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User Forum

All Topics | Topic "Monthly variation"
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Author Message
Jean Claude Manzi Biranga

Subject: Monthly variation   
Posted: 2/24/2014 Viewed: 14311 times
I want to calibrate my WEAP model but I don't know what to put for Monthly variation (in %) for agriculture demand for Rwanda. Any help please?
Stephanie Galaitsi

Subject: Re: Monthly variation   
Posted: 4/23/2014 Viewed: 13514 times
For agriculture, water demands usually vary considerably from month to month. In WEAP, the user fills in Annual Water Use for the activities occurring at the site (Activity Level). But because agricultural demand is highly seasonal, being able to express water demand by month will give you more accuracy over smaller time increments.

Say that one of my crops was bananas, and they needed most of their water in the summer. Then I could write in Monthly Variation:

Bananas: MonthlyValues(Dec, 0, Jan, 0, Feb, 0, Mar, 0, Apr, 0, May, 15, Jun, 17, Jul, 17, Aug, 25, Sep, 16, Oct, 10, Nov, 0, Dec, 0)

(You can enter these values using the Monthly Time-Series Wizard). Note that all the values add up to 100%. Also these are arbitrary values, not meant to be representative for Rwandan banana agriculture. To fill out this section, it is very helpful to have past knowledge of agricultural use to calculate each month’s percentage of annual use for each crop. If you’re having a problem accessing data for Rwanda, you can see if there is agricultural data for regions with similar climates and crops.

I would recommend reviewing the section “WEAP in One Hour/Entering Elements into the Schematic/Create an Agricultural Demand Site” in the WEAP Tutorial. Also, remember that different crops can have different monthly variations.

If you would like to disaggregate the demands for different crops, review the “Refining the Demand Analysis/Disaggregating Demand/Create the Data Structure for “Rural” demand node” – but instead of showers, toilets, you would use different crops for your irrigation demand. Each one then has its own set of parameters entered into the data section for WEAP.
You can also investigate using a catchment node instead of a demand node (see the Hydrology section of the WEAP tutorial) but it has its own data requirements.

Devaraj de Condappa

Subject: Re: Monthly variation   
Posted: 5/7/2014 Viewed: 13441 times
Dear Jean Claude,

Stephanie gave-you a good walk through on the way to enter in WEAP.

In case you need to know the amount of water crop needs in Rwanda, I advise you to use the softwatre CROPWAT (http://www.fao.org/nr/water/infores_databases_cropwat.html) from the FAO which can calculate typical crop water requirements. You would also need to use the database CLIMWAT (http://www.fao.org/nr/water/infores_databases_climwat.html) to pick-up typical meteorological data of your region under study.

So with CROPWAT + CLIMWAT you can calculate typical monthly crop water requirement. And then you follow Stephanie's instruction to enter in WEAP.

Do not forget to consider on the top of this crop water requirement a non-optimal irrigation effiency to calculate the irrigation water demande from the crop water requirement. Basically, [Irrigation Water Demand] = [Crop Water Requirement] / |Irrigation Efficiency] with |Irrigation Efficiency] taking values smaller to 1 (1 is perfectly efficient irrigation, values can be as low as 0.4 or even lower for gravity systems and go up to 0.6 to 0.8 for pressurised systems like sprinklers or drip irrigation).

Cheers!
Jack Sieber

Subject: Re: Monthly variation   
Posted: 5/7/2014 Viewed: 13439 times
The latest version of WEAP now incorporates the "MABIA" method for catchment hydrology, which is very similar to CROPWAT in that both are derived from the FAO-56 method for calculating crop evaportranspiration. See http://www.weap21.org/WebHelp/Mabia_Algorithms.htm for more information.
Topic "Monthly variation"