Drought-flood Abrupt Alternation Research Articles

Response of rice's hydraulic transport and photosynthetic capacity to drought-flood abrupt alternation

Knowledge of the potential interactive effects of drought and flooding on the maximum carboxylation rate at 25°C (Vmax25) and maximum hydraulic conductance (Kmax) is essential for the precise modeling of crop growth, water-carbon cycling, and crop yield formation. However, the lack of data on drought–flood abrupt alternation (DF) experiments and appropriate models to calibrate parameters without the need to specify photosynthetic and hydraulic transport capacity a priori make it difficult to further our understanding of the potential interaction effects on Vmax25 and Kmax. Hence, this study aimed to investigate the potential effects of interactions between the preceding drought and the subsequent flooding on Vmax25 and Kmax. We propose a nested optimization model for calibrating photosynthetic and hydraulic conductance capacity while simultaneously modeling carbon assimilation rate and stomatal conductance. A two-year DF experiment for rice from 2017 to 2018 was conducted to validate the new framework at the Key Laboratory of Water Resources and Hydropower of Anhui Province, Bengbu, China. The results show that reasonable Kmax and Vmax25 from gas exchange data can be extracted with the proposed nested model framework. We find two distinct interactions between the prior drought and the subsequent flooding on Vmax25 and Kmax: (1) the antagonistic effect of the preceding mild drought on the subsequent-flood-induced reduction of hydraulic transport and photosynthetic capacity, and (2) the synergistic effect of the subsequent flooding on the preceding drought-induced reduction in hydraulic transport and photosynthetic capacity. Revealing the interaction of drought and flooding on Kmax and Vmax25 of rice under DF events helps to understand rice’s response to compound water stress on multiple timescales and the stomatal and non-stomatal co-limitations, and these findings can be used as valuable guidelines for accurately predicting the impact of future extreme weather events on agricultural production.

A novel multi-scale standardized index analyzing monthly to sub-seasonal drought-flood abrupt alternation events in the Yangtze River basin

Drought-flood abrupt alternation (DFAA) events are often cause severe disasters that affect economic growth and ecological security. Since the current monthly to sub-seasonal drought-flood abrupt alternation index (DFAI) has the limitations of misjudgments, omissions and neglecting alternation speed, this study proposes a novel multi-scale standardized DFAI index (MSDFAI) based on the definition of the misjudgment and omission rates as well as alternation speed. A comparative test and spatial–temporal characterization analysis in the Yangtze River Basin (YRB) are conducted. The results show that the misjudgment rate of DFAI in the YRB varies between 3 %–181 %, and its omission rate varies between 0.5 %–45 %, which is unable to find a suitable point that will satisfy both misjudgment and omission at the same time. The alternation speed has a significant impact on the level of DFAA events, and there are 30 underestimations of DFAA events in the YRB during 1962–2022 when only considering the alternation intensity. The MSDFAI index makes a conditional judgment on whether a drought or flood event occurs based on the standardized precipitation index (SPI) value, which can effectively avoid these misjudgments and omissions. Meanwhile, the MSDFAI index describes the DFAA events in a more comprehensive manner by introducing the speed factor. The DFAA has a spatial pattern with relatively low frequency in the Poyang Lake basin and the middle YRB, and high frequency in the upper YRB, the Han River, and the lower YRB. The inter decadal variability of DFAA events in the YRB is characterized by a turning point in the 1990 s, when DFAA events are increased after the 1990 s. The proposed MSDFAI index can monitor DFAA events much comprehensively and effectively in the YRB, and provide technique support for identification and prevention of DFAA in the changing environment.

