Search

The study evaluated the adaptive ability of slope regulation and storage measures (SRASM) under drought stress, providing scientific basis for improving water resource management and ecological protection in the arid environment of the Loess Plateau region. Four SRASM including afforestation on the hilltop (forestland engineering), returning farmland to forest on the hillside (grassland engineering), building terraces on the hillside (terraced fields engineering) and damming and silting on the valley floor (silting dam engineering) can effectively solve the problem of water and soil loss on the Loess Plateau. However, it is still unclear how the adaptive capacity (resistance and resilience) of these SRASM under drought stress. This study took the above four SRASM as the study object, used the performance of the four SRASM after drought and rehydration events as the basis for judging the adaptive capacity under drought stress. It proposed evaluation methods for drought and rehydration events, as well as calculation methods for resistance and resilience. Furthermore, it analyzed the adaptive capacity of different SRASM and different sub-basins in the middle reaches of the Yellow River under drought stress, as well as the impact of slope on adaptive capacity. The results showed that when light and moderate drought occurred, four SRASM recovered to their normal state after rehydration. In terms of resilience, forestland engineering > grassland engineering > terraced fields engineering > silting dam engineering, and grassland engineering had the most prominent ability to resist drought. As the slope increased, the adaptive capacity decreased. From a spatial perspective, the resilience in the western part of the middle reaches of the Yellow River was lower than that in the eastern, and the spatial distribution of resistance in the middle reaches of the Yellow River generally decreased from northwest to southeast.

Global climate change has led to an increase in the number of drought events. Agricultural droughts, which are influenced by crops, climate, and soil, are complex and challenging to identify. This study proposed a new index, the available water content of the soil index, based on the soil reservoir theory, which focuses on soil water and considers both crops and soil structure. We constructed the MODCYCLE model to depict soil water dynamics and evaluate agricultural drought by using the available water content of the soil index in a typical North China Plain region. The results showed that the soil in the western and southern regions was relatively dry and that the soil in the eastern and northern regions was humid. Drought occurred owing to the increased water demand during the critical growth period of winter wheat. Irrigation alleviated the drought. When the AWCI is greater than 0.6 in early April, the degree of drought is relatively mild. When the AWCI is less than 0.4, it is very easy to experience severe drought in mid-April.The central and eastern regions were susceptible to drought after mid-April, and the western region experienced drought until late May. Varying soil moisture, particle composition, irrigation, and precipitation conditions influenced the evolution of the drought. Enhancing soil moisture and timely irrigation before the critical growth period of winter wheat effectively prevented severe droughts in the region. The results provide guidance for regional drought monitoring and forecasting, water resource management, and scientific irrigation, effectively ensuring food security.

Study region: Catchment area above the Huaxian station along the Wei River Basin, China. Study focus: This study attempts to construct a new Non-stationary Standardized Streamflow Index (NSSI) applicable to the variable streamflow sequence of the Wei River Basin based on the climate index and the optimal anthropogenic index, and analyse the drought characteristics of the basin. The climate index is used to quantify climate change factors and three anthropogenic indices are used to quantify the factor of human activities, including the reservoir index, the human-induced index calculated based on the Variable Infiltration Capacity (VIC) hydrological model and the Long Short-Term Memory (LSTM) model machine learning approach, respectively. New hydrological insights for the region: The human-induced index based on the LSTM model is more suitable for quantifying anthropogenic factors in the Wei River Basin. The NSSI performs better than the SSI in drought identification. The NSSI based on the LSTM model can capture more frequent severe drought and extreme drought events. The frequency of severe drought and extreme drought is higher in summer and autumn than in the others. The NSSI can better characterize the hydrological drought processes under a non-stationary condition, thus it can provide a more effective reference for regional drought assessment and related policy-making from the perspective of a changing environment.

Permafrost degradation alters the flow rate, direction, and storage capacity of soil moisture, affecting ecohydrological effects and climate systems, and posing a potential threat to natural and human systems. The most widely distributed permafrost regions are coastal, high-latitudes and high-altitudes (mainly by the Qinghai-Tibet Plateau). Past studies have demonstrated that permafrost degradation in these regions lacks sorting out regional driving factors, assessing cascading effects on the hydrological environment and monitoring methods. To address this, we reviewed the historical research situation and major topics of permafrost degradation from 1990 to 2022. We analyzed the spatio-temporal dynamics and driving mechanism of permafrost degradation. Then, we comprehensively discussed the effects of permafrost degradation on the soil physical structure and hydraulic properties, soil microorganisms and local vegetation, soil evapotranspiration and stream runoff, and integrated ecohydrological effects. Permafrost field site data were then collected from existing findings and methods for direct or indirect monitoring of permafrost changes at different scales. These results revealed that the research on the hydrological effects of permafrost change was mainly centered on the soil. In addition, regional environmental factors driving permafrost degradation were inconsistent mainly in coastal regions influenced by sea level, high-latitude regions influenced by lightning and wildfire, and high-altitude regions influenced by topography. Permafrost degradation promoted horizontal and/or vertical hydrological connectivity, threatening the succession of high latitude vegetation communities and the transition from high altitude grassland to desert ecosystems, causing regional water imbalances would mitigate or amplify the ability of integrated ecohydrological benefits to cope with climate warming. The never-monitored permafrost area was 1.55×106 km2, but the limitations of using data for the same period remained a challenging task for soil moisture monitoring. Finally, future research should enhance the observation of driving factors at the monitoring site and combine remote sensing data, model simulations or numerical simulations, and isotope tracers to predict the future degradation state of deep permafrost effectively. It is expected that this review will guide further quantifying the driving mechanisms of permafrost degradation and the resulting cascading effects.

