HomeMy WebLinkAbout10.29.20 FW_ Water use estimates
From:Gosselin, Paul
To:Alpert, Bruce;Bennett, Robin;Clerk of the Board;Connelly, Bill;Cook, Holly;Lambert, Steve;Lucero, Debra;
McCracken, Shari;Paulsen, Shaina;Pickett, Andy;Ring, Brian;Ritter, Tami;Rodas, Amalia;Sweeney, Kathleen;
Teeter, Doug
Cc:Buck, Christina;Hatcher, Casey
Subject:FW: Water use estimates
Date:Thursday, October 29, 2020 8:25:08 AM
Attachments:Land and Water Use Highlights 10272020.pdf
Board Members
th
At the September 29 Board of Supervisor’s meeting, Supervisor Lucero raised questions about
changes in land use and water demand. Christina had a follow up discussion with her and developed
a response to the questions. I am forwarding Christina’s response. If you have any questions please
let me or Christina know.
Thank you
Paul
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Dear Supervisor Lucero,
I’ve put together information in response to our conversations and questions you raised at the
September 29 Board of Supervisors meeting regarding agricultural land use in Butte County and
water use of different crops. These estimates were developed from results of the Butte Basin
Groundwater Model (which as you know is being used to develop the water budgets in the Vina,
Butte, and Wyandotte Creek Subbasins). The attached provides estimated water rates (AF/Ac) of
applied water for different crops, effects on estimated water demand of the changing crop mix in
Vina, and estimates of water use per acre of walnuts in different areas of the Vina subbasin that
have different soil characteristics. It is interesting to note, and I admit somewhat contrary to
intuition, that the shifting crop mix to orchards and specifically walnuts does not seem to be
increasing water demand. This was a question that came up after we rolled out the 2016 Water
Inventory and Analysis Report. It is good to finally have put the numbers together to take a look.
I hope this answers some questions about the impact of different crops and soils on irrigation water
demand, and it probably raises new ones. I’d be happy to meet with you to discuss this further.
Best,
Christina
Christina R. Buck, Ph.D.
Assistant Director
Dept. of Water and Resource Conservation
Butte County
308 Nelson Avenue
Oroville, CA 95965-3302
Off: 530.552.3593
net
Total Irrigated Acreagein Butte CountyChanged less than 1% from 2016 to 2019
The figure shows Butte County agricultural acreage as reported in Ag Commissioner Reports. Total
acreage does not include non-irrigated Pasture (Pasture, Other) but does include Non-bearing Fruit and
Nut Crop Acreage. The Basin Setting Project utilized land use data through 2016 (with 2017 and 2018
acreages only adjusted from 2016 numbers based on changes to rice, wetland and idle acreage). Total
irrigated acreage increased about 0.5% from 2016 to 2019 or 1,338 acres. Total irrigated acreage varies
from year to year largely driven by planted rice acreage that is affected by weather during planting
season and fallowing water transfers during dry years.
Butte County Crop Acreage
237,560
236,222
250,000
230,249
227,388
223,839
200,000
150,000
100,000
50,000
0
20152016201720182019
Acreage
1
Estimated Applied Water Per Acre for Different Crops Varies from about 2 AF/Ac to 4AF/Ac
The figure shows estimated rates of applied water (acre-feet per acre) for different crop types. This is
based on results from the Butte Basin Groundwater Model. Wetlands and rice have the highest water
requirement per acre (although water that runs off or drains from the field is often available for reuse
on other fields) requiring 4.3 and 4.0 AF/Ac, respectively. Vineyards and Miscellaneous Deciduous
require the least applied water per acre: 1.9 and 1.8 AF/Ac, respectively. Much of the planted almonds
(2.3 AF/Ac) and walnuts (2.6 AF/Ac) in recent years and over the past decade have replaced grain (2.3
AF/Ac) and other field crops (3.1 AF/Ac). This amounts to an additional 0.3 AF/Ac of water demand for
walnuts compared to grain, for example. To continue the example, for 20,000 acres of new walnuts, this
would be an additional 6,000 AF of water demand compared to growing grain on that same acreage.
