Background Of Climate Warming Research Articles

Rapid shifts in pond sediment microbiota in response to high ambient temperature in a water-sediment microcosm.

Unlike the extensive research on the response of soil microorganisms to high ambient temperature (HTA), the response of sediment microorganisms to HTA remains unclear. Understanding the response of sediment microorganisms to HTA is important to forecast their impacts on ecosystems and climate warming under projected climate change scenarios. Against the background of climate warming and frequent high ambient temperatures in summer, we conducted a laboratory incubation experiment to clarify the unique assembly characteristics of pond sediment bacterial communities at different temperatures (4, 10, 15, 25, 30 and 35°C). The results showed that the structure and function of the microbial community in pond sediments at 35°C were different from those under other temperatures; the microbial community structure at 35°C had the most large modules and an average module size. Temperature and dissolved oxygen influenced the microbial community network modularity. The CO2 emission rates of pond sediments at 35°C were significantly higher than those at other temperatures. At 35°C, heterogeneous selection was the most important assembly process. Additionally, warming altered the microbial network structure and ecosystem functioning but not the microbial diversity or community composition, which may be related to horizontal gene transfer. Revealing the rapid response of pond sediment microorganisms to HTA is important for identifying their role in nutrient cycling and assessing the ecological impacts of climate warming and high ambient temperatures on inland water sediments.

Dry Climate Filters Gymnosperms but Not Angiosperms through Seed Mass

In the context of climate change in recent years, the fate of woody plant seed has an important impact on forest regeneration. Seed mass is an important reproductive strategy of plants. There are huge differences between gymnosperms (mainly conifers) and angiosperms (flowering plants) in terms of reproduction and hydraulic strategies; however, little is known about changes in seed mass along climate aridity gradients between taxonomical groups such as gymnosperms and angiosperms, which limit our understanding on the fate of woody plants under warming-induced climate drying. We collected seed mass data from a total of 2575 woody plant individuals, including 145 species of gymnosperms and 1487 species of angiosperms, across different climatic zones in China. We mapped the distribution pattern of gymnosperm and angiosperm seed mass in China, with angiosperms being maximal near the 400 mm iso-precipitation line. Our phylogenetic analysis results show that seed mass exhibited significant phylogenic signals (p < 0.001) and was also strongly influenced by functional traits (growth type, fruit type, and dispersal mode). The results of linear regression and hierarchical partitioning analysis showed a stronger correlation between gymnosperm seed mass and environmental factors, and a higher independent aridity index effect on gymnosperm seed mass than angiosperm seed mass. The different patterns of seed mass along a climate aridity gradient between gymnosperms and angiosperms may point to different future fates for these two taxonomic groups, while the higher sensitivity of gymnosperm seed mass to environmental conditions may reduce their reproductive rate under the background of climate warming and drying.

Carbon Dioxide Emission Equivalent Analysis of Water Resource Behaviors: Determination and Application of CEEA Function Table

To achieve the global temperature control target under the background of climate warming, it is necessary to establish a systematic carbon dioxide (CO2) emission accounting method system in the field of water resources as soon as possible. In this study, the carbon dioxide emission equivalent analysis (CEEA) method for different water resource behaviors (WRBs) is proposed from four dimensions of development, allocation, utilization, and protection, and a function table of CEEA (FT-CEEA) for WRBs is constructed. The FT-CEEA includes CEEA formulae for 16 aspects in four categories of water resource development, allocation, utilization, and protection. The CEEA method is applied to 31 provinces in China. The results reveal that: (1) There are significant spatial differences in the carbon dioxide emission equivalent (CEE) of WRBs in different provinces of China under the influence of various factors such as water supply structure and natural conditions. (2) Reservoir storage, tap water allocation, and wastewater treatment are the main contributors to CEE in the categories of water resource development, allocation, and protection behaviors, respectively. (3) The water resource utilization behavior category has the most significant CO2 emission and absorption effects, and industrial and domestic water utilization behaviors are the main sources of emission effects. (4) The overall CO2 emission effect of WRBs is greater than the absorption effect. Measures such as increasing the proportion of hydroelectric power generation, improving ecological water security capacity, and strengthening the level of wastewater treatment and reclaimed water reuse are effective ways to promote the goal of carbon neutrality in the field of water resources.