As one of the critical factors affecting the ecological systems, the effects of land use change should be concerned. However, few studies revealed the ecological effects especially the resilience under different land us changes, especially in alpine areas and in winter. To response the above question, this study conducted the field experiments in the Huangshui River Basin in winter, to compare the different ecological indicators for land use conversion under natural succession (perennial grassland, perennial forest, grassland transformed into forest) and land use conversion influenced by anthropogenic activities (returning farmland to forest, anthropogenic using land transformed into grassland anthropogenic activity zones). The results reveal that land use changed by human activities reduced the stability of ecosystems compared with natural succession. The concentrations or contents of most physicochemical properties in topsoil and grass decreased as well. While the relative abundance of NFB and PSB was slightly higher in the ecosystems with land use conversion influenced by anthropogenic activities. The results could provide references for evaluating the effects of land use changes from the ecological perspective, which could further guide the adaptation facing to climate change.

Based on the VOSviewer software and bibliometric visualization analysis, with 4636 published papers from 2000 to 2021 included in the Web of Science (WOS) Core Collection and China National Knowledge Infrastructure (CNKI) database, this study reviewed the literature on the effects of droughts and floods on phosphorus through three aspects: publication date, keywords, distribution of research discipline, etc. The results show that the research has risen rapidly in recent 20 years, and the average annual literatures in the WOS database increased 18.44 times faster than that in the CNKI database. The main keywords contain growth, responses, plants, tolerance, climate change, eutrophication, soil fertility, management, etc. The research in this field has the characteristics of interdisciplinary development. The paper aims to systematically review the effects of droughts and floods on phosphorus in soil-plant ecosystems, which could guide study trends in the future, such as quantitative evaluation, impact mechanism and adaptation countermeasures.

Measurement(s) distributed global population and water withdrawal Technology Type(s) mathematical statistics and analysis

Study region: High Mountain Asia (Qinghai-Tibet Plateau and surrounding areas) (HMA) Study focus: Soil dryness and wetness in HMA respond dramatically to global climate change. Monitoring soil moisture can provide a scientific foundation for water security in the plateau, middle, and lower basins. In this study, the applicability of the Temperature Vegetation Dryness Index (TVDI) with three improved protocols was evaluated to rectify the long-standing misuse of the TVDI method for regional drought assessment. New hydrological insights for the regions: The unsuitability of the TVDI in alpine regions was demonstrated by the nonlinear correlation between soil moisture and the TVDI. Among the three improvement schemes, TVDIm (obtained by controlling the temperature variable) best reflected the temporal and spatial distribution of soil moisture in the growing season of HMA, especially for surface soil moisture in the middle- and high-altitude areas. The TVDI, TVDIf (obtained by controlling the wet edge), and TVDI_A (obtained by controlling the partition) are not suitable for drought evaluation in medium- and long-term regions because the correlations between the three indicators and soil moisture are inconsistent in space and time. This study provides a new method to identify whether the TVDI can effectively evaluate regional drought. It also provides a more comprehensive reference for monitoring soil moisture and evaluating dryness in alpine regions using optical remote sensing.

The resource allocation of different component organs of crops under drought stress is a strategy for the coordinated growth of crops, which also reflects the adaptability of crops to drought condition. In this study, maize variety namely ‘Denghai 618’, under the ventilation shed, two treatment groups of light drought (LD) and moderate drought (MD), and the same rehydration after drought are set, as well as the normal water supply for control in shed (CS). The drought experiment was conducted in the jointing–tasseling stage in 2021. The effects of different drought stress on the water content and biomass allocation of each component organ were analyzed. The results showed that (1) during the drought period, the water content of each component organ of summer maize decreased in general, but the Water content distribution ratio (WCDR) of the root increased by 1.83%– 2.35%. The WCDR of stem increased by 0.52%– 1.40%. (2) Under different drought treatments, the root biomass (RB) increased 33.94% ~ 46.09%, and fruit biomass (FB) increased 1.46% ~ 2.49%, the leaf biomass (LB) decreased by 8.2% and 1.46% respectively under LD and MD. (3) The allometric growth model constructed under sufficient water is not suitable for drought stress; the allometric exponent α under drought stress is lower than that of the CS: CS (α=1.175) > MD (α = 1.136) > LD (α = 1.048), which also indicates that the impact of existing climate change on grain yield may be underestimated. This study is helpful to understand the adaptive strategies of the coordinated growth of maize component organs under drought stress and provide a reference for the prediction of grain yield under climate change.

