Throughout human history, floods have resulted in significant environmental and economic damages globally, and these impacts are expected to increase with climate change. Despite the occurrence of significant floods in Iran in recent decades, the precise impact of intense rainfall and antecedent soil moisture (ASM) on flood occurrence and how this relationship differs at different locations remains an area that requires further investigation. In this study, we analyzed annual maximum floods at 963 catchments across Iran from 1972 to 2019 (47 years). Moreover, we evaluated the relationship between catchment area and the main factor responsible for flood generation. Our analysis reveals a shift in the dominant factor driving flood generation from rainfall to ASM as the catchment area expands. The correlation between the topographic wetness index and the ratio of the relative significance of ASM (S) and daily rainfall (R) (i.e., Soil moisture-to-Rainfall Ratio; SRR = SR.), is positive, while the correlation between the magnitude of annual floods and SRR ratio is negative. A quantitative estimation of potential flood probability in ungauged catchments in Iran is facilitated by establishing a framework based on the relationship between easily measurable catchment attributes and the primary phenomenon of flood generation.

Due to the differences in the green water (GW) budget patterns of different vegetation, improper vegetation restoration may not only fail to improve the ecological environment but also cause irreversible damage to ecologically vulnerable areas, especially when vegetation restoration continues to be implemented in the future, and the pressure on water scarcity increases further. However, there is a lack of standardized research on the differences in the patterns of recharge, consumption, and efficient use of GW in typical vegetation. This makes the research results vary and cannot provide direct support for water management decision-making. Therefore, in this study, 30-year-old woodlands (R. pseudoacacia and P. orientalis) and two typical grasslands (I. cylindrican and M. sativa) that are similar to each other except for species were selected in a headwater catchment in the rain-fed agricultural area. A new GW concept and assessment framework was constructed to study the GW of long-term revegetation using a combination of field experiments and model simulations during the 2019-2020 growing season. The study findings comprise the following: (1) High-efficiency green water (GWH), low-efficiency green water (GWL), ineffective green water (GWI), and available green water storage (GWA) in the four sample plots during the study period were defined, separated, and compared. (2) An analysis of GWA variations under different water scenarios. (3) The establishment of GWH and GWL thresholds. (4) Strategies to reduce GWI and optimize GW potential while maintaining soil erosion prevention measures. (5) Suggestions for vegetation restoration species based on diverse factors. This research enhances comprehension of the impact of vegetation restoration on green water dynamics in ecologically vulnerable areas such as the rain-fed agricultural zone of the Loess Plateau.

The creation of fractures in bedrock dictates water movement through the critical zone, controlling weathering, vadose zone water storage, and groundwater recharge. However, quantifying connections between fracturing, water flow, and chemical weathering remains challenging because of limited access to the deep critical zone. Here we overcome this challenge by coupling measurements from borehole drilling, groundwater monitoring, and seismic refraction surveys in the central California Coast Range. Our results show that the subsurface is highly fractured, which may be driven by the regional geologic and tectonic setting. The pervasively fractured rock facilitates infiltration of meteoric water down to a water table that aligns with oxidation in exhumed rock cores and is coincident with the adjacent intermittent first-order stream channel. This work highlights the need to incorporate deep water flow and weathering due to pervasive fracturing into models of catchment water balances and critical zone weathering, especially in tectonically active landscapes. The creation of fractures in bedrock facilitates water movement through the subsurface which breaks down rock creating porous soil and weathered bedrock. Water movement is vital for important processes like plant growth, streamflow, and groundwater recharge. However, understanding how fracturing, water flow, and rock weathering interact is challenging because the subsurface is difficult and expensive to measure. Here we use observations from drilling, water level monitoring, and geophysics to understand these interactions. Our results indicate that the subsurface is highly fractured due to the geologic and tectonic setting. The large number of fractures makes it easier for water to flow through the subsurface and causes chemical alteration of bedrock. This may cause water to flow outside of the catchment through the subsurface. This work highlights the role of geologic and tectonic processes in driving fracturing, which dictates the movement of water and subsurface weathering beneath Earth's surface. Deep weathering may be due to enhanced permeability and surface area from inherited rock damage from local geologic and tectonic conditions Weathering and water flow extend to the elevation of the adjacent first-order intermittent stream channel The deep weathering and fracturing front may allow for inter-basin water flow in headwater catchments

