During the study period, from 1970 to 2015, several local, regional, and state water management proposals, decisions, and transactions shaped the distribution and allocation of water resources in the lower Colorado River basin. Thus, to evaluate whether the change points detected above represent bounds of policy change windows, this section discusses the observed water management decisions/actions against our CPM findings.
First, we situate the results within the context of two well-documented droughts that occurred during the study period. Next, we compare the results to several high-profile managerial interventions that coincide with groupings of significant change points (Table 2
) to answer the second research question: how do change points align with documented managerial interventions related to water resource management. These interventions are drawn from: (1) state water legislation and planning; (2) regional water management strategies, proposals, and decisions; and (3) water rights purchases and water resource contracts undertaken in the lower Colorado River basin.
4.2. Managerial Interventions
The first grouping of change points is punctuated by growing urban water use along with increasing temperatures in the central Texas region. During this time, the state, along with regional and local water interests, made several decisions and transactions that affected the management of the water held in the Colorado River basin. First, in 1997, the state shifted how it conducted and compiled its water management plan via the passage of Senate Bill 1 (SB 1). The re-tooled statewide water planning effort committed to prioritizing water conservation efforts to bolster the state’s water supplies [67
]. Additionally, SB 1 established 16 water planning groups throughout the state to create a consensus-driven approach to water management across the state by including local stakeholders in the decision-making and planning processes [35
]. Each water management group consists of 20 members. The members represent the full range of water interests and develop a 50-year regional water plan every five years [68
]. The Texas Water Development Board (TWDB) synthesizes the groups’ plans into the state water plan. Second, the Texas legislature passed House Bill 1437 in 1999 that allowed the LCRA to provide water to Williamson County through an interbasin transfer. The LCRA also purchased water rights from the Garwood Irrigation District, located in the lower reaches of the basin, in 1998. The Garwood rights cost the LCRA approximately USD $
75 million [69
] and consisted of 133,000 AFY (1.64 × 108
). After this purchase, the LCRA and the City of Austin entered into a long-term water supply agreement in 1999. The city agreed to pay the LCRA USD $
100 million to extend water delivery from lakes Buchanan and Travis to 2050. The agreement raised the amount of firm water available to 325,000 AFY (4.01 × 108
). The agreement said that the first 150,000 AF (1.85 × 108
) was free and set a water rate of USD $
105 per AF for the use of water over 150,000 AF to 201,000 AF (1.85 × 108
to 2.48 × 108
). The agreement, however, specified that payment would not commence until Austin’s annual average water use for two consecutive years exceeded 201,000 AF (2.48 × 108
]. The deal reserved a large amount of water for Austin and its future demands, even in drought periods. Additionally, the City of Corpus Christi acquired the rights to 35,000 AFY (4.31 × 107
) of Colorado River water through a purchase and interbasin transfer. Finally, as previously mentioned, the 1995 to 1996 drought affected agricultural productivity in the counties in the lower reaches of the basin.
The policy changes and managerial interventions described above coincide with, or occur shortly after, the first grouping of change points and indicate that significant changes to the water-related variables under analysis were occurring across social and environmental landscapes. In particular, the change points signaled shifts in urban water use and changes in temperature. Significant changes in urban water use signaled in 1994 and 1996, and temperatures in 1997. The direct basin-related managerial events and transactions occurred on the heels of these changes, and the change points correspond to these urban-centric interventions. This suggests that decision makers were responding to changes in urban water use. The role increasing temperatures played in water-related decision-making processes is less clear. Temperatures and precipitation have been shown to affect water use. In particular, residential water use increases under drought conditions [71
]. Urban water use may be signaling due to significant changes in temperature; yet, population growth in the urban counties most likely contributed to the increase as well. Finally, the change points related to agricultural losses (i.e., decline in annual rice harvested in 1996) suggest that the 1996 drought affected these counties with ramifications for agricultural water use punctuated in the second period of change points.
The decline in water use by agricultural counties defines the second grouping of change points (1999 to 2002). The amount of rice and total crops harvested also declined significantly. During this period, a few major water-related policies and transactions were undertaken. In 2001, the Texas Legislature passed Senate Bill 2. This piece of legislation created groundwater management areas (GMAs) [73
]. The creation of GMAs was an important moment for water planning and conservation across the state. Its impact on surface water use across the study area, however, is negligible (i.e., a change point was not observed in groundwater use), and the significant decline of agricultural water use during period 2 did not influence the passage of SB 2. In 2001, the LCRA purchased the rights to 55,000 AF (6.78 × 107
) in the lower portion of the basin. This purchase included the last group of privately held senior water rights in the watershed and allowed the LCRA to control the major irrigation districts in the Texas Rice Belt. Agricultural operations, including rice farmers, began to contract with the LCRA to purchase interruptible water. It is best to view the second group of change points as feedback from managerial interventions and environmental processes that took place during the first period discussed above. In this view, significant declines in agricultural water use and crops are a function of earlier managerial interventions, which were responses to changes in earlier social and environmental conditions. This interpretation suggests that the CPM framework returns change points not only before managerial interventions but also after them. In this way, the CPM framework could be used to monitor the effectiveness of prior interventions across appropriate sets of time series data.
The final grouping of change points corresponds to declines in lake levels (2005 and 2007). The low lake levels were the result of the 2005 and 2010 droughts and severely impacted water use in the basin. During this period, the state enacted and passed two water-related policies, and the droughts triggered multiple managerial responses to extend supplies during a time of extreme water scarcity. In 2007, the Texas Legislature passed a major piece of water legislation. Senate Bill 3 called for the protection of environmental flows in the state’s rivers and estuaries [35
] and required groundwater districts to produce groundwater management plans [67
]. Additionally, in 2013, Texans voted in favor of Proposition 6. Proposition 6 called for the state, using monies from its Economic Stabilization Fund (ESF), to create the State Water Implementation Fund for Texas (SWIFT) and the State Water Implementation Revenue Fund for Texas (SWIRFT). These funds finance priority projects outlined in the state water plan. Within the basin, Austin and the LCRA brokered an extension of their earlier water agreement in 2007. The two entities formed a formal water partnership through 2100 [74
]. Yet, these managerial events were less of a response to the 2005 and 2010 droughts and more of a response to growing urban population demands. The change points link more appropriately to water availability in the basin.
The drought worsened in 2011, and water levels in lakes Buchanan and Travis began to decline. In 2012, the LCRA asked the Texas Commission on Environmental Quality (TCEQ) to grant an emergency order that would change its water management plan. Specifically, the order called for the cutoff of the interruptible water supply contracts held mostly by agricultural interests. By 2013, water levels in lakes Buchanan and Travis measured 43 percent of their combined storage capacity [75
], and the LCRA was forced to file additional emergency orders in 2013, 2014, and 2015. Each year, the TCEQ approved the orders. In 2015, the LCRA updated its water management plan to provide more flexibility to its curtailment and cut-off procedures. The new water management plan made significant changes to the way in which the LCRA manages interruptible water contracts [76
The managerial interventions implemented beginning in 2012 and the redrawn 2015 water management plan were a response to severe drought conditions that occurred in central Texas from 2010 to 2015, which followed directly after the less severe 2005 drought. The CPM signals changes in water levels (2005 and 2007) before the worst years of the drought. These signals indicate that water availability in the basin, beginning with the 2005 drought, never fully recovered. This suggests that the CPM framework is sensitive to extreme fluctuations. Authorities, however, delayed managerial interventions until lake levels threatened urban water security.