P. S. Kuzin, State Hydrological Institute, Leningrad, USSR
SUMkiAKY: Technique and results of investigation of territorial regularities of dktribution of cyclic variations, synphases and asynphases of streamflow mainly of plain rivers of the Northern Hemisphere are reported briefly in lhe paper. Study of cyclic variations, synphases and asynphases of streamflow was performed with the help of normalized difference mass curves and correlation method. T h e main geographical (zonal and intrazonal) regularities of distribution of quantitative characteristics of phases of low streaniflow and high streamflow are described. Division into regions of the USSR territory and of the territories of other countries of the Northern Hemisphere íin Western Europe, Asia, North America and Northern Africa) according to the type of syn- phases of annual streamflow variations was performed. Asynphases of streamflow and the possi- bility of compensation of low river discharge in some regions by high river discharge in other re- gions during the same years was pointed out.
VARIATIONS CYCLIQUES D E
DELITS
D ERIVIERES
D A N S L’HÉMISPHÈRE N O R D
R ~ S U M ~ : O n expose dans le rapport les méthodes et les résultats des recherches sur la distribution territoriale des variations cycliques, ainsi que des syinphases et des asymphases d’écoulement sur les rivieres des plaines dans l’hdmisphère boréal. L’étude des cycles, des symphases et des nsymphases a été faite 5 l’aide des courbes des valeurs cumulées et à l’aide de la corrélation. Les ri-gles géographiques essentielles (zonales et intrazonales) de la distribution des indices quantita- tifs des phases de I’hydraulicité abondante et de I’hydraulicité maigre oiit été établies. O n a effec- tué Ia division en régions (selon les variations symphases de l’écoulement annuel) du territoire de l’URSS et d’autres pays de I’hémisphire boréal (de l’Europe occidentale, de I’Asie, de l’Amérique d u Nord et de I’Afriquc d u Nord). Les asymphases d’écoulement ont été établies et Ia possibilité de la compensation de l’hydraulicité niaigre dans quelques régions par l’liydraulicité abondante dans tl’autrcs régions pcndant les mtmes aiinées a également pu être présentée.
C.vclic iiarialiotts of rioer clischurge in the Northern Heinispjere
VARIACIONES CICLICAS I>EL C A U D A L B E LOS
RIOS
EN EL HEMISFERIO N O RTER E S U M E N : En este docurncnto se hace una breve descripción de las técnicas y resultados de la investigación de las características de regularidad territoriales de la distribución de las variaciones cíclicas fisicas o defasadas del flujo, principalmente en los rios llanos del hemisferio norte.
Elestudio de Ias variaciones ciclicas fisicas o desfasacdas del flujo se realizó utilizando curvas acumulativas diferenciales normalizadas y métodos de correlación. También se describen las principales regularidades geográficas (zonales e intrazonales) de la distribución de las caracte- rísticas cuantitativas de las fases del flujo bajo y del flujo alto. Se eîectuó una división por regiones del territorio de la URSS y de los territorios de otros países del hemisferio norte (en Europa Occidental, Asia, América del Norte y Africa del Nortc), de acuerdo con los tipos de fases de las variaciones anuales del flujo. Se pusieron de manifiesto los defasamientos del flujo y la posibilidad de compensar el caudal de la parte baja del rio en algunas regiones con CI caudal de la parte alta del río en otras regiones durante los mismos años.
I
Water balance, i.e. the ratio of water income (precipitation) and expenditure (runoff and evaporation) on the earth's surface for a long-term period is in equilibrium and is more or less constant. This is confirmed by low values of variation coefficients of the most unstable component of the balance, i.e. annual streamflow. For the USSR rivers this coefficient makes 0.05, and for the rivers of the globe it is close to zero. At the same time, due to uneven heating of land and seas and due to constant atmospheric circulation, high streamflow periods in some regions, and low streamflow periods in other regions are observed.
High streamflow and low streamflow on rivers are formed in the course of several years, but in some individual years they may be very outstanding. As a result in some regions of the globe rivers inundate villages, cities and agricultural fields, while in other regions long low streamflow periods are accompanied by droughts and crop-failure. An exceedingly protracted period of low flow in the Volga basin which started in the thirties caused
an unprecedented fall of the Caspian Sea level. During LL quarter of a century, the sea level fell by 2.6 meters. Thc fa11 of the Caspian Sea level w ccompanied by the reduction oí' the sea surface and its depth, and thus brought a great damage to the national economy.
At present thc level of lhe Caspian Sca is the lowest during the last 400 years.
