Significant reduction of river discharge in the mountainous basins of Uzbekistan over the last decades

Climate change is expected to significantly impact temperature and precipitation, as well as snow accumulations and melt in mid-latitudes, including in the Baltic region, ultimately affecting the quantity and seasonal distribution of streamflow. This study aims to investigate the changes in the magnitude and timing of annual maximum discharge for 30 hydrological monitoring stations across Latvia from 1950/51 to 2021/22. Circular statistics and linear mixed effects models were applied to identify the strength of seasonality and timing. Trend analysis of the magnitude and timing of flood peaks were performed by using the Theil–Sen method and Mann–Kendall test. We analyzed regional significance of trends across different hydrological regions and country using the Walker test. Results indicate strong seasonality in annual flood peaks in catchments, with a single peak occurring in spring in the study sub-period of 1950/51–1986/87. Flood seasonality has changed over recent decades (i.e., 1987/88–2021/22) and is seen as a decrease in spring maximum discharge and increase in winter flood peaks. Alterations in annual flood occurrence also point towards a shift in flow regime from snowmelt dominated to mixed snow–rainfall dominated, with consistent changes towards the earlier timing of the flood peak, with a more or less pronounced gradation from west to east. Analysis shows that a significant trend of decrease in the magnitude and timing of annual maximum discharge was detected.

The relative importance of data on winter snow accumulation and summer (monsoon) rainfall for estimating annual runoff in the Jhelum River basin, Punjab Himalaya, Pakistan, has been investigated. Strong correlations were found between point measurements of the annual maximum of snowpack water equivalent and of total winter precipitation in the Kunhar sub-basin, and total annual discharge. In addition, total winter snowfall showed a generally significant correlation with annual discharge. Elevation did not appear to play a strong role in determining the usefulness of these measurements, whereas location within the basin relative to large scale precipitation patterns did, in some cases. Monsoon rainfall appeared to be a very poor indicator of annual discharge. The results also suggest that the operation of a continental scale negative feedback mechanism between Eurasian snow cover and the Indian monsoon might be felt in this region of the Himalaya.

Chinook salmon (Oncorhynchus tshawytscha) are a keystone species for many ecosystems of western North America, are culturally and spiritually significant for many Indigenous Peoples, and underpin a multi-million dollar industry. However, in recent years extreme summer streamflow droughts have disrupted Chinook migration and rearing patterns. Climate change is driving hydrologic changes throughout the region, but future changes to summer low flows remain highly uncertain. Here we study 375 near-natural catchments throughout the habitat range of Chinook salmon from California to Alaska. The streams span rainfall-dominated, hybrid, snowmelt-dominated, and glacial regimes. Summer discharge has decreased in most catchments, with rainfall-dominated and hybrid catchments seeing the most severe declines.We develop linear regression models which outperform existing process-based models, and project changes to 2100 under four emissions scenarios. Summer low flows have historically been primarily driven by variability in summer precipitation and moderately influenced by winter snow accumulation and summer temperature. However, we find that future changes will probably be driven by rising temperatures because future summer temperatures could greatly exceed the historical envelope of variability. Some further declines in low flows are probably inevitable in rainfall-dominated and hybrid catchments: under a low-emissions scenario, low flows will continue to decline to mid-century but then stabilize. Under a high-emissions scenario, 1-in-50-year low flows could occur almost every summer in many rainfall and hybrid catchments. In glacial catchments summer discharge has been relatively stable in recent years because increased glacial meltwater flows have compensated for increased evapotranspiration. However, many of these glaciers are projected to disappear within 20 to 30 years, and we project severe declines in summer streamflow when this does occur.Many populations of Chinook rear or migrate during the summer months for which we project extraordinary future streamflow droughts. It is unknown whether Chinook populations can shift their life stage timing or find alternate habitats quickly enough to avoid catastrophic impacts. Bold climate action and local mitigation strategies are urgently required to safeguard this ecologically, culturally, and economically vital species against future extreme events.

