Negative ETo

Laura Chávez

LEED AP BD+C, LEED Homes

LEEDuser Basic Member

0 thumbs up

Project location :

Mexico

July 14, 2020

I'm using the Outdoor water use reduction calculator_v02 from the resources tab since the project its outside USA. I'm entering the data for the monthly rainfal and Monthñy ETo from the IWMI site.

I it ok that the table in the calculator is showing negative numbers in the water demand column?

the rest of the results, such as peak watering demand, peak watering month ETo, LWA and LWB are positive numbers but I'm still concerned with the negatives of the water demand column

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Rodolfo Loro, Jr.

Sustainability Coordinator

ecoSolutions

LEEDuser Basic Member

3 thumbs up

Tue, 07/28/2020 - 17:38

I have the same concern with negative numbers in the water demand column (also a project outside the US), nevertheless the percentage reduction from baseline (%) came out quite fine as we used drip irrigation and plants with low-water requirement.

Andrey Kuznetsov

ESG consultant, LEED AP BD+C

Self Employed

LEEDuser Basic Member

36 thumbs up

Wed, 03/30/2022 - 14:10

ETo, as per my understanding, cannot be negative. Since it's "the combination of evaporation and plant transpiration into the atmosphere". Negative ETo says that that soil and plants are netto consuming water from atmosphere. Negative can be Watering demand (mm) - since it's monthly rainfall minus monthly ETo, and if monthly ETo is less than monthly rainfall - watering demand even in peak month can be negative.

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