Study region: The Urumqi River basin located in eastern Tien Shan in Central Aisa Study focus: Glacier runoff plays a pivotal role in water resources and stabilizing streamflow in mountainous regions. To assess the characteristics of glacier ice melt runoff in sub-basins within a single basin, three sub-basins with glacier ratios varying from 4% to 46% in the Urumqi River basin are investigated. Through the simulation by HBV light model on the basis of the observed meteorological and hydrological data. The characteristics and behaviour of glacier ice melt runoff in the three sub-basins are analysed. New hydrological insights for the region: It was found that both the contribution ratios of ice melt runoff and glacier runoff increase linearly with the increasing glacier ratio for the three catchments, rather than logarithmically or exponentially as observed in previous studies. This is due to the relatively high contributions of ice melt and glacier runoff to river flow in a catchment characterized by high elevation and extensive glacier coverage (Catchment 1), resulting from the coincidence of summer precipitation maxima with snow and ice melt in this region. The coefficient of variations (CV) of river flow tends to decrease with the decreasing glacier ratio in subbasins in the Urumqi River basin, indicating that river flow becomes more stable as it flows farther from the headwater in the Urumqi River basin. The lowest glacierized Catchment 3 exhibited the minimum CV value, demonstrating a stable outflow.

Environmental damages are inherent to urbanization processes and therefore need to be carefully measured and mitigated, especially those that affect hydrological regimes, because they reverberate beyond the urbanized area and reach the entire watershed. Although essential for mitigating environmental damages affecting suburban subdivisions, drainage systems and rainwater management are usually given secondary status during urban land planning. The present study evaluated the implications of the absence of adequate subdivision planning, focusing on the process of occupation and regularization of the Gated Community Alto da Boa Vista - in the Sobradinho Administrative District (in Brazil's Federal District). Our sources were land regularization documents, data on rainfall, soil typology and remote sensing imagery. The images allowed us to detect changes in soil cover over several years and to identify resulting changes in infiltration and runoff. Data analysis showed that faulty attention was given to environmental and urban aspects during the planning phase and the installation of the gated community and contributed to the occurrence of erosion processes. It was found that it is necessary to improve public management routines to expedite the granting of urban and environmental licenses, in addition to defining technically adequate and integrated requirements for the installation of drainage systems and the management of rainwater runoff in areas affected by urban expansion.

There is an increased awareness that the biogeochemical cycling at high latitudes will be affected by a changing climate. However, because biogeochemical studies most often focus on a limited number of elements (i.e., C, P and N) we lack baseline conditions for many elements. In this work, we present a 42-element mass-balance budget for lake dominated catchment in West Greenland. By combining site specific concentration data from various catchment compartments (precipitation, active layer soils, groundwater, permafrost, lake water, lake sediments and biota) with catchment geometries and hydrological fluxes from a distributed hydrological model we have assessed present-day mobilization, transport and accumulation of a whole suite of elements with different biogeochemical behavior. Our study shows that, under the cold and dry conditions that prevails close to the inland ice-sheet: i) eolian processes are important for the transport of elements associated with mineral particles (e.g., Al, Ti, Si), and that these elements tend to accumulate in the lake sediment, ii) that even if weathering rates are slowed down by the dry and cold climate, weathering in terrestrial soils is an important source for many elements (e.g., lanthanides), iii) that the cold and dry conditions results in an accumulation of elements supplied by wet deposition (e.g., halogens) in both terrestrial soils and the lake-water column, and iv) that lead and sulfur from legacy pollution are currently being released from the terrestrial system. All these processes are affected by the climate, and we can therefore expect that the cycling of the majority of the 42 studied elements will change in the future. However, it is not always possible to predict the direction of this change, which shows that more multi-element biogeochemical studies are needed to increase our understanding of the consequences of a changing climate for the Arctic environment.

Improving our understanding of streamwater age knowledge is critical for revealing the complex hydrological processes in alpine cryosphere catchments. However, few studies on water age have been conducted in alpine cryosphere catchments due to the complicated and inclement environment. In this study, the Buqu catchment, a typical alpine catchment covered by glaciers and permafrost on the central Tibetan Plateau (TP), was selected as the study area. Using the sine-wave ap-proach anda gamma model based on the seasonal cycle of stable isotopes in water, the young water fraction (Fyw) and mean transit time (MTT) of the Buqu catchment outlet and 23 sub-catchments was estimated to comprehensively reveal the potential driving mechanism of water age variability. The streamwater MTT for the entire catchment was 107 days, and 15.1 % of the streamwater was younger than 41 days on average. The estimated water age showed significant spatial heterogeneity with shorter water ages in high-elevation and glacier catchments and longer water ages in low-elevation and non-glacier catchments. Precipitation was the primary driver for spatial variations in water age, while the thickness of the permafrost active layer may function as an intermediate hub to drive water age variability. Mechanically, the thick-ness of the permafrost active layer controls the water ages by modifying the flow direction and length of water flow path. Spatially, this control mechanism is indirectly driven by the elevation gradient. The TDS concentration in streamwater is significantly related to water age, thus revealing a close link between water quality and hydrology. Our findings suggest that cryosphere retreats likely alter water age, thereby slowing water circulation rates and affecting water quality security under global warming. This study provides insights into the evolution of water ages, thereby deepening our understanding of the hydrological processes and guiding the protection of water resources in alpine headwater catchments.

