Water-limited Regions Research Articles

Analysis of seasonal rainfall variability with innovative graphical methods of Konya Closed Basin, Türkiye

This study looked into the variability of seasonal rainfall in the semi-arid Konya Closed Basin (KCB), a water-limited region with high exploitation demand for water resources due to agricultural activities. In the study, seasonal precipitation data of eleven stations in the basin for the period 1971–2020 were used and analyzed with four trend methods (Şen-ITA, CWTSD, IPTA, and TPSC). Visual and statistical findings from the analyses showed generally increasing trends in winter and summer precipitation and decreasing trends in spring precipitation in the basin. In autumn precipitation, according to Şen-ITA, there is an increasing trend in seven stations and a decreasing trend in four stations, while according to CWTSD, there is an increasing trend in six stations and a decreasing trend in five stations. Based on the arithmetic mean IPTA graphs, Winter-Spring transitions in all stations occur from a rising trend region to a falling trend region, but Spring-Summer transitions take the reverse direction. In the standard deviation IPTA graphs, similar transitions in the trend regions are predominant. To the mean and standard deviation TPSC graphs, most of the stations generally have similar behavior. Spring-Summer transition arrows are dominant in Zone III, while Summer-Autumn and Autumn-Winter transitions are dominant in Zone I. Although Winter-Spring transitions are variable, they are more intense in Zone I and III. CWTSD and Şen-ITA methods are also consistent with the results obtained from IPTA graphs, both visually and numerically.

Enhanced relationship between seasonal soil moisture droughts and vegetation under climate change over China

Climate change could intensify seasonal soil moisture droughts and subsequently degrade vegetation, but it can also facilitate vegetation growth with the rising temperature and CO2 concentrations. Therefore, the change of the vegetation-drought relationship under climate change remains elusive. Here, we investigate the effects of vegetation greening (i.e., increasing leaf area index (LAI)) on seasonal soil moisture drought trends by performing a set of land surface model simulations with the Conjunctive Surface-Subsurface Process model version 2 (CSSPv2), as well as the impact of seasonal soil moisture drought change on vegetation productivity via a statistical fitting model. Our results indicate that both the impact of increasing LAI on exacerbating seasonal droughts and the impact of increasing seasonal droughts on reducing vegetation productivity have been enhanced over China during 1961–2018. Specifically, increased LAI accounts for 48 % of the rising drought frequency through escalated evapotranspiration losses, with more pronounced effects in northern semiarid regions. The decrease in vegetation stomatal conductance caused by rising CO2 concentrations limits transpiration and alleviates 11 % of the increase in drought frequency, but it cannot fully offset the drought aggravation induced by increased vegetation water consumption under climate warming. Meanwhile, increased drought frequency and intensity have reduced the upward trend in vegetation productivity by 5 % over China, and by 8 % in water-limited northern regions. Our study shows the relationship between seasonal soil moisture droughts and vegetation over China has strengthened, indicating that vegetation greening will lead to increased water shortages and further impact vegetation growth and carbon sequestration. This challenges water resources management and environmental sustainability, especially in semiarid regions.

Forecasting Soil Moisture in Caragana Shrubland Using Wavelet Analysis and NARX Neural Network

It is important for sustainable use of soil water resource and high-quality development to forecast the soil moisture in forestland of water-limited regions. There are some soil water models. However, there is not the best model to forecast the change of soil moisture in the caragana shrubland. In this paper, the plant water relationship has been investigated at the same time for a long term in the caragana shrubland of semiarid region of the Loess Plateau of China. The data of soil moisture was divided and then NARX neural network was used to build model I and model II. For model I, low frequency component was the input variable, and for model II, low frequency component and high frequency component were predicted. The results showed the average relative error for model I is 3.5% and for model II is 0.3%. The average relative error of predicted soil moisture in 100 cm layer using model II is 0.8%, then soil water content in the 40 cm and 200 cm soil depth is selected and the forecast errors are 4.9% and 0.4%. The results showed that using model II to predict soil water is well Predicting soil water using model II will be important for sustainable use of soil water resource and high-quality development.

