Agricultural drought is a natural and damaging phenomenon that is especially harmful to rainfed agriculture. It occurs when there is insufficient soil moisture in the root zone for plants to survive between two rainfall events. In the absence of soil moisture, a variety of losses, including soil evaporation and plant transpiration, cause an imbalance between water supply and water loss. An evapotranspiration-based index was used here to assess agricultural drought. We applied this framework to a less studied area near Fariman City in the northeast part of IRAN. Two time periods were selected for comparison including 2015 and 2016 spring season that are associated with dry and wet conditions, respectively. To calculate the drought index, actual and potential evapotranspiration were estimated by the Surface Energy Balance Algorithm for Land (SEBAL), the upgraded Priestley-Taylor method and remote sensing data. The Relative Water Deficit Index (RWDI) illustrated that lack of water in rainfed lands and pastures for the dry period was obtained from 80 to 100 percent, whereas this was between 50 and 70% for the wet period.

The study applies the Minimum Impact Design Standards (MIDS) calculator to assess urban trees' effectiveness in reducing surface runoff along five flood-prone streets in Hue City, analyzing evapotranspiration, rainfall interception, and infiltration, along with Leaf Area Index (LAI), Canopy Projection (CP), tree pit size, and soil structure. Results show that urban trees retain 1,132.39 m(3) of stormwater, but runoff reduction is not solely dependent on tree quantity. Although tree numbers vary 1.56 to 3.8 times, runoff reduction differs only 1.39 to 1.79 times. Evapotranspiration plays the largest role, contributing 2.8 times more than interception and 2.6 times more than infiltration. Small tree pits and compacted soil limit infiltration, while pruning and height reduction decrease Pc and LAI, reducing flood mitigation benefits. Annual storm damage further weakens this capacity. To enhance effectiveness, the study suggests prioritizing storm-resistant species, increasing tree numbers, enlarging tree pits, and using structured soil. Implementing these measures can improve urban flood resilience and maximize trees' hydrological benefits. Future research should focus on optimizing tree selection and planting strategies for long-term flood management in urban areas, ensuring sustainable solutions that enhance both stormwater control and environmental resilience.

Mercury (Hg) poses significant risks to human health, the environment, and plant physiology, with its effects influenced by chemical form, concentration, exposure route, and organism vulnerability. This study evaluates the physiological impacts of Hg on Handroanthus impetiginosus (Ip & ecirc; Roxo) seedlings through SPAD index measurements, chlorophyll fluorescence analysis, and Hg quantification in plant tissues. Four-month-old seedlings were exposed for eight days to distilled water containing Hg at 0, 1, 3, 5, and 7 mg L-1. The SPAD index decreased by 28.17% at 3, 5, and 7 mg L-1, indicating reduced photosynthetic capacity. Chlorophyll a fluorescence analysis revealed a 50.58% decline in maximum efficiency (Fv/Fm) and a 58.33% reduction in quantum yield (Phi PSII) at 7 mg L-1, along with an 83.04% increase in non-photochemical quenching (qn), suggesting oxidative stress and PSII damage. Transpiration decreased by 26.7% at 1 mg L-1 and by 55% at 3, 5, and 7 mg L-1, correlating with Hg levels and leaf senescence. Absorption, translocation, bioconcentration, and bioaccumulation factors varied among treatments. Hg accumulated mainly in stems (40.23 mu g g-1), followed by roots (0.77 mu g g-1) and leaves (2.69 mu g g-1), with limited translocation to leaves. These findings highlight Hg's harmful effects on H. impetiginosus, an ecologically and commercially valuable species, addressing a gap in research on its Hg tolerance and phytoremediation potential.

Evapotranspiration (ET) is a critical component of the soil-plant-atmosphere continuum, significantly influencing the water and energy balance of ecosystems. However, existing studies on ET have primarily focused on the growing season or specific years, with limited long-term analyses spanning decades. This study aims to analyse the components of ET within the alpine ecosystem of the Heihe River Basin, specifically investigating the dynamics of vegetation transpiration (T) and soil evaporation (Ev). Utilizing the SPAC model and integrating meteorological observations and eddy covariance data from 2013 to 2022, we investigate the impact of solar radiation and vegetation dynamics on ET and its partitioning (T/ET). The agreement between measured and simulated energy fluxes (net radiation and latent energy flux) and soil temperature underscores the validity of the model's performance. Additionally, a comparison employing the underlying water use efficiency method reveals consistent T/ET values during the growing season, further confirming the model's accuracy. Results indicate that the annual average T/ET during the 10-year study period is 0.41 +/- 0.03, close to the global average but lower than in warmer, humid regions. Seasonal analysis reveals a significant increase in T/ET during the growing season (April to October), particularly in May and June, coinciding with the thawing of permafrost and increased soil moisture. In addition, the study finds that the leaf area index and canopy stomatal conductance exhibit a logarithmic relationship with T/ET, whereas soil temperature and downward longwave radiation show an exponential relationship with T/ET. This study highlights the importance of understanding the stomatal conductance dynamics and their controls of transpiration process within alpine ecosystems. By providing key insights into the hydrological processes of these environments, it offers guidance for adapting to climate change impacts.