Integrating SWAP and SIF anomaly to assess the responses of vegetation to the drought-flood abrupt alternation in the middle and lower reaches of the Yangtze River basin, China

Study regionThe middle and lower reaches of the Yangtze River basin, China. Study focusUnder the background of global warming, drought-flood abrupt alternation (DFAA) events are occurred frequently, with substantial impact on ecosystems and water resources. Therefore, this study calculated the Standard Weighted Average Precipitation (SWAP) based on daily precipitation to verify the applicability of SWAP in the middle and lower reaches of the Yangtze River basin (MLRYRB). The response of Solar-Induced Chlorophyll Fluorescence (SIF) anomaly to DFAA events was determined based on lagged time correlation coefficients. Finally, based on Partial Wavelet Coherence (PWC), the impact of atmospheric circulation factors on the response relationship between DFAA events and vegetation was analyzed. New hydrological insights for the regionThe results indicate that: (1) the evolutionary characteristics of DFAA events determined by SWAP were consistent with historical records. (2) the DFAA events frequency with most regions experiencing 8–11 events during 2001–2019, with intensity of 2–3, and in the northern and southwestern Jiangxi and southeastern Hubei regions were more intensive and frequently. (3) the stronger correlations were mainly in eastern Guizhou and eastern Jiangxi, with SIF anomaly more sensitive to SWAP at 2-month lag time. (4) The El Niño-Southern Oscillation (ENSO) and sunspots have a significant influence on the response relationship between DFAA events and vegetation anomaly. This research can provide a scientific basis for the integrated response to DFAA events and ecological management in the MLRYRB.

Spatial-Temporal Variations of Drought-Flood Abrupt Alternation Events in Southeast China

Under climate change, the frequency of drought-flood abrupt alternation (DFAA) events is increasing in Southeast China. However, there is limited research on the evolution characteristics of DFAA in this region. This study evaluated the effectiveness of the drought and flood indexes including SPI (Standardized Precipitation Index), SPEI (Standardized Precipitation Evapotranspiration Index), and SWAP (Standardized Weighted Average Precipitation Index) in identifying DFAA events under varying days of antecedent precipitation. Additionally, the evolution characteristics of DFAA events in Fujian Province from 1961 to 2021 were explored. The results indicate that (1) SPI-12d had the advantages of high effectiveness, optimal generalization accuracy, and strong generalization ability of identification results, and it can be used as the optimal identification index of DFAA events in Southeast China. (2) There was an overall increase in DFAA events at a rate of 1.8 events/10a. The frequency of DFAA events showed a gradual increase from the northwest to the southeast. (3) DTF events were characterized by moderate drought to flood, particularly in February, July, and August, while FTD events were characterized by light/moderate flood to drought, with more events occurring from June to October. (4) DTF event intensity increased in the northern and western regions from 1961 to 2021. For FTD events, the intensity notably increased in the western region from 1961 to 2001, while a significant increase occurred in all regions except the central region from 2001 to 2021. These findings emphasize the need for precautionary measures to address the increasing frequency and severity of DFAA events in Southeast China.

Responses of the maize rhizosphere soil environment to drought-flood abrupt alternation stress.