The permafrost headwater catchments in the Tibetan Plateau (TP) have experienced extensive permafrost degradation, which may cause major changes in riverine solutes. However, surface water hydrochemistry and its influencing factors in such catchments are poorly understood. Hydrochemistry data for different surface waters were obtained for the Yakou catchment in the Northeastern TP. The results indicate that the ionic and organic concentrations of frozen soil seeps (FSS) were higher on the north-facing slope compared to the south-facing slope, and that FSS may be involved in streamflow generation processes and in determining the spatial pattern of riverine solutes. The north-facing slope of the catchment has a thin active layer and wet moisture conditions compared to the south-facing slope; hence supra-permafrost water, with high ionic concentrations, can drain to the ground surface as FSS in the riparian zone and then recharge the surface ponding water and the main stream water. The high ionic concentrations of the supra-permafrost water and FSS can be attributed to intense rock weathering and evaporative effect, together with the high mobility of elements and the transport of organic matter. The tributaries, with low ionic concentrations, comprise a mixture of infiltrating precipitation and diluted supra-permafrost water. Carbonate weathering is the dominant weathering type within the catchment, but the weathering of evaporite and silicate is more important on the north-facing and south-facing slopes, respectively, and chemical weathering on the north-facing slope may be enhanced by strong physical erosion during repeated freeze-thaw cycles due to the wet conditions. The results indicate that the surface water hydrochemistry is heterogeneous on the different hillslope units, and that a thicker active layer under climate change may lead to a shift of hydrological and hydrochemical pathways, and thus a decrease in water and solute flux from the hillslopes, with underlying permafrost, to the river channel.

This paper addresses the nexus of climate change and variability, soil moisture and surface runoff over the Lake Baikal catchment. Water level and distribution of dissolved and suspended matter over Lake Baikal are strongly affected by river inflow during rain-driven floods. In this study, we evaluate river flow changes at 44 streamflow gauges as well as related precipitation, evaporation, potential evaporation and soil moisture obtained from the ERA5-Land dataset. Based on Sen's slope trend estimator, Mann-Kendall non-parametric test, and using dominance analysis, we estimated the influence of meteorological parameters on river flow during 1979-2019. We found a significant correlation between the precipitation elasticity of river flow and catchment characteristics. Half of the gauges in the eastern part of the Selenga River basin showed a significant decreasing trend of average and maximum river flow (up to -2.9%/year). No changes in the central volume date of flood flow have been found. The reduction in rainfall amount explains more than 60% of runoff decrease. A decrease in evaporation is observed in areas where precipitation decrease is higher than 0.8%/year. Catchments, where the precipitation trends are not as substantial, are associated with increasing evaporation as a result of the increasing potential evaporation. Negative precipitation trends are accompanied by negative trends of soil moisture. Finally, the study reveals the sensitivity of catchments with steep slopes located in humid areas to precipitation change.

The glacier river is highly sensitive to the temperature and precipitation change in the alpine regions. However, to what extent of this sensitivity is still not clear. In this work, a procedure to quantify the impact of temperature and precipitation on water runoff components is proposed with a benchmark study at a typical temperate glacier catchment of Mingyong in the southeastern Tibetan Plateau (SETP). Firstly, we use Bayesian Monte Carlo Mixing Model to calculate contributions of different recharging sources to runoff from 213 water samples within a whole hydrological year (from August 2017 to July 2018). Hydrograph separation results show that the meltwater occupied the highest proportion in runoff from June to September (up to 58.4%) and the contribution of groundwater to runoff reached the maximum in January. Secondly, by establishing the relationships between temperature, precipitation and fractions of runoff components, we find that temperature change contributes about 78% to affecting the runoff components in Mingyong catchment at the intra-annual scale. Meanwhile, precipitation change occupies approximately 22% in influencing contributions of different endmembers to stream mainly by accelerating the melting process of glacier and accumulated snow as well as recharging the river directly. Finally, a conceptual model is developed to show the influence of temperature and precipitation on the runoff components in Mingyong catchment. The findings can not only provide essential evidence on gaining more insights into the mechanism of glacier river flow variation but also benefit for the strategy making for water resources management in alpine regions.