Due to the complex and multi-dimensional nature of droughts, it is not possible to assess droughtinduced damage and its consequences for various social, economic, and environmental aspects of societies by relying only on a univariate index such as precipitation-based drought indices. The present study aimed to develop a practical and scientific framework based on hazard, vulnerability (social, economic, and environmental), and coping capacity to generate a drought risk map for the hot and dry climate regions of Iran. Accordingly, the Drought Hazard Index (DHI), Drought Vulnerability Index (DVI), and Drought Coping Capacity Index (DCCI) were derived from the Standardized Precipitation Evapotranspiration Index (SPEI), 16 social, economic and environmental variables and three social, economic variables, respectively. The layers of all variables of the three indices in the GIS were provided, and they were combined in the form of an equation to produce a drought hazard map of central and southeastern Iran. The results indicate that the counties most and least vulnerable to drought were located in the southeast and west of the case study area, respectively. A number of large households, long distances from provincial centers, and soil erosion were the most important social, economic, and environmental factors making the southeast of the case study (including south of Sistan and Baluchestan and south of Kerman provinces) most vulnerable to drought. Due to their high drought coping capacity, counties located in the west of the case study (west of Kerman and south of Yazd provinces) were least vulnerable to drought. Extended support for low-income households by charitable organizations, tertiary education, and most importantly, a variety of jobs and career opportunities were the most important factors in reducing vulnerability in this part of Iran. Furthermore, our methodology by taking social, economic, and environmental dimensions into account as risk, vulnerability, and coping capacity indices can be far more efficient than the methods considering only risk and vulnerability factors.

Evapotranspiration (ET) is an important water budget term for understanding the recovery of stormwater retention in green roof systems (GRs). However, ET evaluations, particularly in full-scale GRs, remain challenging. This study investigated ET dynamics within a GR in the City of Pittsburgh, USA, using a water balance based on continuously monitored soil moisture from moisture sensors over 15 months. Results suggest under well-watered soil conditions, daily moisture loss correlated with solar radiation, temperature, and humidity, in decreasing order of correlation strength, while wind speed had limited effects. Compared to sensor-informed moisture loss (using moisture-based water balance), the Hargreaves and FAO-56 Penman-Monteith equations predicted cumulative ET that was 1.8 and 2.1 times higher, respectively. When soil moisture declined and approached the temporary wilting points, a noticeable reduction in daily moisture loss was observed. This suggests the necessity of using a water stress coefficient alongside a crop coefficient to represent actual ET based on FAO-56 Penman-Monteith estimates. Seasonal crop coefficients from dominant native plant species present at our monitored location, eastern bluestar (Amsonia tabernaemontana) and creeping woodsorrel (Oxalis corniculata), had mean values of 0.48, 0.62, and 0.65 for fall, spring, and summer, respectively. The impact of water stress on ET could be characterized by a linear relationship with moisture content. Our results highlight the importance of soil moisture in regulating ET processes and demonstrate the utility of soil moisture data for evaluating ET in GRs and informing irrigation practices.

Elevation plays a crucial role in modulating the spatiotemporal distributions of climatic variables in mountainous regions, which affects water and energy balances, among which reference evapotranspiration (ET0) is a key hydrological indicator. However, the response of ET0 to climate change with elevation continues to be poorly understood, especially in the Tibetan Plateau (TP) which has elevation variations of more than 4,000m. The spatiotemporal variations of ET0 with elevation were investigated using long-term (1960-2017) meteorological observations from 82 stations on the TP. The results suggest that the average annual ET0 showed an insignificant increasing trend. A significant negative correlation between ET0 and elevation was found (p<.01). The positive trends of ET0 decreased with elevation, whereas the negative trends of ET0 increased significantly with elevation (p<.05). The magnitude of trends of ET0 becomes smaller at higher-elevation stations. Sensitivity analysis indicated that ET0 was most sensitive to shortwave radiation (R-s). Moreover, the sensitivities of temperature (T) and wind speed (U) significantly decreased with elevation, whereas those of R-s and vapour pressure deficit (VPD) increased slightly with elevation. The contribution and path analyse indicated that increasing VPD was the dominant contributor to the increase in ET0. The effect of elevation on ET0 variation mainly depended on the tradeoff between the contributions of U and VPD. U was the largest contributing factor for the change in ET0 below 2,500m, whereas VPD was the primary contributor to the increase in ET0 above 2,500m. This study provides insights into the response of ET0 to climate change with elevation on the TP, which is of great significance to hydrometeorological processes in high-altitude regions.

