New productivity forces (NPF) are crucial for advancing high-quality economic growth and achieving modernization in the Chinese context. This paper utilized Theil index, exploratory spatial-temporal data analysis framework, and spatial econometric model to assess and examine the spatial-temporal evolution pattern and influencing factors of NPF development in the Yangtze River Economic Belt (YREB) through a comprehensive evaluation index system. The results showed that: (1) The NPF advancement in the YREB increased from 2013 to 2021, however it remained relatively low. The average level of NPF in 2013 was 0.040, while in 2021 it rose to 0.101. The spatial distribution exhibited a pattern of high in the east and low in the west, high in the north and low in the south, indicating a clear regional clustering. The cities with high value points included Shanghai, Suzhou, Nanjing, Hangzhou, Chengdu, and other municipalities that are directly under the Central Governmentthat or are capital cities. The cities with low value points included Guang'an, Bazhong, Zhaotong, Dazhou, Suining, and other upstream cities. (2) There were notable disparities in the NPF progress across the entire region, with variations observed in the upper, middle, and downstream areas. These differences initially decreased and then increased. Within the regions, the disparities ranged from strong to weak in the upstream, downstream, and middle reaches, respectively. The contribution rates ranging from large to small to the overall regional development differences followed the order of downstream, middle reaches, and upper reaches. (3) The global spatial autocorrelation of NPF development was evident, with a correlation degree that fluctuated between weakening and strengthening. Both overall and local spatial structures remained relatively stable, displaying a strong spatial dependence during the evolution process, and indicating a dynamic spatial integration dominated by high cooperative elevation. (4) In terms of direct effects, the improvement of government administrative capacity had negative effects on the urban NPF development, while other factors had positive effects. In terms of spatial spillover effects, economic development and the improvement of marketization degree had positive spatial spillover effects on the NPF, while other factors had negative effects. (5) Thus, in urban construction, it is essential to establish policies and strategies to enhance the NPF growth based on local circumstances. Secondly, it is crucial to leverage regional economic development, financial restructuring, industrial upgrading, system enhancement, market reform, and government function transformation to support the NPF advancement. Lastly, it is necessary to strengthen the regional coordination mechanism, boost the impact of central cities on promoting small and medium-sized cities, and foster collaboration across many sectors to support the growth of the NPF.

Scientific and technological innovation is the fundamental driving force of green development. Clarifying the coupling coordination law of scientific and technological innovation and green development and the driving mechanism will help to realize the integration of regional innovation and green development. Based on the panel data of 41 cities in the Yangtze River Delta Region from 2010 to 2020, this paper quantitatively calculated the integrated development index of scientific and technological innovation and green development. The evolution characteristics and driving mechanism of the spatio-temporal pattern of the coupling and coordination of the two systems were analyzed. The results showed that: (1) The comprehensive index of scientific and technological innovation and green development level showed a slowly increasing trend. The green development level was generally ahead of the scientific and technological innovation level. (2) The coupling and coordination degree of the two systems showed s a growth trend on the whole. The number of coordinated cities increased from 14 in 2010 to 35 in 2020, among which Shanghai and Suzhou had entered the stage of high-quality coordination; Spatially, a "core-edge" feature was presented, with the high value area clustered on the "Z-shaped" axis, and the low value area decreased in a stepped pattern from east to west. (3) Various factors affected the degree of coupling coordination of the two systems. The main driving forces included economic driving force, social promoting force, market driving force, external competitiveness and government regulation. Based on this, there was a need for the Yangtze River Delta region to take advantage of the integrated development strategy, to implement innovation-driven development measures according to the local conditions, and to comprehensively enhance the green technology innovation capacity.