Phenological changes in the wintering end date of Pelophylax ridibundus (Pallas, 1771) (Ranidae, Anura) in the Medveditsa river valley (Saratov region) under conditions of climate transformation

The time series of dates of the end of wintering and the beginning of spawning migrations of the marsh frog in the valley of the middle reaches of the Medveditsa river (Don basin, Saratov region) was analyzed. It has been established that in the period from 1892 to 2021, the phenological norm of this phase of the annual cycle shifted to earlier dates by an average of 6 days (from May 2 to April 26) against the background of climate warming. Possible consequences of this transformation of the spring phenology of anurans in connection with the changes established are discussed. Continued monitoring of phenological changes in the spring phase of the annual cycle is required to form a forecast of the population dynamics of this anuran species and the scientific basis for their conservation.

Characteristics of Rainstorm Intensity and Its Future Risk Estimation in the Upstream of Yellow River Basin

Under the background of climate warming, the occurrence of extreme events upstream of the Yellow River Basin has increased significantly. Extreme precipitation tends to be even more intense, and occurs more frequently. The impacts of various extreme weather and climate events in the basin have become increasingly complex, which is increasingly difficult to cope with and affects the basin’s long-term stability and ecological security. Based on the daily precipitation data of 33 meteorological stations in the upper reaches of the Yellow River Basin from 1961 to 2021, this paper analyzes the characteristics of rainstorm intensity. Moreover, combined with the simulation results of 10 global climate models of the Coupled Model Intercomparison Project (CMIP6) and the social and economic prediction data from SSPs, it analyzes the possible changes of rainstorm disaster risk in the upper reaches of the Yellow River Basin in the 21st century, under the three emission scenarios of SSP126, SSP245, and SSP370. The results show that the precipitation in the upstream area of the Yellow River Basin is increasing at a rate of 8.1 mm per 10 years, and the number of rainstorm processes and their indicators is increasing, which indicates an increase in the extremeness of precipitation; the rainstorm process intensity index shows an increasing trend, especially in the northeast region with a concentrated population and economy, where the rainstorm process intensity index is high; it is estimated that the number of rainstorm days in low-, medium-, and high-risk scenarios will increase, which leads to an increase in the social risk by at least 60% by around 2050 (2036–2065); with the increasing disaster risk, the population exposure to rainstorm disasters is also on the rise. If no measures are taken, the population exposure will increase to 7.316 million people per day by around 2050, increasing by more than double, especially in the northeast. This study shows that, with the increasing rainstorm disaster risk and population exposure in the upper reaches of the Yellow River Basin, relevant measures need to be taken to ensure the safety of people’s lives and property.

High Spatial and Temporal Resolution Methane Emissions Inventory from Terrestrial Ecosystems in China, 2010–2020

Methane (CH4) is not only an important greenhouse gas next to carbon dioxide (CO2), but also an important chemically active gas. Under the background of climate warming, the measurement of CH4 emissions from terrestrial ecosystems in China is not only very important for exploring the impact of climate change on the ecological environment, but also of great significance for the in-depth study of ecosystem carbon cycling. In this study, we used the Emission-Factor Approach to estimate CH4 emissions from terrestrial ecosystems in China from 2010–2020 and explored the spatial distribution characteristics of CH4 emissions. The estimated CH4 emission inventory of terrestrial ecosystems with 0.05 spatial resolution on monthly time scale is in good agreement with the results of the latest emission inventory. It is estimated that CH4 emissions from terrestrial ecosystems in China are 19.955 Tg yr−1, including 18.61% (3.713 Tg yr−1) from vegetation, 21.47% (4.285 Tg yr−1) from wetlands and 59.92% (11.957 Tg yr−1) from paddy fields, with the largest contribution from paddy fields. The regions with high CH4 emissions from terrestrial ecosystems in China are mainly located in the central, eastern and southeastern regions of China, and show a decreasing trend from southeast to northwest. The CH4 emission from terrestrial ecosystems in China has obvious seasonal variation characteristics, with the lowest emission in January (0.248 Tg month−1) and the highest emission in August (3.602 Tg month−1). The emissions are high in summer and autumn and low in spring and winter. CH4 emissions from terrestrial ecosystems in China showed an overall upward trend from 2010–2020.