The retreat of glaciers has altered hydrological processes in cryospheric regions and affects water resources at the basin scale. It is necessary to elucidate the contributions of environmental changes to evapotranspiration (ET) variation in cryospheric-dominated regions. Considering the upper reach of the Shule River Basin as a typical cryospheric-dominated watershed, an extended Budyko framework addressing glacier change was constructed and applied to investigate the sensitivity and contribution of changes in environmental variables to ET variation. The annual ET showed a significant upward trend of 1.158 mm yr(-1) during 1982-2015 in the study area. ET was found to be the most sensitive to precipitation (P), followed by the controlling parameter (w), which reflects the integrated effects of landscape alterations, potential evapotranspiration (ET0), and glacier change ( increment W). The increase in P was the dominant factor influencing the increase in ET, with a contribution of 112.64%, while the decrease in w largely offset its effect. The contributions of P and ET0 to ET change decreased, whereas that of w increased when considering glaciers using the extended Budyko framework. The change in glaciers played a clear role in ET change and hydrological processes, which cannot be ignored in cryospheric watersheds. These findings are helpful for better understanding changes in water resources in cryospheric regions.

While the direct impact of climate change on reference evapotranspiration (ET0) has been extensively studied, there is limited research on the indirect impact resulting from the interaction between climatic variables. This gap hinders a comprehensive understanding of climate change effects on ET0. Additionally, there is scarce exploration into the quantitative effect of freeze-thaw cycles on ET0 variation. In this study, we employed path analysis and dependent variable variance decomposition methods to discern the direct and interactive effects of climatic variables on ET0 in the Tibetan Plateau from 1960 to 2022. Annual ET0 exhibited variation across basins, with the coefficient of variability during the thawed period smaller than that during the non-thawed period. On an annual scale, the largest contribution to ET0 variation came from water vapor pressure deficit (VPD) at 47.7%. This contribution was amplified by its coupled interaction with temperature (T) at 47.1%, although the contribution was partially offset by the interactive effects of VPD with downward shortwave radiation and wind speed at -2.4% and - 27.6%, respectively. During different freezing-thawing periods, VPD primarily controlled ET0 variation, with its interaction with other climatic variables enhancing its impact. Furthermore, soil moisture, influenced by freeze-thaw cycles, exhibited a strong correlation with T and VPD, indicating the significant effect of freeze-thaw cycles on ET0 variation. The weak correlation between ET0 and NDVI suggested that vegetation growth had a limited regulatory effect on ET0. These findings provide valuable insights into the impact of interactions between climatic variables on hydrological processes, enhancing our understanding of the interactive roles of hydrometeorological variables.

Estimation of evapotranspiration (ETa) change on the Tibetan Plateau (TP) is essential to address the water requirement of billions of people surrounding the TP. Existing studies have shown that ETa estimations on the TP have a very large uncertainty. In this article, we discuss how to more accurately quantify ETa amount and explain its change on the TP. ETa change on the TP can be quantified and explained based on an ensemble mean product from climate model simulations, reanalysis, as well as ground-based and satellite observations. ETa on the TP experienced a significant increasing trend of around 8.4 +/- 2.2 mm (10 a)-1 (mean +/- one standard deviation) during 1982-2018, approximately twice the rate of the global land ETa (4.3 +/- 2.1 mm (10 a)-1). Numerical attribution analysis revealed that a 53.8% TP area with the increased ETa was caused by increased temperature and 23.1% part was due to soil moisture rising, because of the warming, melting cryosphere, and increased precipitation. The projected future increase in ETa is expected to cause a continued acceleration of the water cycle until 2100. (c) 2024 Science China Press. Published by Elsevier B.V. and Science China Press. All rights are reserved, including those for text and data mining, AI training, and similar technologies.