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

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.

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Measurement of flows for two irrigation districts in the lower Colorado River basin, Texas

10.3133/wri964225 ◽

1996 ◽

Keyword(s):

River Basin ◽

Colorado River ◽

Colorado River Basin ◽

Irrigation Districts ◽

Lower Colorado River Basin ◽

Lower Colorado River

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Winter Inputs Buffer Streamflow Sensitivity to Snowpack Losses in the Salt River Watershed in the Lower Colorado River Basin

Water ◽

10.3390/w13010003 ◽

2020 ◽

Vol 13 (1) ◽

pp. 3

Author(s):

Marcos D. Robles ◽

John C. Hammond ◽

Stephanie K. Kampf ◽

Joel A. Biederman ◽

Eleonora M. C. Demaria

Keyword(s):

River Basin ◽

Colorado River ◽

Snow Accumulation ◽

Colorado River Basin ◽

Scale Model ◽

Annual Streamflow ◽

Basin Scale ◽

Salt River ◽

Lower Colorado River Basin ◽

Lower Colorado River

Recent streamflow declines in the Upper Colorado River Basin raise concerns about the sensitivity of water supply for 40 million people to rising temperatures. Yet, other studies in western US river basins present a paradox: streamflow has not consistently declined with warming and snow loss. A potential explanation for this lack of consistency is warming-induced production of winter runoff when potential evaporative losses are low. This mechanism is more likely in basins at lower elevations or latitudes with relatively warm winter temperatures and intermittent snowpacks. We test whether this accounts for streamflow patterns in nine gaged basins of the Salt River and its tributaries, which is a sub-basin in the Lower Colorado River Basin (LCRB). We develop a basin-scale model that separates snow and rainfall inputs and simulates snow accumulation and melt using temperature, precipitation, and relative humidity. Despite significant warming from 1968–2011 and snow loss in many of the basins, annual and seasonal streamflow did not decline. Between 25% and 50% of annual streamflow is generated in winter (NDJF) when runoff ratios are generally higher and potential evapotranspiration losses are one-third of potential losses in spring (MAMJ). Sub-annual streamflow responses to winter inputs were larger and more efficient than spring and summer responses and their frequencies and magnitudes increased in 1968–2011 compared to 1929–1967. In total, 75% of the largest winter events were associated with atmospheric rivers, which can produce large cool-season streamflow peaks. We conclude that temperature-induced snow loss in this LCRB sub-basin was moderated by enhanced winter hydrological inputs and streamflow production.

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Challenge and response in the Colorado River Basin

Water Policy ◽

10.2166/wp.2014.003 ◽

2014 ◽

Vol 16 (S1) ◽

pp. 12-57 ◽

Cited By ~ 2

Author(s):

Jason Robison ◽

Katja Bratrschovsky ◽

Jaime Latcham ◽

Eliza Morris ◽

Vanessa Palmer ◽

...

Keyword(s):

River Basin ◽

Water Regime ◽

Colorado River ◽

Water Rights ◽

Colorado River Basin ◽

Western United States ◽

Past Century ◽

The Past ◽

Salinity Control ◽

Indian Tribes

The Colorado River Basin supplies water to roughly 40 million people in the south-western United States. A complex interstate regime that has evolved across the past century governs allocation and management of these coveted flows, and formidable challenges face this regime in contemporary times – a historical era aptly dubbed the ‘era of limits’. This paper illuminates these challenges and offers modest input regarding potential responses to them. We initially survey the evolution of the interstate water regime and outline its essential features as well as those of the basin. We then turn to the contemporary challenges and potential responses, which generally concern an unprecedented imbalance between water supplies and demands, long-standing disagreements over the meaning of the Colorado River Compact, water rights held by American Indian tribes on reservations throughout the basin, and ongoing biodiversity protection and salinity control efforts. We conclude by reflecting on lessons from and for the Colorado River Basin vis-à-vis the interstate water regimes existent in the other four basins encompassed within the Harvard Water Federalism Project.

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