Characterization of the Water Supply of the Rio Grande Project Based on Rio Grande Compact Reports 1940-2020

The focus of this study is the 1938 Rio Grande Compact water supply. The compact is an interstate agreement signed in 1938 between the states of Colorado, New Mexico, and Texas to evenly apportion the waters of the Rio Grande Basin. A shortage in deliveries is at the center of a lawsuit that began in 2011, went to the Supreme Court in 2013, and has not been resolved. This research statistically characterized the differences between water available and water delivered by Colorado and New Mexico, signatories of the Rio Grande Compact with Texas, to understand changes over time and uncover potential autocorrelations. Unexpected changes in water deliveries can have serious financial impacts on communities, thus the importance of shedding light into the behavior of the differences between water available and delivered. One of the findings of the research was that the annual credit/debit time series for Colorado was significantly correlated with the current and immediately previous scheduled delivery as well as with itself in the two previous years, and the behavior is explained by a transfer function model (TFM). For New Mexico, the annual credit/debit series did not display a clear pattern; therefore, it was not possible to characterize its relationship with scheduled delivery with the method examined. This technical note contributes to the extensive body of literature of the Rio Grande Compact in a way no other study has done as well as contributing to the wealth of literature related to the use of the transfer function model in hydrology. The main contribution of the study is the methodology developed and used, which could be useful to other river systems and transboundary water sharing agreements. This research statistically characterized the differences between water available and water delivered, also known as credits and debits, by Colorado and New Mexico, signatories of the Rio Grande Compact with Texas, to understand changes over time and uncover potential autocorrelations. A legal conflict between the signatories of the compact has lasted over a decade. Texas alleges that New Mexico is extracting groundwater, shortening their share of the water. Unexpected changes in water deliveries can have serious financial impacts on communities so shedding light on the differences between water available and water delivered can contribute to the debate. One of the research findings was that the annual credit/debit time series for Colorado was significantly correlated with the current and immediately previous scheduled delivery as well as with itself in the two previous years, and the behavior is explained by a TFM. For New Mexico, the annual credit/debit series did not display a clear pattern; therefore, it was not possible to characterize its relationship with scheduled delivery with the method examined. The main contribution of the study is the methodology developed and used, specifically the TFM, which could be tweaked to fit other river systems and transboundary water sharing agreements.