Snow accumulation, melt, mass loss, and the near-surface ice temperature structure of Irenebreen, Svalbard

Greenland’s peripheral glaciers and ice caps contribute disproportionately to sea-level rise relative to their small area. Winter snow accumulation directly influences glacier mass balance and downstream hydrology, but spatially extensive observations of this important mass balance component remain sparse. In this study, we present a unique multi-year (2008–2024) dataset of winter snow accumulation over A.P. Olsen Ice Cap, Northeast Greenland, from ground-penetrating radar surveys covering an average of 47 km per survey year. Our results reveal strong spatial heterogeneity that is likely influenced by wind redistribution and local topography, especially in the ablation zone. We compare our findings with automatic weather station data from three sites and outputs from the Copernicus Arctic Regional Reanalysis (CARRA). Governed by the high spatial variability, the automatic weather station point-based observations significantly underestimate regional accumulation by 40–45%. Despite the high spatial variability, the CARRA accumulated precipitation variable provides a reasonable overall mean winter snow accumulation (RMSE of 0.07 m w.e.); however, it fails to reproduce the complex non-linear relationship between snow depth and elevation observed in the radar data. Our findings emphasize the need for high-resolution, spatially extensive measurements to better understand snow accumulation on ice caps and glaciers and improve reanalysis assessments.

Abstract. Winter snow accumulation obviously has an effect on the following catchment runoff. The question is, however, how long this effect lasts and how important it is compared to rainfall inputs. Here we investigate the relative importance of snow accumulation on one critical aspect of runoff, namely the summer low flow. This is especially relevant as the expected increase of air temperature might result in decreased snow storage. A decrease of snow will affect soil and groundwater storages during spring and might cause low streamflow values in the subsequent warm season. To understand these potential climate change impacts, a better evaluation of the effects of inter-annual variations in snow accumulation on summer low flow under current conditions is central. The objective in this study was (1) to quantify how long snowmelt affects runoff after melt-out and (2) to estimate the sensitivity of catchments with different elevation ranges to changes in snowpack. To find suitable predictors of summer low flow we used long time series from 14 Alpine and pre-Alpine catchments in Switzerland and computed different variables quantifying winter and spring snow conditions. In general, the results indicated that maximum winter snow water equivalent (SWE) influenced summer low flow, but could expectedly only partly explain the observed inter-annual variations. On average, a decrease of maximum SWE by 10 % caused a decrease of minimum discharge in July by 6–9 % in catchments higher than 2000 m a.s.l. This effect was smaller in middle- and lower-elevation catchments with a decrease of minimum discharge by 2–5 % per 10 % decrease of maximum SWE. For higher- and middle-elevation catchments and years with below-average SWE maximum, the minimum discharge in July decreased to 70–90 % of its normal level. Additionally, a reduction in SWE resulted in earlier low-flow occurrence in some cases. One other important factor was the precipitation between maximum SWE and summer low flow. When only dry preceding conditions in this period were considered, the importance of maximum SWE as a predictor of low flows increased. We assessed the sensitivity of individual catchments to the change of maximum SWE using the non-parametric Theil–Sen approach as well as an elasticity index. Both sensitivity indicators increased with increasing mean catchment elevation, indicating a higher sensitivity of summer low flow to snow accumulation in Alpine catchments compared to lower-elevation pre-Alpine catchments.

The seasonal cycle of snow cover in Eastern Siberia is characterized, and synoptic preconditions of snow accumulation in winter and snow ablation in spring are determined using daily datasets. It was ascertained that cyclone activity has a strong impact on the occurrence of abundant snowfalls in Eastern Siberia. Negative anomalies of sea level pressure (SLP) usually spread westward or southwestward from the place of recorded substantial snowfalls, and they are associated with positive anomalies of air temperature located to the east or northeast of SLP depressions. Cyclonic circulation causes inflow of relatively warm and humid southern air masses originating from the Pacific Ocean, to the eastern parts of cyclones. During the days with snow ablation in spring much lower SLP anomalies occur than during snow accumulation in winter. This may suggest smaller influence of air circulation on snow cover reduction in spring and higher impact of insolation; both result in strong positive anomalies of air temperature which extend over entire Asia. These findings imply that the position, intensity, and dimension of pressure patterns are crucial for determining the location and intensity of rapid changes in snow cover depth during the snow cover season in Eastern Siberia.

