Climate and Socioeconomic Factors Drive Irrigated Agriculture Dynamics in the Lower Colorado River Basin

Abstract

The Colorado River Basin (CRB) includes seven states and provides municipal and industrial water to millions of people across all major southwestern cities both inside and outside the basin. Agriculture is the largest part of the CRB economy and crop production depends on irrigation, which accounts for about 74% of the total water demand cross the region. A better understanding of irrigation water demands is critically needed as temperatures continue to rise and drought intensifies, potentially leading to water shortages across the region. Yet, past research on irrigation dynamics has generally utilized relatively low spatiotemporal resolution datasets and has often overlooked the relationship between climate and management decisions such as land fallowing, i.e., the practice of leaving cultivated land idle for a growing season. Here, we produced annual estimates of fallow and active cropland extent at high spatial resolution (30 m) from 2001 to 2017 by applying the fallow-land algorithm based on neighborhood and temporal anomalies (FANTA). We specifically focused on diverse CRB agricultural regions: the lower Colorado River planning (LCRP) area and the Pinal and Phoenix active management areas (PPAMA). Utilizing ground observations collected in 2014 and 2017, we found an overall classification accuracy of 88.9% and 87.2% for LCRP and PPAMA, respectively. We then quantified how factors such as climate, district water rights, and market value influenced: (1) annual fallow and active cropland extent and (2) annual cropland productivity, approximated by integrated growing season NDVI (iNDVI). We found that for the LCRP, a region of winter cropping and senior (i.e., preferential) water rights, active cropland productivity was positively correlated with cool-season average vapor pressure deficit (R = 0.72; p < 0.01). By contrast, for the PPAMA, a region of summer cropping and junior water rights, annual fallow and active cropland extent was positively correlated with cool-season aridity (precipitation/potential evapotranspiration) (R = 0.46; p < 0.05), and active cropland productivity was positively correlated with warm-season aridity (precipitation/potential evapotranspiration) (R = 0.42; p < 0.01). We also found that PPAMA cropland productivity was more sensitive to aridity when crop prices were low, potentially due to the influence of market value on management decisions. Our analysis highlights how biophysical (e.g., temperature and precipitation) and socioeconomic (e.g., water rights and crop market value) factors interact to explain seasonal patterns of cropland extent, water use and productivity. These findings indicate that increasing aridity across the region may result in reduced cropland productivity and increased land fallowing for some regions, particularly those with junior water rights.

Drivers of enhanced evaporative demand in U.S. croplands: Determining relative contribution using constrained input scenarios

“…Our results show Colorado's water basins have undergone significant ET o increase (Figure 1), which has primarily resulted from interplay between T , RH, and U 2 change (Figure 3). Having ignored RH and U 2 dynamics, it is suspected that the decision support systems may not realistically represent the evolution of crop water requirements in this region, which can hinder management efforts against the water stress experienced in these basins (Averyt et al, 2013; National Research Council, 2007; Norton et al, 2021). Overall, assigning explicit relative contributions for each county (Figure 3 and Figures S5–S8) aid in understanding region and timescale‐specific importance of T , R s , RH, and U 2 for driving ET o increase in the context of water planning efforts.…”

Spatiotemporal Analysis and War Impact Assessment of Agricultural Land in Ukraine Using RS and GIS Technology

“…The fallow-land algorithm based on neighborhood and temporal anomalies (FANTA) method is used to identify active and fallow land by using NDVI time series data, which compares the current greenness of a cropland pixel to its historical greenness and its neighborhood greenness [31,32]. Temporal anomalies (T_NDV I m max and T_NDV I m range ) are calculated using a z-score transformation as follows:…”

“…This method analyzes relative temporal and spatial greenness patterns to extract fallowed land information based on statistical indicators derived from long-term Normalized Difference Vegetation Index (NDVI) time series data. Without the need for field data for training, FANTA has the advantage of effectively monitoring the agricultural management status in regions where it is difficult to conduct fieldwork and obtain sufficient fundamental geographic data [32].…”

Irrigation response to drought in the Western United States, 1987–2021

“…Most irrigated lands in the U.S. that use off-farm water are served by large irrigation districts, and while drought may fundamentally alter the economic prospects of irrigation and cropping decisions, few irrigation districts in the U.S. have plans in place to affect an organized response, such as curtailing water deliveries (Wallander et al, 2022). Water rights, fallowing patterns, crop rotation cycles, and long-term trends in crop profit expectations may further influence differences in irrigation management at the farm scale during drought (Norton et al, 2021).…”