Full Freezing and Drying Up of River Channel as Opposite Phenomena in High and Low Latitudes
Asabina, E.; Asabina, E.
Ugra State University
It is shown that phenomenon of full freezing of river channel in high latitudes is opposite to drying up of rivers in low latitudes of Northern hemisphere. These phenomena are being observed simultaneously in very distant areas and have symmetric nature with conditional axis of symmetry in the middle latitudes.
Investigation of hydrological variation of river runoff was conducted for the territories located in the north between 56 and 67° and in the south between 2 and 11° of northern latitude. Northern area includes middle and low stream of the Ob drainage basin (Siberia). Southern area includes catchments of the Niger (upper and middle stream) and the Chary, rivers of Cameroon. Hydrology of all the rivers is not studied sufficiently. Total area is 3.2 million km2.
Hydrological variability of river runoff in different latitudes was compared under following conditions:
(1) areas of river catchments have to be approximately equal to exclude influence of runoff reduction due to river length. In this research, most of hydrometric gauging points limit catchments with area from 1000 to 15000 km2.
(2) river catchments have to be of approximately equal height to exclude influence of vertical gradient of precipitation on runoff values. In this research, the catchments have mean height from 100 to 600 m.
(3) runoff values have to be measured but not estimated. Data of 225 gauging stations with total observation period of 4081 years were used in this research.
(4) only average water years have to be taken into account to exclude influence of rare events. Runoff probability used in the research was 40-60%.
In studied areas, full freezing and drying up of rivers take place from November till April leading to similar result such as absence of river runoff both in the north and in the south. In Siberia, rivers are covered by ice annually because of low air temperature. Precipitation falls on a catchment surface as snow and does not effect directly on runoff value. In this period, river discharges depend only on ground water alimentation that terminates completely after frost penetrating of soil. There is no precipitation at the same period in Africa. Ground water lie deep from land surface and do not feed rivers. These circumstances as well as high temperature lead to drying up of river channels.
There are some common features in these phenomena. Absence of river runoff takes place during:
(a) equal length of time, which is 5-6 months,
(b) one and the same period of time from November till April,
(c) the same hydrological period of winter low water.
Reasons of absence of river runoff are:
(a) air temperature (very low or very high),
(b) precipitation (its accumulation on surface of catchment and river ice or complete absence of precipitation),
(c) seasonal absence of interaction with groundwaters because of freezing of soil or deep location under land surface.