Weather is defined as current meteorological conditions such as temperature, wind, and precipitation over a particular area and short time period. Weather conditions describe typical weather phenomena for a region over 1-2 weeks. Climate is the long term average weather conditions over at least 30 years for a specific location. Climate components that determine weather include radiation, air pressure, humidity, temperature, wind, evapotranspiration, precipitation, condensation, and cloud cover. Climate is influenced by both climate components and climate factors such as latitude, altitude, land/water patterns, relief, vegetation cover, and exposure. The characteristics and interactions between the different spheres that make up a watershed - atmosphere, hydrosphere, lithosphere, biosphere, and

1. Britannica Dictionary definition of WEATHER
: the state of the air and atmosphere at a particular time and place : the temperature
and other outside conditions (such as rain, cloudiness, etc.) at a particular time and
place.
ACCORDING TO CAMBRIDGE DICTIONARY, “the conditions in
the air above the earth such as wind, rain,
or temperature, especially at a particular time over a particular area.”
Weather
Weather is the combination of the current meteorological components, e.g.
temperature, wind direction and speed, amount and type of precipitation, sun shine
hours, etc. The weather is defining a short time period up to several days.
Weather conditions
Weather condition is the regional weather during a defined time period from one up
to several weeks. Weather condition is describing typical weather phenomena, such
as a series of thunderstorm in hot summer, foggy month in autumn or other weather
conditions which are typical for a specific region and/or season.
Climate
The climate is describing the long term (min 30 years) and average weather
conditions for a specific region. Examples: maritime climate, cold-dry desert climate,
tropical climate. Global climate classification maps highlight the high variety of
climates

2. Climate components
Meteorological station Kenyatta University Nairobie
Image Credit: Anette Stumptner 2012
Climate components are describing in integrated manner the current weather and
weather condition. Climate components are dynamic and change permanently;
continuous measurement is necessary for defining and forecasting weather. They
are:
 Radiation
 Air pressure
 Humidity
 Temperature
 Wind speed and direction
 Evapo-transpiration
 Precipitation
 Condensation
 Cloud cover

3. Climate factors
Exposition
Image Credit: Stefan Thiemann
Climate factors are terrestrial factors influencing the weather and weather condition.
Climate components and climate factors are composing the climate in its variations.
Climate factors are stable and/or only slightly changing factors, except the vegetation
cover (land use):
 Geographic latitude
 Altitude
 Land and water pattern
 Relief
 Vegetation cover (land use)
 Exposition
Interaction of geospheres

4. Interaction of geospheres; arrows symbolise the interactions (not all interactions are illustrated).
Image Credit: Anette Stumptner 2007
Watersheds consists - like all ecosystems - of different geospheres:
 atmosphere;
 hydrosphere;
 lithosphere;
 morphosphere;
 pedosphere;
 biosphere;
 human sphere;
These spheres are not independent, they interact. For example, the characteristics
and interactions of the atmo-, hydro-, litho-, morpho-, bio- and human sphere
determine which soil is formed in the watershed (soil forming factors). In other
watersheds with changed characteristics of geospheres (e.g., changed
meteorological parameters) may the interactions of geospheres result in another soil
type. Changes within a watershed (such as intensified resource use) may cause
changed soil characteristics.
Thus, the characteristics and interactions of the geospheres shape the nature of a
watershed. They thus also determine the availability of natural resources and their
quality. A sufficient precipitation rate with moderately intensity may supply an
adequate amount of water available for human use. If it really sufficient, is depending
of the actual demand of water. On the other hand, inappropriate land use practices
may degrade the soil and finally reduce the usable agricultural area. These
interactions of geospheres are the reason why Integrated Watershed
Management takes an integrated approach of natural resource management.
The interactions of geospheres are complex (see slope dynamics and river bed
dynamics).
Slope dynamics

5. Morphological processes on a slope
Image Credit: Anette Stumptner 2007
Slopes occurring in the landscape are not static, but rather highly dynamic. Several
processes proceed on slopes which cause changes in the landform (see figure).
According to the characteristics of the individual geospheres these processes take
place unequally and with varying intensity. Two important morphological processes
are
 soil erosion and
 mass movements.
Both are explained on the following pages
Erosion and soil erosion
Severe soil erosion in the Gina River catchment, Ethiopia
Image Credit: Rüdiger Hahl 2003
Erosion is a natural process resulting in a levelling of the relief [8].
The intensity of erosion by water is determined by the amount of surface runoff
available and the given energy.
Potential Erosion Risk
The processes generating surface runoff determine the potential erosion risk.
These processes are dependent on a variety of factors which are interacting in a
multidimensional and non-linear relationship [8].
Actual Erosion Risk
Human activities such as agriculture affect erosional processes which are then summed up
to soil erosion.
In general, soil erosion shows an increased intensity compared to natural erosion
processes. Human impact causes a reduction of natural vegetation cover or even
complete destruction [8]. If vegetation is reduced the amount of precipitation which is

6. intercepted and evapotranspirated decreases and no natural barrier holds up the
downward moving water. This results in a higher proportion of precipitation which
runs unhampered on the surface downslope causing, rill or gully erosion. This is
aggravated if the soil is compacted by human and animal activities. Soil compaction
reduces the infiltration rate. The splash effect is also higher if the protecting
vegetation cover is lacking which causes sheet erosion [9]. Soil erosion risk
increases.
However, positive effects can arise from human activities such as practicing soil and
water conservation measures [8].
These interactions of land use, vegetation cover and soil erosion risk are important
to understand in order to prevent soil erosion and its damaging impacts. These can
be found not only in the immediate surrounding (on-site damages) but also in
downstream areas of the watershed (off-site damages). This is an important reason
for tackling the problems by the Intergated Watershed Management approach.