Solving Water Crises Begins With Good Data

Negotiations over future allocations of water from the Colorado River (southwestern US) are contentious, and intensifying. A new study providing comprehensive accounting for all uses of the river's water can aid design of strategies for bringing use back into balance with available supplies.
Published in Earth & Environment
Solving Water Crises Begins With Good Data
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The Colorado River in the southwestern US is getting a lot of media attention lately, for good reason. Since 2000, more water has been consumed from the river basin and its reservoirs than melting snows and summer monsoons have been able to replenish. As a result, Lakes Mead and Powell -- the two largest reservoirs in the US -- are now three-quarters empty, the river no longer reaches the Gulf of California in Mexico,  and persistent water shortages threaten the security of cities, farms, electricity generation, recreation, and ecological health. 

As I've long advised my university students and fellow water professionals, any efforts to resolve a water crisis must be founded on  accurate and complete data characterizing available water supplies and uses. Detailed knowledge of how and where a river’s water is being used can aid design of strategies and plans for bringing water use back into balance with available supplies, while ensuring that sufficient water remains in freshwater ecosystems to sustain their health. Yet despite the Colorado River’s importance to more than 40 million people and more than two million hectares (>5 million acres) of cropland,  a full sectoral and crop-specific accounting of where all of the river's water goes en route to its delta has never been attempted, until now.

The seven 'accounting units' used in this study are displayed here. 

We have just published a complete water budget for the Colorado River in Communications Earth & Environment. Ironically, our motivation for compiling this water budget  emerged from our frustrations over the manner in which our previously published research was being regularly miscommunicated in the media! In 2020, we  published a paper in Nature Sustainability that included a partial water budget for the Colorado River. That study did not attempt to account for the 12% of the river's water that is exported outside of the basin's physical boundary, nor did it account for the substantial volume of water (30%) that either evaporates from reservoirs or is evapotranspired from riparian and wetland vegetation. However, many media reporters overlooked the fact that our water budget did not account for all water consumed from the river basin, and media statements based on our research began suggesting that "Nearly 80% of the Colorado River's water goes to irrigated agriculture," which is not accurate, and is misleading. As our new study reports, when accounting for ALL water consumed from the river,  the proportion of river water going to farms amounts to just over 50%.

Water consumption by sector in the Colorado River Basin and sub-basins (including exports), based on 2000-2019 averages.

These differences in water accounting matter greatly in a river basin with so much at stake. The region has been experiencing a 'megadrought' since 2000 that has reduced river flows by  20%. Climate scientists assert that this is a bellwether of long-term, climate-driven aridification in the region. It is of critical importance that the state and federal negotiators presently debating future water allocations are being informed with an accurate tabulation of where all of the river's water goes presently. Such accounting is essential in designing strategies for rebalancing water consumption with available supplies.

Our water budget details how and where the water is being consumed, including estimates of the volume of water being consumed by individual crops in different areas of the river basin. This level of detail can help water managers understand how much water might be saved by shifting to alternative crops, or by repurposing some portion of farmlands for habitat restoration or renewable energy generation. It is also important to understand trends in water use; our data indicate that during 2000-2019, combined urban and agricultural water use in the Upper Basin increased by 5% while these uses decreased in the Lower Basin by 24%.

An accurate tabulation of a water budget can also be useful to media reporters in formulating comparisons among water-use categories that can capture reader attention, educating them in the process. For instance, our study found that water consumed in irrigated agriculture is three times greater than the volume used in cities, and in fact, the irrigation of just two crops -- alfalfa and grass hay fed to cows for beef and dairy production -- consumes as much water as all of the cities using Colorado River water. 

Another important achievement of our study was our estimation of the volume of water being consumed by riparian and wetland vegetation through evapotranspiration.  Over recent decades, this volume has been reduced considerably because of the drying of the river's delta in Mexico, which wiped out a vast and highly productive wetland along with the native tribe of Cucupa that depended on the delta's natural bounty.  If human uses of the river's water are not substantially reduced, and climate warming continues to reduce the river's natural flow, more losses of riparian and wetland vegetation -- and greater imperilment of native species -- can be expected.

Summary of the Colorado River Basin’s water supplies (left side) and all water consumed in each sub-basin, in each water use sector, and by individual crops. All estimates based on 2000-2019 averages. MCI = municipal, industrial, and Industrial uses

    

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