Projecting future excess deaths associated with extreme precipitation events in China under changing climate: an integrated modelling study

Climate-change-induced extreme precipitation events have attracted global attention; however, the associated excess deaths burden has been insufficiently explored and remains unclear. We first defined an extreme precipitation event for each county when the daily total precipitation exceeded the county-specific 99·5th percentile of the daily precipitation from 1986 to 2005; then we estimated the associations between extreme precipitation events and cause-specific deaths in 280 Chinese counties using a two-stage time-series model. Second, we projected the excess deaths related to extreme precipitation events by combining the bias-corrected multi-model precipitation predictions derived under different combined emission-population scenarios of three representative concentration pathways (RCPs; RCP2·6, RCP4·5, and RCP8·5) and three shared socioeconomic pathways (SSP2, a business-as-usual scenario) populations (S1, low fertility rate; S2, medium fertility rate; and S3, high fertility rate). We quantified the climate and population contributions to the changes of future excess deaths nationwide and by climatic zones. Compared with the non-extreme precipitation days, the percentage increase of deaths associated with exposure to extreme precipitation days is 13·0% (95% CI 7·0-19·3) for accidental cause, 4·3% (2·0-6·6) for circulatory disease, and 6·8% (2·8-10·9) for respiratory disease. The number of annual average excess deaths related to extreme precipitation events during 1986-2005 was 2644 (95% CI 1496-3730) for accidental cause, 69 (33-105) for circulatory disease, and 181 (79-279) for respiratory disease. In the 2030s, the total number of excess deaths of these three causes will increase by 1244 (43%), 1756 (61%), and 2008 (69%) under RCP2·6, RCP4·5, and RCP8·5 scenarios combined with a medium-fertility-rate population (SSP2-S2), respectively, but will decrease by 3% under RCP2·6-SSP2-S2 and increase by 25% under RCP8·5-SSP2-S2 in the 2090s. Humid and water-limited regions in subtropical, middle-temperate, and plateau climate zones will face highly increased risks. Climate and population factors contributed disproportionally among the five climate zones. This study is the largest integrated projection exploring the disease burden associated with extreme precipitation events. The excess deaths will be amplified by climate and population changes. Improving mitigation and adaptation capacities is crucial when responding to precipitation extremes. National Natural Science Foundation of China and Wellcome Trust.

Integrating calibrated PTFs and modified OpenKarHydro framework to map the responses of ecohydrological processes to climate change across the Loess Plateau

Climate change is exacerbating the risk of soil water stress, soil erosion and ecological degradation in the Loess Plateau (CLP). However, the spatiotemporal dynamics of ecohydrological processes, including soil water balance (SWB), soil erosion (SE) and vegetation net primary productivity (NPP), in response to climate change remain isolated and ambiguous. Additionally, existing studies often rely on limited measured data from specific watersheds with particular land use/cover types to establish the pedotransfer functions (PTFs) for single soil hydraulic parameter (SHP). There is a notable lack of comprehensive studies that explore PTFs encompassing all SHPs applicable to the entire CLP, predict the spatiotemporal response of ecohydrological processes to climate change, and identify future risk periods and regions for SWB, SE, and NPP. To address these gaps, we first screened the PTFs applicable for the whole CLP, and then projected the spatiotemporal dynamics of ecohydrological processes from 2020 to 2030 under CMIP6 scenarios by integrating the PTFs with the OpenKarHydro, RUSLE, and CASA model, and finally classified the soil water content, SE and NPP to identify their risk periods and regions. The results showed that the PTFs achieved satisfactory accuracy, with RMSEs for Ks, θs, θr, α, n, θfc and θw being 2.682, 0.109, 0.016, 0.111, 0.897, 0.060 and 0.058, BIASs of 1.365, 0.182, 0.012, 0.031, 0.214, 0.057 and 0.048, R2s of 0.445, 0.500, 0.430, 0.400, 0.694, 0.453 and 0.453, and NSEs of 0.645, 0.737, 0.874, 0.349, 0.567, 0.756 and 0.458, respectively. SE decreased significantly from 2020 to 2030, with an average annual rate of −6.18 %. Soil water storage decreased significantly between 2020 and 2030, and declining from southeast to northwest. The proportion of area in the wet zone decreased by 4 %, while the proportion of area in the dry zone increased by 11.9 % from 2020 to 2030. The average NPP in 2020–2030 is 320.07 gC·m−2·a−1, with the largest in summer and smallest in winter, and decreasing from southeast to northwest. The NPP increased significantly in 2020–2030, with average annual value and rate of 19.61 gC·m−2·a−1 and 70.84 %, respectively. The NPP increased significantly in spring, summer and autumn, but remained stable in winter. This investigation bridges the gap between existing soil properties, missing SHPs, the strong regional applicability of PTFs, and isolated ecohydrological processes. It is promises to provide valuable insights into the response to climate change in the CLP and another water-limited regions.