County is the basic unit of ecological civilization construction. Exploring the interactive evolution county land urbanization and carbon emissions is of great significance for promoting green and high-quality development and achieving the goal of "double carbon.". Based on DMSP-OLS and NPP-VIIRS nighttime light data, raster data and energy consumption data, this paper analyzed the interactive evolution characteristics of land urbanization and carbon emissions in Jiangxi Province from 2011 to 2020. The driving mechanism was explored with the help of spatial panel Tobit model. The results showed that: The land urbanization rate, carbon emissions and the coupling coordination degree of the two showed a continuous upward trend, but the degree was still low. The LISA agglomeration map was dominated by H-H and L-L types, and the spatial and temporal pattern was relatively stable. The H-H type was concentrated in the districts and counties under the jurisdiction of Nanchang City, Jiujiang City and Jingdezhen City, while the L-L type was mainly located in the southern mountainous and hilly areas. Among the driving factors, the level of population agglomeration, the level of economic development, the ability of government governance and the level of industrial development played a significant role in promoting the coordinated development, while the level of ecological greening demonstrated an inhibitory effect.

Revealing relationship of non-coordinated coupling between ecological carrying capacity and high-quality development is of great practical significance for promoting ecological security and human-land coordination.Based on the mechanism of non-coordinated coupling between ecological carrying capacity and high-quality development, we constructed an ecological carrying capacity assessment indicator system from three dimensions of ecological resilience, resource carrying, and environmental carrying. Additionally, we built a high-quality development assessment indicator system from five dimensions of innovation drive, coordination capability, green transformation, openness level, and shared development. The non-coordinated coupling model, exploratory spatial data analysis, standard deviation ellipse, and GM (1,1) model were applied to analyze the spatiotemporal pattern of non-coordinated coupling between ecological carrying capacity and high-quality development in the Dongting Lake area from 2004 to 2022. The trend of the changes from 2023 to 2028 was also predicted. The results showed that: (1)Non-coordinated coupling degree decreased from 0.532 3 to 0.363 1 in 2004-2022 and was predicted to be 0.309 2 in 2028. However, the coupling degree remained relatively high, and coupling and coordination were not synchronous.There existed significant spatial variations, i.e. the central region > peripheral region > edge region. (2)The non-coordinated coupling degree exhibited a significant negative global spatial autocorrelation. It was anticipated that in 2028, the coupling type would still be predominantly characterized by antagonistic non-coordinated coupling. The situation of non-coordinated coupling was expected to remain severe, with three types of spatial agglomeration, i.e. high-high, high-low, and low-high. (3)The directionality of the spatial distribution of non-coordinated coupling was dominated by the east-west direction, with the gravity center moving slowly towards the northwest of Dongting Lake. But the agglomeration and the location of the center of gravity were basically stable. (4) The edge region of Dongting Lake should be given full play to the driving and radiation roles while steadily reducing their own non-coordinated coupling.The central region should strengthen regional cooperation, give full play to the advantages of soil and water resources, and promote the concept of eco-agriculture.The peripheral region shoulddevelop special ecological industries according to the local conditions.

The resettlement work in the Three Gorges Reservoir Region has entered a new stage of post-assistance. The challenge lies in achieving "common prosperity" for resettlers and non-settlers without discrimination based on the foundation of "moving out, stabilizing, and becoming wealthy". Income and expenditure are the most critical aspects of any household's economic activity, and the level and structure of expenditure reflect the family's quality of life. Taking 119 rural resettled families in Zigui and Badong counties in the Hubei Province as examples, this article attempted to use the extended linear expenditure model (ELES model) from the perspective of expenditure-based povertyto conduct a systematic quantitative analysis of the current consumption expenditure structure of rural resettled families. The analysis showed that the situation of resettled households was continuously improving, but the resettlement consumption expenditure only met the basic needs. The basic needs such as food occupied a large proportion of all needs. The high-level demand expenditure was severely insufficient. Major diseases and other sudden temporary expenses were likely to cause the failure of long-term government support efforts. In response to the above issues, this article exploredthe optimization suggestions on post-relocation support paths in terms of strengthening temporary assistance, "precise dripping" assistance, embedding post-resettlement policies into the urban and rural social security system, increasing income and consumption "dual drive", and removing the "label" of resettlers. The research conclusions and suggestions could be used as useful reference for decision-making aiming to improve the post-relocation support policies for resettlers in the new stage and to optimize the post-assistance work in the Three Gorges Reservoir Region.