Extreme events normally have negative effects on crop growth. Many studies have reported findings on drought and flood events, while only sparse studies have focused on new types of extreme events, such as drought-flood abrupt alternation (DFAA). We attempted to gain an insight on the effects of DFAA over two-year field experiment on biomass, grain yield and quality, then simulated the yield loss to DFAA in history and future in summer maize planting area in the Northern Anhui Plain. Results show that DFAA significantly reduced root biomass and shoot biomass by 77.1% and 60.1% compared with that in the control systems. The negative effect lasted until mature stage. The grain yield loss was 14.1%–38.4% in different DFAA treatments. The numerical simulation reveals that the average annual yield loss due to DFAA has been increasing in the Northern Anhui Plain, with 21.19%–30.98% during 1964–2017, 14.10%–33.40% during 2020–2050. The spatial distribution of yield loss changed as well. This study increases our knowledge of the effects of DFAA on crop production and highlights the need to consider the targeted countermeasures.

Crop resilience refers to the adaptive ability of crops to resist drought at a certain level. Currently, most of the research focuses on the changes in root or photosynthesis traits of crops after drought and rehydration. Still, the persistence effect (drought period (T2) - rehydration period (T3) - harvest period (T4)) of drought stress on crops and quantitative estimation of resilience is still unclear. Field experiments were conducted in this study to determine the persistence effects on above-ground and below-ground growth indicators of summer maize at different levels and durations of drought. Next, an evaluation method for integrated resilience of summer maize was proposed, and a quantitative assessment of integrated resilience was made by Principal Component Analysis (PCA) and resilience index calculation. The results showed that the resilience of summer maize decreased with increasing drought levels, which persisted until harvest. Although summer maize resilience was strong after rewatering under light drought (DR1), declined after sustained rewatering. At the same time, production had decreased. However, a specific drought duration could improve the resilience of summer maize under light drought conditions. In particular, leaf biomass and root growth in the 30-50 cm layer could be enhanced under long duration light drought (LDR1), thus improving summer maize resilience and yield. Thus, under water shortage conditions, a certain level and duration drought could improve the resilience and yield of summer maize, which would persist until harvest. Clarifying the persistent effects on the growth indicators of summer maize and quantitatively evaluating the resilience of summer maize could improve agricultural food production and water use efficiency.

Accurate calculation of root water uptake (RWU) is the key to improving vegetation water use efficiency and identifying water cycle evolution patterns, and root tips play an important role in RWU. However, most of the current RWU models in the alpine meadow are calculated based on the root length density (RLD) function. In this study, a large number of roots, soil hydraulic conductivity, and physicochemical property indices were obtained by continuous field prototype observation experiments for up to 2 years. It was found that the RLD and root tip density (RTD) in alpine meadows decrease by 16.2% and 14.6%, respectively, in the wilting stage compared to the regreening stage. The RTD distribution function of the alpine meadow was constructed, and the RWU model was established accordingly. The results show that the RTD function is more accurate than the RLD function to reflect the RWU pattern. Compared with RLD, the simulated RWU model constructed by using RTD as the root index that can effectively absorb water increased by 24.64% on average, and the simulated values were more consistent with the actual situation. It can be seen that there is an underestimation of RWU calculated based on the RLD function, which leads to an underestimation of the effect of climate warming on evapotranspiration. The simulation results of the RWU model based on RTD showed that the RWU rate in the regreening stage increased by 30.24% on average compared with that in the wilting stage. Meanwhile, the top 67% of the rhizosphere was responsible for 86.76% of the total RWU on average. This study contributes to the understanding of the alpine meadow water cycle system and provides theoretical support for the implementation of alpine meadow vegetation protection and restoration projects.

The adaptability of crops reflects the ability to continue to grow in the changing environment. Its adaptability in adversity plays an important role in its own growth and development. The root system is the main organ for crops to absorb water and nutrients, it can adjust its own morphology, physiological, biochemical to improve its water absorption and thus adapt to drought stress. Previous studies mostly focused on the above ground part of crops, but less on the underground part of crops due to the complexity of root observation. In order to study the adaptability of summer maize under different drought conditions, taking “Denghai 618” as the experimental material, with prototype observation and micro root window as technical support, under the ventilation shed, two treatment groups of light drought (LD) and moderate drought (MD) and the same rehydration after drought are set, as well as the normal water supply for control inside the shed (CS) and Control outside the shed (COS). The changes of root morphology and the law of root water absorption under drought and Rehydration after different drought were analyzed. The results showed that: 1) Under drought stress, the root system of maize adapts to drought by thinning and increasing fine roots to improve root water absorption. Under the MD, the root adaptation to drought is more obvious: promoting root growth. Root biomass was no significant difference between the drought treatment group and the CS. The root biomass of the drought treatment group was significantly lower than that of the COS due to the thinner root system. 2) The total amount of root water absorption in the CS and COS increased steadily with the increase of days. In the drought treatment group, the root water absorption decreased with the increase of drought degree, that is, COS > CS > LD > MD. This study provides a reference for revealing the self-adaptive regulation mechanism of summer maize roots under drought conditions.