Evaluation and prediction of engineering construction suitability in the China–Mongolia–Russia economic corridor

It is proposed to build a high-speed railway through the China‒Mongolia‒Russia economic corridor (CMREC) which runs from Beijing to Moscow via Mongolia. However, the frozen ground in this corridor has great impacts on the infrastructure stability, especially under the background of climate warming and permafrost degradation. Based on the Bayesian Network Model (BNM), this study evaluates the suitability for engineering construction in the CMREC, by using 21 factors in five aspects of terrain, climate, ecology, soil, and frozen-ground thermal stability. The results showed that the corridor of Mongolia's Gobi and Inner Mongolia in China is suitable for engineering construction, and the corridor in Amur, Russia near the northern part of Northeast China is also suitable due to cold and stable permafrost overlaying by a thin active layer. However, the corridor near Petropavlovsk in Kazakhstan and Omsk in Russia is not suitable for engineering construction because of low freezing index and ecological vulnerability. Furthermore, the sensitivity analysis of influence factors indicates that the thermal stability of frozen ground has the greatest impact on the suitability of engineering construction. These conclusions can provide a reference basis for the future engineering planning, construction and risk assessment.

Multi-depth evolution characteristics of soil moisture over the Tibetan Plateau in the past 70 years using reanalysis products

Soil moisture (SM) is a crucial component of the hydrological cycle. Both the spatial–temporal distribution and the variation characteristics of SM are effective indicators of regional land surface water resource homogeneity and heterogeneity. With consideration of the crucial role of the Tibetan Plateau (TP) in the hydrological process in Asia, this study investigated the fluctuation of multi-depth soil moisture across the TP during 1950–2020 on a monthly scale against the background of global warming by using ERA5 reanalysis datasets. The correlation and potential causality between soil moisture and associated driving factors were explored. Our research revealed that the soil moisture across the TP shows a slight wetting trend at 0–100 cm depth for the past 70 years against the background of climate warming and increasing precipitation. Additionally, the wetting region (variation trend ≥ 0.005 m3/m3 per decade) had sufficient water supplementation from precipitation and a mild soil temperature increase. By comparison, there is a noteworthy warming tendency and falling precipitation in the sparsely distributed drying region (variation trend ≤ −0.005 m3/m3 per decade). In terms of vertical variation features, the temporal dynamic fluctuation of soil moisture and soil temperature evidently decreases as the depth increases, suggesting high sensitivity of the surface layer soil to atmospheric conditions. Precipitation and snowmelt preliminarily proved to be the dominant drivers causing spatial and temporal variations in soil moisture (occupying over 70% of the TP region), and bidirectional causality (ranging between 15.52% and 50.56%) was found between soil moisture and these two parameters. In summary, this study explored the spatial–temporal fluctuation in the evolutionary characteristics of SM, which is expected to advance our understanding of soil moisture dynamics under the conditions of climate change across the TP.

Meta-analysis of the correlation between vegetation and precipitation in the temperate deserts of the Northern Hemisphere over the last 40 years

Temperate desert vegetation (TDV) is subjected to long-term seasonal or intermittent water stress, and precipitation is the main water source for desert vegetation. However, due to the limitations of existing research methods, data resources and spatiotemporal differences, universal conclusions and benchmark references at large spatial scales under the background of climate warming have been lacking in recent decades. In a systematic review, we evaluated primary studies and comprehensively analyzed the pooled correlation (pooled r (Pr)) between precipitation and TDV (P-TDV) in the Northern Hemisphere (NH) over the past 40 years by using a meta-analysis method to explore the monthly scale response pattern and heterogeneity pattern and to reveal the key TDV growth period under drought stress at a large spatial scale. The results showed the following. (1) In the mean state, the correlation between precipitation and TDV was at a moderate level in the NH over the last 40 years (Pr = 0.31). The spring Pr value was lowest, and the results were nonsignificant (p > 0.05). The highest Pr value was 0.40, and this value appeared in summer, followed by a value of 0.22 in autumn; the strongest relationship was found in June (Pr = 0.56). (2) The Pr values of TDV and precipitation with 1- and 2-month lag times were 0.34 and 0.31, respectively; these values were higher than those derived using lag times longer than 2 months. The statistical results were all significant and reflected a moderate correlation level. The above conclusions showed that TDV growth has the strongest demand for water in June and that spring drought conditions may have been one of the main stress factors affecting the growth of desert vegetation at the intra-annual scale in the northern temperate zone over the past 40 years.