Changes in the soil environment in the root zone will affect the growth, development and resistance of plants. The mechanism underlying the effect of drought and flood stress on rhizosphere bacterial diversity, soil metabolites and soil enzyme activity is not clear and needs further study. To analyze the dynamic changes in bacteria, metabolites and enzyme activities in the rhizosphere soil of maize under different drought-flood abrupt alternation (DFAA) stresses, the barrel test method was used to set up the 'sporadic light rain' to flooding (referring to trace rainfall to heavy rain) (DFAA1) group, 'continuous drought' to flooding (DFAA2) group and normal irrigation (CK) group from the jointing to the tassel flowering stage of maize. The results showed that Actinobacteria was the most dominant phylum in the two DFAA groups during the drought period and the rewatering period, and Proteobacteria was the most dominant phylum during the flooding period and the harvest period. The alpha diversity index of rhizosphere bacteria in the DFAA2 group during the flooding period was significantly lower than that in other stages, and the relative abundance of Chloroflexi was higher. The correlation analysis between the differential genera and soil metabolites of the two DFAA groups showed that the relative abundance of Paenibacillus in the DFAA1 group was higher during the drought period, and it was significantly positively correlated with the bioactive lipid metabolites. The differential SJA-15 bacterium was enriched in the DFAA2 group during the flooding period and were strongly correlated with biogenic amine metabolites. The relative abundances of Arthrobacter, Alphaproteobacteria and Brevibacillus in the DFAA2 group were higher compared with DFAA1 group from rewatering to harvest and were significantly positively correlated with hydrocarbon compounds and steroid hormone metabolites. The acid phosphatase activity of the DFAA1 group was significantly higher than that of the DFAA2 group during the flooding period. The study suggests that there is a yield compensation phenomenon in the conversion of 'continuous drought' to flooding compared with 'sporadic light rain', which is related to the improvement in the flooding tolerance of maize by the dominant bacteria Chloroflexi, bacterium SJA-15 and biogenic amine metabolites. These rhizosphere bacteria and soil metabolites may have the potential function of helping plants adapt to the DFAA environment. The study revealed the response of the maize rhizosphere soil environment to DFAA stress and provided new ideas for exploring the potential mechanism of crop yield compensation under DFAA.

The Interaction Effects of Drought–Flood Abrupt Alternation on Rice Yield and Dry Matter Partitioning

The frequent occurrence of drought–flood abrupt alternation (DFAA) seriously affects crop yield. It is particularly important to explore the dynamics of material accumulation and distribution under DFAA stress to analyze the mechanism of yield formation. In this study, a bucket experiment with DFAA stress groups, drought control (DC) groups, flood control (FC) groups, and normal irrigation (CK) groups was set up from the jointing to the heading stage of rice to analyze the interaction effects of DFAA stress on rice yield and dry matter partitioning. The results showed that compared with the CK group, the average yield reduction rate of rice in the DFAA groups was 23.03%, and the number of grains per panicle, total grain number, thousand-seed mass, and seed setting rate decreased. Compared with the DC groups, the DFAA groups had a significant reduction in yield and its components during the flooding period. Compared with the FC groups, the DFAA groups showed a compensation phenomenon in the yield and its components during the drought period. From the end of DFAA stress to the harvest period, the root partitioning index (PI) of the DFAA groups decreased, the stem PI increased first and then decreased, the leaf PI decreased, and the panicle PI increased. The results showed that the rice leaves increased and thickened, and the stems thickened under DFAA conditions to enhance the ability to resist drought and flooding stress, but the panicle rate was reduced, the growth period of rice was delayed, and the redundant growth of stems and leaves was increased. It is suggested that the depth and duration of stagnant water storage during the flood period of DFAA should be controlled, and the transfer and supply of photosynthetic products to grains should be increased to avoid serious yield reductions. The research results provide a theoretical basis for the rational development of farmland DFAA mitigation measures.

Monitoring and Evaluating the Severity of Drought-flood Abrupt Alternation Events Using Daily Standardized Precipitation Index

A drought-flood abrupt alternation (DFAA) event is an extreme combination of an overlapping drought and flood resulting in adverse impacts on ecosystems and human society. As precipitation variability increases due to climate change, the occurrence and magnitude of DFAA events are expected to increase. Using daily precipitation data for 1966–2018, we calculated the daily standardized precipitation index for middle-sized watersheds and evaluated the severity of DFAA events in South Korea. The severity of DFAA events was evaluated in two ways: the severity of whole period (SWP) represents the total magnitude of DFAA event, and the severity of transition period (STP) indicates the instantaneous severity of DFAA event during the transition from drought to flood. The severities were also graded by the quantiles to identify risk regions, and we used precipitation concentration degree (PCD) and precipitation concentration period (PCP) to analyze the relationship between DFAA events and precipitation trends in South Korea. The results showed that the STP in the Yeongsan River basin and SWP in the Han River and the Nakdong River basin were higher than in the other basins. In addition, considering patterns and trends of the PCF and PCP in South Korea, this study found that the frequency and severity of DFAA events were high during flood seasons when precipitation was concentrated.

