Meteorological Measurements are made to characterize
the climate of that location and to supply meteorological
information related to hydrologic processes.
Meteorological data are especially important on hydrologic
research because the climate and weather of an area exert
a profound influence on most hydrologic processes.
Precipitation is directly related to river runoff
forecasting and is obviously a key component for any
hydrologic modeling. Wind speed and wind direction are at
least partial determinants of rain or snow distribution
over a watershed, and temperature data are vital to
parameters such as soil freezing or snow melt. The
hydrologic regime is so intimately related to climactic
factors that almost every hydrologic study has a
meteorological aspect.
The key meteorological parameters necessary for
hydrologic study are:
Precipitation - includes any moisture falling
from the atmosphere in liquid or frozen form. Collected by
rain gages, both non-recording, which retains the total
precipitation between observations and recording which
gives time of precipitation so intensities can be computed
and transmitting rain gage sites for sending data to a
central station for analysis.
Air Temperature- is commonly measured because of
its importance to evaporation, transpiration, soil
conditions and snowmelt.
Humidity - of the air near the surface has a
definite influence on the rate of evaporation from lakes
and on evapotranspiration from land areas.
Wind - Hydrologically, wind influences the
magnitude of evapotranspiration and windspeed and
direction influence rain gage catch and snowfall drift.
Anemometers are designed to measure windspeed and
direction.
Solar Radiation - It provides the energy that
drives regional and global hydrologic cycles. Radiation is
the most important factor in the evaporation and
transpiration processes. Pyranometers and Net Radiometers
are used to measure solar radiation.
Evaporation - Rate of evaporation or potential
evapotranspiration is dependent on the temperature of the
evaporating surface and the wind flow over the water
surface and is one of the hydrologic processes most
influenced by climactic conditions. It can be measured by
lysimeters but is best measured by the Type A Evaporation
Pan.
Barometric Pressure - This is required for the
potential evapotranspiration and dew points. Water level
in a confined aquifer will be affected by barometric
pressure.
Soil Temperature- measurement indicate the
sensible heat stored in the soil and are important to
hydrologic investigations as soil freezing can drastically
reduce infiltration rates of soil causing significant
change in runoff in a watershed.
Infiltration - Movement of water through the
soil which indicates the water retention capacity or
saturation thus predicting surface water run off.
Infiltration ring tests are a common predictor of
infiltration.
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