Effects of High Temperature on Quality of Japonica Rice at Early and Middle Heading Stage under Different Planting Modes

With the intensified greenhouse effect, high temperature has gradually become an adverse factor in growth of rice. Transplanting (TP) and direct seeding (DS) are two common rice planting modes. At present, the response of rice quality to high temperature under different planting modes and at different growth stages have not yet to be identified. Therefore, in our study, high-quality japonica rice Nanjing 9108 (NJ9108) and Nanjing 46 (NJ46) were cultivated through TP and DS under the setting of normal temperature (NT), moderate heating (2 °C higher than NT, MT) and extreme high temperature (5 °C higher than NT, HT) at early heading stage (EH, 0–14 d after heading) and middle heading stage (MH, 15–28 d after heading) respectively. The results showed that better resistance to high temperature was achieved with TP. The head rice rate, gel consistency and amylose content of rice decreased with the increase of temperature, while chalkiness degree, setback viscosity, average particle size, crystallinity and gelatinization temperature were opposite. Compared with high temperature at MH, the effect of EH on rice quality was more significant. In terms of varieties, the resistance to high temperature was stronger for NJ46 relative to NJ9108, mainly because NJ46 has a longer growth period and can avoid the stress of high temperature at heading stage. Above all, our results suggest that NJ46 could have better resistance with a longer growth period through TP under background of climate warming.

Spatial patterns and drivers of forest ecological functions in a typical soil-rock mountain area of northern China along an elevational gradient

Because of the gradient effect of various environmental factors, mountain areas provide favorable conditions for studying the responses of vegetation to global climate change. As a crucial part of the soil-rock mountain area in northern China, the Beijing mountain area is an important ecological barrier to the capital of China. We investigated the main ecological functions of the forest ecosystem in a typical soil-rock mountain area. Taking elevation and slope direction as the spatial quantity, the spatial heterogeneity of the main ecological functions of the forest ecosystem at elevations from 150 to 1,050m were analyzed. The five functions were mostly intercorrelated; the highest correlation was found between water yield and biodiversity. The most important ecological element was soil moisture, and the high content of soil gravel limited water availability. Against the background of climate warming and drying in North China, water yield and diversity may continue to decreased in the near future, further enhancing ecological pressure. Therefore, we suggest that the afforestation density in this area should not exceed 1,500 trees/ha, and the stand structure should be optimized to obtain a canopy closure of less than 0.6, thereby ensuring sustainable forest development.

Regeneration of Pinus sibirica Du Tour in the Mountain Tundra of the Northern Urals against the Background of Climate Warming

Climate is one of the key drivers of the plant community’s structure and trends. However, the regional vegetation-climate features in the ecotone have not yet been sufficiently studied. The aim of the research is to study features of Pinus sibirica Du Tour germination, survival, and growth in the mountain tundra of the Northern Urals against the background of a changing climate. The following research objectives were set: To determine the abundance and age structure of P. sibirica undergrowth on the mountain tundra plateau, identify the features of P. sibirica growth in the mountain tundra, and examine the correlation between the multi-year air temperature pattern, precipitation, and P. sibirica seedling emergence. A detailed study of the Pinus sibirica natural regeneration in the mountain stony shrub-moss-lichen tundra area at an altitude of 1010–1040 m above sea level on the Tri Bugra mountain massif plateau (59°30′ N, 59°15′ E) in the Northern Urals (Russia) has been conducted. The research involved the period between 1965 and 2017. Woody plant undergrowth was considered in 30 plots, 5 × 5 m in size. The first generations were recorded from 1967–1969. The regeneration has become regular since 1978 and its intensity has been increasing since then. Climate warming is driving these processes. Correlation analysis revealed significant relationships between the number of Pinus sibirica seedlings and the minimum temperature in August and September of the current year, the minimum temperatures in May, June, and November of the previous year, the maximum temperatures in May and August of the current year, and precipitation in March of both the current and previous years. However, the young tree growth rate remains low to date (the height at an age of 45–50 years is approximately 114 ± 8.8 cm). At the same time, its open crowns are rare single lateral shoots. The length of the side shoots exceeds its height by 4–5 times, and the length of the lateral roots exceeds its height by 1.2–1.5 times. This is an indicator of the extreme conditions for this tree species. With the current rates of climate warming and the Pinus sibirica tree growth trends, the revealed relationships allow for the prediction that in 20–25 years, the mountain tundra in the studied Northern Urals plateau could develop underground-closed forest communities with a certain forest relationship. The research results are of theoretical importance for clarifying the forest-tundra ecotone concept. From a practical point of view, the revealed relationship can be used to predict the trend in forest ecosystem formation in the mountain forest-tundra ecotone.