Exploring two-decadal risk variability of drought-flood abrupt alternation in a high-plateau basin

The escalating intensity and frequency of drought-flood abrupt alternation (DFAA) events, intensified by climate change, pose a significant threat to both the eco-environment and human life. Despite their evident impacts, the risk associated with DFAA events has received limited attention. In this study, we present a comprehensive risk assessment model incorporating multifold natural and anthropogenic indicators to analyze the spatiotemporal variations of DFAA risk. Utilizing a DFAA index (DFAAI) based on river flow data from seven monitoring stations spanning 1999 to 2019, we investigate DFAA events in the Dianchi Basin, the largest lake in the Yunnan-Guizhou Plateau, China. Our analysis reveals that 56% of total DFAA events occurred between June and August, with drought-to-flood (DTF) events accounting for 62.5% of DFAA occurrences in the Dianchi Basin. Notably, the intensity and frequency of DFAA events exhibit significant spatial variations across the basin. The hazard, vulnerability, exposure, and disaster defense indices further exhibit substantial spatial discrepancies, with hazard indicators being the most influential, notably the DFAA rate accounting for 72.4% of the overall impact. Spatial correlations in DFAA risk among monitoring stations were found to be low, primarily influenced by variations in meteorological conditions, underlying surface characteristics, and human activities. The findings of this study can offer valuable insights for effective water resource management in an ever-changing environment.

Projection of drought-flood abrupt alternation in a humid subtropical region under changing climate

Drought-flood abrupt alternation events (DFAAEs) bring about detrimental impacts on economics and environment. Projection of the future change in the DFAAEs is a challenging issue. Incorporated with the datasets of the Coupled Model Intercomparison Project Phase 5 under two Representative Concentration Pathway scenarios (RCP4.5 and RCP8.5), we applied the Soil and Water Assessment Tool model and the drought-flood abrupt alternation index (DFAAI) to detect climate change impacts on the DFAAEs in the Poyang Lake Basin for the period from 2020 to 2099. Our results demonstrated that the projected DFAAEs would become more frequent and be mainly distributed from January to October. Among them, the drought-to-flood events mainly occur from January to July, while the flood-to-drought events mainly occur from July to October. The occurrence of the DFAAEs is more frequent, and the occurrence frequency of DFAAEs under RCP4.5 is 75. The mild DFAAEs would be the dominated events in the Poyang Lake Basin, while the moderate and extreme DFAAEs are spatially unevenly distributed. The annual maximum and minimum of DFAAI would increase, and the frequency and intensity of the DFAAEs tend to increase. The projected runoff tends to increase but spatially homogenous. The projected peak flow would delay leading to a change in the transition time of the DFAAEs' type. This study provides a future projection on DFAAEs, valuable for policy makers to mitigate flood disasters at a basin scale.

Identification, physical mechanisms and impacts of drought–flood abrupt alternation: a review

Climate change has led to an increase in the frequency of extreme events, such as droughts and floods. This study aims to review the literature on the newly proposed phenomenon known as drought-flood abrupt alternation (DFAA). A comprehensive summary is provided to round up the numerous approaches employed to identify DFAA events, as well as its mechanisms and impacts. To provide a reference for responding and managing the emerging intensity and frequency of DFAA events, we conclude the paper by listing the insufficiency of current research and suggesting possible future research directions. As for the impact of DFAA, besides the loss of life and property which can be caused by any natural disaster, a DFAA event severely threatens food security by making a lasting and profound impact on the land productivity through the alteration of the combining conditions of water, soil, and temperature. As for the future research directions, existing indexes developed for DFAA identification should be improved by downscaling the temporal and spatial scale, with interactions of neighboring drought and flood events taken into consideration. What’s more, to better protect human society from the losses caused by DFAA, researches on accurate DFAA prediction are encouraged.