Controlling water pollution and improving water environment quality is conducive to the high-quality development of the South-to-North Water Diversion Project's Central Route. On the basis of calculating the grey water footprint of 20 water-receiving cities of the Project's Central Route, this paper calculated the grey water footprint load coefficient of each water-receiving city, analyzed the spatial-temporal distribution characteristics. The Logarithmic Mean Divisia Index model was used to decompose the driving factors. The results showed that: (1) From 2009 to 2020, the grey water footprint in water-receiving area decreased by 24.54%, and the water environment quality was improved; From the perspective of the composition of grey water footprint, agriculture accounted for the highest proportion, followed by living, and industry for the lowest. Moreover, the effective control of pollution from agricultural and industrial sources was the main reason for the overall decline of the total grey water footprint. (2) After the water supply of the Central Route, the grey water footprint load coefficient of the water-receiving area decreased to certain extent. However, the total amount of water resources still failed to meet the dilution demand of water pollutants, and hence, the water environment pressure was large. The load coefficient of grey water footprint in water-receiving cities was significantly different. The difference within the regions, especially within Henan Province, was the main source of the unbalance of grey water footprint load coefficient. (3) The capital deepening effect, resource endowment effect and economic activity effect mainly showed positive effects on the grey water footprint load coefficient, while the capital output and economic environment effects showed negative driving effects. All water-receiving cities should continue to take the road of green development and promote the sustainable utilization of water resources in the South-to-North Water Diversion Project's Central Route.

The landscape pattern in rural areas is constantly changing with urbanization and new rural development, resulting in corresponding changes in ecosystem services. Taking Lishui District of Nanjing as the research area, this study used landscape pattern index, InVEST model and geographical detector model to analyze the temporal and spatial changes of landscape pattern and ecosystem services in 2000, 2010 and 2018. The relationship between landscape pattern index and ecosystem services was identified. The following conclusions were drawn: (1) During the past 18 years, the aggregation degree of all land types in Lishui District were high. The fragmentation degree of cultivated land, forest land and construction land changed greatly, while that of other land types changed little. The overall landscape fragmentation was low and changed slightly. The patch Statistical dispersion and landscape spatial connectivity between different land use types changed inversely. (2) During the past 18 years, the level of water and soil conservation in Lishui District was stable, but the level of carbon sequestration, water production and habitat quality showed a downward trend. In terms of spatial distribution, the areas that demonstrated a high carbon sequestration, water production and habitat quality decreased, while those that had low values increased. (3) The mean fractional dimensionality index and the aggregation index were the main landscape pattern factors affecting ecosystem services in Lishui District. The correlation between the interaction of any two of the four landscape pattern indices and the three ecosystem services were higher than that of the single index effect. The combined effects of multiple factors of landscape pattern led to changes in ecosystem services.

Assessing the nitrogen (N) and phosphorus (P) contents, as well as the reabsorption characteristics of plants, proves to be a valuable approach for unveiling nutrient utilization strategies in forest trees. However, previous work on this topic is still very limited.  To address this knowledge gap, we selected seven broad-leaved tree species plantations as research objects in a subtropical homogeneous garden, including Cinnamomum platyphyllum, C.longepaniculatum, C.camphora, Toona sinensis, T.ciliate, C.japonicum and Alnus cremastogyne. We collected samples of branches and leaves in green and senescent, to determine the N and P contents and calculated reabsorption efficiency. The results showed that: (1) The N and P contents in the green leaves and senescent leaves of T. ciliate, Toona sinensis, and Alnus cremastogyne were generally higher than those in other tree species. Conversely, the N content in the green branches and senescent branches of Alnus cremastogyne was significantly higher than that of other tree species, while its P content exhibited the opposite trend. All tree branches and leaves had ratios less than 14, indicating that N was the primary limiting nutrient for the species in this area. (2) The green leaf N-to-P allometric index was 0.744, following the 2/3 rule of N-P stoichiometry, while the green branches and senescent branches and leaves deviated from this pattern. Compared to green branches and leaves, N elements in senescent branches and leaves exhibited greater variability, while their P elements followed an opposing trend. (3) The N reabsorption efficiency in branches and leaves of Alnus cremastogyne, T. ciliate and Toona sinensis was significantly lower than that of other trees (with the exception of Toona sinensis branches). Conversely, the P reabsorption efficiency in branches and leaves was higher overall compared to other trees (except for Alnus cremastogyne branches). (4) The N-to-P stoichiometry in leaves was primarily influenced by a combination of tree characteristics and soil physicochemical properties, whereas branches were  mainly affected by soil physicochemical properties. Our findings suggested that, in comparison to other native tree species, the deciduous varieties such as Alnus cremastogyne and T. ciliate be selected as reforestation species for mixed artificial forests to enhance the quality of subtropical artificial forests.