Quantifying Vegetation Stability under Drought in the Middle Reaches of Yellow River Basin, China

Under the background of climate warming, the increase in the frequency and severity of drought leads to vegetation facing severe challenges. A comprehensive and systematic assessment of the stability of vegetation under drought stress in the middle reaches of Yellow River basin (MRYRB) will help to grasp the characteristics of vegetation response to drought. In this study, the normalized difference vegetation index (NDVI) was used to achieve quantitative and qualitative assessments of vegetation stability to drought, and the smoothed monthly standardized precipitation evapotranspiration index (SPEI) was used to describe the characteristics of drought events in 2005/2006 and identified vegetation stability parameters using a standardized anomaly of NDVI across space, which included the resistance duration, resilience duration, drought threshold, and lag time. Vegetation was dominated by less resistance and less resilience. The 2005/2006 drought event affected most of the study area, and vegetation growth was inhibited. The duration of vegetation resistance over 100 days accounted for 65.7%, and vegetation in 89.4% of the regions could return to normal within 100 days. The drought threshold of vegetation gradually decreased from northwest to southeast, and the lag time was mainly concentrated from 1 to 3 months. These findings contribute to a better understanding of the effects of drought on the environment, as well as scientific references for reducing ecological, economic, and social losses in future droughts, and promoting ecological environmental governance and high-quality development in the MRYRB.

Variation characteristics of normalized difference vegetation index in Northwestern Sichuan Plateau and its response to extreme climate during 2001-2020

The northwestern Sichuan Plateau is a typical eco-climate sensitive area, where vegetation condition is closely related to climate change. We used the MODIS-NDVI and the meteorological data during 2001-2020 to investigate the change trend of normalized difference vegetation index (NDVI) and the mechanism underlying its responses to climate factors in the growing season of northwestern Sichuan Plateau by using the methods of maximum value composite, geodetector model, trend analysis, and correlation analysis. The results showed that vegetation coverage in northwestern Sichuan Plateau was overall good during the study period. 86.8% of the regional vegetation was stable, 12.6% of the regional NDVI was weakly and continuously increasing, and 0.6% of the regional NDVI was decreasing. The ecological environment of the whole region exhibited a steady and good development trend. The vegetation coverage in the study area exhibited apparent spatial variation with a general tendency of increase from southwest to northeast, as well as obvious variation with elevation. The NDVI rose with elevation below 1350 m, varied slightly from 1350 to 3650 m, dropped from 3650 to 5900 m, with a rapid drop between 4750 to 5900 m. There was almost no vegetation above 5900 m. The NDVI of northwestern Sichuan Plateau was affected by the interactions of natural factors. Thermal factors were the dominant climate factors, including monthly maximum value of daily maximum temperature, monthly minimum value of daily minimum temperature, growing season length, annual mean temperature, mean temperature over the growing season. All these factors were positively correlated with NDVI excepted for monthly maximum value of daily maximum temperature. The response of NDVI to temperature index was higher than that of precipitation index. Under the background of climate warming, extreme temperature warming index played a major role in promoting the growth and improvement of vegetation in northwestern Sichuan Plateau, especially in high-altitude areas.