It is essential to quantify the rate of root water uptake (RWU) and characterize the variability of RWU, which benefits understanding the water use of alpine meadows and its response to environmental changes. In addition, model simulation is one of the feasible methods to obtain the RWU characteristics of alpine meadows. However, recent research on RWU models mainly focused on crops and trees, while barely on alpine meadows. Thus, it is of great significance to develop an RWU model applicable to alpine meadows, which can describe local plant water consumption processes. In this paper, we measured the distribution characteristics of root density and soil characteristics of alpine meadows in the Qinghai-Tibet Plateau (QTP) with prototype observation experiments. The root length density (RLD) of the wilting stage decreased by 16.2% on average compared to the re-greening stage, and the ability of root growth was poorer in the high altitude area. Based on the distribution characteristics of root length density (RLD) and the three soil resistance indexes (soil water potential, soil hydraulic diffusivity, and soil hydraulic conductivity), which have obvious impacts on RWU. The improved Feddes model, Selim-Iskandar model, and Molz-Remson model were selected to simulate the RWU in alpine meadows, which fully considered the above impact factors, but the applicability in alpine meadows was not discussed. The results showed that the model performance of the Selim-Iskandar model was better than the improved Feddes model and Molz-Remson model, and its simulation performance was improved by 44.76 and 22.16% compared to the improved Feddes model and Molz-Remson model, respectively. Based on the quantified RWU rate, the RWU characteristics showed that the top 50% of the rhizosphere was responsible for 72.65% of the water uptake of the entire rhizosphere. At the same time, the obvious difference in RWU rate in different phenological stages was obvious, showing that the RWU rate in the re-greening stage increased by 36.52% compared to that in the wilting stage. This study can provide technical support for a more accurate estimation of transpiration and water use efficiency in alpine meadows, and could provide theoretical support for the implementation of vegetation.

Study region: The Nagqu River Basin in the central part of the Qinghai–Tibet Plateau, China. Study focus: Groundwater flow systems in permafrost regions are characterized by a unique circulation. Understanding the groundwater circulation mechanism is essential for studying the hydrological effect of permafrost degradation in alpine regions. In this study, potential water sources and origin of solutes in the groundwater of a typical alpine region were studied using hydrochemistry, 18O, 2H and 3H analyses. This research is essential for studying the hydrological effects of permafrost degradation. New hydrological insights for the region: Upon moving from the mountainous region to the plains, the renewal rate decreases from 10.5% to 0.6% and the mean transit time increases from 5–30 to 20–32 years. Groundwater is mainly recharged by ground ice meltwater and infiltration of glacier meltwater, snow meltwater and precipitation in mountainous areas, and by deep groundwater near faults. Discharge to surface water, evaporation, and overflow into springs are the main drainage modes. Water/ice–rock/soil interactions, such as dissolution of aluminosilicate minerals, are the main factors affecting the hydrochemical evolution. This study provides a data-driven approach for understanding groundwater recharge and evolution in similar systems.

Soil microbial communities are essential to phosphorus (P) cycling, especially in the process of insoluble phosphorus solubilization for plant P uptake. Phosphate-solubilizing microorganisms (PSM) are the dominant driving forces. The PSM mediated soil P cycling is easily affected by water condition changes due to extreme hydrological events. Previous studies basically focused on the effects of droughts, floods, or drying-rewetting on P cycling, while few focused on drought-flood abrupt alternation (DFAA), especially through microbial activities. This study explored the DFAA effects on P cycling mediated by PSM and P metabolism-related genes in summer maize field soil. Field control experiments were conducted to simulate two levels of DFAA (light drought-moderate flood, moderate drought-moderate flood) during two summer maize growing periods (seeding-jointing stage, tasseling-grain filling stage). Results showed that the relative abundance of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) increased after DFAA compared to the control system (CS), and PSF has lower resistance but higher resilience to DFAA than PSB. Significant differences can be found on the genera Pseudomonas, Arthrobacter, and Penicillium, and the P metabolism-related gene K21195 under DFAA. The DFAA also led to unstable and dispersed structure of the farmland ecosystem network related to P cycling, with persistent influences until the mature stage of summer maize. This study provides references for understanding the micro process on P cycling under DFAA in topsoil, which could further guide the DFAA regulations.