Evaluation of Mediterranean perennials for extensive green roofs in water-limited regions: A two-year experiment

Extensive green roofs (EGRs) play a crucial role in urban environments, offering numerous environmental, economic, and social benefits. However, their performance largely depends on plant selection and adaptation to local climatic conditions. This study investigates the suitability of six perennial Euro-Mediterranean species for EGRs in Mediterranean and semi-arid regions, under different water regimes. A two-year experimental analysis was conducted in Rome (Italy) assessing flowering and mortality rates. Results revealed species-specific responses to irrigation levels, with notable performances observed in Thymus serpyllum, Saponaria ocymoides, and Teucrium chamaedrys, showcasing resilience to water stress. Conversely, Lavandula stoechas and Cerastium tomentosum exhibited sensitivity to water availability, emphasizing the importance of species selection for EGRs. No species completely adhered to the expected flowering period, but showed a general tendency of anticipation, and sometimes an extended flowering period, with some differences between the species. The study underscores the complexity of plant-environment interactions and highlights the need for diversified species composition to enhance EGR functionality and resilience.

Delineating groundwater potential zones using integrated remote sensing and GIS in Lahore, Pakistan.

Groundwater depletion and water scarcity are pressing issues in water-limited regions worldwide, including Pakistan, where it ranks as the third-largest user of groundwater. Lahore, Pakistan, grapples with severe groundwater depletion due to factors like population growth and increased agricultural land use. This study aims to address the lack of comprehensive groundwater availability data in Lahore's semi-arid region by employing GIS techniques and remote sensing data. Various parameters, including Land Use and Land Cover (LULC), Rainfall, Drainage Density(DD), Water Depth, Soil Type, Slope, Population Density, Road Density, Normalized Difference Vegetation Index (NDVI), Normalized Difference Built-Up Index (NDBI), Moisture Stress Index (MSI), Water Vegetation Water Index (WVWI), and Land Surface Temperature (LST), are considered. Thematic layers of these parameters are assigned different weights based on previous literature, reclassified, and superimposed in weighted overlay tool to develop a groundwater potential zones index map for Lahore. The groundwater recharge potential zones are categorized into five classes: Extremely Bad, Bad, Mediocre, Good, and Extremely Good. The groundwater potential zone index (GWPZI) map of Lahore reveals that the majority falls within the Bad to Mediocre recharge potential zones, covering 33% and 28% of the total land area in Lahore, respectively. Additionally, 14% of the total area falls under the category of Extremely Bad recharge potential zones, while Good to Extremely Good areas cover 19% and 6%, respectively. By providing policymakers and water supply authorities with valuable insights, this study underscores the significance of GIS techniques in groundwater management. Implementing the findings can aid in addressing Lahore's groundwater challenges and formulating sustainable water management strategies for the city's future.

Light rain exacerbates extreme humid heat

Humid heat waves pose significant risks to human health and the ecosystem. Intuitively, rainfall often alleviates extreme humid heat. However, here we show that light rain often accompanies extreme humid heat, exacerbating its frequency and intensity, especially over arid and semi-arid regions compared to no rain and moderate-to-heavy rain cases. This is because light rain does not dramatically reduce solar radiation but increases near-surface humidity through enhanced surface evaporation. The water replenishment from light rain as well as a shallower planetary boundary layer is crucial for consecutive extremes where there are commonly sporadic drizzle days amidst several rain-free days. These extremes last longer than rain-free extremes. Current global climate models (GCMs) overestimate light rain. After reducing this bias in a GCM, underestimations of humid heat waves in energy-limited regions and overestimations in water-limited regions are largely alleviated. These findings underscore the underappreciated impact of light rain on extreme humid heat.

