Board approves adjustments to ET calculations for fallowed acreage, cattle ground, and non-commercial ag parcels to prevent overestimates of water use

At the East Kaweah Board Meeting on October 24th, the Board approved staff recommendation to refine evapotranspiration (ET) demand measurements for fallowed, non-irrigated cattle ground, and small acre non-commercial ag parcels.

Landowners with acreage falling under these unique cases will benefit from these adjustments that prevent over-estimation of water use on their parcels.

The adjustments keep non-irrigated lands from appearing like they are using more water than actual use by assigning an “error credit”. The error credit means the acreage ET will reflect no more than effective precipitation, removing errors with over-estimating water use for these cases.

Evapotranspiration (ET): the amount of water consumed by the plant through evaporation and transpiration. 

ET data gives us a picture of water use across acreage, measured as consumptive use. The East Kaweah GSA is using ET to quantify water use under new groundwater allocations.

The adjustments were necessary for these groups for the following reasons:

Fallowed acres

Current technology calculating ET can overestimate water use on fallowed acres that have no irrigation water demand. The adjustment to assign the error credit means ET would only reflect the precipitation that falls on the field, removing errors associated with ET calculations.

Cattle ground 

Non-irrigated cattle ground ET accuracy has improved, but investigations throughout the 2022 allocation year found that there may still be an overestimate for these land types. Staff working to investigate these cases found there are factors that can influence ET readings, including riparian influence and natural wooded areas. It was determined that these parcels with variances in ET readings are not using groundwater for irrigation, and therefore will be assigned the error credit of effective precipitation.

Non-commercial parcels 5 acres and less

Like with fallowed acres, current methodologies to calculate ET does not report water use accurately for small acreage. Due to the current pixel size of satellite imagery used for ET analysis, there reaches a point where too few pixels exist for small fields/parcels to ensure valid calculations. Given this issue, there is also potential for neighboring land’s water use can influence water use calculations on the small acre parcels.

The East Kaweah GSA understands it is important for stakeholders to have accurate information about their water use to remain within the groundwater allocations, and to make sure they are not receiving inaccurate bills. Staff is continually working with stakeholders to refine and iterate water use measurements to ensure highest possible accuracy, critical for implementing groundwater allocations.

If you have questions, want to provide input, or need clarification, please contact us at 559-697-6095 or send us an email at groundwater@ekgsa.org.

Learn more about topics related to the Groundwater Allocation, on our YouTube channel: “Groundwater Allocation Updates”