Study region: The Nagqu River watershed (NRW) on the Qinghai–Tibet Plateau (QTP). Study focus: Precipitation, snowmelt, streamflow, and groundwater samples were collected in the NRW and used to analyze the contribution of different water sources to streamflow during different freeze–thaw periods. Stable isotopes of hydrogen (D) and oxygen (18O) and water chemistry were analyzed for the period ranging from 2016 to 2019, and tritium (T) and carbon-14 (14C) isotopes were analyzed for 2019. New hydrological insights for the region: Rain and snowmelt were found to reflect the chemical characteristics of precipitation, and the primary ions in both water types were Ca2+ and SO42−. The δD and δ18O isotope values of rain and snowmelt were relatively low during the entire thaw period (from June to October) and relatively high in the entire frozen period (from November to May). The results of the optimum multiparameter and mass balance analyses showed that groundwater and snowmelt accounted for approximately 39.8 % and 32.2 % to the Nagqu River water flow, respectively, whereas precipitation accounted for approximately 28.0 %. The groundwater in clastic rock fissures around the northern Cuona Lake, and permafrost and ground ice in the bedrock layer were identified as older water types with relatively low infiltration rates, and bedrock fissures in the southeastern and southwestern areas contained younger water with better recoverability.

Study region: The Nagqu River Watershed in the Qinghai–Tibet Plateau. Study focus: A computational unit is the basic spatial unit employed in distributed hydrological models (DHMs), which combines the spatiotemporal distributions of meteorological variables and physical parameters denoted within a region to reveal the characteristics affecting the water cycle of watersheds. However, the current methods developed for spatially divided regions into computational units fail to consider the physical meaning and impact of climate change in montane altitudinal zones (MAZs), which significantly affects alpine watersheds. This study proposes a method for assigning the computational units of alpine DHMs according to one-period MAZ that explicitly account for physical meaning and climate change. New hydrological insights for the region: The benefits of the proposed altitudinal discretization method are verified by applying it to construct a DHM based on the water and energy transfer processes in large river basins (WEP-L) models. The results obtained using the WEP-L, SWAT model and the new regional division method (denoted as the WEP-C model) that applies the proposed altitudinal discretization method are compared. The results demonstrate that the simulation accuracy of the daily and monthly streamflows and daily soil moisture from the alpine watershed is improved by the use of the proposed altitudinal discretization method, which provide guidance for further DHM development and can be applied to other hydrological models.

Region: The Nagqu River Basin in the Qinghai-Tibet Plateau. Focus: Climate change and human activities have altered the type of land use in the Qinghai-Tibet Plateau (QTP), which has affected the variation laws of water resources. We calibrated and verified the Water and Energy Transfer Process for a Large basin model (WEP-L), and calculated the impacts of climate change and human activities on runoff change and separated the impact of land use. New hydrological insights: The Archimedean Copula function was used to diagnose the variance between precipitation and runoff. The contribution of climate change to the runoff in the Dasa and Jiayuqiao subbasin was 81.7% and 71.5%, of which the contribution of land use was 39.3% and 32.6%, respectively. Human activities contributing to the runoff in the Dasa and Jiayuqiao subbasins were 18.3% and 28.5%, of which the contribution of land use is 7.9% and 2.8%, respectively. Climate change has led to the melting of glaciers, permanent permafrost and the shift of the vertical distribution of vegetation, which is the main reason for the runoff variation in the NRB. This research provides a scientific basis for the rational protection and utilization of water resources, as well as soil and water conservation work. Keywords: Precipitation–runoff, Mutation diagnosis, Climate change, Human activities, Land use, Hetao area

Climate change has emerged as a significant man-made global environmental challenge marked by rising temperature. The global rising temperature is supposed to alter climatic patterns like floods and droughts, thereby affecting human life supporting system and global food production. In order to clarify the impact of weather events on agricultural production in karst landforms, this study selected the indices of the growth period of crops (start time and duration), growing season precipitation, intense precipitation, number of consecutive rainless days, and number of drought-flood abrupt alternation events to evaluate the variation trend of future weather events and their impact on crop growth in Guizhou Province, China. The results show that (1) the climate is generally getting warmer. From 2019 to 2050, the sowing period of winter wheat and rice tends to be postponed. The duration of maize and rice’s growth period will be shortened, and the life cycle of wheat also emerges as having a decreasing tendency except for those from the southern region. Comparing with the mean value during 1961 to 2018, the average crop cycle length of winter wheat, summer maize, and rice was shortened. The rate of shortening of crop cycle length is faster than the value during 1961 to 2018. (2) In the next 30 years, extreme precipitation concentrates in June and mainly falls in the central and southeast parts of Guizhou Province. In addition, summer is the outbreak period of drought events and drought-flood abrupt alternation events, which has a great impact on crop’s growth. This study can provide references for the planting system, structure, layout, and management of crops in the karst region.

In order to study the effect of the construction of the sponge cites on the process of urban water circulation in China, we analyzed the precipitation data from 756 stations across China between 1961 and 2011 and national land-use data in 2014. The spatial distribution characteristics of built-up area and amount of annual average runoff interception in sponge cities were explored in five different zonal scale levels. Assuming that the sponge cities have been built at the national-level construction land and the volume capture ratio of annual runoff is taken as 85%, the amount of annual average runoff interception in sponge cities is 988.58 × 108 m3 during 1961 to 2011 in China, where the annual precipitation is greater than or equal to 400 mm. The cities with more amount of annual average runoff interception are mostly distributed in Beijing-Tianjin-Hebei region, the Yangtze River Delta, and the Pearl River Delta. As to the Haihe River Basin, the annual average amount of surface water resources is 135.69 × 108 m3 between 2005 and 2014, and the amount of annual average runoff interception is 219.58 × 108 m3 from 1961 to 2011. The construction of sponge cities has the greatest impact on the surface water resources in the Haihe River Basin. Taking 80%–85% as the volume capture ratio of annual runoff in sponge cities is not reasonable, which may lead to the irrational exploitation and utilization of regional water and soil resources.

