Irrigation Assisted Rain-fed AgricultureA Sustainable Adaptation Strategy

Richard McNider John Christy

University of Alabama in Huntsville

Dennis BraggBragg Farms

James Hairston Donn Rodekohr

Auburn University

SECC/WMOOrlando, FL

mcnider@nsstc.uah.edu

In the coming century the United States will be faced with three critical agricultural issues

Food Security

Can the US maintain its agricultural output in the face of potential declines in production due to water pressures in the West and High Plains?

Energy Security

Can the US expand its agricultural output to meet biofuel needs and not impact food supplies?

World Food

With the world as a whole still facing a calorie deficit can the U.S. provide leadership to increase food production in a sustainable fashion?

Rain-fed Agriculture in the Eastern U.S.

•At the turn of the 20th century most of the U.S food and fiber production was found in the East and Midwest based on rain-fed agriculture

Precipitation>Evaporation

100W

Rain-fed Agriculture

This 1900 Eastern agricultural system was broad based

Drought was a natural part of this system and drought losses were reflected in prices.

Corn was grown in most every State.

Potatoes

Cotton Vegetables

By 1980 with transportation improvements corn became concentrated in the deep water holding soils of a few states in the mid-west which insulated farmers from drought losses.

Irrigation in the West removed drought losses.

Potatoes

Cotton

Vegetables

Corn

ALABAMA

Headland, ALRainfed Corn Yield

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Average Mid-west Yields

Crop Model

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In the SE with our shallow soils we are almost always in a drought.

Energy, fertilizer and time wasted

The next 50 years may be much different than the last 50 years.

New pressures are now forcing a cost-accounting for Western irrigated-agriculture. In the long-term many observers feel this desert agriculture is not sustainable.•Ground water overdrafts from pumping in Ogallalah

•Water demand from rapid urban growth

•Salt and selenium surface poisoning

•River restoration and endangered species initiatives

Demand for water may not be the biggest issue facing the west. Rather, it may be supply.

Recent reconstruction of climate indicate that the past 70 years may have been abnormally wet and future supply could be much

less. The recent drought may be the norm.

From Piechota et a. 2004

Abnormally Wet

Climate Change?

IPCC

Regional precipitation changes are uncertain.

Dry areas likely to become drier and wet areas wetter.

What is the solution to declining production in west and need for more land in production for bio-fuels?

Put land in the East back into production!

Sustainable Southeastern Model - Storage of Winter Surface Water

Even in dry years crops need less than a foot of water.

Run-off

Alabama River

10 to 34 million ac-ft/yr

One million acre-ft withdrawn

Even Year Withdrawal

Irrigation can be practiced in the Southeast with undetectable fractions of rivers withdrawn while in the West whole rivers are consumed

Pure rain-fed agriculture in most areas is inefficient. Energy, fertilizers and time are wasted if rains don’t come at the right time.

Irrigation solves these problems but it must be sustainable

World should encourage irrigation where water is plentiful!

Tools Developed to Determine the Economic Feasibility and Environmental Sustainability of

Irrigation in the SE.

We have embraced crop models (DSSAT) and long-term climate data to examine economic and environmental issues in the context of climatology.

Water Run-off Irrigated Acreage

Why haven’t more farmers in the East not irrigated?

Is it not economically viable?

Headland, AL 1951 - 1999Irrigated vs Rainfed

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Irrigated profit

Rain-fed profit

State investment would ensure that a choice for irrigation would be a “no-brainer” decision

How large should on-farm reservoirs be?

•Made detailed calculations of daily evaporative losses

E=C(eo- ea)(1+a*u)

Used dew points and wind speed from first order National Weather Service stations

•Used DSSAT to determine irrigation amounts

Jan 1 Jul 31

1.8 acre ft of water needed in reservoir per acre

Figure 1. Example of Drought Monitor

Example of the Lawn and Garden Index (LGI) for July 25, 2008.

Developing Next Generation Agricultural Drought Index Using Crop Models and High

Resolution Radar and Insolation

Incorporates both physical inputs and the physiological state of the crop

DSSAT run in a gridded mode

DSSAT driven by

•High resolution (4km) radar derived precipitation

•High resolution (4 km) satellite derived insolation

•High resolution gridded tmin and tmax

Radar derived rainfall

Satellite derived insolation

Dry Year

Wet Year

Water stress from DSSAT for corn simulation

We believe the DSSAT derived spatial drought index has great potential for determining drought impacts in agriculture.

Forward runs of DSSAT to maturity can provide running estimate of yields.

DSSAT run with observed data

DSSAT run with forecast data (e.g. ENSO phase years)

Current Day

Thank You!

Support Provided by

USDA Risk reduction in SE Agriculture (FSU)

NOAA RISA (U. Miami)

NOAA Drought Studies (UAH)

In filling off-stream reservoirs how much water can be withdrawn from a stream or river without adversely impacting the ecology?

Reservoirs filled during winter high flows.

But flood events and flood plain inundation important to

•reproduction cycles

•sediment deposition

•Nitrogen sequestration

Are critical flood characteristics preserved ?

•Inundation depth

•Inundation area

•Inundation time

Goal: Withdrawals limited so that the above parameters are not significantly altered in a statistical sense (95% confidence interval)

GIS Area Model

Rating CurveRating curve based on USGS dataRelates discharge (known) to gage height (needed)

• USGS provides table of Discharge versus Gage Height

• Estimated gage height in region of interest (approximately 4.5 miles downstream of Elrod station)

• Interpolation routine for Rating data is statistically accurate.

• Currently have rating data 11 & 12 (1995 – present).

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Interpolated Gage Height

Actual Gage Height

2001 365-day Analysis

• Before withdrawal in orange (burnt?)

• After withdrawal in blue (39.5% of discharge withdrawn)

• This was the highest flow day during withdrawal period (January through April)

2001 120-day Analysis

• Before withdrawal in orange…

• After withdrawal in blue (16.7% of discharge withdrawn)

• This was the highest flow day during withdrawal period (January through April)

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1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361

Area of inundation BW (acreas)

Area of Inundation AW (acres)

Discharge (cfs)

Discharge AW (cfs)

Approximate Area before/after Synthetic Withdrawal