Event Title

Water Year Classification in a Nonstationary Climate

Presenter Information

Sarah Null

Location

ECC 216

Event Website

http://water.usu.edu/

Start Date

4-4-2012 1:50 PM

End Date

4-4-2012 2:10 PM

Description

The sensitivity of water indexing methods to climate change may affect water management decisions and allocations. Many water management decisions, such as environmental flow requirements and water supply allocations, are based on categorical water year type designations. Thresholds for water year type designations vary by region and index, but most are defined by some measure of runoff in the current water year compared to average historical runoff. Climate change is anticipated to alter the timing and volume of runoff, and change the relative frequency of water year types as presently defined. California’s Sacramento Valley and San Joaquin Valley Indices are used as case studies to examine climatic changes. These indices provide a framework for allocating and transferring water among users. Streamflow estimates for 1951 – 2099 are from the climate-forced Variable Infiltration Capacity hydrologic model and are used to estimate potential changes in runoff and water year type frequency (using 6 GCMs for the A2 and B1 emissions scenarios). Results vary by emissions scenario and global circulation model, but indicate that critically dry water years in the Sacramento Valley and San Joaquin Valley are expected to be about 8 percent and 32 percent more likely by the latter half of the 21st century, respectively, if water year type definitions remain unchanged. We show that if current water year type thresholds are maintained, more years are classified as dry and less water is allocated for environmental outflows, perhaps failing to provide adequate hydrologic variability to support species, habitats, and ecosystems. If thresholds are redefined to reflect the historical distribution of year types, the burden of climate change falls to consumptive users and water exporters. This case study illustrates how water policy and allocation frameworks were designed assuming climatic stationarity, and that adapting water policy (or maintaining the status quo) affects which users are most impacted by climate change.

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Apr 4th, 1:50 PM Apr 4th, 2:10 PM

Water Year Classification in a Nonstationary Climate

ECC 216

The sensitivity of water indexing methods to climate change may affect water management decisions and allocations. Many water management decisions, such as environmental flow requirements and water supply allocations, are based on categorical water year type designations. Thresholds for water year type designations vary by region and index, but most are defined by some measure of runoff in the current water year compared to average historical runoff. Climate change is anticipated to alter the timing and volume of runoff, and change the relative frequency of water year types as presently defined. California’s Sacramento Valley and San Joaquin Valley Indices are used as case studies to examine climatic changes. These indices provide a framework for allocating and transferring water among users. Streamflow estimates for 1951 – 2099 are from the climate-forced Variable Infiltration Capacity hydrologic model and are used to estimate potential changes in runoff and water year type frequency (using 6 GCMs for the A2 and B1 emissions scenarios). Results vary by emissions scenario and global circulation model, but indicate that critically dry water years in the Sacramento Valley and San Joaquin Valley are expected to be about 8 percent and 32 percent more likely by the latter half of the 21st century, respectively, if water year type definitions remain unchanged. We show that if current water year type thresholds are maintained, more years are classified as dry and less water is allocated for environmental outflows, perhaps failing to provide adequate hydrologic variability to support species, habitats, and ecosystems. If thresholds are redefined to reflect the historical distribution of year types, the burden of climate change falls to consumptive users and water exporters. This case study illustrates how water policy and allocation frameworks were designed assuming climatic stationarity, and that adapting water policy (or maintaining the status quo) affects which users are most impacted by climate change.

https://digitalcommons.usu.edu/runoff/2012/AllAbstracts/57