Climate change, especially precipitation change, will significantly change soil moisture, which then influences root growth, further affecting yield and grain quality. Previous studies focused on the drought or flood effects on summer maize growth. However, few studied the effects of drought-flood abrupt alternation (DFAA) on the growth of summer maize. We explored the DFAA impacts on the roots, leaf area index (LAI), yield, and grain quality in field. The main results show that DFAA had different impacts on the summer maize growth in the seeding-jointing stage (SJS) and tasseling-grain filling stage (TGS). In general, the DFAA reduced the yield. Roots at the depth of 40 cm had obviously positive impacts on the yield. The DFAA reduced the LAI and promoted the maximum LAI achieving in advance. The grain crude protein augmented under DFAA. The drought had evidently negative impacts on the grain crude fat in the TGS, while it had no obvious influence in the SJS. DFAA had no apparent impact on the grain crude starch. These results could provide some references for the effects and adaptation-strategies study of extreme climate events and their impacts on growth of summer maize.

High temporal-spatial precipitation is necessary for hydrological simulation and water resource management, and remotely sensed precipitation products (RSPPs) play a key role in supporting high temporal-spatial precipitation, especially in sparse gauge regions. TRMM 3B42V7 data (TRMM precipitation) is an essential RSPP outperforming other RSPPs. Yet the utilization of TRMM precipitation is still limited by the inaccuracy and low spatial resolution at regional scale. In this paper, linear regression models (LRMs) have been constructed to correct and downscale the TRMM precipitation based on the gauge precipitation at 2257 stations over China from 1998 to 2013. Then, the corrected TRMM precipitation was validated by gauge precipitation at 839 out of 2257 stations in 2014 at station and grid scales. The results show that both monthly and annual LRMs have obviously improved the accuracy of corrected TRMM precipitation with acceptable error, and monthly LRM performs slightly better than annual LRM in Mideastern China. Although the performance of corrected TRMM precipitation from the LRMs has been increased in Northwest China and Tibetan plateau, the error of corrected TRMM precipitation is still significant due to the large deviation between TRMM precipitation and low-density gauge precipitation.

The physical-based drought indices such as the self-calibrated Palmer Drought Severity Index (sc-PDSI) with the fixed time scale is inadequate for the multiscalar drought assessment, and the multiscalar drought indices including Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI), and Standardized Precipitation Evapotranspiration Index (SPEI) based on the meteorological factors are lack of physical mechanism and cannot depict the actual water budget. To fill this gap, the Standardized Water Budget Index (SWBI) is constructed based on the difference between areal precipitation and actual evapotranspiration (AET), which can describe the actual water budget but also assess the drought at multiple time scales. Then, sc-PDSI was taken as the reference drought index to compare with multiscalar drought indices at different time scale in Haihe River basin. The result shows that SWBI correlates better with sc-PDSI and the RMSE of SWBI is less than other multiscalar drought indices. In addition, all of drought indices show a decreasing trend in Haihe River Basin, possibly due to the decreasing precipitation from 1961 to 2010. The decreasing trends of SWBI were significant and consistent at all the time scales, while the decreasing trends of other multiscalar drought indices are insignificant at time scale less than 3 months.

Alpine regions’ groundwater is crucial to the worldwide hydrological cycle. However, due to the harsh environmental conditions, the distribution and evolution characteristics await clarification. The study area was selected to be the Nagqu River Basin in the Nu-Salween River’s source region. In 2019-2021, we gathered 88,000 monitoring data from nine observation wells and examined the spatiotemporal groundwater table changes in various permafrost zones and freeze-thaw cycles. During the freezing period, entirely frozen period, thawing period, and entirely thawed period, the groundwater table change rates in the permafrost zone were 2.14, 1.54, 1.55, and 2.01 times larger than in the seasonal frost zone, and fluctuation amplitudes were 1.97, 1.28, 1.01 and 1.31 times larger. The average groundwater table change rate and fluctuation amplitude were greatest during the entirely thawed period and lowest during the thawing period, with the maximum change rate reaching 3.64 cm/d during the entirely thawed period of 2019-2020 in the permafrost zone and the minimum change rate of 0.12 cm/d during the thawing period of 2019-2020 in the seasonal frost zone. [ABSTRACT FROM AUTHOR]