A New Automatic Extraction Method for Glaciers on the Tibetan Plateau under Clouds, Shadows and Snow Cover

Accurately assessing the dynamic changes of glaciers under the background of climate warming is of great significance for taking scientific countermeasures to cope with climate change. Aiming at the difficulties of glacier identification, such as mountain and cloud shadow, cloud cover and seasonal snow cover in high altitude areas, this paper proposes a reflectivity difference index for identifying glaciers in shadow and glacial lakes and a multi-temporal minimum band ratio index for reducing the influence of snow cover. It establishes a new large-scale glacier extraction method (so-called Double RF) based on the random forest algorithm of Google Earth Engine (GEE) and applies it to the Tibetan Plateau. The verification results based on 30% sample points show that overall accuracies of the first and second classification of 96.04% and 90.75%, respectively, and Kappa coefficients of 0.92 and 0.83, respectively. Compared with the real glacier dataset, the percentage of correctly extracted glacier area of the total area of glacier dataset (PGD) was 84.07%, and the percentage of correctly extracted glacier area of the total area of extracted glacier (PGE) was 89.06%; the harmonic mean (HM) of the two was 86.49%. The extraction results were superior to the commonly used glacier extraction methods: the band ratio method based on median composite image (Median_Band) (HM = 79.47%), the band ratio method based on minimum composite image (Min_Band) (HM = 81.19%), the normalized difference snow cover index method based on median composite image (Median_NDSI) (HM = 83.48%), the normalized difference snow cover index method based on minimum composite image (Min_NDSI) (HM = 84.08%), the random forest method based on median composite image (Median_RF) (HM = 83.87%) and the random forest method based on minimum composite image (Min_RF) (HM = 85.36%). The new glacier extraction method constructed in this study could significantly improve the identification accuracy of glaciers under the influences of shadow, snow cover, cloud cover and debris. This study provides technical support for obtaining long-term glacier distribution data on the Tibetan Plateau and revealing the impact of climate warming on glaciers on the Tibetan Plateau.

The Outburst of a Lake and Its Impacts on Redistribution of Surface Water Bodies in High-Altitude Permafrost Region

The lakes distributed in permafrost areas on the Tibetan Plateau (TP) have been experiencing significant changes during the past few decades as a result of the climate warming and regional wetting. In September 2011, an outburst occurred on an endorheic lake (Zonag Lake) in the interior of the TP, which caused the spatial expansion of three downstream lakes (Kusai Lake, Haidingnor Lake and Salt Lake) and modified the four independent lake catchments to one basin. In this study, we investigate the changes in surficial areas and water volumes of the outburst lake and related downstream water bodies 10 years after the outburst. Based on the meteorological and satellite data, the reasons for the expansion of downstream lakes were analyzed. Additionally, the importance of the permafrost layer in determining hydrological process on the TP and the influence of from lake expansion on engineering infrastructures were discussed. The results in this study showed the downstream lakes increased both in area and volume after the outburst of the headwater. Meanwhile, we hope to provide a reference about surface water changes and permafrost degradation for the management of lake overflow and flood on the TP in the background of climate warming and wetting.

Effect of agricultural meteorological disasters on the production corn in the Northeast China

<p id="C2">Agricultural meteorological disasters are the main natural disasters that threaten grain output. In recent years, with climate change, agricultural meteorological disasters are more and more frequent, and their impact on northeast China is also increasing. In this paper, to make better use of advantages and avoid disadvantages in actual production to ensure food production safety, spring corn in three provinces of northeast China was taken as the research object to discuss the impact of major agricultural meteorological disasters in this region on spring corn yield and its degree. The results showed that agricultural meteorological disasters could explain about 50% of the fluctuation of spring corn yield in Northeast China, and the main agricultural meteorological disasters that affected spring corn production had changed from cold damage in the traditional sense to drought. Under the background of climate warming, the main factor affecting spring corn production was changed from thermal condition to water condition, and drought had become the primary disaster threatening spring corn production. The agricultural meteorological disasters that affected the spring corn yield in Liaoning province were drought, flood, and wind in order of the degree of influence. The agricultural meteorological disaster that affected spring corn yield in Jilin province was only drought. The agricultural meteorological disasters affecting the yield of spring corn in Heilongjiang province were ranked as flood, drought, and cold damage according to the degree of impact. In conclusion, due to geographical differences, the main agro-meteorological disasters affecting the corn production in the three provinces of Northeast China were also different, and their complexity was not the same, which cannot be generalized in the specific study.