Globally assessing how evapotranspiration feedbacks govern the impacts of multi-year droughts

Multi-year droughts constitute a natural experiment for testing the hydrological legacy across different climate regimes. Evapotranspiration (ET) responses to drought have not been fully elucidated because the underlying mechanisms involve complex interactions of climate, soil, and vegetation. This study collected monthly hydrometeorological data during 1982–2011 from 1069 catchments worldwide to investigate multi-year droughts and their impacts on ET and to analyse the underlying mechanisms of ET. As expected, multi-year droughts generally induced ET reductions across different climate regimes, while ET exhibited asymmetric hydrological responses with a greater portion of precipitation (P) being partitioned into ET in water-limited regions, and a smaller portion of P being partitioned in ET in energy-limited regions. Multi-year droughts induced soil moisture droughts and leaf area index decreases, which often led to increases in the vapour pressure deficit, while inconsistent responses occurred for air temperature. Interestingly, when long-term catchment wetness [i.e., (precipitation − streamflow) / precipitation] exceeded 0.50 we found that catchment wetness played a vital role in controlling the response of catchment properties to climate changes. During the multi-year droughts, attribution analysis revealed the enhanced role of available water (represented by P) in controlling ET, followed by available energy and vegetation. Although vegetation played vital role in controlling ET in energy-limited regions, it was P that controlled ET during drought periods. Taken together, these findings indicate that ET responses and their underlying mechanisms induced by multi-year droughts vary under different climate regimes. Specifically, a two-stage mechanism drove the ET responses in wet catchments, suggesting that catchments with higher catchment wetness (>0.50) could more effectively mitigate the impact of multi-year droughts.

Soil water consumption along the profile in response to soil water content variations in a black locust plantation with a rainfall exclusion in Loess Plateau

Soil drying is frequently observed in mature forests in water-limited regions, and poses a threat to sustainable development of the ecosystems. Herein, we assessed the effects of rainfall reduction on the water-use characteristics of a black locust (Robinia pseudoacacia) plantation in a sub-humid region of the Loess Plateau, China. Paired plots were established in the plantation, including a treatment with 30 % throughfall exclusion and a control. We comparatively investigated the dynamics of soil water content (SWC) throughout the profile in the two plots after four years of the treatment and determined the contribution of soil water storage (SWS) in each soil layer to water consumption according to the SWS budget. While SWC across the profile in the control plot showed general responses to replenishment and consumption under rainy and dry weather conditions, respectively, the treatment plot had smaller replenishment and consumption in deep layers, causing an aggravated deficiency in SWS and the formation of a temporary dried soil layer (DSL) at a depth of 55–100 cm. The cumulative decrement in SWS during each dry event (consecutive rainless days of ≥ 5-day duration) in the control plot was significantly correlated with SWC at 100–160 cm, suggesting a substantial contribution of water consumption from this layer. However, the treatment plot showed a major contribution to water consumption from the 0–100 cm soil layer during dry events. The vertical distribution of the root system supports these findings, which differed from our hypothesis that deep soil water would be used in response to reduced rainfall input. The distribution of fine root density in the treatment plot was relatively shallower (0–22 and 0–73.1 cm accounting for 50 % and 90 % of fine roots, respectively) than in the control plot (0–31.2 and 0–103.5 cm for corresponding values). These findings indicate that soil water deficiency resulted in the formation of DSL, which hindered water consumption and root development deeper in the soil profile. The severity and recovery of the DSL may be jointly determined by the vertical distribution of SWS and transpiration demand of the plantation. These findings provide insights for water resource management and sustainable development of the plantations in this region.