In order to provide technical supports for the planning of Water and drought prevention and control, this work studied the change of runoff and hydrological drought of the Jialing River Basin under the background of climate change. Based on the hydro-meteorological data of the Basin from 1980 to 2020, a hydrological model was developed using SWAT. Driven by four scenarios of the CMIP6 data from five meteorological models, the model was used to project future changes in runoff in the Basin under future climate change from 2021 to 2100. The results showed that (1) The SWAT model performed well in the Basin. The R2 , NES of the simulated monthly runoff at the Beibei hydrological station were both greater than 0.8, with PBIAS less than ±10; (2)The CMIP6 data after statistical downscaling based on the historical period provided reliable runoff and drought estimates; (3)A weighted multi-model ensemble could improve the simulation accuracy and reduce the uncertainty of a single CMIP6 climate model; (4) Compared with the historical period (1980-2014), the temperature, precipitation, and evapotranspiration in the Basin all showed an increasing trend, for future climate scenarios, which implied that the Basin may become more humid and hotter. The runoff showed a significant increasing trend under the SSP1-2.6 scenario, while for other scenarios, the trend was not significant. The annual average runoff was lower than the historical runoff; (5) From the perspective of SRI at the scale of 12 months, the overall trend of the Basin was becoming more humid. Hydrological droughts were reduced under the SSP1-2.6 scenario, while in the other scenarios there was a fluctuation of various drought indicators; (6) From the perspective of SRI at the scale of one month, hydrological droughts in the Basin was mainly concentrated in autumn and winter. It was shown that there existed a shift from autumn drought to winter drought, in the scenarios other than SSP5-8.5.

Soil soluble carbon and nitrogen play an important role in carbon and nitrogen cycle of urban ecosystem.In order to understand the distribution characteristics of soluble organic carbon and nitrogen in urban soil, this study took urban soil in Nanchong as the research object, and conducted relevant studies from multiple perspectives.The results showed that the contents of soil soluble organic carbon in surface urban soil was between 99.84 and 188.13 mg·kg^-1, and the contents of soil soluble organic nitrogen was between 7.57 and 75.09 mg·kg^-1, both of which decreased with soil depth.There existed significant differences in soil soluble organic carbon and nitrogen under different vegetation types, eg.the former followed an order of evergreen forest > herbaceous > deciduous forest > shrub, and the latter decreased significantly in the order of evergreen forest, deciduous forest, shrub, and herbaceous.There was a significant difference in soluble organic carbon in urban soil among the five types of green space with a decreasing order of protective green space, affiliated green space, road green space, street green space, and park green space.However, there was no significant difference in soil soluble organic nitrogen among the different types of green space.The differences in soluble organic carbon and nitrogen in the soils of green space in different urban functional areas were at extremely significant levels.The former decreased in the order of cultural and educational area, commercial area, industrial area, and residential area, while the latter followed an order of cultural and educational area > commercial area > residential area > industrial area.The longer the urban soil was used, the higher the contents of soluble organic carbon and nitrogen in the soil, however, these differences were not significant through the years.The differences in soluble organic carbon and nitrogen in urban soil under different vegetation types, green space types, functional zones, and utilization years were the consequence of the interaction between the natural and human factors.

