Understanding drought propagation through coupling spatiotemporal features using vine copulas: A compound drought perspective.

Accurately evaluating drought impact on agriculture poses a challenge to regional food security, particularly in compound drought (i.e., meteorological and agricultural drought co-occurring) scenarios. This study presents a novel approach utilizing Vine copula for coupling spatiotemporal features to evaluate drought propagation. Three-dimensional clustering method was employed to identify meteorological and agricultural drought events, which excelled in capturing dynamic evolution characteristics (duration, area, severity, etc.) as well as integrating them into comprehensive meteorological drought intensity (IMD) and agricultural drought intensity (IAD). Through spatiotemporal matching, compound drought events were extracted from the meteorological-agricultural drought event pairs. From compound drought perspective, compound duration (CD) and compound area (CA) were devised to characterize drought propagation potential across time and space. Finally, the Vine copula method was employed to model the interdependence between four key coupling features, namely IMD, IAD, CD, and CA, and evaluate the probability of triggering agricultural drought with different intensity levels. Results showed that CD and CA can respectively characterize the temporal and spatial accumulation scale of drought propagation. At a certain IMD level, CD significantly influences the propagation probability (i.e., "stratification" phenomenon), while CA increases the probability proportionally. Probability evaluation lacking spatiotemporal information may underestimate the likelihood of drought propagation characterized by "low-IMD" but "long-CD" or "large-CA". The four-dimensional Vine copula structure can effectively couple dependence relationships of compound drought characteristics, and exhibits reliable robustness. This research provides stakeholders accurate probabilistic evaluation under compound drought scenarios, offering new insight into drought propagation.

The grain Food-Energy-Water nexus in China: Benchmarking sustainability with generalized data envelopment analysis.

Food insecurity can be considered as a significant cause to instability in some regions around the world. Grain production utilizes a multiple of inputs, such as: water resources, fertilizers, pesticides, energy, machinery, and labor. In China, grain production has led to huge irrigation water use, non-point source pollution, and greenhouse gas emissions. It is necessary to emphasize the synergy between food production and ecological environment. In this study, a grain Food-Energy-Water nexus is delivered and an eco-efficiency sustainability evaluation metric is introduced, Sustainability of Grain Inputs (SGI), for investigating the sustainability of water and energy use in grain production across China. SGI is constructed by using generalized data envelopment analysis to comprehensively incorporate differences of water and energy inputs (including indirect energy use contained in agricultural chemicals such as fertilizers, pesticides, agricultural film, and direct energy use such as the electricity and diesel used for irrigation and agricultural machinery) in different regions across China. Both water and energy are considered by the new metric at the same time, which is built on the single resources metrices that are often used in the sustainability literature. This study evaluates the water and energy use of wheat and corn production in China. Wheat production uses water and energy sustainably in Sichuan, Shandong, and Henan; Corn production has the highest combined sustainability index in Shandong, Jilin, Liaoning, and Henan. In these areas, the grain sown area could be increased. However, wheat production in Inner Mongolia and corn production in Xinjiang rely on unsustainable water and energy inputs, and their grain sown areas could be reduced. The SGI is a tool that researchers and policy makers can use to better quantify the sustainability of water and energy inputs to grain production. It facilitates formulating policies about water saving and carbon emission reduce of grain production.

Do Greener Urban Streets Provide Better Emotional Experiences? An Experimental Study on Chinese Tourists.

Compared to the usual environment, the potential momentary emotional benefits of exposure to street-level urban green spaces (UGS) in the unusual environment have not received much academic attention. This study applies an online randomized control trial (RCT) with 299 potential tourists who have never visited Xi'an and proposes a regression model with mixed effects to scrutinize the momentary emotional effects of three scales (i.e., small, medium and large) and street types (i.e., traffic lanes, commercial pedestrian streets and culture and leisure walking streets). The results identify the possibility of causality between street-level UGS and tourists' momentary emotional experiences and indicate that tourists have better momentary emotional experiences when urban streets are intervened with large-scale green vegetation. The positive magnitude of the effect varies in all three types of streets and scales of intervention, while the walking streets with typical cultural attractions, have a larger impact relative to those with daily commute elements. These research results can provide guidance for UGS planning and the green design of walking streets in tourism.

Coupling water cycle processes with water demand routes of vegetation using a cascade causal modeling approach in arid inland basins.