However, walnuts have replaced a mix of crops including almonds, prunes, corn, alfalfa and some rice.
Applied Water Requirement (AF/Ac)
5.0
4.3
4.5
4.0
4.0
3.7
3.6
3.4
3.3
3.5
3.1
3.0
2.9
2.8
3.0
2.6
2.5
2.4
2.3
2.3 2.3
2.3
2.5
1.9
1.8
2.0
1.5
1.0
0.5
-
2
Vina Subbasin: Total water demand based on change in crop mix from early 2000s to 2016 shows a
decrease by about 13,000 AF
In the Vina Subbasin, land use changes over time have seen a shift from almost every crop category to
primarily more walnuts and more Miscellaneous Deciduous orchards. Shifting crop mix can lead to an
increase or decrease in overall water demand depending on whether the shift is from a more to less
water intensive crop, or vice versa. In the case of the Vina Subbasin, estimated water demand driven by
land use shifts decreased by about 13,000 AF using average 2000-2009 acreage compared to 2016. This
includes the effects of decreased wetlands acreage. For agricultural land uses only, the decrease in
water demand is estimated at about 7,800 AF. This amounts to about a 4% decrease in total agricultural
water demand. Many factors drive agricultural water demand including wet and dry year cycles, the
timing of precipitation, irrigation method and efficiency, and soil type in addition to crop mix. Shifts in
the crop mix of the Vina Subbasin does not appear to be creating increased water demand overall.
In the Vina subbasin, agricultural water demand is largely met by groundwater pumping although
surface water supplies serve about 9% of agricultural water needs, mostly from Butte Creek diversions.
Average Applied Water (AF)
Average Acreage 2016 Difference
Land Use
Applied Water
2000-2009Acreage(AF)
2000-20092016
(AF/AC)
Alfalfa526 128 3.7 1,938 470 (1,468)
Almonds34,804 32,918 2.3 81,569 77,149 (4,420)
Barren373 458 0.0 - - -
Beans144 332.5 363 83 (280)
Corn661 170 3.6 2,363 608 (1,756)
Grain1,540 718 2.3 3,472 1,619 (1,853)
Idle5,805 4,6920.0 - - -
Misc. Deciduous921 3,5831.8 1,669 6,491 4,822
Misc. Field92 13.1 284 3 (281)
Misc. Pasture2,123 1,0893.3 6,974 3,577 (3,396)
Misc. Subtropical332 168 3.4 1,121 566 (554)
Misc. Truck569 382 2.8 1,600 1,076 (524)
Olives889 795 2.3 2,025 1,813 (212)
Prunes5,110 2,8462.3 11,662 6,496 (5,166)
Safflower162 743.0 486 222 (264)
Semiagricultural1,308 1,2500.0 - - -
Sunflowers397 110 2.9 1,142 317 (825)
Tomatoes603 302 2.4 1,419 710 (709)
Vineyards35 521.9 68 101 33
Walnuts16,688 25,280 2.6 44,211 66,974 22,763
Rice10,865 8,2265.2 56,555 42,822 (13,733)
Wetlands2,304 1,0724.3 9,888 4,603 (5,285)
Native73,667 71,761 0.0 - - -
Riparian3,977 4,3770.0 - - -
Urban21,423 25,318 - - -
Total 185,318 185,804 228,811 215,702 (13,110)
Total Ag82,26781,568 218,923 211,099 (7,824)
3
Soil type effects applied water demand.
Walnuts are grown throughout the region on a variety of soil
Walnut: Applied Water Estimates
types. Estimated applied water requirements of walnuts vary
BBGM Region AF/Ac
from 2.2 AF/Ac to 3.1 AF/Ac in different subregions in the Butte
Unorg Tehama (1) 2.2
Basin Groundwater Model. The map shows the subregions
Vina (2) 2.7
(numbered) and is colored according to the soil texture (clay,
M&T (4) 2.4
sand, loam etc).
Durham-Dayton (5) 2.7
Esquon (6) 2.6
Cherokee (9) 3.1
Average 2.6
4