On the basis of systematic analysis of the non-linear impact of agglomeration of agricultural product processing industry on environmental pollution and the regulatory mechanism of digital economy, this paper used the panel data of 11 provinces and cities in the Yangtze River Economic Belt from 2010 to 2020 to measure the level of agglomeration of agricultural industry and environmental pollution index, by the entropy method and location entropy index. The panel fixed effect model was used to empirically test the impact mechanism of agglomeration of agricultural industry and the moderating effect of the digital economy. The research results indicated that there was a significant "inverted U-shaped" curve relationship between agglomeration of agricultural industry and environmental pollution. The digital economy had a significant inhibitory and regulatory effect on the process of agglomeration of agricultural industry. The regional heterogeneity test showed that the role of agglomeration in environmental pollution in the middle reaches of the Yangtze River was on the left side of the "inverted U-shaped" curve, indicating that the improvement of agglomeration was exacerbating environmental pollution. The role of agglomeration in downstream areas shifted to the right side of the "inverted U-shaped" curve, indicating an inhibitory effect on environmental pollution. However, the development of agricultural industry in upstream areas was still relatively weak, The promoting effect on environmental pollution had not yet emerged; The digital economy in the upper reaches of the Yangtze River played a significant inhibitory role in the process of agglomeration of agricultural industry, with a significant regulatory effect, while the regulatory effect in the middle and lower reaches was not significant.In view of this, we should vigorously develop the primary and intensive processing of agricultural products, accelerate the ecological and intensive development of agricultural products processing industry, and promote the ecological civilization through digital upgrading.

In the context of global warming, the frequency, intensity, and duration of heat waves are increasing, which seriously threatens the population health and socioeconomic development.How to identify the frequency belts of heat waves and clarify the potential population exposure risk of heat waves has been becoming a hot topic of academic concern.According to meteorological station data and demographic data, we used heat wave index to measure the severity of heat waves, and combined the heat wave days defined by wet bulb global temperature and population census data to construct the population exposure risk model of heat waveWe revealed the spatial-temporal evolution characteristics of heat waves and population exposure risk at the county scale in the Yangtze River economic Belt from 1964 to 2021.The results showed that: (1)The cumulative heat wave index in the Yangtze River Economic Belt showed a trend of first decreasing and then significantly increasing, with a spatially decreasing feature from the southeast to the northwest, and has an obvious spatial agglomeration.(2)In the past 60 years, the population exposure risk of heat waves in the Yangtze River Economic Belt increased by 962%, and the spatial distribution pattern was "one low and three high", which implied that the western region was low, while the Chengdu-Chongqing urban agglomeration, core areas in the middle and lower reaches of the Yangtze River Economic Belt were high.The agglomeration mode of population exposure risk of heat waves mainly presented an overall agglomeration, with local spatial agglomeration characteristics consisting of high exposure risk districts and counties and low exposure risk districts and counties.(3)Population factors and climate factors played a key role in changes in population high temperature exposure riskAfter 2000, the role of climate factors gradually strengthened, with the contribution rate increasing from about 50% to about 80%From a regional scale, population factors and climate factors contributed the most to the change of population exposure risk of heat waves in the middle and lower reaches.

Urban parks can play the role of “cooling islands”. A comprehensive understanding of the cooling benefits of urban parks can effectively alleviate the urban heat island effect and improve the adaptability to climate change. Taking 25 urban parks in Nanjing city as the research object, this paper conducted a comprehensive study on the cooling benefits of parks with two maximum impact indicators of park cooling area, cooling efficiency and two cumulative impact indicators of park cooling intensity and cooling gradient. The results showed that: (1) The urban park had a significant cooling effect, by reducing the ambient temperature by 0.16 ℃-2.28 ℃. (2) The correlation analysis showed that the park cooling area was significantly positively correlated with PP, PA and NDVI, and the park cooling efficiency was significantly negatively correlated with PP, PA and LSI. The cooling intensity and gradient were positively correlated with NDVI, PP and PA. The correlation between the four cooling indexes and MNDWI was not significant. (3) Different cooling benefits were shown for different types of parks. Special parks or community parks were better fitted to the areas of tight land use. Construction of comprehensive parks should take more consideration of complex boundary conditions and vegetation conditions to maximize the cooling benefits. This study was expected to guide the construction and optimization of urban parks in the future, to effectively respond to the urban heat island effect.

