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Glacier area changes on the Tibetan Plateau were studied in different drainage basins based on Landsat satellite images from three epochs: 263 in the mid-1970s, 150 in 1999–2002 and 148 in 2013/14. Three mosaics (M1976, M2001 and M2013) with minimal cloud and snow cover were constructed, and the uncertainty due to each epoch having a finite span was accounted for. Glacier outlines (TPG1976, TPG2001 and TPG2013) were digitized manually with guidance from the SRTM DEM v4.1 and Google Earth imagery. To achieve complete multi-temporal coverage in a reasonable time, only debris-free ice was delineated. Area mapping uncertainty was evaluated at three study sites, Mount Qomolangma (Everest), Mount Naimona'Nyi, Mount Geladandong, where the largest differences between present and earlier measurements were within ~±4%. Area differences with previous inventories ranged from −19.6% (TPG1976 minus the first Chinese Glacier Inventory) to −3.6% and −1.1% (TPG2013 and TPG2001, respectively minus the second Chinese Glacier Inventory), while the difference TPG2001 minus the GAMDAM Glacier Inventory was +10.4%. Glacier area on the plateau decreased from 44 366 ± 2827 km2 (1.7% of the study area) in the 1970s to 42 210 ± 1621 km2 in 2001 and 41 137 ± 1616 km2 in 2013. Shrinkage was faster in external drainage basins of the southeast than in the interior basins of the northwest, from a maximum of −0.43% a−1 (−1.60% a−1 during 1994–2013) in the Mekong catchment down to a minimum of −0.12% a−1 in the Tarim interior drainage.

GIS and remote sensing approach is an effective tool to determine the morphological characteristics of the basin. Gilgel Abay watershed is stretched between latitude 10.56° to 11.22° N and longitude 36.44° to 37.03° E which is one major contributing river of Lake Tana which is the source of Blue Nile. The present study addressed linear and areal morphometric aspect of the watershed. The study deals with emphasis on the evolution of morphometric parameters such as stream order, stream length, bifurcation ratio, drainage density, stream frequency, texture ratio, elongation ratio, circularity ratio, and form factor ratio. The morphometric analysis of the basin revealed that Gilgel Abay is firth-order drainage basin with total of 662 drainage network, of which 511 are first order, 111 are second order, 30 are third order, 9 are fourth order, and 1 is fifth-order stream. The total length of stream is longer for first order and decrease with increasing stream order. The mean bifurcation ratio is 5.16 which is greater than the standard range, and it indicates that basin is mountainous and susceptible to flooding. Low drainage density is observed which is 0.6 km−2. It indicates that basin is highly permeable and thick vegetation cover. Areal aspect of the morphometric analysis of the basin revealed that the basin is slightly potential to flooding and soil erosion, indicating that runoff generated from the upland area of the watershed is significantly infiltrated at the gentle downstream part and contributing to groundwater potential. Further studies with the help of GIS and remote sensing with high-resolution remote sensing data integrating with ground control data in the field are more effective to formulate appropriate type of natural resource management system.

At a time, when the five riparian countries have renewed consultation with each other about the future of the Caspian Sea, it is appropriate to propose a state of the art of the potential natural threats to the regional environment. We present a critical review of geological, meteorological–climatological and hydrological hazards and disasters illustrated by many examples from within the Caspian drainage basin. Our work is set in the frame of an analysis of the factors contributing to the scale of the disasters. A brief overview of the mitigation measures in place and their future development is also included underlining the current limited warning systems (especially transboundary) despite improvements. While analysing past disasters is an essential source of information on which to base new mitigation, current and future conditions have poor or even no analogue in the past. Even though it clearly turns out that earthquakes are certainly the most deadly hazard, Caspian Sea level changes are by far causing the largest economical impact and affect the largest area and thus population. This review has also highlighted the need to create a Caspian database of natural hazards and disasters.

The morphometric analysis of drainage basins provides a quantitative description of the drainage networks. The accuracy of a morphometric analysis depends on the resolution of digital elevation models (DEMs) and estimation technique. We present an efficient MATLAB tool ‘Basin-Morph’ to estimate various morphometric parameters of a drainage basin, which minimizes redundant steps and extensive calculations as in GIS-based applications. The ‘Basin-Morph’ is applied for the morphometric parameter estimations on four DEMs of varying spatial resolutions to demonstrate their consistency in characterizing thirteen fourth–fifth-order drainage basins along the tectonically active Shillong plateau front. The Pearson correlation coefficient of morphometric parameters is calculated and correlated across catchments that compare well with the lateral variation in tectonic setup along the plateau front. The areal, linear, and relief parameters show distinct trends across the varying tectono-climatic setup and provide primary landscape characterization criteria.