The response of soil carbon mineralization losses to changes in rainfall frequency is seasonally dependent in an estuarine saltmarsh

Altered rainfall distribution patterns resulting from climate change have substantial effects on soil carbon (C) cycling in terrestrial ecosystems particularly in water-limited regions. However, how rainfall redistribution affects soil C mineralization (CO2 and CH4 fluxes) in humid regions such as of the coastal saltmarshes remain unclear. We conducted mesocosm experiments in an estuarine saltmarsh in the Yellow River Delta of China, where we simulated three rainfall frequency scenarios (high-frequency, medium-frequency and low-frequency) with the same total rainfall amount in the dry and wet seasons, respectively. Soil CO2 and CH4 fluxes were measured before and after rain frequency treatment during a 40-day period for each season. The decrease in rainfall frequency significantly reduced the mean soil CO2 and CH4 fluxes during the dry season, but had no effect on either flux during the wet season. The seasonal variation in the response of soil C mineralization to rainfall frequency changes could be explained by the changes in antecedent soil water and salinity conditions, soil C substrate, microbial activities and diversity. Thus, the effects of changes in rainfall frequency on soil C mineralization are regulated by season, and should be considered when predicting the future C balance of coastal wetland ecosystems. Furthermore, the shift in precipitation frequency distribution towards increasing heavy rainfall events during the dry season in this region will have a great effect on soil C losses, potentially feeding back into the soil C budget and stability in this estuarine saltmarsh.

Establishing a water-use boundary function for potato through crop modeling

The yield to water-use boundary function is a valuable method for estimating attainable yield and yield gap (the difference between attainable yield and actual yield) in water-limited regions. However, the water-use boundary function for potato has not been clearly defined yet. In current research, we established a water-use boundary function for fresh potato tubers in a climatic transition zone (Longzhong Plateau, China) using a simple crop growth model. We validated this function using extensive long-term experimental data collected from field experiments and the literature. The results showed that the crop model accurately simulated the weight of fresh potato tubers with a relative root mean square error (RRMSE) of less than 30 %, a coefficient of determination (d) greater than 0.7, and a root mean square error (RMSE) of 5426 kg ha−1. The established water-use boundary function for fresh potato tubers is defined as: yield (kg ha−1) = 167 × (water use [mm] - 121), with a plateau yield of 48,082 kg ha−1 when water use exceeds 410 mm. Furthermore, the water-use boundary function was found to be highly applicable to water use-yield data collected from the literature and precipitation-yield data for the potato growing season from long-term observations. Utilizing precipitation data for the potato growing season from 1988 to 2018, the water-use boundary function was employed to calculate the average attainable yield for fresh potato tubers, ranging from 10,000 to 48,082 kg ha−1 in the Longzhong Plateau. The water-use boundary function for potato could aid farmers in water-limited regions in identifying the most profitable crop management systems.

Water use characteristics and drought tolerant ability of different winter wheat cultivars assessed under whole growth circle and at seedling stage

Using drought-resistant cultivars is important to increase crop production in water limited regions. Cultivar performance is influenced by genetic, management and environmental factors, and selection good performance cultivars is often a challenge. Five seasons (2016–2021) of field experiments and three seedling growing durations in a greenhouse, both under three water supply levels (serious water deficit, moderate water deficit and normal water supply), were conducted to assess 10 winter wheat cultivars for their water use characteristics and drought tolerance ability based on seven drought resistance indices and agronomic traits. The performance of the cultivars varied seasonally under field growing conditions. Drought resistance screened by a single index or based on the results from a single season was inconsistent. To avoid seasonal changes in cultivar performance, principal component analyses (PCA) and hierarchical cluster analysis (HCA) were conducted based on the seven indices to classify the ten cultivars into four types of drought responses. The drought resistance classification under field growing conditions at the grain yield level was highly consistent with that obtained under greenhouse growing conditions for biomass at the seedling stage. The results showed that the biomass at the seedling growing stage of the winter wheat cultivars could be used to predict the yield performance and water use characteristics when grown in the field under different water supply conditions. Precisely controlled greenhouse pot experiments could amplify the water use characteristics of different wheat cultivars for assessment. The cultivars with strong stomatal control ability had higher drought resistance and biomass production. Under field growing conditions, lower canopy temperature, deep root growth, a high root/shoot ratio and the maintenance of stomatal conductance under water stress were associated with high drought resistance. These findings provide references for selection methods and indicators for assessing drought-resistant winter wheat cultivars under different growing conditions.

