Analyse How the Inputs and Outputs from a River Basin Can Vary Over Time

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Analyse How the Inputs and Outputs from a River Basin Can Vary Over Time

Both the inputs to and outputs from a river basin can vary both spatially (in different areas) and temporally (over time), due to daily, seasonal and annual occurrences.

        Precipitation mainly reaches the grounds surface from the atmosphere as snow and rain. Heavy snow is often intercepted and stored on the tops of hills and mountains and may lead to a decrease in river levels. Some rainfall may fall directly into the stream or river and some may fall onto the land and flow into the river basin through a variety of routes including throughflow, stemflow and overland flow.

The intensity and duration of precipitation has a short term but regular effect upon both the inputs and outputs of a river basin due to the weather patterns. Over a short period of time, for example a week, the precipitation levels over the river basin can significantly vary, as on some days of the week the total precipitation can be extremely high and the next it could be virtually zero.

        Long periods of rainfall are the main cause of flooding as the soil has become saturated it reaches its infiltration capacity and infiltration is reduced, therefore increasing the frequency of surface run off and the risk of flooding.

        In addition to the weather having a large impact on the inputs over a short period of time in and around the catchment area of the river basin the seasons also influence the levels of precipitation. For example in winter precipitation can fall in the form of snow and in summer the precipitation levels often decrease dramatically, due to the vast heat imposed on the surface of the land.

High temperatures especially in summer increase evapotranspiration rates which in turn can reduce the river discharge but also can have an effect upon the stored water. This stored water is in the form of snow and icecaps on mountains and high temperatures cause the snow to melt and the discharge to increase rapidly at a dangerous rate. On a daily basis, this meltwater can fluctuate because at the hottest time of the day, the increase in temperature accelerates the rate at which the ice melts and creates more meltwater.

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In spring and summer these increased temperatures result in greater melting of glacial areas which come to a halt in autumn and winter due to the decrease in temperature.  Cold temperatures in winter may increase the levels of surface runoff and total discharge as the ground may become frozen and restrict the frequency of infiltration into underwater stores, but also may decrease the amount of melting in glacial areas due to the decrease in temperature. Between spring and autumn there is a period of adjustment where the precipitation can vary widely and can be extremely increased or decreased.  

        Climatic ...

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This is a reasonable answer to what appears to be a simple question but isn't! It is difficult to stick to the question as set. The temptation is to drift on to other factors affecting discharge - which has happened here. Overall the author shows an understanding of the key ideas. The answer would benefit from a clearer explanation at the beginning of the idea of the river basin as a "system" .