteorological services found that the increase or decrease of heat resources has a significant impact on agro-meteorological services, which can prolong the growing season of crops, relatively reduce the damage of frost, improve comprehensive utilization of land, and increase crop yields; at the same time, with the increase of heat resources and the northward expansion of the isoline of accumulated temperature, the area affected by pests and diseases has expanded, which has aggravated the harm to agriculture economic burden.


Introduction
Heat resources are one of the important climatic resources and are closely related to human life. Studying the changes and spatial distribution of heat resources is of great significance to agricultural economy, the layout of agricultural planting, and the coordinated development of rural agriculture, forestry, animal husbandry and fishery. Since the 1980s, the climate has been warming significantly (Zuo et al., 2001;Ren et al., 2005). According to the research of the World Meteorological Organization (IPCC), the annual average temperature will increase by 1.1˚C to 6.4˚C by the end of the 21st century (Qin et al., 2007). The positive and negative effects of the increase in the heat resources of the climate warming on the natural world exist at the same time. Zhang et al. (2015), Qu (2010), Liu et al. (2005) and other studies believe that the positive effects of the increase in the heat resources of the climate warming can prolong the growth period of crops. The possibility of multiple cropping index also brings development space for frost season agriculture and facility agriculture. Zhou et al. (1997), Jiang et al. (2003) and other studies believe that the negative impact of climate warming on human beings is more obvious, such as exacerbating extreme meteorological disasters, destroying inherent natural ecosystems, glaciers melting, sea level rise, land salt Alkalization, and massive transpiration of water make land desertification, etc. The heat resource changes with time and space, which directly affects the plant distribution, crop maturity and planting structure in a region, and is an important factor that causes changes in the yield of agricultural products (Zhang et al., 2004;Shi et al., 2005;Cai et al., 2009). With the gradual warming of the climate, studying the changes in the temporal and spatial distribution of heat resources in Liaoning Province, China has an important reference role in the utilization of climate resources and land resources, the rational distribution of agriculture, the promotion of targeted poverty alleviation in rural areas, and the sustainable development of agriculture. Therefore, this paper selects the accumulated temperature data of ≥0˚C and ≥10˚C in the past 60 years from 1958 to 2017, and uses the climate diagnostic analysis method to analyze the temporal and spatial evolution of heat resources in Liaoning. Aiming at the zoning of heat resources in Liaoning, the research results are expected to provide decision-making basis for the development and utilization of heat resources, agro-climatic zoning and adjustment of agricultural industry structure.

Data Sources
The research data comes from the Liaoning Meteorological Information Service Center, and 46 national-level meteorological reference stations are selected to compile climate data. According to the principles of agrometeorology (Feng, 1991), the heat resources in the climate resources from 1958 to 2017 were counted, that is, the accumulated temperature of ≥0˚C and the accumulated temperature of ≥10˚C with obvious agricultural significance. ≥0˚C accumulated temperature is the sum of the daily average temperature between the beginning and the end of the day when the daily average temperature stably passes 0˚C, which is the ploughing period in agricultural production and the heat index at the beginning and end of the growth of cool plants; ≥10˚C accumulated temperature is the sum of the daily average temperature between the beginning and the end of the day when the daily average temperature is stable at 10˚C, and it is the heat index for the start and end of the rapid growth period of temperature-loving crops (Gao et al., 2004).

Analysis Methods
In order to study the regional distribution, inter-annual variation trend and mutation characteristics of heat resources in Liaoning, the Surfer mapping software (Lu & Lu, 2005) was used to draw the regional distribution of ≥0˚C accumulated temperature and ≥10˚C accumulated temperature in Liaoning Province from 1958 to 2017 and regions in different time periods. Distribution map; the variation characteristics of heat resources in Liaoning were analyzed using methods such as the univariate linear regression climate tendency rate (Wei, 2007) and the Mann-Kendall climate abrupt change test (Duan & Jiang, 2006). Computational analysis is performed with the support of the Excel program (An, 2003).

