With water availability being an important concern, water managers often use water budgets to quantify and manage water resources.  A water budget is an accounting of the rates of the inflows, outflows, and changes in water storage in a specific area; however, as simple as that might sound, developing an accurate water budget can be a difficult and challenging endeavor.

To address this problem, the Department of Water Resources has developed a water budget handbook, which is intended to demystify the process of developing a water budget by distilling the process down into specific steps, providing guidance as well as specific advice on how to determine a water budget, with or without the use of models.  In the spring of 2020, Department staff held a webinar to introduce water managers and interested stakeholders to the content in the water budget handbook.

The water budget is important because it provides an understanding of historical conditions and how future changes to supply, demand, hydrology, population, land use, and climate may affect the water resources of the area.  Water budgets are an important tool for water agencies for things such as water supply planning and evaluating the effectiveness of management actions to ensure long-term sustainability of surface water and groundwater resources in the area.

Recent legislation, including the Sustainable Groundwater Management Act and Assembly Bill 1668, has codified water budget development to be part of groundwater sustainability plans and agricultural water management plans.  Recently released governor’s draft water resilience portfolio has actions recommending the development of water budgets as an integral component of planning to advance water resilience in California. 

The Department of Water Resources developed the draft Handbook for Water Budget Development as a practical reference guide for the California water resources community for determining water budgets for any geographic area and time period using either a modelling or a non-modelling approachs.  Development of the handbook was informed through two water budget pilot projects in Tulare Lake and Central Coast hydrologic regions which identified challenges in water budget development such as inconsistent definition of water budget components, non-standard accounting techniques, and inadequate documentation.  Development of the handbook was an effort between staff from multiple DWR programs, the USGS, the State Water Board, academia, and others.

Read more of the original article here.