Rain fall data is measured by rain gauge

Et is measured by Lysimeter or by empirical methods available.

Evaporation by Evaporimeter

Deep percolation by Lysimeter

Initial solo moisture by gravimeteric method.

Irrigation application by parshall flume method

You must have all the instruments for accurate measurement of the above parameters and the put all these parameters inth e Water balance equation....

For the first question: You needed to continuous climate data for a period of thirty years at a minimum in order to obtain scientifically credible results.

As for the second question: You need to calculate the amounts of runoff and total evaporation and infiltration to the aquifers.

I agree with Som if you want to measure most of the data for water balance. If you want to determine or estimate you can run any hydrologic model using minimum input data (e.g., precipitation and temperature). The duration of data based on your research questions which you wanted to address. Hope it helps.

Please, Dr Keerthi, allow me to suggest a more realistic water balance by including the groundwater component, that is:

- How much rainfall infiltrates beyond the soil?

- How much groundwater is discharging as upward flow into the farm?

- How much groundwater is reaching/leaving your farm horizontally?

Two main questions are to be given further consideration: i) to define how to cross-check your intended budget with other tools as chemistry or isotopes; and ii) how your farm is hydraulically connected with the region by means of surface or groundwater components....

Do get from Mexico saludos,jjoel carrillor

I will participate in the discussion later

What is a water budget? A water budget reflects the relationship between input and output of water through a region. The water balance graph shows precipitation and potential evapo-transpiration both as line graphs. Thus we have a direct comparison of supply of water and the natural demand for water. It is possible to identify the periods when there is plenty of precipitation and when there is not enough.

The following terms will be used in the questions that follow:

•Potential Evapotranspiration (PE): All the water that could enter the air from plants and evaporation if present.

•Precipitation (P): All moisture from the atmosphere, rain, snow, hail and sleet.

•Surplus: Water above what is lost naturally from the soil (when P is greater than PE)

•Deficit: Water that would be lost above what is in the soil if it were present (when P is less than PE)

1- Withdrawals must be ≤ deposits

2– Over allocating surface supplies & groundwater mining are like over-drafting bank account

3- Deposits ~ water supplies • Withdrawals ~ water demands

Regarding to first question..

1. How many years of rainfall data do I need?

Water balance modelling can be performed on various data sets depending upon the data available and the degree of precision provided by the modelling calculations. Historical rainfall recordings for your location (maybe 100 years), and the daily evaporation data, or do you use computed monthly historical rainfall and evaporation data. Remember that rainfall is random - there is no connection with previous rainfall to current rainfall. The next 20 years may not resemble the last 20 years or any other 20 year period - that's the nature of global weather!!

( If you have not the 100 years. More years, you have will better. 20 years better than 10) I think you need 10 years as a minimum

2. How to calculate other parameters?

A water budget describes the various components of the hydrologic cycle.

 Precipitation (P)  Evaporation (E)  Evapotranspiration (ET)  Surface runoff (SRO)  Groundwater flow (GF)

The water budget is expressed as an equation relating these components: ΔS = P – E – ET ± SRO ± GF

Precipitation

Precipitation is the primary water input to the hydro-logic cycle and is evaluated for all water budget calculations. Precipitation data for a normal year should be used to evaluate the long term impacts of a project.

Evaporation

Evaporation, as distinguished from evapotranspiration, is the process by which liquid water from an open water surface is converted directly to water vapor.

The evaporation measured in the pan is always greater than what would occur from a lake or pond. The measured evaporation must be multiplied by a coefficient to convert the observed values to an estimated value for lakes and ponds. That coefficient is usually around 0.7.

Surface Runoff

Surface runoff is not normally an important component in these calculations unless the pond or wetland is at the bottom of a slope that normally collects and holds surface runoff. This runoff may be needed to keep the wetland from going dry in the summer or at least provide enough water on a seasonal basis.

Surface runoff is computed using the runoff curve number method (RCN), which was developed by the Soil Conservation Service in 1954. The combination of a hydrologic soil group and a land use and treatment class is a hydrologic soil-cover complex. Each combination is assigned a RCN, which is an index to its runoff potential.