Contrast in vulnerability to freezing-induced xylem embolism contributes to divergence in spring phenology between diffuse- and ring-porous temperate trees

The spring phenology and growth strategy of temperate tree species can be strongly linked to their sensitivity to frosts, which deserve more profound investigations under the background of climate warming particularly considering the advancement of spring phenology as well as the increase in frequency and intensity of spring cold waves. Spring phenologies, stem radial growth characteristics, frost sensitivity of leaves and stem hydraulic systems were studied in five diffuse-porous and five ring-porous temperate tree species under a common garden condition. The results showed that the spring leaf phenology of the diffuse-porous species was one to two weeks earlier than that of the ring-porous species. The ring-porous species had significantly higher stem hydraulic conductivity than the diffuse-porous species (1.81 and 0.95 kg·m −1 ·s −1 ·MPa −1 , P < 0.05) but were more vulnerable to freeze-thaw induced xylem embolism than the latter. After a simulated freeze-thaw event, the average percentage loss of hydraulic conductivity in the current year shoots increased from 26.0% (native embolism) to 86.7% in the ring-porous species, while it only increased from 21.3% to 38.3% in the diffuse-porous species. The spring phenology was clearly correlated with vulnerability to freeze-thaw induced embolism, with the more vulnerable ring-porous species exhibited substantially delayed phenology to reduce risks of catastrophic hydraulic dysfunction during spring frosts. Nevertheless, ring-porous species can offset the postponed onset of growth and gained even higher annual growth due to significantly higher hydraulic efficiency and leaf gas exchange rates. Contrasts between ring-porous and diffuse-porous species in resistance to freeze-thaw induced embolism suggest that they face different selective pressures from early spring frosts, which may at least be partially responsible for their divergence in spring phenology and growth strategy and can potentially lead to different responses to climate regime shifts.

Dynamic variation of meteorological drought and its relationships with agricultural drought across China

Under the background of climate warming, the global water cycle is gradually accelerating, which will lead to increased drought frequency and severity. China is one of the countries with the highest drought risk and the most serious drought impact, accompanied by abnormal and variable drought characteristics in recent decades. However, the dynamic variation of meteorological drought and its complicated relationships with agricultural drought are still unclear across China. In this study, the characteristics of meteorological drought were comprehensively identified across China during 1960–2019. The spatio-temporal variations and gridded trend characteristics of meteorological drought were revealed during the study period. Subsequently, the return period of meteorological drought was quantitatively determined based on copula models. Finally, the relationships between meteorological and agricultural drought were explicitly clarified. The results indicated that: (1) meteorological drought showed an increasing trend across China from 1960 to 2019, especially since the 1990s; (2) the most serious meteorological drought occurred in 2011, with a minimum standardized precipitation evapotranspiration index (SPEI) value of –0.81; (3) the percentage of drought area (PDA) with an increasing trend in spring, summer, autumn and winter was 85.8%, 77.4%, 97.7% and 12.9%, respectively; (4) the most appropriate copula model of meteorological drought severity and duration was Frank copula; and (5) the propagation time from meteorological to agricultural drought was longer in winter and shorter in summer, which can determine the appropriate irrigation period and predict the occurrence of agricultural drought. This study sheds new viewpoints into the identification of meteorological drought variation and its relationships with agricultural drought, which can also be applied in other areas.

Estimation of Long-Term River Discharge and Its Changes in Ungauged Watersheds in Pamir Plateau

The Pamir Plateau is an extremely important water resource area for over 60 million people in Central Asia. With the increasingly significant response of water resources to climate change, timely hydrological predictions for the future supply are necessary. In the plateau, accessing and monitoring the glaciers and their melt outflow are challenging due to the harsh geographic environments. Unmanned aerial vehicles (UAVs) combined with remote sensing technologies offer great potential for providing information to improve water resources management and decision-making. In this study, we integrated UAV and satellite remote sensing data, and applied a water balance model to estimate monthly and annual river discharges for the ten river sections in the Eastern Pamir Plateau, China from 1999 to 2020. We found that the glacier area in the controlled basins of these sections has decreased by approximately 63% from 1999 to 2020. Basins with smaller glacier areas are more sensitive to climate change. The ten river sections are characterized by decreasing trends in monthly river discharge, with an average reduction of −21.05%. The annual variation of total runoff and glacial meltwater discharge is consistent with the monthly variation of discharge, and the average discharge from glacier meltwater accounts for 83% of the total runoff. We conclude that the overall decreasing trend of discharge is closely related to the recession of glaciers. Under the background of climate warming in the region, glaciers are no longer sufficient to support the increase in river discharge, which has passed its peak value and shows a decreasing trend.