University of Texas at Austin

Improving Irrigation Water Use Estimates with Remote Sensing Technologies:

An initial feasibility study for Texas

Program Overview

Accurate estimates of crop evapotranspiration (ET) are needed annually to determine irrigated water use per county and to feed into irrigation demand estimates state-wide. Remote sensing has the potential to improve the accuracy of crop ET (water out) and precipitation (water in) by increasing the spatial and temporal resolution state-wide. However, operational crop ET is in its early stages and currently requires significant expertise to produce quality estimates. Our goal is to assess the feasibility of the current state-of-the-science remote sensing approaches to quantify crop ET across the climatically and agriculturally diverse landscape of Texas. We use a variety of metrics to assess the various needed components including the ET algorithms by accuracy tiers and complexity, as well as other requirements such as gridded weather data. Each of these components was evaluated to assess their respective feasibility for state-wide implementation.

LDCM (Landsat 8) image

Figure 1. Sample LDCM (Landsat 8) image from April 3, 2013 showing agricultural fields near Wiggins, CO. Left is a color composite of shortwave infrared, near-infrared and visible green light and right is the same area as shown by one of the LDCM thermal bands. The inset pair shows three center pivot irrigation fields in greater detail. Darker areas in the thermal band indicate cooler temperatures (and higher ET).

We are currently implementing 2 remote sensing algorithms, SEBS and METRIC, as Tier 2 and Tier 4, respectively, over 8 counties in Texas to determine crop ET estimates. We will also assess Landsat image quality for each climate zone and various time integration methods needed to develop annual totals of crop irrigation requirements (CIR).

Figure 2. Six monitoring networks in Texas

Figure 2. Six monitoring networks in Texas were used for observational data in Texas including (1) West Texas Mesonet (WTM) from Texas Tech University, Texas ET Network (TETN) from Texas A&M University, NOAA’s Climate reference Network (CRN), USDA’s Soil Climate Analysis Network (SCAN), and the Lower Colorado River Authority’s (LCRA) Hydromet. Monitoring stations were further categorized based on their (a) mean annual precipitation from 30-year normal from 4 km gridded PRISM (1990-2010), and (b) their 5 climatic zones.

Figure 3. feasibility study

Figure 3. This feasibility study is determining annual, 2010 and 2011, per county crop irrigation requirements for 8 counties across Texas using remote sensing and numerical models.