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evaporation to transfer approximately 577×1012 m3 of water from surface of the
Earth to the atmosphere of which 86% is contributed by oceans and remaining
14% by land (Shiklomanov, 1993; Pimentel et al., 2004). Evaporated water from
Earth’s surface reaches the atmosphere where it is condensed to form water
droplets and subsequently it reaches the land in the form of precipitation (rain and
snow) accounting for almost 20% of world’s precipitation. The surplus water, thus
received on land, returns to oceans through rivers and groundwater thereby
completing the water cycle (Shiklomanov, 1993; Pimentel et al., 2004). Therefore,
solar energy moves a significant amount of water from oceans to land via
atmosphere every year, thus making the hydrologic cycle vital not only to human
life and natural ecosystem, but also to agricultural and industrial production.
Figure 6.1. Hydrologic cycle showing the cyclic transfer of water between
atmosphere, lithosphere and hydrosphere.
Modified from Trenberth, K.E., Jones, P.D., Ambenje, P., Bojariu, R., Easterling, D., Klein Tank, A.,
et al., 2007. Observations: surface and atmospheric climate change. In: Solomon, S., Qin, D.,
Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M., Miller, H.L. (Eds.), Climate Change
2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change. Cambridge University Press,
Cambridge (UK), pp. 235–336.
However, the hydrologic cycle has started to alter due to the adverse effects of
climate change and rising global temperatures. The processes that are involved in
the hydrologic cycle are highly dependent on temperature. It has been observed
that global temperatures have steadily been rising over millions of years and
directly influencing the precipitation patterns, monsoonal intensity, water vapor
concentrations, cloud formation, seasonal changes and river flow patterns. The
rising temperature and changing climate has partly intensified this cycle because
rising global temperature evaporates more water from the ocean and land. The
warm air holds more water vapor which in turn produces more intensified rainfall
causing flooding of coastal regions. Warm air also increases rate of evaporation
that intensifies the evaporative process on the land which causes soil moisture to
evaporate over a time period and thus, intensifying the drought condition on the
hinterland areas of the continent. Therefore, shifts in climatic patterns and rising
global temperature speeds up the water cycle leading to changes in extreme
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climatic phenomenon of more intensified rainfall, cloud burst situations, frequent
storms and drought conditions. This direct effect on hydrologic cycle will also lead
to changes in water resources.
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URL: https://www.sciencedirect.com/science/article/pii/B9780128202005000154
Watersheds of Want
John F. Shroder, in Natural Resources in Afghanistan, 2014
Abstract
The hydrological cycle in Afghanistan is one of the high altitude snow and rain,
commonly torrential, which produces catastrophic downstream effects such as
avalanches and floods. Most of the precipitation that drives the river-flow lifeblood
of the country outward from the tops of the watersheds in Afghanistan diminishes
toward the borders from its highs in the northeast of the nation. The main river
systems, listed in a counterclockwise direction around Afghanistan. include the
Amu Darya, Hari Rud–Murgab, Helmand–Arghandab, and the Kabul, each of
which is discussed in more detail herein. Lakes in Afghanistan include glacial,
landslide-dammed, carbonate-precipitate types, diastrophic (tectonic and volcanic)
lakes, tectonic—mixed types, and multiple deflation-basin sorts of lakes, many of
which are intermittently dry. Underground water in Afghanistan occurs in aquifer
basins throughout the country, with the basin beneath Kabul City undergoing
severe drawdown.
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URL: https://www.sciencedirect.com/science/article/pii/B9780128001356000052
Characteristics of the Regional Hydrological Cycle
J. Shroder, in Transboundary Water Resources in Afghanistan, 2016
Abstract
The hydrological cycle in Central and Southwest Asia, of course, operates
essentially the same as it does in the rest of the world, but it does have regional
variations in character and timing of its phases, energy sources, winds,
distributions, climate and topographic influences, and other controlling factors
that need to be understood. The high mountains of the region serve as the water-
tower catchments for the elusive moisture that passes over the dry lowlands, but
fortunately for the people who live there, that moisture precipitates orographically
in the mountains above them. Not so fortunately, however, the common
devegetation and soil erosion that also occur so commonly in the region, end up
despoiling the surficial environments and reducing water infiltration into the
surficial soils so that the runoff is accelerated into flashfloods and is thereby
wasted. In any case, multiple drainage basins have resulted, the development and
use of which are the focus of this book.
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URL: https://www.sciencedirect.com/science/article/pii/B978012801886600001X
Rivers of the Boreal Uplands
Jan Henning L'Abée-Lund, ... Lars-Evan Pettersson, in Rivers of Europe, 2009
15.2.3 Hydrology
The hydrological cycle is influenced by several factors such as solar influx, rotation
of the earth, distance from the ocean, topography, and general atmospheric
circulation patterns. In the Boreal Uplands, topography and distance from the
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ocean vary considerably among watercourses. In general, the mean annual
precipitation is highest in the west and north with values exceeding 4000 mm. In
the east and in inland areas of large fjords, the mean annual precipitation is <1000
mm. The maximum and minimum mean annual precipitation during 1961–1990
was 6944 and 128 mm, respectively.
Runoff is not evenly distributed throughout the year and can be divided into
specific runoff regions (Gottschalk et al. 1979). In coastal areas, with a so-called
Atlantic regime, the lowest runoff occurs during May–August and runoff is similar
during the other months. The inland regime, situated between the Atlantic and the
mountain regime, is characterized by low runoff in winter (January–March), a
marked increase due to snow melt in April and May, and low values in summer
that increase from August until winter begins. The geographical variation in
precipitation is reflected in the flow regime of the rivers (Figure 15.2). In some
rivers, the period of recording covers several years prior to and after development
of hydropower schemes. Hydropower development has resulted in a significant
reduction in the ratio between flood and minimum discharge.
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