The resource allocation of different component organs of crops under drought stress is a strategy for the coordinated growth of crops, which also reflects the adaptability of crops to drought condition. In this study, maize variety namely 'Denghai 618', under the ventilation shed, two treatment groups of light drought (LD) and moderate drought (MD), and the same rehydration after drought are set, as well as the normal water supply for control in shed (CS). The drought experiment was conducted in the jointing-tasseling stage in 2021. The effects of different drought stress on the water content and biomass allocation of each component organ were analyzed. The results showed that (1) during the drought period, the water content of each component organ of summer maize decreased in general, but the Water content distribution ratio (WCDR) of the root increased by 1.83%-2.35%. The WCDR of stem increased by 0.52%- 1.40%. (2) Under different drought treatments, the root biomass (RB) increased 33.94% ~ 46.09%, and fruit biomass (FB) increased 1.46% ~ 2.49%, the leaf biomass (LB) decreased by 8.2% and 1.46% respectively under LD and MD. (3) The allometric growth model constructed under sufficient water is not suitable for drought stress; the allometric exponent α under drought stress is lower than that of the CS: CS (α=1.175) > MD (α = 1.136) > LD (α = 1.048), which also indicates that the impact of existing climate change on grain yield may be underestimated. This study is helpful to understand the adaptive strategies of the coordinated growth of maize component organs under drought stress and provide a reference for the prediction of grain yield under climate change. [ABSTRACT FROM AUTHOR]

The "land use" and "water use" competitions appear more seriously between lake-marsh wetland system and its surrounding socio-economic system, also inside the lake-marsh wetland system. However, few studies focus on solving the contradictions mentioned above. While this study proposed an optimal lake-marsh pattern determination method based on the joint regulation of ecological land and ecological water, on considering the ecological services values and water shortage amount in the lake-marsh wetland system. The optimal lake-marsh pattern determination should explore the land and water demand of the protection objects, also the water supply and water demand (especially evapotranspiration) in annual and monthly time-scale. Calculation and analysis were performed for the optimal pattern of the Wolonghu Wetlands as an example. The results mainly showed that the optimal lake-marsh pattern of the Wolonghu Wetlands can be obtained with the area ratio of lake-marsh equaling to 0.651 : 0.349 and the corresponding water level of 87.4 m in annual scale. In monthly scale, except July and August, the optimal area ratio of lake and marsh varied from 0.634 : 0.366 to 0.738 : 0.262. This study could provide references for the Wolonghu Wetlands management, also for similar lake-marsh wetland system and other ecological system. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the different performance of bioelectricity generation and wastewater treatment between constructed wetland (CW) respectively coupled with air-cathode microbial fuel cell (ACMFC) and microbial fuel cell (MFC) under a fed-batch mode. During a 75-day-operation, the voltage of CW-ACMFC and CW-MFC ranged from 0.36 to 0.52 V and from −0.04 to 0.07 V, indicating that the bioenergy output of CW-ACMFC was significantly higher than that of CW-MFC system. In addition, the maximum of power density of CW-ACMFC and CW-MFC was 4.21 and 0.005 mW m−2. Notably, the chemical oxygen demand (COD) and NH3-N removal efficiency of CW-ACMFC was slightly higher than that in CW-MFC, which resulted from a higher voltage accelerating the transport of electron donors and the growth of microorganisms and plants. This study possesses a probability of using ACMFC coupled with CW to enhance the pollutant removal performance in CW system. [ABSTRACT FROM AUTHOR]

To enhance our understanding of the regional hydroclimate in the Central Tibetan Plateau, different types of water samples were collected across the Naqu River basin in the summer (July, August) and winter (January, December) of 2017 for isotopic analysis. With Cuona Lake as the demarcation point, the δ18O values of the river water increased initially and then decreased from upstream to downstream along the river's mainstream. In the Naqu River system, a general decrease of δ18O values in the trunk stream of the lower reaches (from the head of Cuona Lake) was revealed owing to the gradual dilution of increased isotopically-depleted tributary inflow. Lakes play an important role in regulating runoff and changes in the levels of stable isotopes in rivers or streams. Additionally, the decrease of δ18O is controlled by processes involved in the 'isotopic altitude effect'. Larger contributions of winter precipitation in surface runoff at higher elevations would produce higher deuterium excess in stream water. On the regional scale, with Cuona Lake as the demarcation point, one of the clearest findings was that the river/stream's deuterium excess values decreased first and then increased from the south to the north in the summer; but there was a positive linear increase in the winter. From geographical and climatological perspectives, the changes of deuterium excess could result from increasing effects of summertime, and the generation of continental/local recycled and monsoonal water vapor in the surface runoff northward. The study area is at the critical transition between the Indian monsoon system in the South and the Northern belt of the westerlies, as revealed by the intermediate deuterium excess values. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is the roof of the world and water towers of Asia. However, research on hydrological processes is restricted by the sparse gauge network in the TP. The distributed hydrological model is an efficient tool to explore hydrological processes. Meanwhile, the spatial distribution of precipitation directly affects the precision of distributed hydrological modelling. The latest TRMM 3B42 (V7) precipitation was evaluated compared with gauge precipitation at station and basin scales in the Naqu River Basin of the TP. The results show that Tropical Rainfall Measuring Mission (TRMM) precipitation overestimated the precipitation with BIAS of 0.2; the intensity distributions of daily precipitation are consistent in the two precipitation data. TRMM precipitation was then corrected by the good linear relation between monthly areal TRMM precipitation and gauge precipitation, and applied into the Water and Energy Process model. The results indicate that the simulated streamflow using both precipitation data produce a good fit with observed streamflow, especially at monthly scale. Furthermore, the better relations between average slopes and runoff coefficients of sub-basins from the corrected TRMM precipitation-based model implies that the spatial distribution of TRMM precipitation is closer to the spatial distribution of actual precipitation, and has an advantage in driving distributed hydrological models. [ABSTRACT FROM AUTHOR]