The Doce River Basin (DRB) suffers with the adverse impacts of mining activities, due to its high level of urbanization and numerous industrial operations. In this study, we present novel insights into contaminant flow dynamics, seasonal variations, and the primary factors driving concentration levels within the region. We conducted an extensive analysis using a database sourced from the literature, which contained data on the contamination of arsenic (As) and lead (Pb) in the Doce River. Our primary aim was to investigate the patterns of As and Pb flow throughout the entire basin, their response to seasonal fluctuations, and the key parameters influencing their concentration levels. The results showed significant seasonal fluctuations in As and Pb fluxes, peaking during the rainy season. The 2015 Fundão dam breach in the DRB led to notable changes, elevating elemental concentrations, particularly As and Pb, which were subsequently transported to the Atlantic Ocean. These increased concentrations were primarily associated with iron and manganese oxides, hydroxides, and sulfates, rather than precipitation, as evidenced by regressions with low R 2 values for both As ( R 2 = 0.07) and Pb ( R 2 < 0.001), concerning precipitation. The PCA analysis further supports the connection between these elements and the oxides and hydroxides of Fe and Mn. The approach employed in this study has proven to be highly effective in comprehending biogeochemical phenomena by leveraging data from the literature and could be a model for optimizing resources by capitalizing on existing information to provide valuable insights for drainage basin management, particularly during crises.

In this paper, an attempt has been made to ascertain the erosion susceptibility of the Mayurakshi Drainage System in Eastern India using the 12.5 m resolution ALOS-PALSAR DEM dataset by the morphometric attributes viz. relief, surface, drainage texture and topography. The Analytical Hierarchy Process (AHP) was carried out for ascertaining the erosion susceptibility of the area under consideration. The methodology followed essentially differs from the traditional AHP technique because while assigning weights to multiple parameters, the study has depended on the Principal Component Analysis (PCA) instead of the opinion of the experts which are often contradictory. The relative importance of each parameter was calculated from the loading ratios of different parameters under PCA. Furthermore, instead of taking only one PC, we have taken six PCs with a cumulative explained variance of 99.13%. Finally, these AHP-based erosion susceptibility maps were weighted with respect to their explained variances (obtained from PCA for individual component) and the final map displaying the spatial variation of erosion susceptibility in the Mayurakshi Drainage System was obtained. Analysis reveals that, by and large, the area is characterized by lower susceptibility scores with the solitary exception of the middle domain of the Mayurakshi Basin and the upper reach of the Dwarka River. Here, the erosion susceptibility is greatly elevated due to the fact that the rivers have to encounter and incise across a number of low-lying hills which may be considered to be offshoots of the Chhotanagpur Plateau. In other areas, the susceptibility of erosion is reasonably modest.

The occurrence of drought indicates that there is no rainfall or little rainfall within a certain period. Nevertheless, no or little rainfall within a certain time implies that drought may not happen. The drought occurrence in different regions or seasons shows a certain lag to some extent. The lag time and intensity (i.e., the contribution rate of rainfall in previous period to runoff in current period) are deeply affected by watershed water storage capacity. Subsequently, rainfall deficit is a necessary and insufficient for the droughts. To reveal the mechanism of watershed lagged effects and the impact of human activities on droughts, the characteristics of lagged effects and human activities in Central Guizhou of China are analyzed by the Lagged index and Landscape index based on land use data, rainfall and runoff data during the period 1971–2016. The results demonstrate that the impact of the same land use type in different ages (1970s–2010s) on watershed lagged intensity has a significant difference (P < 0.001). Especially for the influence of the woodland and grassland on lagged intensity is increasing with the increase of time scales and the impact difference gradually decreases in cultivated land, water body and construction land. The impact (R-value) of land use type transfer on watershed lagged effect is particularly significant (p < 0.001), and the influence (R-value) of land use type transfer on lagged frequency is shown with a W-shaped pattern in cultivated land and grassland with the ages changing, a single peak character in woodland and a peak valley alternation in water body. The impact of principal component factors (Zs) of land use morphological characteristics on watershed lagged effect has a particularly significant difference (p < 0.001) in different lag periods (Xt−0–Xt−3), different ages (1970s–2010s) and different time scales (1–12 months). Among them, the impact (F-value) of the Zs in the Xt−0–Xt−3 on lagged intensity/frequency is the largest in grassland, followed by in water body and woodland, and the smallest in cultivated land and construction land. The F-value in the 1970s–2010s is larger in construction than in cultivated land and woodland, and it is the smaller in water body and grassland. The F-value in the 1–12 month scales is grassland > water body > cultivated land > construction land > woodland. As a subsequence, this study enriches the research content of landscape ecology, and it provides a theoretical basis for revealing the mechanism of agricultural and hydrological droughts in Karst drainage basins.