This paper presents an evaluation of the spatio-temporal patterns of hydrologic alteration induced by dam construction and precipitation variability in the Lancang River Basin of southwest China from 1957 to 2000. Analyses were conducted using the linear regression method, the Mann–Kendall test, and the Range of Variability Approach. The results indicate that there was considerable variation in the average monthly precipitation between the pre- and post-dam periods in the Lancang River Basin. Second, the magnitude of monthly runoff was strongly related to precipitation, which showed an up-down annual variation, and was significantly altered by dam construction and precipitation variability. In the modified series (hydrologic series with the precipitation impacts removed), runoff deviations between the pre- and post-dam periods became larger. Third, the extreme runoff cycles were influenced by dam construction and precipitation variability downstream from the dam, and the monthly maximum runoff increased from the pre-dam to post-dam period at all hydrologic stations. Fourth, the degree of hydrologic alteration (DHA) indicates that the precipitation variability not only affected the hydrologic regime of unregulated river reach but also modified the negative impacts of dam construction, which could provide a modest mitigation of the hydrologic alterations induced by dam construction, possibly decreasing the level of DHA. Last, the overall degree of hydrologic alteration in the observed series reached 25.2, 25.3, and 29.1 % for the upstream, midstream, and downstream areas, respectively. These results show that the hydrologic regimes of the Lancang River during the 1957–2000 period were affected by damming and precipitation variability, but the hydrologic alteration was relatively low in the upstream areas of the river without a dam.

Winter snow accumulation is important for summer water supply in Central Asia, and contributes more than 50 % to the annual runoff. The region’s water availability is highly dominated by snow reserves in the mountain, which will be affected by climate change. Volumetric snow data play a vital role for hydrologic forecast in mountainous river basins, where snow is considered as a dominating hydrological component. This study quantifies decadal snow depth changes in the Western Tian-Shan in the Chirchik River Basin in Uzbekistan. The snow depth measurements from Uzhydromet have been used in this research. The historical changes in snow depth has been statistically analyzed for the 1963-2020 hydrological years. Correspondingly, the impact of climatic factors (temperature and precipitation) on snow dynamics were assessed as well. The results of hydrometeorological parameters such as snow depth, air temperature at 2 meters and precipitation were plotted as the trend line on monthly, seasonal, and annual scales. To verify statistical significance of the trend dynamics, the slope method and the Mann-Kendall trend test were applied. Our results show that snow cover (duration) days were significantly decreased by 4 days per decade or 21 days for 57 years from 1963 to 2020. Particularly, the initial occurrence of a permanent snow onset day was significantly delayed by 3 days per decade or 16 days for 57 years. Likewise, annual peak snow depth day was significantly shifted earlier by 4 days per decade or 20 days for 57 years. Interestingly, the maximum snow depth did not change statistically significant, but we observe a decline of 3.33 cm per decade or 19 cm for 57 years. Overall, we conclude that the duration of snow cover (snow reserve) has significantly decreased in the Chirchik basin due to climate warming in the last 57 years.     

The aim of this work is to determine the variability of precipitation in the area of the sub-basin of the South Curve up to the hydrological station Korvingrad. Data from the synoptic stations Leskovac, Vranje and Kuršumlija for a period of 30 years (1991-2020) were used. The mean relative variability of monthly, seasonal and annual precipitation and their ten-year values were used to compare the results of all synoptic stations in the sub-basin. The results showed that the highest mean variability of precipitation in the studied period was recorded at the Vranje synoptic station (22.4%) and the lowest value at the station in Leskovac (18.4%). The comparison of ten-year values showed that the lowest values of mean relative variability of annual precipitation in the period 2001-2010 were recorded at all synoptic stations. The study showed that the extreme values of mean relative variability of precipitation occurred earlier or later during the second and third ten-year periods compared to the first ten-year period. The study showed that the values of mean relative variability of monthly precipitation were lowest in months with high precipitation.