Vegetation degradation is the key cause of land desertification in arid areas. Water stress is one of the most critical factors leading to vegetation degradation. The water needed for vegetation growth is inseparable from the water cycle processes. It is a new scope to reveal the vegetation water demand mechanisms from the water cycle processes. Water cycle processes in arid inland basins can be conceptually separated as RFA (runoff formation area) and RCA (runoff consumption area). In this study, both the water demand mechanisms of natural vegetation and farmland were discovered by creatively constructing the vegetation water demand route model. The TRB (Tarim River Basin), a typical arid inland basin system that RFA is separated from RCA, is considered as the study area. The tendency and relevance of water cycle factors and NDVI were detected. The dominant factors of vegetation growth were identified. According to the interaction causality of water cycle factors and vegetation, the PLS-SEM (partial least squares structural equation models) were constructed in RFA and RCA. Results displayed that SMroot (root-zone soil moisture), groundwater and precipitation were the dominant water sources for natural vegetation in RFA. The water demand for natural vegetation in RCA mainly came from SMroot and that for farmland mainly came from SMsurf (surface soil moisture). New findings showed that blue and green water circulations were more active in RFA than in RCA. Natural vegetation had better adaptability and resilience to water shortages compared with farmland. The higher effect of vegetation on AET (actual evapotranspiration) denoted the better growth status. It is contributed to the rational utilization of water resources in arid basins.

Disclosing the future food security risk of China based on crop production and water scarcity under diverse socioeconomic and climate scenarios.

Climate change and human development may lead to a serious crisis in food security in China, especially in areas with both water shortages and large grain production. Thus, the quantitative evaluation of future food security risk considering water scarcity is increasingly important. Here, we combined water scarcity and crop production data under different scenarios of representative concentration pathways (RCPs) and shared socioeconomic pathways (SSPs), incorporating demographic, food habit and water resource factors, to develop a new framework for measuring China's food security risk. The results show that the water scarcity and crop production-water crisis (CPWC) of China would both be aggravated during the 21st century. In particular, northern China might face more serious water scarcity than southern China and has a higher contribution rate to the national crop production-water crisis. Food scarcity in China might occur at some point in the 21st century under all SSP scenarios, except SSP1 (sustainability development pathway). The next 40 years could be the most critical period for ensuring China's food security. Moreover, by comparing the RCP2.6 and RCP6.0 scenarios, we also find that higher food production does not represent lower food security risk. The food security risk of the RCP26 scenario with higher food production was significantly higher than that of the RCP6.0 scenario at the same SSP because higher grain production comes from water shortage areas. From the perspective of societal development scenarios, SSP1 provided better results for both the risk of food security and water security in the 21st century. Our findings therefore provide useful information for a comprehensive understanding of long-term food security and water security of China.

Assessing the drought mitigation ability of the reservoir in the downstream of the Yellow River.

Due to climate change and human activities, drought frequency and its corresponding impact have intensified in many regions across China. Reservoirs are key in regulating streamflow and mitigating a drought's impact. Therefore, it is vital to analyze their drought mitigation ability. In this study, the drought adaptation capacity and drought resistance capacity of the reservoir are selected as two drought mitigation ability metrics to measure the effectiveness of a reservoir when facing a drought. The drought adaptation capacity represents the ability of a reservoir to prevent and mitigate damage caused by drought. It is assessed from two viewpoints, one reflecting the reservoir scale and layout reasonability, while the second reflecting the engineering operation and management. The drought resistance capacity refers to the ability of a reservoir to meet the water demand under a certain level of a drought (i.e. drought joint return period, which is defined later), and is calculated based on the reservoir's water supply and water demand. These two drought mitigation ability metrics can be applied not only for a single reservoir, but also for a group of reservoirs. This study applies these two metrics in the downstream of the Yellow River for a group of reservoirs. The results show that: 1) the ability of reservoirs in the downstream of the Yellow River for prevention and mitigation of damage caused by drought rates in the normal grade; and 2) the reservoirs can better resist the drought whose joint return period is smaller than 2 years while the drought resistance capacity is weak when the joint return period is over 6 years. Overall, the basin's drought adaptation and resistance capacity need to be improved. Management and operation of current water conservancy projects still need to be enhanced.

Analysis of temporal and spatial trends of hydro-climatic variables in the Wei River Basin.

The Wei River is the largest tributary of the Yellow River in China. The relationship between runoff and precipitation in the Wei River Basin has been changed due to the changing climate and increasingly intensified human activities. In this paper, we determine abrupt changes in hydro-climatic variables and identify the main driving factors for the changes in the Wei River Basin. The nature of the changes is analysed based on data collected at twenty-one weather stations and five hydrological stations in the period of 1960-2010. The sequential Mann-Kendall test analysis is used to capture temporal trends and abrupt changes in the five sub-catchments of the Wei River Basin. A non-parametric trend test at the basin scale for annual data shows a decreasing trend of precipitation and runoff over the past fifty-one years. The temperature exhibits an increase trend in the entire period. The potential evaporation was calculated based on the Penman-Monteith equation, presenting an increasing trend of evaporation since 1990. The stations with a significant decreasing trend in annual runoff mainly are located in the west of the Wei River primarily interfered by human activities. Regression analysis indicates that human activity was possibly the main cause of the decline of runoff after 1970.