Substantial increase in abrupt shifts between drought and flood events in China based on observations and model simulations

Drought-flood abrupt alternation (DFAA) refers to the rapid transformation between droughts and floods, posing serious threats to ecological security, food production, and human safety. Previous studies have insufficiently investigated DFAA events at large regional scales using high-resolution observations and model simulations. In this study, the standardized precipitation evapotranspiration index was used to construct the DFAA magnitude index, which considers the asymmetric effects of drought and flood alternations. Four types of DFAA events were then investigated using high-resolution station observations and NEX-GDDP-CMIP6 model simulations. The results showed that hotspot areas of drought-flood and flood-drought alternation events were mainly in the northern and eastern parts of China, while the hotspot areas of drought-flood-drought and flood-drought-flood alternation events were obviously smaller than those of drought-flood and flood-drought alternation events. Drought-flood, flood-drought, and drought-flood-drought alternation events showed significant upward trends at rates of 0.075, 0.057, and 0.051 events/decade, respectively, and these increases were attributed to significant increases in moderate, severe, and extreme events across China during 1981–2020. Generally, the total number of DFAA events above moderate grade in the northern, central, and some areas in the southern parts of China increased obviously (>50 %) during 2001–2020 compared to 1981–2000. NEX-GDDP-CMIP6 can reasonably represent the multi-year averages and long-term trends of precipitation, temperature, and DFAA events in China. Except for the flood-drought-flood alternation events, the other three types of DFAA events showed significant increasing trends in the future, with higher rates under the SSP585 scenario than under the SSP245 scenario (e.g., drought-flood alternation events at rates of 0.033 and 0.046 events/decade under SSP245 and SSP585, respectively, during 1981–2100). DFAA events above the moderate grade were predicted to increase significantly in both 2032–2065 and 2066–2099 compared to 1981–2014, especially in northern China for the 2066–2099 under the SSP585 scenario.

Drought-flood abrupt alteration events over China

Drought-flood abrupt alternation (DFAA) is characterized by a period of persistent drought followed by sudden heavy precipitation at a certain level, with impacts on ecosystems and socioeconomic environment. At present, previous studies have mainly focuses on the monthly scale and regional scale. However, this study proposed a multi-indicator daily-scale method for identifying the DFAA occurrence, and explored the DFAA events over China from 1961 to 2018. The DFAA events mainly occurred in the center and southeast of China, especially in the Yangtze River Basin, Pearl River Basin, Huai River Basin, Southeast Rivers Basin, and south part of the Southwest Rivers Basin. The spatial coverage has a statistically significant (p < 0.05) increasing trend over China, of 0.355 %/decade. The occurrence and spatial coverage of DFAA events increased by decades, and were mainly concentrated in summer (around 85 %). The possible formation mechanisms were closely related to global warming, atmospheric circulation index anomalies, soil properties (e.g., soil field capacity), etc.

Identification and frequency analysis of drought–flood abrupt alternation events using a daily-scale standardized weighted average of the precipitation index

Drought–flood abrupt alternation (DFAA), which is defined as the rapid transition between drought and flood in a short period, amplifies the negative impacts of individual drought or flood. DFAA is divided into drought to flood (DTF) and flood to drought (FTD) according to the sequences of drought and flood. Previous studies of identifying DFAA events have mostly been conducted over a long timescale (e.g., over a month), leading to inaccurate identification or omissions of DFAA events. In addition, frequency analysis of DTF and FTD events, which is vital for the design of hydraulic structures and water supply systems, has rarely been studied. This study establishes an identification method for DFAA events based on a daily-scale standardized weighted average of the precipitation index (SWAP) and conducts frequency analysis of DTF and FTD events based on copula theory. The Han River Basin (HRB), China, a crucial area for water resource management, was selected as the study area. Our findings disclose that DFAA events occurred less frequently with larger intensities and durations between 1961 and 2020. The temporal trends of DTF and FTD events varied similarly, while the number of DTF events were less than that of FTD events, indicating that FTD is the main performance of DFAA in HRB. In addition, the identification processes of DFAA events at the Wuhan station were analyzed in detail and proved that SWAP is an effective index for capturing the change of precipitation and accurately depicting the occurrences of droughts and floods. Furthermore, drought intensity (DI) and flood intensity (FI) were selected for bivariate frequency analysis. An OR case was defined as DI ≥ di or FI ≥ fi, while an AND case was defined as DI ≥ di and FI ≥ fi. The results of frequency analysis showed that joint return periods (JRPs) of DFAA events under the OR case are basically equal in three sub-basins, meaning a similar occurrence of probability of drought–flood disaster. JRPs under the AND case increased from the upper and middle basins to the lower basin as a whole, indicating the decreasing risk of abrupt drought–flood transitions. Overall, this study may have potential value in the early warning and mitigation of DFAA disaster.