Intensified future heat extremes linked with increasing ecosystem water limitation

Abstract. Heat extremes have severe implications for human health, ecosystems, and the initiation of wildfires. While they are mostly introduced by atmospheric circulation patterns, the intensity of heat extremes is modulated by terrestrial evaporation associated with soil moisture availability. Thereby, ecosystems provide evaporative cooling through plant transpiration and soil evaporation, which can be reduced under water stress. While it has been shown that regional ecosystem water limitation is projected to increase in the future, the respective repercussions on heat extremes remain unclear. In this study, we use projections from 12 Earth system models to show that projected changes in heat extremes are amplified by increasing ecosystem water limitation in regions across the globe. We represent the ecosystem water limitation with the ecosystem limitation index (ELI) and quantify temperature extremes through the differences between the warm-season mean and maximum temperatures. We identify hotspot regions in tropical South America and across Canada and northern Eurasia where relatively strong trends towards increased ecosystem water limitation jointly occur with amplifying heat extremes. This correlation is governed by the magnitude of the ELI trends and the present-day ELI which denotes the land–atmosphere coupling strength determining the temperature sensitivity to evaporative cooling. Many regions where ecosystem functioning is predominantly energy-limited or transitional in the present climate exhibit strong trends towards increasing the water limitation and simultaneously experience the largest increases in heat extremes. Sensitivity of temperature excess trends to ELI trends is highest in water-limited regions, such that in these regions relatively small ELI trends can amount to drastic temperature excess trends. Therefore, considering the ecosystem's water limitation is key for assessing the intensity of future heat extremes and their corresponding impacts.

Distinct variations of soil infiltrability of contrasting root types in a temperate mosaic-pattern grassland in northern China

Soil infiltration capacity is an important factor affecting soil moisture, and is of great significance to plant growth and groundwater recharge in arid and semiarid areas. Patchiness of grasslands widely exist and have a crucial effect on hydrological processes in water-limited regions. This study investigated soil infiltrability under natural grasslands with patchy mosaic patterns based on a series of in-situ tests. Two dominated natural restoration vegetation communities (Bothriochloa ischaemum (B. ischaemum) with fibrous root systems and Artemisia gmelinii (A. gmelinii) with tap root systems) and abandoned land (as control) were selected in the loess hilly and gully region of the Loess Plateau, China. The results showed that natural restoration grasslands significantly improved soil infiltrability in both plant and bare patches, and the emergence of patchy mosaic patterns can result in infiltration heterogeneity to redistribute water on a hillslope scale. Compared to B. ischaemum, A. gmelinii are more likely to facilitate the formation of preferential flow, contributing to the increased soil infiltration rates. The initial, steady and average infiltration rates (IIR, SIR, and AIR, respectively) and soil infiltration capacity index (SIC) were all negatively correlated with both root length density (RLD) and root surface area density (RSAD) of fine roots (diameter < 2 mm) but positively correlated with those of coarse roots (diameter ≥ 2 mm). The main factors influencing the infiltration capacity were the mean weight diameter in the 10−20 cm layer and the RSAD of the fine roots in the 0−20 cm layer, which can explain 98.6 %, 81.7 %, 63.9 %, and 91.3 % of the total variance of IIR, SIR, AIR, and SIC, respectively. This work highlights the important roles of patchy mosaic patterns in affecting soil water redistribution and the stabilization of ecological systems, providing a scientific basis for vegetation selection in the process of vegetation restoration in water-limited regions.

Light thinning effectively improves forest soil water replenishment in water-limited areas: Observational evidence from Robinia pseudoacacia plantations on the Loess Plateau, China

