InnerSoft - ISBH Water Balance version 0.1 Beta
Inputs
P Precipitation. Precipitation in the form of rain, snow, sleet, hail, etc. makes up the primarily supply of water to the surface. In some very dry locations, water can be supplied by dew and fog.PE Potential evapotranspiration. Potential evapotranspiration is the amount of water that would be evaporated under an optimal set of conditions, among which is an unlimited supply of water. Think of potential evapotranspiration of "water need". In other words, it would be the water needed for evaporation and transpiration given the local environmental conditions. One of the most important factors that determines water demand is solar radiation. As energy input increases the demand for water, especially from plants increases. Regardless if there is, or isn't, any water in the soil, a plant still demands water. If it doesn't have access to water, the plant will likely wither and die.
Field Capacity. The maximum amount of water the soil can hold (water holding capacity).
User must check 'Soil is NOT dry on first month of hydrological year' if soil store water on first month of hydrological year. Then user must input % of water reserve refered to Field Capacity.
Use Decimal Symbol of your Operating System on data inputs.
You can select the first month of hydrological year from the list at right-top window. Month changes will not change data inputs, only month table reference.
Click on 'Compute' button to calculate outputs. You can make changes over data inputs (P and PE) and compute again.
Outputs (After Compute)
ST Soil Moisture Storage. Soil moisture storage refers to the amount of water held in the soil at any particular time. The amount of water in the soil depends soil properties like soil texture and organic matter content. The maximum amount of water the soil can hold is called the field capacity. Fine grain soils have larger field capacities than coarse grain (sandy) soils. Thus, more water is available for actual evapotranspiration from fine soils than coarse soils. The upper limit of soil moisture storage is the field capacity, the lower limit is 0 when the soil has dried out.DST Change in Soil Moisture Storage. The change in soil moisture storage is the amount of water that is being added to or removed from what is stored. The change in soil moisture storage falls between 0 and the field capacity.
AE Actual evapotranspiration. Evaporation is the phase change from a liquid to a gas releasing water from a wet surface into the air above. Similarly, transpiration is represents a phase change when water is released into the air by plants. Evapotranspiration is the combined transfer of water into the air by evaporation and transpiration. Actual evapotranspiration is the amount of water delivered to the air from these two processes. Actual evapotranspiration is an output of water that is dependent on moisture availability, temperature and humidity. Think of actual evapotranspiration as "water use", that is, water that is actually evaporating and transpiring given the environmental conditions of a place. Actual evapotranspiration increases as temperature increases, so long as there is water to evaporate and for plants to transpire. The amount of evapotranspiration also depends on how much water is available, which depends on the field capacity of soils. In other words, if there is no water, no evaporation or transpiration can occur.
S Surplus. Surplus water occurs when P exceeds PE and the soil is at its field capacity (saturated). That is, we have more water than we actually need to use given the environmental conditions at a place. The surplus water cannot be added to the soil because the soil is at its field capacity so it runs off the surface. Surplus runoff often ends up in nearby streams causing stream discharge to increase. A knowledge of surplus runoff can help forecast potential flooding of nearby streams.
D Deficit. A soil moisture deficit occurs when the demand for water exceeds that which is actually available . In other words, deficits occur when potential evapotranspiration exceeds actual evapotranspiration (PE>AE). Recalling that PE is water demand and AE is actual water use (which depends on how much water is really available), if we demand more than we have available we will experience a deficit. But, deficits only occur when the soil is completely dried out. That is, soil moisture storage (ST) must be 0. By knowing the amount of deficit, one can determine how much water is needed from irrigation sources.
P-PE, DST and ST values on TOTAL data column have not physical meaning.
Thornthwaite Moisture Index (Im). As used by C. W. Thornthwaite in his 1948 climatic classification: an overall measure of precipitation effectiveness for plant growth that takes into consideration the weighted influence of water surplus and water deficiency as related to water need and as they vary according to season. For a given station, it is calculated by the formula: Im = (100S - 60D)/PE
where Im is the moisture index, S the water surplus, D the water deficiency, and PE the water need. The calculation of S and D is made on a normal month-to-month basis, with S being the total surplus from all months having a water surplus, and D the total of all monthly deficiencies; each is represented by the difference between monthly precipitation and monthly potential evapotranspiration (in centimeters or inches). Here PE is the annual potential evapotranspiration.
Menu File
New: Set P and PE to zero. Set January as first month of hydrological year. Set Field Capacity to 10. Remove TOTAL data column and output rows.Open: Open a text file storing inputs, the kind of files that is generated on item 'Save As...'.
Save As...: Save in a text file the data inputs: P, PE, Field Capacity, first month of hydrological year, % field capacity... It will not store data outputs.
Export to Excel: Export inputs and outputs to a MS Excel file.
Close: Close the application.
Reference Documents
About CLIMATIC CLASSIFICATION
http://amsglossary.allenpress.com/glossary/search?id=moisture-index1
About Water Balance
http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/hydrosphere/water_balance_1.html
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