Based on the national precipitation dataset in the Huang-Huai-Hai River Basin of China for the 1961-2011 period, the China-Z growing season index was calculated to analyze the characteristics of the evolution of meteorological droughts. Data from statistical droughts (the droughts which are defined and classified by the actual statistic data) were compared with those of meteorological droughts during the 2000-2011 period. Nine indexes were selected to evaluate the drought coping ability of water conservancy projects based on the fuzzy comprehensive assessment model. The results showed that the China-Z growing season index was a downward trend with a rate of -0.063 per decade from 1961 to 2011, which indicates an increasing trend in drought intensity. Droughts were more frequent than average during the 1961-1979 period and returned to normal frequency during the 1980-2011 period. Both the ratio of drought affected area (RDAA) and the ratio of drought suffering area (RDSA) of statistical droughts decreased more quickly than those of meteorological droughts (2000-2011). The indexes of water conservancy projects were lower than the average all-China indexes. Half of the 59 three-level water resources districts exhibited a relatively poor drought coping ability, which means that enhancing the drought coping ability of the water conservancy project was quite important. [ABSTRACT FROM AUTHOR]

Drought impacts not only nature, but also the socioeconomic system and results from the imbalance of water supply and demand. It is necessary to estimate the ability of drought mitigation on the basis of water allocation. In this research, the drought mitigation ability index (DMAI) was constructed by the ratio of theoretical water supply and demand obtained from the optimal water allocation. Then, the DMAI was applied to Daqinghe watershed for temporal-spatial validation compared with the agricultural affected areas and the distribution of groundwater overexploitation. In addition, the historical (1961-2010) and future (2020) DMAI in Daqinghe watershed were analyzed. The results show that DMAI can overall represent the temporal-spatial characteristics of the drought mitigation ability. Furthermore, the DMAI of Daqinghe watershed is significantly decreased in the last 50 years, and groundwater resources play a prominent role in drought mitigation. Although the water from the South-to-North Water Transfer Project (SNWTP) can improve DMAI of Daqinghe watershed, the drought risk continues to be serious in the future. [ABSTRACT FROM AUTHOR]

Under the climate changes and human activities, large areas of lakes shrunk and wetlands degenerated. Evapotranspiration (ET) is the primary water loss in the water balance of closed-basin and lakes. However, ET is difficult to estimate, especially in the data-scarce or ungauged zones. For a closed lake without outflow, the inflow could be used to estimate the water shortage of ecological water demand. Based on meteorology data and the pan evaporation (ETpan) data, Penman-Monteith and Hargreaves Model were used to estimate potential evapotranspiration (ET0), which was used to estimate ET, and used the water balance model to assess the water inflow of Wolong Lake. PM model proposed the satisfactory estimation of ET0 from Wolong Lake. The empirical formula of the net radiation was built based on the coefficient that derived from data fitting with function of the measured ETpan and the estimated ET0. The temperature was the dominant factor for the increment of the ETpan. In the data-scarce or ungauged zones, ET0 could be used to evaluate the evapotranspiration from the lake surface (ETlake), instead of the ETpan. The results found that the inflow of Wolong Lake could not meet the demand of the evaporation and water volume advancement. [ABSTRACT FROM AUTHOR]

The Huaihe River Basin is located in-between the north-south climate transitional zone in China and is China's important congested area and production base. The land-use of the environment was occupied by the land-use for social and economics. This paper aims to have a comprehensive understanding about land-use and vegetation evolution of the basin over the past 30 years. In view of 5 years (1985, 1990, 2000, 2005, and 2014) land-use data and remote sensing data about NDVI, land-use dynamic degree, and land-use transfer matrix were used to analyze the dynamics of land use. Spatial overlay was used to study vegetation change characteristics of the basin. The present study investigates the evolution trend of vegetation coverage based on spatial overlay analysis. We found that water bodies and urban lands of the basin increased during 1985-2014. On the other hand, the area of artificial vegetation, natural vegetation, and wetland were reduced. The impact was gradually increased by human intervention on various land use types. Overall vegetation coverage level shows deteriorative development, and distribution areas were discrete. The excellent vegetation coverage of natural vegetation and wetland didn't have obvious changes, but the high coverage significantly decreased. Taken as a whole, the natural vegetation coverage was reduced. The vegetation coverage level of artificial water in the land-use for social and economics had greatly increased, but the overall trend of vegetation coverage level of artificial vegetation and resident construction land showed a decreasing trend. [ABSTRACT FROM AUTHOR]