Terrestrial ecosystem carbon uptake is an important parameter to measure the surface ecology, and also a key variable of global carbon cycle. Chenzhou City of Hunan Province was selected as the study area, which is one of low-carbon city pilots and the Innovation Demonstration Zones for National Sustainable Development. Combined with multi-source data, Geostatistical Model of Soil Respiration (GSMSR), trend analysis, GeoDetector and residual analysis were used to reveal the spatial and temporal variation characteristics and driving factors of Net ecosystem productivity systematically. The results showed that: (1) Temporally, Chenzhou was a carbon pool from 2001 to 2020, with an average carbon sequestration of 5.943×106 T Ca^-1, mean value of 310.351 g Cm^-2 and an average rate of increase of 2.066 g Cm^-2a^-1. (2) Spatially, NEP changes was obvious, with higher NEP in the west and north and lower NEP in the east and south. NEP of different land types varied noticeably, among which forest was the highest (328.10 g Cm^-2), followed by grassland (318.65 g Cm^-2) and farmland (257.51 g Cm^-2). (3) The driving mechanisms of carbon fluxes in terrestrial ecosystems were diverse. NEP was positively correlated with temperature, sunshine hours, relative humidity and elevation. On the contrary, NEP was negatively correlated with precipitation and net surface radiation. In addition, the effect of two-factors interaction on NEP was obviously higher than that of the single factor. (4) Natural factors dominated the change of NEP, with an average contribution of 95.896%, while the contribution rate of land use was about 4.104%. However, in areas with intense human activities such as urban fringe, the contribution rate of land use increased significantly, with an average rate of 59.761%. The above results can help accurately grasp the spatio-temporal characteristics of the carbon sink effects of regional terrestrial ecosystems and the intrinsic driving mechanisms. Outcomes of this study provide a scientific basis for regional ecosystem management and sustainable development.

The plantation production in the mountainous sub-watersheds of the Three Gorges Reservoir Area is distributed in units of blocks. The plantation blocks can be used as the basic unit to implement non-point source pollution control. The risk assessment of non-point pollution in mountainous small watersheds includes four sub-processes: block division, risk identification, risk assessment, risk prevention and control. By constructing a risk evaluation model focusing on the screening and quantification of risk factors, and by establishing a supportive evaluation index system in the dimensions of source factors and migration factors, the risk assessment of plantation non-point pollution was carried out and graded. The targeted control and management of plantation non-point pollution was proposed in three aspects: source control, process control and end control, based on the influence of single index. Based on the influencing degree of single index, we proposed several targeted control measures for plantation non-point pollution control in three aspects including source control, process control and end control, to guide an improved management strategy.

The change in lake ice phenology is a sensitive indicator reflecting climate change.Lake ice phenology over the QinghaiXizang Plateau (QXP) is however rarely observed and recorded.The numerous lakes in the QTP have significant functions within the climate system, influencing the balance of water and energy in the region, and are additionally viewed as key indicators of local climate change.Based on lake ice phenology dataset from 126 lakes on the QXP and meteorological data, this article analyzes the changes of lake ice phenology and influencing factors in the QXP from 1978 to 2016.Some conclusions can be drawn as follows.(1) The freezeup start (FUS) and freezeup end (FUE) of lake ice appears in midNovember, and midDecember, respectively.The time of breakup start (BUS) and breakup end (BUE) of lake ice is relatively dispersed, and appears in early April and early June, respectively.The average freezing duration (IceD, between BUE and FUS), complete freezing duration (CID, between BUS and FUE) were 168 days and 114 days, respectively.(2) The spatial difference of the change trend of the lake ice phenology in the QXP is relatively significant.The freezing time, melting time and duration of the ice period of most lakes show an obvious trend of advancing, delaying and shortening, while some lakes have no obvious trend of change.(3) The spatial distribution characteristics of lake ice phenology in the QXP have obvious regional differences, but the spatial distribution characteristics of each index are relatively similar, that is, there is a spatial distribution pattern of early lake ice formation date, delayed ice melting date, and extended ice period duration from the south to the north.(4) The spatiotemporal variability of lake ice phenology is the result of the combined effects of climate change and lake conditions.Temperature is a key factor affecting lake ice phenology, while precipitation, latitude, and lake area are the main factors influencing the dates of iceon and iceoff.On the other hand, the dates of beginning and complete ice melting are mainly influenced by wind speed, latitude, and altitude.Wind speed, precipitation, latitude, and altitude are the main factors affecting the duration of the ice period and complete ice cover.In summary, under the background of global warming, the formation, melting, and duration of the ice period in the lakes on the QXP are undergoing significant changes.