Indices measuring drainage basin shape are of great significance because they not only measure forms (shape) of basins but provide quantitative information upon basin shape that controls the flow hydrograph of the channel. We reviewed different measures of basin shape and found the Elongation ratio (E), Form factor (F), Lemniscate ratio (k), and Shape factor (S) can not detect differences between shapes of a very long narrow basin without indenture in perimeter and a highly indented star-fish-shaped basin. Limitation of these indices was felt in the context of indenture studies of shapes. The present study adopted the Indenture index (I) to have a detailed insight into the indented plan view of drainage-basin outline. We also added Circularity index (Ci), a refined form of Compactness coefficient (Cc), which bears the traits of an ideal index and is a good tool for measuring basin shapes. Eight indices were applied for testing the hydrologic implications of the shape of a drainage basin. Indenture index (I) could effectively be employed for measuring indented basin-shapes (1 = no indenture, a higher value indicates indented shape) and assessing the impact of basin shape on the Flood Inducing Capacity (FCI) of a basin (R2 = 0.208). The present study will not only bridge the gaps in the existing hydro-geomorphic research but also has some policy implications in the context of basin hydrology. The use of simulation and artificial intelligence (AI) for overcoming the limitation of data size may open better avenues in the directions of basin-shape research and its hydrologic implications.

Tropical rainforests in the central hilly section of Hainan Island are the source of the Nandu, Changhua, and Wanquan rivers, which are crucial for water conservation and ecological protection. The quantitative assessment of water yield in the three basins is beneficial for developing regional water resource protection plans, establishing ecological compensation mechanisms, and maintaining ecological balance. Based on land use data from five periods between 1980 and 2020, this paper adopts the InVEST model and geographic detectors to investigate the spatial-temporal variation characteristics and driving factors of water yield in three major basins of Hainan Island. The results demonstrate that forestland, which makes up more than 70% of the total area in the three basins of Hainan Island, is the predominant land use type. With a depth of 1269.18 mm, Wanquan Basin is the deepest of the three basins, followed by Nandu Basin and Changhua Basin. The total water yield of three basins shows a slightly decreasing trend from 17.991 billion m 3 in 1980 to 17.864 billion m 3 in 2020. The spatial distribution of water yield is high in the southeast region and low in the northwest region, with strong autocorrelation and significant aggregation. According to geographic detection, land use type is the dominant factor for the spatial differentiation of water yield in the three basins, with a contribution rate of 0.563, and soil type and annual precipitation are important impact factors. The interaction and synergy of soil types and land use types jointly affect the spatial differentiation of water yield in the basin. The results of this study can provide data support and scientific references for biodiversity conservation and ecosystem restoration in the three major basins of Hainan Island.

This study used morphometric techniques to generate new information describing the evolution and hydrogeological behaviour of the Limpopo River Basin in Botswana, based on the analysis of drainage surface features, form, and size. Drainage basins provide basic information on their evolution, which, when quantified, yield information on the interaction between tectonics, climatic, and surface processes. Drainage networks were extracted from the Shuttle Radar Topographic Mission (SRTM) Digital Elevation Model (DEM) (90 m × 90 m), and subsequently, morphometry indices were computed using ArcGIS 10.5. Drainage network extraction was performed using the Arc Hydro extension in ArcGIS 10.5. ArcGIS 10.5 image processing technique was used to extract lineaments and create rose diagrams. The results showed that the Limpopo sub-basins in Botswana were drained by fourth- and fifth-order streams, with a total drainage area of 107, 871 km 2 . Additionally, the basin asymmetry and mean bifurcation ratios showed tilting in the sub-basins, suggesting tectonic instability and structural control in a low - to-moderate active tectonic zone. The sub-basins also had a coarse texture, indicating a high infiltration capacity. These results are essential for planning and managing watershed systems, flood risk assessment, and potential groundwater assessment for the different sub-basins of the Limpopo River Basin in Botswana.