Response of summer maize growth to drought-flood abrupt alternation

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.

Evolution and prediction of drought-flood abrupt alternation events in Huang-Huai-Hai River Basin, China

Drought-flood abrupt alternation (DFAA) as a compound natural disaster can cause severe socioeconomic loss and environmental destruction. Under climate change, the Huang-Huai-Hai River Basin has experienced evident increases in temperature and variability of precipitation. However, the study of the evolution characteristics of DFAA in the Huang-Huai-Hai River Basin is limited and the risk of exposure to DFAA events under future climatic conditions should be comprehensively assessed. In this study, the DFAA events including drought to flood (DTF) and flood to drought (FTD) events in the Yellow River Basin (YRB), Huai River Basin (HuRB), and Hai River Basin (HaRB) are identified by the long-cycle drought-flood abrupt alternation index (LDFAI) and the temporal variation and spatial distribution of the number and intensity of DFAA events from 1961 to 2020 are examined. The 24 climate model simulations of Coupled Model Intercomparison Project Phase 6 (CMIP6) are used to evaluate the variation of DFAA events based on the bias-corrected method. The results show that both DTF and FTD events occurred >10 times in most areas of the Huang-Huai-Hai River Basin from 1961 to 2020, and severe DFAA events occurred more frequently in the HaRB. The occurrence of DTF events decreased and FTD events continuously increased in the YRB, while they showed opposite trends in the HuRB and HaRB. In the future, the Huang-Huai-Hai River Basin is projected to experience more DTF events under the SSP1-2.6 and SSP2-4.5 scenarios, while more FTD events under the SSP3-7.0 and SSP5-8.5 scenarios. Most areas in the Huang-Huai-Hai River Basin are projected to be at medium or high risk of the frequency and intensity of DFAA events under different future scenarios, especially in the central part of the YRB. These findings can provide scientific reference to the formulation of management policies and mitigation strategies.

Cumulative Responses of the Photosynthetic Capacity to Drought–Flood Abrupt Alternation Revealed Based on a Stomatal Optimization Model

Cumulative Responses of the Photosynthetic Capacity to Drought–Flood Abrupt Alternation Revealed Based on a Stomatal Optimization Model

Quantifying the superimposed effects of drought-flood abrupt alternation stress on vegetation dynamics of the Wei River Basin in China