Groundwater

Groundwater flow can be an important consideration when evaluating applications for sand and gravel mining. The main concern of a mining operation that excavates a lake or pond is that it exposes the groundwater to the air, which increases losses through evaporation. For this case, 3/3/2010 General Guidelines for Calculating a Water Budget page 8 the water budget is calculated using groundwater flow, precipitation, and evaporation. Surface runoff is usually a minor consideration for these projects. In order to determine the groundwater flow component, one needs to have an estimate of the hydraulic conductivity (K) of the soil, or its ability to transmit water. The K can be estimated from well records and is usually determined by the applicant. The total groundwater flow into the project area also requires the cross sectional area and the slope (S0) of the groundwater head contours. The saturated thickness of the aquifer (B) can usually be determined from well records. The width (W) of the aquifer that flows to the project area requires knowledge of the groundwater head contours. A good estimate of this value is the maximum width of the excavated lake, viewed looking “into” the direction of the groundwater flow. The slope of the groundwater head contours is determined from well records or other recorded water levels and should be calculated by the applicant.

The total groundwater flow (GF) into the excavated lake is then:

GF (ft3/day) = K (ft/day) * B (ft) * W (ft) * S0 (ft/ft)

Dear all, in any water balance (water divergence = net change of inflow over outflow in a 3D-region in a certain time) there is a need to consider the about 97% of the water present (that is under natural boundary conditions from surface to basement rock). Note that only some 3% of the water is surface water (in precipitation, transpiration, evaporation, runoff); in fact, the relation between surface water and groundwater needs to be fully understood. This understanding is based in the cross-checking of any computation on what appears to be a surface component, ie.: if the groundwater component is neglected in natural discharge as in evapotranspiration (with a relative shallow watertable), it has to be proved that the water sent to the air and consumed by plants is only comming from rainfall. Streamflow, needs to be understood as well, how much water in the river is baseflow (that is, groundwater).... So, any called "surplus" or "deficit" by a "water balance" will need further assistance by extra tools so the values thus obtained could be validated...

Please, do get from Mexico saludos,jjoel carrillor

The only data I have is the total precipitation and the soil type.. I have the area and the GIS map. I have no clue what to do next.

I would agree with Atef's response here.

We can solve the problem without making it more complex.

Water budget would comprise of your precipitation and or surface water supply with your evapotranspiration from the farm which is dependent on the crop type. A detailed budget would then look into runoffs as well as groundwater recharge.

You can also use remote sensing to estimate the evapotranspiration in this case.

Evaporation and evapotranspiration considered as loss an precipitation as gain. We need to balance between these components. The runoff, deep percolation of water, soil moisture status are the others components. But the issue in the discussion is that of availability of single parameter viz rainfall data. In this case ET need some to estimated which is not easy elbeit you have the lysimter. Therefore satellites image can give some clue in this situation. Developing regional model and algorithm will be helpful using remote sensing data and software to find out loss of moisture and be used for water balance studies..

I suggest to perform a monthly water balance using the method of Thornthwaite Mather (1957), for 10 or more years, depending on data availability. It is a simple widely used approach that determines the monthly water balance in the soil and its surplus as groundwater recharge and (or) streamflow and interflow. It only requires monthly precipitation data, monthly temperature data (for potential evapotranspiration ETP, for example using the Thornthwaite formula) and the soil and vegetation parameters of your area - field capacity, permanent wilting point and the root depth of the plants. These parameters can be found in various tables, and so can be radiation data for ETP calculations. The method first determines the maximum soil retention capacity (from the above soil and vegetation data), and then compares each month the precipitation with the ETP. This either generates a deficit (if P is smaller than ETP) or (if P is greater than ETP) water fills up the soil until the maximum retention has been reached and later generates surplus in form of recharge. LAter in dry periods the accumulated retention amount is used to support evapotranspiration. This concept is very simple and has been widely used in various countries to determine the monthly evolution of retention and surplus, particularly in areas with pronounced wet and dry seasons.

Hope this may help.

I have 30 years of precipitation data, i have other factors such as humidity and temperature. The soil type is coarse gravel cobble. I also have area of the farm and slope of different sections. I need to find our evapotranspiration, runoff and infiltration. The vegetation is just grass and coniferous forests. If anyone could help based on this update, i'll be grateful.. Thanks

The region is St. John's Newfoundland ( Avalon peninsular) , Eastern Canada.

Dear Keerthi Stephen

What is the area of the farm?

it's 31 acres sir

Follow

Well,

https://slideplayer.com/slide/7804312/

Regards