Soil water plays a key role in vegetation growth and recovery, mainly replenished by rainfall in the water-limited areas. Thinning is an important practice for forest reconstruction and soil water regulation. However, the effects of different thinning intensities on the dynamics of soil water and its replenishment by rainfall have been inadequately quantified, which could provide a guide for reasonable thinning intensity determination for in high-density forests from a hydrological perspective. In this study, one nonthinning plot and 5 plots with different thinning intensities, i.e., 35 % (light), 45 % (medium), 55 % (moderate), 65 % (heavy) and 80 % (extremely heavy) in Robinia pseudoacacia plantations, which are widely planted on the Loess Plateau, were set up. The volumetric soil water content (SWC) at 0–200 cm depths and rainfall were observed simultaneously and continuously for up to two years. The soil properties and vegetation structure in each plot were also measured regularly. The results showed that (1) the SWC in all the thinning plots was significantly greater than that in the nonthining plot (P < 0.05). (2) The replenishment increased with increasing thinning intensity, and then decreased after reaching a maximum at T35 % under most rainfall events except for light events. (3) The variations in the soil water response characteristics among the plots with different thinning intensities were mainly significantly correlated with the initial soil water content (ISWC), leaf area index (LAI) and understorey vegetation characteristics (P < 0.05). (4) Based on the relationship between soil water replenishment and retention with thinning intensity and stand density, quantitative equations were fitted to determine the reasonable thinning intensity (22–28 %) and retained stand density (1019–1091 trees/ha), respectively. Our study concluded that thinning could effectively improve soil water, especially light thinning, which could obviously enhance the replenishment of soil water by rainfall in Robinia pseudoacacia plantations. This study can provide a reference for determining forest thinning intensity or stand retention density, which is beneficial for water and reforestation management in water-limited regions.

Transition from opportunistic to conservative water use strategy with the growth of Robinia pseudoacacia in a typical watershed in the semiarid Loess Plateau

Understanding water use strategy is essential to evaluate plant adaptability in water-limited regions, but whether this strategy changes with plant growth needs further investigation. Robinia pseudoacacia is an exotic pioneer plantation species widely planted in the semiarid Loess Plateau of China to restore degraded ecosystems. Plant water uptake proportion from different soil layers and the water uptake pattern calculated through soil water uptake niche breadth (B index) were determined for R. pseudoacacia in 11-, 25-, 33–, and 43-yr plantations. Leaf physiological parameters and carbon stable isotopic composition (δ13C) were measured concurrently to calculate short-term and long-time integrated water use efficiency (WUE). Then, the water use strategy for R. pseudoacacia at different plantation ages was assessed through water uptake patterns, stomatal conductance (gs), and WUE variation under varied soil water conditions. Results showed that R. pseudoacacia maintained high gs and low short-term WUE and δ13C through a relative equal water uptake pattern and absorbed water within 0 − 400 cm soil depths in 11- and 25-yr plantations. However, this species exhibited an exclusive water uptake pattern and absorbed water mainly from 50 − 400 cm soil depth, adopted low gs and high short-term WUE and δ13C in 33– and 43-yr plantations. Therefore, R. pseudoacacia transited from an opportunistic to a conservative water use strategy with plant growth. The short-term WUE and δ13C were mainly and significantly influenced by gs and specific leaf area, respectively. Furthermore, the significant influence of B index on gs, δ18OΔ, short-term WUE, and δ13C indicated that R. pseudoacacia coordinated both water uptake pattern and water use behavior to contend with varied soil water conditions. This study suggested that changes in age-related water use strategy were essential for the adaptability of R. pseudoacacia in water-limited conditions.

Improving Irrigation Management of Cotton with Small Unmanned Aerial Vehicle (UAV) in Texas High Plains

The rapid decline in water availability for irrigation on the Texas High Plains (THP) is a significant problem affecting crop production and the viability of a large regional economy worth approximately USD 7 billion annually. This region is the largest continuous cotton-producing area in the United States, and the timely delivery and efficient use of irrigation water are critical to the sustainability and profitability of cotton production in this region. Current irrigation scheduling must be improved to reduce water consumption without compromising crop production. Presently, irrigation scheduling based on reference evapotranspiration (ETo) is limited due to the lack of reliable and readily available in-field weather data and updated crop coefficients. Additionally, in-field variability in crop water demand is often overlooked, leading to lower irrigation efficiency. To address these challenges, we explored the potential use of an unmanned aerial vehicle (UAV)-based crop monitoring system to support irrigation management decisions. This study was conducted in Lubbock, Texas, in 2022, where high temporal and spatial resolution images were acquired using a UAV from a cotton field experiment with four irrigation levels. Soil moisture and canopy temperature sensors were deployed to monitor crop response to irrigation and rainfall. The results indicated a significant effect of water stress on crop growth (revealed by UAV-based canopy cover (CC) measurements), yield, and fiber quality. Strong correlations between multi-temporal CC and lint yield (R2 = 0.68 to 0.88) emphasized a clear trend: rainfed treatments with lower yields exhibited reduced CC, while irrigated plots with higher CC displayed increased yields. Furthermore, irrigated plots produced more mature and uniform fibers. This study also explored various evapotranspiration calculation approaches indicating that site-specific CC measurements obtained from a UAV could significantly reduce irrigation application. A regression model linking evapotranspiration to canopy cover demonstrated promising potential for estimating water demand in crops with an R2 as high as 0.68. The findings highlight the efficacy of UAV-based canopy features in assessing drought effects and managing irrigation water in water-limited production regions like the THP.