• A quantitative framework was proposed for assessing the DFAA superposition impacts on vegetation. • The drought-flood synergistic and antagonistic effects on vegetation were fully examined. • The response time of vegetation to DFAA conditions was identified. • FTD and DTF showed drought-flood synergistic and antagonistic effects, respectively. • The JRB is an FTD-sensitive area, while the UWRB is a summer-autumn DTF-compensation area. Understanding the response mechanism of vegetation growth to hydro-meteorological events is essential at the global or regional scales, especially in context of global warming and anthropogenic interventions. Previous studies have focused mainly on the responses of vegetation vulnerability to single drought or flood extremes but rarely on those of drought-flood abrupt alternation (i.e., coexistence and rapid transformation of drought and flood, DFAA) events on vegetation growth. Here, this study proposed a binary copula evaluation model to quantitatively explore the internal mechanism of vegetation activity response to DFAA events (flood to drought (FTD) and drought to flood (DTF)) from probabilistic perspective. The Wei River Basin (WRB), the largest tributary of the Yellow River, was selected as a case study. Normalized Difference Vegetation Index (NDVI) was used as a proxy to reveal the spatial–temporal dynamics of vegetation coverage. Then, the response time of vegetation vitality to spring-summer and summer-autumn DFAA events was diagnosed. Finally, the conditional possibility of different vegetation states under DFAA stress was examined. Results showed that: (1) the lag time of optional vegetation response to DFAA events was more than 4 months; (2) FTD and DTF showed drought-flood synergism and antagonism by strengthening and weakening single stress, respectively; and (3) the Jing River Basin is an FTD-sensitive area, whereas as a summer-autumn DTF-compensatory area, the decision-makers should control the stress degree of the upper of the WRB to have a favorable impact on vegetation. Generally, this study sheds new insights into vegetation response to DFAA events, which provides effective theoretical support for decision-makers to formulate effective strategies for DFAA mitigation and sustainable development of ecosystems.

Dynamics and potential synchronization of regional precipitation concentration and drought-flood abrupt alternation under the influence of reservoir climate

Study regionThree Gorges Reservoir area, the largest reservoir area in China Study focusThe frequency and intensity of extreme weather events increase with climate warming, and the local climate effects in the large reservoir area may also change the local precipitation structure. Therefore, based on the precipitation sequence data in the Three Gorges Reservoir (TGR) area from 1959 to 2019, the proposed multi-time-scale mutual information entropy (MTSMIE) method was used to reveal the cyclic synchronous changes of drought-flood abrupt alternation and precipitation concentration. New hydrological insightsThe results demonstrate that (1) the spatial distribution of the precipitation concentration index in the TGR area has obvious regional variability. On the temporal scale, the precipitation concentration increased by 5.5% and decreased by 8.2% after impoundment at the head and tail of the TGR, respectively. (2) The frequency of drought-to-flood (DTF) events from the head of the reservoir area to the tail of the reservoir area presents a "more-less" feature. The frequency of DTF events after impoundment was less than that before the impoundment of the reservoir. However, the flood-to-drought (FTD) events are the opposite. (3) The period of reliable research and monitoring of DFAA and precipitation concentration in the Three Gorges region is about 15–17 years through the MTSMIE method.

Responses of Phosphate-Solubilizing Microorganisms Mediated Phosphorus Cycling to Drought-Flood Abrupt Alternation in Summer Maize Field Soil.

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.

Soil phosphorus loss increases under drought-flood abrupt alternation in summer maize planting area

Phosphorus (P), critical nutrient for plant growth and environment, has been greatly concerned. Abundant studies have been focused on soil P loss, while only sparse studies have concerned on soil P loss under extreme hydrological events, even less on drought-flood abrupt alternation (DFAA). This study explored the P migration in summer maize farmland systems based on field experiments, further obtained the proportion of soil P loss. We also simulated the soil P loss to DFAA in summer maize planting area in the Northern Anhui Plain based on history, future, and hypothetical natural (assuming no DFAA events) scenarios. The field experiments revealed that DFAA events reduced plant P storage by 47.7% than that in the natural control systems (CS). The mean proportion of soil P loss increased in the DFAA treatments (8.96%) than that in the CS treatments (1.60%). The numerical simulation results show that the proportion of average annual soil P loss due to DFAA has been increasing in the Northern Anhui Plain, with 7.98–10.34% during 1964–2017, 2.07–14.16% during 2020–2050. The spatial distribution of annual soil P loss changed as well. The soil P loss in hypothetical natural scenario was 5.1 times and 5.9 times lower than that in history and future scenarios, which indicates significantly negative impacts of DFAA on environment. This study can provide references for estimating the environmental effects of DFAA on P in farmland systems.