Welcome to WEAP's Website WEAP
WEAP is an initiative of the Stockholm Environment Institute.


About WEAP

Home
Why WEAP?
Features
What's New?
Sample Screens
Demonstration
Publications
History and Credits

Using WEAP
Download
Licensing
User Guide
Tutorial
Videos (YouTube)

User Forum
Discussions
Members List
Edit Profile

Additional Support
Training
University Courses
Collaboration

About Us
SEI-US Water Resources Program
Please Contact Us

LEAP
Interested in Energy?
Read about LEAP: SEI's software for energy planning.

Link WEAP and LEAP for combined Water-Energy planning.
Watch a video demo!
   

User Forum

All Topics | Topic "Solar radiation estimation using the soil moisture method"
Log in to post new messages or reply to existing messages.
 
Author Message
Eng. Denny Rivas

Subject: Solar radiation estimation using the soil moisture method   
Posted: 10/25/2016 Viewed: 9033 times
Hi, I'd like to know what method WEAP applies to estimate solar radiation when using the soil moisture method (not MABIA). Is it the hargreaves-samani equation?
Mr. Jack Sieber

Subject: Re: Solar radiation estimation using the soil moisture method   
Posted: 10/27/2016 Viewed: 8986 times
WEAP uses equations from Chapter 4 of the Handbook of Hydrology for calculating net solar radiation, specifically equations 4.2.5, 4.2.6, 4.2.7 and 4.2.13.

You can view pages in the book on Amazon. Equations for solar radiation start on page 114 (search for "solar"): https://www.amazon.com/Handbook-Hydrology-David-Maidment/dp/0070397325#reader_0070397325

Jack
Eng. Denny Rivas

Subject: Re: Solar radiation estimation using the soil moisture method   
Posted: 10/27/2016 Viewed: 8975 times
Thanks a lot Jack. I checked the handbook and the equations are very clear now.

Denny
Dr. Andrea Momblanch Benavent

Subject: Re: Solar radiation estimation using the soil moisture method   
Posted: 11/10/2021 Viewed: 885 times
Hi Jack,

The Soil Moisture Method uses Angstrom equation to calculate incoming shortwave radiation (Rs) from cloudiness fraction (CF). That equation considers that Rs is always between 25% and 75% of extraterrestrial solar radiation (Ra) since coefficients a and b in that equation are 0.25 and 0.5 respectively.

I am modelling the Santa River basin in the Peruvian Andes and I am using observed Rs to calculate cloudiness fraction (CF) as an input for WEAP by inverting the Angstrom equation. However, in that basin Rs/Ra is sometimes (many times in fact) larger than 0.75 and that results in CF values above 1. I know if I use those CF values I will get the right Rs that WEAP uses to then calculate ETo, but WEAP does not run with CF>1. Do you have any ideas as to how I can overcome the problem? The only way I see at the moment would be removing the CF>1 condition from WEAP.

Thanks,
Andrea

Topic "Solar radiation estimation using the soil moisture method"