Fluctualions oí' climate and of streamflow rale bring great damage in other regions, of our country and of the globe. Disaslrotis inundations took place recenily in Europe, Asia, North and South Ainerica. Therefore the study of long-term streamflow variations is one of the most important tasks in hydrology.
The knowledge of cyclic fluctuations of streamflow and of the type of their variation in lime and space occupies an important place in the practice of hydrological and water management computations for combining of energy systems with prevailing hydroelectric power stations and for transfer of streamflow from regions with abundant water resources to arid regions for the purposes of irrigation and water supply.
Asynchronous varialions of river discharges caused by the difference in streamflow and in the regime of rivers create favourable conditions for compensation in the operation of hydroenergetic systems, situated on rivers of different regions, and thus m a y stimulate additional energy output. The study of streainflow variations in basins situated far away from each other and especially of rivers of different continents is of great importance for the knowledge of general laws of long-term streamflow variations.
The problem of long-term streamflow variations is so complicated that it is not possible to cover all its aspects within the framework of one study. Therefore the present paper deals only with a part of this problem, that is, with the study of the regularities of the territorial distribution of cyclic variations, synphases and asynphases of streamflow mainly on the plain rivers of the Northern Hemisphere without including heliosynoptical characteristics.
Cyclic variations, synphases and asynphases of streamflow are first studied on the basis of the USSR rivers, and then on that of the rivers of other countries.
Basic gauging stations to obtain the regularities of cyclic variations of streamflow were chosen in accordance with the following criteria:
1 j middle size of the basins reflecting the zonal regime of streamflow;
2) even distribution of the basins in geographical zones;
3) availability of long term observational series.
Altogether there were used 300 gauging stations on the USSR rivers and on the rivers of other countries. In view of unequal duration of observations on middle-size rivers in the European and Asiatic parts of the USSR the design period was assumed to be equal to 40 years for the European part of the USSR (from 1921 to 1960) and 30 years for the Asiatic part of the USSR (from 1931 to 1960).
To study the cyclic variations of streamflow normalized difference mass curves were used, which were plotted for annual discharge, spring flood discharge and dry-weuther discharge of middle-size USSR rivers and only for annual discharge of big rivers and of rivers of other countries. To study synchronous and asynchronous variations the inethod of correlation of the values of annual discharge was used.
The normal values, coefficients of correlatjon and of asymmetry of annual discharge for the design period were computed by the grapho-analytical method. In the majority of cases empirical frequency curves corresponded to the ratio C,, = 2C,.
The comparison of streainflow rate of the assumed 40-year observation period and of the 80-year period available for somc stations on rivers of the European part of the USSR as well as of 30- and 60-year obscrvation periods on the Asiatic rivers of the Sovict Union showed great similarity of the coinpared values. Thc maximum diffcrcnces in the avcrage values of inodiilus coeíTìcients of streamflow for the above periods CIO not excced 0.05-0. I O, and of variation coefficients do not excccd 0.02-0.04.
C.vclic ooritrtions o/ riaer disciiurge in the Nortlieriz Hetnispllere
While studying streainflow variations 3 stages of streamflow rate (frequency) were assumed:
-
high streamflow rate : 1-25”h;-
normal streainflow rate : 26-74% and - low streamflow rate : 75-99%.The separation of the phases of different streamflow rate on the difference mass curves was pcrformed by breaking points which were outlined on the majority of rivers of a region.
In the course of studies there were discovered phases of short duration (2-8 years) and of long duration (10-20 years for annual discharge and spring flood discharge and even of 30 years for dry weather flow). Modulus coefficients of phases of low annual streamflow (of medium duration) for the zone of excessive moistening usually lie within the limits of 0.5-0.9, and for the rivers of the arid zone they are considerably smaller (for instance for the river Bolshoi Uzen for the 1933-40 period K,
=
0.17). Modulus coefficients of high streamflow phases vary within 1.2-2.6.The estimation of n-year means by the statistical test method with respect to 1000-year modelled series, showed great similarity with the obtained values.
In studying zonal and intrazonal variations of phases of high streamflow and low streaniflow on the USSR territory the data from watersheds situated along 12 longitudinal and 6 latitudinal profiles were used.
The main regularities of the changes of characteristics of phases of low streamflow and high streamflow of plain rivers are observed in longitudinal and latitudinal directions in all geographical zones:
1. Modulus coefficients of low streamflow phases decrease from North to South, while the frequency increases; modulus coefficients of high streamflow phases on the contrary increase from North to South and the frequency becomes less.
2. The zonal changes (from North to South) of modulus coefficients and of frequency of low and high streamflow phases are gradual; intrazonal changes (from West to East) of the above characteristics of streamflow are uneven, that is the tendency of alternations of opposite streamflow phases is observed.