The influences of surface climate conditions and atmospheric circulation on seasonal river discharges of the Ob, Yenisei, and Lena River basins during 1936-95 have been examined and quantified. Climatic variables include seasonal basin-averaged surface air temperatures, precipitation, maximum snow accumulation depth, and starting and ending dates of the basins' continuous snow cover. Atmospheric circulation is represented by the Northern Hemisphere annular mode (NAM) index. The combinations of these climatic and atmospheric variables explain about 31% to 55% of the variance of the annual total discharges of these rivers. On average, climatic and atmospheric variables explain 35% to 69% variance of spring discharges, 34% to 47% variance of summer discharges, 21% to 50% variance of fall discharges, and 18% to 36% variance of winter discharges. This study reveals that the spring thermal condition is most significant for spring discharge and negatively affects summer discharge. Climatic conditions during the previous winter through fall influence fall discharges, while the atmospheric conditions of the previous summer and fall affect winter discharges. Also, winter snow accumulation influences summer and fall discharges of the Ob and Yenisei Rivers but affects winter and spring discharges of the Lena River, suggesting the importance of topography and permafrost conditions to river discharges over high-latitude regions.

Abstract. Spring flooding in the Red River basin is a recurrent issue in the Province of Manitoba, Canada. There have been a number of flood events in recent years and climate change has been suggested as a potential cause. This paper employs a relatively simple model for predicting changes in the frequency distribution of annual spring peak discharge of the Red River as a response to increased GHG concentrations. A regression model is used to predict spring peak flow from antecedent precipitation in the previous fall, winter snow accumulation, and spring precipitation. Data from the Coupled Model Intercomparison Project – Phase 5 (CMIP5) are used to estimate changes in the predictor variables and this information is then employed to derive flood distributions for future climate conditions. Most climate models predict increased precipitation during winter months but this trend is partly offset by a shorter snow accumulation period and higher winter evaporation rates. The means and medians of an ensemble of 16 climate models do not suggest a particular trend toward more or less frequent floods of the Red River. However, the ensemble range is relatively large, highlighting the difficulties involved in estimating changes in extreme events.

This review article is intended to introduce periglacial environment present and past in Japan, and to summarize some studies on it. The periglacial climate in Japan is characterized by a wide annual range of air temperature and much snow accumulation in winter. This makes for local variability in appearance of periglacial processes on the mountain slopes near crests. In Japan, the main interest in periglacial studies concerns the above-mentioned variability and its causes, that is, how periglacial processes relate to vegetation, local climate especially snow accumulation and its seasonal duration, soil, micro-relief, properties of bed rock etc. Seasonal soil freezing was measured in lowlands of Hokkaido. Depth of frost penetration without snow cover increases proportionally to the increments of accumulated degree-days. Depth of frost penetration on natural conditions is affected not only by the degree-days but also by the depth of snow cover which differs locally even within a small area. The oldest frozen ground phenomena was recognized in a horizon about 50,000 years old in the lowlands of Hokkaida. Involutions about 40,000 years ago exceeded active earth hummocks in size. And the phenomena reached the maximum phase is represented by icewedge casts of the En-a pumice (ca. 15,000 abp). Most of fossil features are covered with undisturbed Ta-d pumice (cz. 9,000 abp), but earth hummocks and vertical stones have been still formed in the Holocene tephra layers.

River flow is an essential parameter in hydrology and water resources studies with mutual interaction with climate elements. So, studying the discharge change trend in the rivers is crucial for management programs and the design of irrigation and drainage systems. In the present study, river flow data measured at six hydrological stations at Neka (Ablu, Golverd, SefidChah) and Tajan (KordKhil, Rigcheshmeh, Soleimantangeh) rivers in Mazandaran Province have been studied by using Mann-Kendall test, age test, and regression analysis during the statistical period of 1976–2006. The MAKESENS 1.0 software was used to reveal annual and seasonal discharge change trends. Results of the present study showed that only two stations – Soleimantangeh and Rigcheshmeh – had decreasing trend at 5% significance level in yearly terms. In contrast, the regression analysis showed just significant trends at Soleimantangeh station. No crucial trends have been observed in the seasonal scale; in spring and autumn, most of the stations had a non-significant negative trend. By considering the methods used to evaluate trends in this study (Mann-Kendall test, age test, and regression analysis), it was observed that all the rivers had had decreasing and negative trends. The performance of parametric and non-parametric tests was similar in most cases.

For most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid‐twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow‐affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm‐season runoff in many mid‐ to high‐latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high‐latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt‐derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd.