Long-term variations of water balance components are compared for the deltas of the Pechora and Koluma rivers, flowing in the occurrence area of discontinuous and continuous permafrost rocks. Trends in the variations in the major components of water balance equation (river water flow, precipitation, and losses or increment of runoff in the delta) are considered for the conditions of climate warming (the late XX–early XXI centuries). A distinct increase, most pronounced in 2008–2018, was recorded in the major components of water balance.

River deltas which are among the most variable and vulnerable geographic objects may be considered as effective indicators of large-scale global and regional, natural and anthropogenic changes of environment. The up-to-date state of deltas of the main rivers in Russia and all over the world are described in the Register which is presented in this paper. The Register includes geographic characteristics of deltas (including their hydrologic-ecologic state), hydrographic, morphometric and hydrologic characteristics of the deltas.

The current values of the components of the water balance of the Parana delta, one of the largest deltas of South America, as well as the results of calculations of the actual distribution and redistribution of water runoff and sediment yield in the delta branches are presented. Response of the components of the Parana delta water balance on climate variations is revealed. Long-term changes in the water and sediment flow distributions in the delta branches are considered. Analysis of dynamics of estuarine delta coastline shows stable increase of the river delta area, which could cause dangerous hydrological phenomena at the Parana delta.

The article presents a study of the hydrological regime of the Lena and Mackenzie rivers, flowing in the zone of permafrost rocks of different types. Features typical of river mouths in subarctic zone are identified. Sediment transport in both deltas and the export of material into the Laptev and Beaufort seas is studied. Permafrost rock characteristics are given and their changes under the current rise of air temperature are discussed. The possible effect of permafrost rock thawing under climate warming on water and sediment runoff in arctic deltas is discussed.

The relationships between various hydrological and morphometric characteristics of branch channels in the backwater zone are analyzed in the case of the Chilia channel system in the large nontidal Danube delta. This zone shows a stabilizing effect of the weakly varying Black Sea level. Criteria for determining the boundaries of this zone are discussed.

The article describes the Ili River hydrological regime, provides an insight into multiyear and intra-annual changes in the discharge in the Ili delta head, given natural water flow versus water flow regulation. It shows the spatial distribution and re-distribution of runoff between delta watercourses and estimates the degree of delta submergence during floods. The article considers the findings in the studies of the water regulation function of the delta depending on forest coverage and offer projections related to further possible hydrological and morphological changes in the Ili delta.

The types and specific features of the internal and external water exchange in nontidal deltas are discussed. The results of hydraulic calculation of water exchange in the branchbypassdelta lake are given. The conclusions are confirmed by data of observations in several large nontidal and microtidal deltas.

The hydroclimatic conditions of water runoff formation and the hydrography of Parana and Uruguay river basins in the South America are considered. A survey of the recent studies of the hydrological regime of these rivers is given. Observation data are used to evaluate the long-term average values of water runoff and suspended sediment yield in the Parana and Uruguay and their variations along the rivers. Characteristics of many-year runoff variations in the rivers were evaluated. A climate-induced increase was identified in the Parana and Uruguay water runoff, and the corresponding present-day trends in river runoff variations in both rivers were evaluated. The total water runoff and suspended sediment yield of the Parana and Uruguay into La Plata estuary were calculated. Water balance of the drainage basin of La Plata estuary was characterized.

The general geographic, hydrographic, climatic, and hydrological characteristics of the Congo R. basin are considered. The major features of the riverine and marine factors that have their effect on the hydrological regime and morphology of the delta and estuary of the Congo R. are identified; the effect of a submarine canyon on the morphological features of the estuary is analyzed in detail; and changes in river delta structure in the XX century and currently are considered. The hydrological. morphological characteristics of the largest mouths of African rivers, the formation conditions of water and sediment runoff, and variations of their deltas are compared.

The recent general geographic characteristics of the Zambezi River basin and its delta are discussed. The main hydroclimatic features of the river basin and delta are revealed. The fluvial and marine factors that influence the river delta are discussed in detail. Close attention is given to the effect of the large reservoirs of Kariba and Cahora Bassa on the hydrological regime, morphology, and ecosystem of the Lower Zambezi valley and the river delta. Considerable changes in the delta and its coastline that occurred over the last decades are revealed.

Рассмотрены современные общегеографические характеристики бассейна р. Замбези и ее дельты. Выявлены основные гидроклиматические особенности бассейна реки и дельты. Подробно рассмотрены речные и морские факторы, влияющие на дельту реки. Особое внимание уделено воздействию крупных водохранилищ Кариба и Кахора-Баса на гидрологический режим, морфологию и экосистемы долины Нижней Замбези и дельты реки. Выявлены существенные изменения дельты и ее морского края в последние десятилетия.

The results of field studies near Gelendzhik C. are used to analyze the stability of the basin of the small Ashamba R. and intermittent streams under the impact of an extreme shower. Water discharge in the Ashamba R. is estimated, and the obtained values are compared with the standard hydrological characteristics accepted for design works. The existing calculation procedures and the standard climate characteristics are shown to allow the observed flood to have been anticipated. The hydrological-morphological changes in the river caused by the passage of an extreme flood are demonstrated. The land inundation and the destruction of economic facilities is shown to be a result of violation or neglect of the regulations for estimating the characteristics of extreme natural phenomena. The natural landscapes not disturbed by human activity are found to show a high stability under the effect of an extreme shower.

Рассмотрены современные изменения режима и строения устьев рек, впадающих в Каспийское море. Выявлены сходства и различия этих процессов в устьях разных рек Каспийского региона. Оценено влияние на рассматриваемые процессы изменений стока воды и наносов рек и уровня Каспия, а также рельефа устьевого взморья и местных гидротехнических мероприятий. Установлены и объяснены аномальные особенности процессов в устьях Волги и Терека. Установлены характерные для современных устьев Урала, Сулака и Куры гидролого-морфологические процессы, которые могут быть признаны универсальными и возможными аналогами при оценке ожидаемых изменений в устьях других рек России и мира в XXI в.

Present changes in the regime and structure of mouths of rivers, which empty into the Caspian Sea, are discussed. The similarities and differences of these processes at the mouths of different rivers of the Caspian Region were revealed. Assessment was made of the impact of changes in river water runoff and sediment load and in the Caspian Sea level as well as the nearshore zone relief and local hydraulic engineering activities on the processes under study. Anomalous features of the processes occurring at the mouths of the Volga and Terek rivers were revealed and explained. Hydrological and morphological processes typical of the present mouths of the rivers of Ural, Sulak, and Kura were revealed; these processes could be accepted as universal and possible analogs in assessing the expected changes at the mouths of other rivers in Russia and the world in the XXI century.