3. Cyclic streamflow fluctuations of big rivers situated in the same geographical zone coincide with the fluctuations of streamflow of the adjacent middle-size rivers.
To study the correlation of streainflow of different rivers of the USSR about 2000 correlation coefficients have been used and their reliable values were taken into account.
The correlation coefficients of annual discharges, spring flood discharges and dry weather discharges of different rivers (which are in the limits from 0.5 to 0.9) as well as correlation coefficients of streamflow of consecutive years (autocorrelation) were studied.
In accordance with direct correlation between annual discharge of middle-size rivers certain groups of rivers were selected, which were used while performing the division in to regions.
Inverse correlations of annual discharges of rivers of the European and the Asiatic parts of the USSR, as well as correlation between the rivers of these two territories were treated separately. Besides, schematic maps of isocorrelates of annual and spring flow, aimual and dry weather flow, spring ñow and dry weather flow of the European rivers of the USSR were plotted.
Despite the variety of quantitative characteristics of streamflow phases on individual rivers it was possible to select 15 regions with similar types of cyclic variations of stream- flow on the USSR territory.
Division into regions of the USSR territory according to homogeneity (synphases) of cyclic streaniflow fluctuations was performed for: rt) annual and spring flood flow;
b) for dry weather flow.
I’. .Y. Kuzin
Asynphases of annual, spring flood and dry weather ílow are observed on the rivers of individuai regions, both in the European and Asiatic parts of the USSR area, as wcll as of rivers of the above-mentioned Lerritories, Certain .regions were .pointed out, ror ,which the combination of energy systems with prevailing hydroelectric plants may increasc the total guaranteed energy output. The selected regions pointed out are connected with the direction of the main air fluxes over the USSR territory. It was underlined that the bound- aries of regions in a long-term aspect should be rather stable, since basic changes in the dynamics of atmospheric circulation are required to disturb synphases or streamflow.
This m a y happen only in connection with a sharp change of the climate.
It was pointed out that the fluctuation of streamflow of rivers have a cyclic character, but each n e w cycle is not the reiteration of the previous cycles. This makes the greatest difficulty in long-term forecasting of streamflow.
To study long-term fluctuations of streamflow of rivers of the Northern Hemisphere besides the USSR rivers, available data on streamflow of rivers of Western Europe, Asia, North America and Northern Africa were used.
According to the types of cyclic variations and synphases of annual flow there were selected 5 regions in Western Europa, 4 regions in Asia, 10 regions in North America and 3 regions in Northern Africa. While dividing into regions the above-mentioned areas asynphases of streamflow were studied and the possibilities of compensation of low streamflow of some regions by high streamflow of other regions in the same years were mentioned. In conclusion asynphases of annual streamflow of the USSR rivers and of rivers of other countries were analyzed.
To study the above-described regularities, besides mass curves, correlation coefficients of annual streamflow and quantitative characteristics of streamflow of consecutive 10 year mean were used. The analysis of annual streamflow correlations with the use of nearly 6000 correlation coefficients gives possibility to draw some new conclusions. G o o d direct or inverse correlations of streainflow of rivers of the USSR and other countries are not numerous. Therefore it is only possible to state the presence of direct or inverse correlation fields of streamflow fluctuations of the compared countries and continents.
If synphases and asynphases are analyzed in a broad aspect, then it should be noted first of all that there exist latitudinal and longitudinal alternations of asynphases.
While comparing mass curves and correlation fields synphases and asynphases of streainflow of rivers of certain regions of the USSR, Western Europe and Asia were determined.
Comparing mass curves and correlation fields synphases and asynphases of streamflow of the USSR rivers and North America rivers were discovered.
Atmospheric circulation in the Northern Hemisphere is a more or less integrated process and its fluctuations in the western and eastern parts are somewhat homogeneous.
This explains the synphases of streamflow fluctuations on the greater part of Western Eurasia and North America. But asynphases of streamflow fluctuations may occur within individual regions of these territories.
Actually there exists a very complicated differentiation of streainflow rate, but deep knowledge of it requires more copious and long observations on streamflow.
Further studies in this field should be devoted to the improvement of physical know- ledge of cyclic streamflow fluctuations and to the development of methods of super- long-term forecasting of streamflow rate. The study of long-term streamflow fluctuations is a complex global problem, which requires considerable efforts not only of hydrologists, but also of climatologists, synoptic forecasters, geophysicists, geographers, as well as international co-operation of hydrologists.
Corititrental precipitcrliori and coaporafiori