With the accelerated pace of global climate change, the frequent occurrence of extreme weather events such as high temperatures, heavy rains, droughts and low temperatures cause an increased frequency of agro-meteorological disasters, which  poses a huge challenge to the stable supply of grain production. Based on the daily temperature, rainfall meteorological and agricultural production data of 28 cities and municipalities in the Huaihe River Ecological Economic Belt from 2001 to 2020, this paper adopted the linear trend estimation and spatial Durbin model to study the extreme weather variations and the impacts on grain production. The results showed that: (1) The number of extremely high-temperature days (SU35) showed an increasing trend, the number of extremely low-temperature days (FD5) showed a decreasing trend, and the inter-annual tendency rate for SU35 and FD5 were 1.85 days/10a and -2.24 days/10a, respectively. However, the inter-annual trends of rainstorm days (R50) and the longest continuous days without precipitation (CDD) were not significant. The days of SU35 was higher in the central and western regions, while the days of FD5 was higher in the northern regions. The days of RD50 showed a decreasing trend from the east to the central and western regions, and then to the northern regions, while the days of CDD showed the opposite trend. (2) Extreme weather had significantly negative impacts on grain production. 1% increase in the days of FD5, SU35, CDD, and R50, resulted in a decrease of 0.069%, 0.021%, 0.018%, and 0.008% in grain production, respectively. (3) The impact of extreme weather on grain production was regionally heterogeneous. Extreme weather mainly affected grain production in the central and western regions and the northern region, while this impact in the eastern region was not significant. In the future, grain yields stability in the Huaihe River Ecological Economic Belt can be maintained through measures of cultivating new crop varieties that are resistant to drought and flooding, improving the ability to monitor extreme weather changes, strengthening synergistic linkages among region governments, and continuing to maintain high-standard farmland.

Reference crop evapotranspiration (ET0) is a basic parameter for formulating irrigation systems and a necessary variable for drought assessment. In order to comprehensively explore the temporal and spatial variation and the main causing factors of ET0 in the humid subtropical regions of Central and Southern China, we calculated ET0 using Penman-Monteith method. The Mann-Kendall test, Pettitt, sliding t and cumulative anomaly mutation method were used to explore the variation of meteorological elements and ET0. The Pearson correlation analysis was applied for the analysis of driving factors of ET0 based on the daily meteorological data of 246 stations in the region, together with atmospheric circulation indices from 1961 to 2020. Results indicated that Tmean, Tmin, and Tmax showed an upward trend (0.028, 0.029, 0.019 ℃/a), while n, us, and RHmean showed a fluctuating downward trend (-0.018 h/year, -0.005 m/(s·year), and -0.052 %/year). The mutation points of meteorological elements in sequence were in 1996, 1997, 1996, 1980 and 1988, 1981 and 1988, 2002.The overall trend of ET0 decreased with a tendency rate of -0.45 mm/year. A significant decrease in ET0 in summer would lead to a decrease in annual ET0. The spatial distribution of ET0 at the annual and seasonal scales was relatively complex. The correlation coefficients between ET0 and NAHAI, NANRP, APVA, NAPVA, PPVI, AEPVI and AO, AAO, NAO, EM, TSN, SOI were -0.86~0.85 and -0.07~0.09, respectively. The decline trend of ET0 was reflected in time and space, with a close relation to the changes of meteorological elements. The Pacific polar vortex intensity index (PPVI) was regarded as the most relevant factor affecting the change of ET0. The above conclusions are of great significance to provide scientific support of formulating irrigation systems.