Spatial Variation of Heat Resources
The spatial variation characteristics of accumulated temperature ≥0˚C in Liaon- According to the threshold value of 200˚C·d (Feng, 1991;Gao et al., 2004;Duan & Jiang, 2006), the accumulated temperature distribution of Liaoning ≥0˚C was divided into three different regions. The first area ≥0˚C accumulated temperature ≤3750˚C·d, with an average of 3514˚C·d, is located in the Laoha River The second zone is 357˚C·d more than the first zone, the third zone is 240˚C·d more than the second zone, and the third zone is 597˚C·d more than the first zone.
For the spatial distribution of accumulated temperature ≥0˚C in three time periods from 1958 to 1980, 1981 to 1999 and 2000 to 2017 in Table 1 According to the threshold value of 250˚C·d (Feng, 1991;Gao et al., 2004;Duan & Jiang, 2006), the spatial distribution of accumulated temperature of ≥10˚C in Liaoning is divided into three regions, which are consistent with the division of accumulated temperature of ≥0˚C. The accumulated temperature of ≥10˚C in the first zone is below ≤3300˚C·d, with an average of 3076˚C·d; the accumulated temperature of ≥10˚C in the second zone is between 3300˚C·d -3600˚C·d The average temperature is 3431˚C·d during the period; the accumulated temperature of ≥10˚C in the third area is above ≥3600˚C·d, and the average is 3676˚C·d.
the second zone is 355˚C·d more than the first zone, the third zone is 245˚C·d more than the second zone, and the third zone is 600˚C·d more than the first zone.
From the spatial distribution map of accumulated temperature ≥10˚C in the three time periods of 1958-1980, 1981-2000 and 2001-2017 in

Time Distribution and Trend Change of Heat Resources
The accumulated temperature ≥0˚C in Liaoning region averaged 3826˚C·d from 1958 to 2017, the lowest value appeared in 1976 (Jianping) was 3028˚C·d, and the highest value appeared in 2014 (Anshan) was 4731˚C·d. Figure 1    , the average accumulated temperature ≥10˚C was 3562˚C·d, and after the mutation  was 3803˚C·d on average, an increase of 241˚C·d year-on-year.
Among the three heat resource climate zones, the third zone has the largest increase in accumulated temperature ≥10˚C and the earliest climate abrupt change, while the first and second zones have a relatively late increase in accumulated temperature.

Conclusions
According to the topography, topography and geographical distribution charac-

Discussion
In summary, the heat resources in Liaoning have increased significantly in the past 25 years , and the southern coast is higher than the northwestern hills and eastern mountainous areas. The isolines of accumulated temperature ≥0˚C and ≥10˚C representing the agricultural limit temperature advance 100 -160 km northward, and the accumulated temperature value increases by about 200˚C·d on average. Judging from the interannual variation of accumulated temperature, it is a fluctuating and increasing trend, not a steady increase process. For example, 2010 was a low temperature year, and the accumulated temperature value ranked seventh from the bottom in the past 60 years . It can be seen that climate change Warm instability.
In addition, for agriculture, the increase in heat resources can prolong the growing season of crops, accelerate the growth rate of crops, and relatively reduce the harm of frost. It can introduce crops with longer growth periods to increase biological yield, which is helpful for adjusting the structure of crop varieties and intercropping in the farming system. It is very beneficial to expand the facility agriculture to the north, improve the comprehensive utilization rate of land, and increase the yield per unit area. However, the negative impact brought by the increase of heat resources cannot be ignored. For example, with the increase of heat resources and the northward expansion of the isoline of accumulated temperature, the overwintering and reproduction of pests and diseases increase, and the damage area expands, etc. Harm to agriculture, the temperature rises, the evaporative power increases, and the warming and aridification become more and more serious, which increases the economic burden on The temporal and spatial distribution of heat resources is one of the important elements of agro-climatic resource zoning and agricultural resource zoning. The results of this study are greatly changed and different from the results of agroclimatic zoning studies in the 1980s, which are reasonable for the current guidance of agricultural production. The development and utilization of heat resources in Liaoning has important reference value.