Response of deep soil water deficit to afforestation, soil depth, and precipitation gradient

In semi-arid and semi-humid regions, deep soil water resources are crucial for vegetation restoration to mediate the ecosystem sustainability. Yet it is still limited on understanding soil water deficit (SWD) caused by vegetation restoration and its response to soil depth and precipitation. To obtain a more accurate measurement of regional SWD, we conducted a two-year soil water monitoring to a depth of 1800 cm under typical vegetation restoration with a precipitation gradient ranging from 300 mm/y to more than 600 mm/y across the Loess Plateau of China. With increasing precipitation gradient, soil water storages in 0–1800 cm depth under both arable cropland and artificial vegetation significantly increased (p < 0.05). Compared to arable cropland, artificial vegetations (forest and shrub) had a significantly greater SWD regardless of either precipitation gradient or soil depth. In particular, the deep-rooted vegetations (R. pseudoacacia and C. korshinskii) on the Loess Plateau demonstrated the greatest SWD in the 0–1800 cm layer due to their great water consumption. Indeed, a positive relationship between the accumulated SWD and the accumulated root biomass was detected, suggesting that the increased root biomass in soil depth may promote soil water consumption. In addition, the relative SWD in artificial vegetation at a depth of 1800 cm decreased significantly (p < 0.05). These findings reveal that there is a mechanism of precipitation self-regulation on the deep SWD, of which is more sensitive in the sub-shallow soil layers. We conclude that the SWD depends on vegetation restoration, soil depth, and precipitation self-regulation, offering a reference for how afforestation affects deep soil water in the Loess Plateau region. This finding also benefits to mediate water balance processes and develop sustainable land management in water-limited regions around the world.

Rapid recovery of desert shrubs is attributed to imbalance of water supply to demand after disturbance in Northwest China

BackgroundDisturbance is a key driver of changes in terrestrial ecosystems, especially in water limited regions. In the desert ecosystem of Northwest China, shrubs are often foraged by camels and this causes the shrubs lost their aboveground tissues. Although the aboveground tissue could recover after the disturbance, the mechanisms of resprouts’ recovery after the disturbance are still poorly understood. We investigated the morphological and physiological characteristics and root water uptake sources of resprouts and non-disturbed seedlings of four desert shrub species that were often foraged by camels.ResultsThe results showed that the resprouts grew rapidly after the removal of aboveground tissue. The height and aboveground biomass of resprouts reached the level of 5-year-old seedlings following a growing season. Compared to un-disturbed seedlings, higher leaf water potential, leaf hydraulic conductance and photosynthesis rate were observed in resprouts, indicating that resprouts grew rapidly after disturbance. Furthermore, we found that the root water uptake source did not change after disturbance. This indicated that the roots of resprouts kept intact water uptake capacity after disturbance, which could keep supplying sufficient water to the aboveground tissue. Due to the removal of aboveground tissue of the resprouts, the water demand of aboveground tissue decreased, which induced an imbalance of water supply from roots to demand of aboveground tissues of resprouts. This explained the improved physiological performance and rapid recovery of resprouts after disturbance.ConclusionsThe imbalance of water supply to demand contributes to the rapid recovery of desert shrubs after disturbance. The findings provide insight into the eco-physiological mechanism for the maintenance of desert ecosystems that are facing disturbance.