Economic and Water Supply Effects of Ending Groundwater Overdraft in California's Central Valley

Abstract

Surface water and groundwater management are often tightly linked, even when linkage is not intended or expected. This link is especially common in semi-arid regions, such as California. This paper summarizes a modeling study on the effects of ending long-term overdraft in California's Central Valley, the state's largest aquifer system. The study focuses on economic and operational aspects, such as surface water pumping and diversions, groundwater recharge, water scarcity, and the associated operating and water scarcity costs. This analysis uses CALVIN, a hydro-economic optimization model for California's water resource system that suggests operational changes to minimize net system costs for a given set of conditions, such as ending long-term overdraft. Based on model results, ending overdraft might induce some major statewide operational changes, including large increases to Delta exports, more intensive conjunctive-use operations with increasing artificial and in-lieu recharge, and greater water scarcity for Central Valley agriculture. The statewide costs of ending roughly 1.2 maf yr -1 of groundwater overdraft are at least $50 million per year from additional direct water shortage and additional operating costs. At its worst, the costs of ending Central Valley overdraft could be much higher, perhaps comparable to the recent economic effects of drought. Driven by recent state legislation to improve groundwater sustainability, ending groundwater overdraft has important implications statewide for water use and management, particularly in the Sacramento-San Joaquin Delta. Ending Central Valley overdraft will amplify economic pressure to increase Delta water exports rather than reduce them, tying together two of California's largest water management problems.

An Integrated Approach Toward Sustainability via Groundwater Banking in the Southern Central Valley, California

“…The Central Valley of California is an example where groundwater consumption has been estimated to be annually around 60% of the total water storage changes (snow water equivalent, surface water, soil moisture, and groundwater) in the basin (Famiglietti et al, 2011). Intensive groundwater withdrawals in the valley have contributed to depletion of streams (Fleckenstein et al, 2004), subsidence and irreversibly reducing storage (Farr & Liu, 2015;Faunt et al, 2016), drying up of wells and increased cost of pumping (Nelson et al, 2016), and disconnection of stream-aquifer systems (Bolger et al, 2011;Dogrul et al, 2016), among others. All these studies emphasize that the groundwater resources are under high pressure, their sustainability is at risk, and therefore, they need to be replenished as soon as possible.…”

Does More Storage Give California More Water?

“…Although California's overdraft occurs mostly in its Central Valley (DWR ), eliminating groundwater overdraft is expected to have statewide effects (Nelson et al. ). Scanlon et al.…”

“…Nelson et al. () and Escriva‐Bou et al. () have concluded that ending groundwater overdraft requires reducing net water use or increasing surface water imports.…”

“…California recently adopted the Sustainable Groundwater Management Act (SGMA), a policy that aims to regulate groundwater, empower local agencies for sustainable management, and eliminate overdraft and adverse effects of overdraft, such as land subsidence, increased pumping cost, degraded water quality, seawater intrusion, and reduced streamflow if hydraulically connected to underlying aquifers. Although California's overdraft occurs mostly in its Central Valley (DWR 2016), eliminating groundwater overdraft is expected to have statewide effects (Nelson et al 2016). Scanlon et al (2012) showed that more surface water deliveries can reduce groundwater overdraft and expanding storage might help resolve temporal disconnection between supply and demand.…”

“…Scanlon et al (2012) showed that more surface water deliveries can reduce groundwater overdraft and expanding storage might help resolve temporal disconnection between supply and demand. Nelson et al (2016) and Escriva-Bou et al (2017) have concluded that ending groundwater overdraft requires reducing net water use or increasing surface water imports. Modeling of this policy, and its implications for storage, is discussed in the Methods section below.…”